TOPIC 1: WHY STUDY THE MECHANISMS OF MYOPIA?
KEYNOTE LECTURE 1
High Myopia in Humans and Its Clinical Management
François Jean Malecaze and Laurence Mahieu
Research Unit UMR 563,Toulouse Hospital, Toulouse, France
High myopia (HM) is defined as refractive error above −6.0 diopters with axial eyeball length above 26 mm, and is connected with the process of degenerative myopia. Refractive error is the first problem, even though not the most incapacitating, people suffering from HM have to face. Management of the refractive error depends upon the amount and severity of the condition. Glasses, contact lenses, and refractive surgery consisting of surgical remodeling of the cornea with Excimer lasers or phakic intraocular lens implantation or cataract surgery may be used to correct myopia.
But the real challenge is the course of HM as for many patients, the progressive elongation of the globe is accompanied by degenerative changes in the retina and the choroid. The most common changes in the eye fundus are myopic crescent, peripapillary chorioretinal atrophy, a tilted, rotated and larger disc, posterior pole staphyloma, posterior pole and peripheral degenerative changes including lattice degenerations, snail-tracks, paving stones, pigment degeneration, diffuse chorioretinal atrophy, lacquer cracks, choroidal neovascularization, holes and tears in the retina leading to rhegmatogenous retinal detachment, vascular narrowing, and vitreous degenerations such as extensive vitreous liquefaction and early posterior vitreous detachment. Moreover, posterior subcapsular cataract, early onset of nuclear sclerosis and increased prevalence of primary open-angle glaucoma are associated with HM. To date, no efficacious treatment has been described to inhibit HM progress. Nevertheless some complications due to HM can be treated: rhegmatogenous retinal detachments are operated on using scleral buckling or vitrectomy with tamponading agents; predisposing peripheral retinal degenerations require prophylactic laser photocoagulation treatment; subfoveal myopic choroidal neovascularization can be treated either by verteporfin photodynamic therapy, but its long-term effectiveness has been disappointing or by antivascular endothelial growth factor (anti-VEGF) drugs with significant improvement of visual acuity and an excellent safety profile. With so many ocular pathologies that can lead to vision impairment, the highly myopic eye is considered to be a vulnerable eye and required systematic ophthalmic monitoring and careful examination of the fundus. HM and its complications are the most significant causes of blindness and visual impairment in young, professionally active people, becoming an important social problem.
SYMPOSIUM 1: OCULAR PATHOLOGY ASSOCIATED WITH HIGH MYOPIA AND POSSIBLE THERAPIES
Chairs: Elena Tarutta and Wei-han Chua
Papers from Denmark, Russia, USA and Ukraine were presented.
Elena Tarutta discussed clinical features of myopia in children and adolescents, the treatment to inhibit its progression and the development of myopic complications.
Brian Ward reported on degenerative myopia in adults and on the results of scleral buckling of the posterior pole to control axial myopic progression and to reverse myopic macular traction syndrome and schisis.
Irina Boychuk stated the correlation between myopia progression in children and OCT features (primarily, peripapillary retinal nerve fiber layer thickness).
Nina Jakobsen analyzed the limited but unselected population of adults with high myopia and found no significant link between central retinal thickness and myopia degree, axial length and visual acuity.
Hans Fledelius presented natural history of juvenile high myopia in unselected Danish adolescents followed up till the age of 60.
A lively final discussion was focused on the past and present of sclera reinforcing treatment.
Symposium 1: Paper 1 Progressive Myopia in Children and Adolescents: Clinical Features and Control of Progression
Moscow Helmholtz Research Institute of Eye Diseases, Moscow, Russian Federation
Purpose: Both congenital and acquired axial progressive myopia can lead to peripheral and macular degeneration. Our goal is to elaborate a comprehensive system of prevention and treatment of high progressive complicated myopia.
Methods: Optical methods – binocular (1) and alternating monocular (2) low myopic defocus (by spectacles) as well as orthokeratology (3) – were used to prevent (1) and slow down the progression of low (2) and moderate (3) myopia in children. Various scleroplastic techniques, partially combined with orthokeratology – low invasive (4) and buckling (5) – were used for moderate (4) and high (5) myopia. Repeated scleroplastic surgeries were performed in cases of myopia progression recurrence. Various types of nonsurgical treatment to improve hemodynamics and accommodation were applied twice a year.
Results: In group 1, no cases of myopia emergence were observed throughout the follow-up period (3-10 years). In 81.8% of cases of group 2, no myopia progression was noted during the 4 to 7-year follow-up period. Group 3 showed a retardation or arrest of myopia progression in 80% of cases over 3-6 years. Repeated scleroplastic interventions brought a 3-fold slowdown of myopia progression rate, while the frequency of peripheral dystrophies and macular degeneration fell 1.7 times. In children with an initial posterior pole staphyloma, scleral buckling led to its flattening, stabilization of myopia degree, axial length and macular dystrophic process over the 3-8 (average 4.2±1.3) years' follow-up in 90.2% of cases.
Discussion and Conclusions: A synergy of optical, functional and surgical techniques of treatment slows down the rate of axial eye elongation and myopia progression, which in its turn reduces the frequency and severity of chorioretinal myopic dystrophies. As the basic period of myopia progression falls to the second decade of life, it should best be arrested at this time to minimize the prevalence and severity of myopic maculopathy that could otherwise develop later in life.
Symposium 1: Paper 2 Degenerative Myopia and the Treatment Options in Adults
Campbell Retinal Diagnostics Center, Campbell, California, and Stanford University Medical Center, Stanford, California
Purpose: To describe and evaluate the means for minimizing visual disability in High Axial Myopia, by the control of axial myopia progression and the treatment of various forms of myopic macular degeneration.
Methods: The myopic maculopathies result from ocular enlargement that has its origins in genetic defects expressed in the scleral shell of the eye. Mechanical restraint was surgically implanted to control adult axial myopia. Such buckling techniques were also used in the Treatment of Myopic Macular Schisis. Treatment methods previously developed for the control of complications of the age-related maculopathies were employed in the control of exudative complications of Myopic Macular Degeneration.
Results: External scleral buckling of the posterior pole was shown to be safe and effective in the control of progressive high axial myopia in adults, and, in addition, was shown to be effective in the treatment of several forms of myopic macular schisis. The courses of specific forms of exudative macular complication of Degenerative Myopia were successfully, and safely, modified by interventions with Anti-VEGF drugs and Photodynamic Therapy.
Discussion and Conclusions: The control of progressive high axial myopia can limit vision loss from myopic macular degeneration and may offer protection of the macula from such neural disruptive complications as myopic macular traction syndrome, macular hole and myopic macular schisis. Scleral buckling has been shown to be able to control axial myopic progression and to reverse macular traction and schisis in cases of Degenerative Myopia. Chemotherapeutic approaches, with both photodynamic therapy and Anti-VEGF intra-vitreal injections can help control exudative macular complications. The identification and treatment of at-risk eyes, in stages before the evolution of macular pathology, is likely to reduce visual disability later in life.
Symposium 1: Paper 3 OCT Features and Their Functional Correlations in Children With Acquired Myopia
Iryna M. Boychuk and T. L. Gorbatyuk
The Filatov Institute of Eye Diseases and Tissue Therapy AMS, Odessa, Ukraine (IMB, TLG)
Purpose: To find correlation between peripapillary retinal nerve fiber layer thickness (PRNFLTh) and the functional state of visual nerve to reveal early signs of myopia dystrophy and progression 135 children aged (6-17) with bilateral myopia (2,0–14,0) diopter were observed (myopia degree difference between both eyes was below 1,5 diopter).
Methods: Morphostructural indices (PRNFLTh) in four segments (nasal, temporal, superior, inferior) were investigated by optical coherent tomography SOCT Copernicus, OPTOPOL Tech.Sp.z o.o. applying standard protocols. Functional state observation included routine methods: determination of visual acuity, refraction and eye's axial length, kampimetry of blind spot vertical and horizontal sizes, thresholds of electro sensitivity (ESTh) and liability of optic nerve (CFFph).
Results: Significant correlations were found between PRNFLTh in temporal segment and blind spot vertical size (BSVS) - Rs = - 0, 88); ESTh (Rs - 0, 27) and CFFph (Rs - 0,26). If PRNFLTh values in the temporal segment were less than 33, 5 mk - visual acuity values were lower (0,007-0,24), refraction higher (4,13-7,52 dptr) than in those patients who had PRNFLTh above 33,5 mk (0,3-0,45 and 2,7-3,9 diopter accordingly). (BSVS) above 7,84sm had patients with PRNFLTh in temporal segment (33,3 ±SD15,27) mk and if (BSVS) was less than 7,84sm PRNFLTh in temporal segment was (61,9±SD20,1) χ2=4,27, (P=0,03).
Discussion and Conclusions: PRNFLTh in temporal segment less than 33, 5 mk in myopic patients can be identified as an early sign of myopia progression and retinal dystrophy. It is followed by increased BSVS (above 7,84sm) and ESTh values (above 80 mkA).
Symposium 1: Paper 4 OCT Central Field Retinal Thickness in High Myopia With and Without Posterior Irregular Eyeshape
Nina Jacobsen, Hans C. Fledelius, Ernst Goldschmidt, and Birgit Sander
Copenhagen University Eye Clinic, Glostrup & Rigshospitalet (NJ, HF, BS), and Danish Institute for Myopia Research Glostrup University Hospital, Glostrup, Denmark (EG)
Purpose: To describe the OCT retinal thickness and posterior pole contour in an unselected series of adults (aged approximately 60 years) with high myopia.
Methods: In 1962, 39 14-year-old teenagers with myopia of at least - 6 D, in one or both eyes, were identified in a 1948 Copenhagen birth cohort (n = 9243). At follow-up in 2009, 39 eyes (34 with high myopia and five fellow eyes; n = 23 subjects) had a supplementary ultrasonic B-scan evaluation of the posterior pole contour. Further, OCT was performed to investigate the central retina and to compare the central retina in highly myopic eyes with and without a posterior irregular eye-shape.
Results: A multiple linear regression analysis showed no association between central retinal thickness measured by the Cirrus OCT and spherical equivalent refraction (SER), nor between central retinal thickness and axial length (AL) or visual acuity (VA). An irregular posterior pole contour was observed in 7 eyes, unilaterally in five subjects and bilaterally in one. When comparing central retinal thickness, VA and AL in subjects with irregular posterior pole with subjects with normal posterior pole, we observed a significant association (respectively p=0.054; p=0.039; p=0.019) (Mann Whitney). Thus, subjects with an irregular posterior pole had lower VA, longer AL and tended to have a thicker central retina.
Discussion and Conclusions: In this limited – but unselected – population there was no significant association between central retinal thickness and SER, AL or VA. Subjects with an irregular posterior pole had lower VA, longer AL and tended to have a thicker central retina.
Symposium 1: Paper 5 Visual Prognosis and Ocular Complications in High Myopia. as Based on Our Danish 1948 Copenhagen High Myopia Cohort
Hans C. Fledelius, Nina Jacobsen, and Ernst Goldschmidt
Copenhagen University Eye Clinic, Glostrup & Rigshospitalet (HCF, NJ), and Danish Institute for Myopia Research, Glostrup University Hospital, Glostrup, Denmark (EG)
Purpose: To document the natural history of juvenile high myopia, with emphasis on the incidence of visual impairment, in a representative sample of Danish adolescents with high myopia followed-up till age 60 years.
Methods: Regular ophthalmic follow-up over 40 years of 39 otherwise unselected Copenhagen 14 year olds with uni- and bilateral myopia of at least −6 D, as screened from a 1948 birth-year school cohort comprising 9243 pupils. Thirty-four of the 39 had satisfactory refractive and corrected visual acuity data for a longitudinal analysis.
Results: Myopia progression for the full period ranged 0-14 diopters, and peak myopia value increased from −14 to −26 D (in a unilateral case). Mean progression from age 16 to 26 years was 2.09 D, and after age 26 myopia worsened by 1D. At the present end-point of age 60, 33 of the 34 had a best eye corrected visual acuity of at least 0.6. Eyes above 9 D myopia at inclusion - and in particular if unilateral - suffered more visual acuity decrease than those of the 6-9 D myopia subgroup. According to subsequent year 2010 information, a relatively high number have now been operated for cataract (n = 8), which usually restores vision. A total of three had had retinal detachment.
Discussion and Conclusions: With only a slight over-risk recorded due to high myopia, the visual prognosis throughout working age appeared better in our unselected sample than usually claimed with reference to selected eye hospital series. Within our series, a relatively poorer prognosis seems to pertain to the eyes with adolescent myopia already above 9 D, though with no specific early markers suggested for pointing out increased risk.
SYMPOSIUM 2: HIGH MYOPIA - EPIDEMIOLOGY AND GENETICS
Chairs: Terri L. Young and Ernst Goldschmidt
This symposium highlighted current research interests in myopic refractive error phenotype and genetics, ranging from familial case studies to single nucleotide genome-wide association studies. Familial clinical observations emphasized mildly better prognosis and ocular morbidity for highly myopic individuals in a homogenous cohort of Caucasians than that reported in the literature. This same cohort also offered insights into inter- and intra-family variation in the high myopia phenotype. Genome-wide association studies in Asians and Caucasians have revealed genes of interest, with confirmed replicate groups. An overview presentation provided integrative analytical approaches to incorporate biologic information converging from multiple sources to enhance discovery of genetic influences of refractive error development.
Symposium 2: Paper 1 Inter- and Intra-Family Variation in High Myopia Phenotype
Ernst Goldschmidt, Hans C. Fledelius, and Thomas Rosenberg
Danish Institute for Myopia Research, Glostrup University Hospital, Glostrup, Denmark (EG, HCF), and Gordon Norrie Center for Genetic Eye Diseases (TR)
Purpose: To demonstrate the clinical phenotype heterogeneity and the genetic influence in hereditary high myopia, based on the 1948 Copenhagen High Myopia Cohort, by analyzing interfamily variation and intrafamily similarities.
Methods: A family study of parents and offspring with 36 probands having uni- or bilateral myopia of at least −6 D was undertaken in 1964 and the 36 pedigrees with detailed refraction data published in 1968. A reexamination of selected families including offspring of the probands was performed in 2008.
- In two sisters, one has unilateral high myopia, the other bilateral. three myopic eyes have a peaked cornea (r=7.03 – 7.12) and an axial length(AL) around 24 mm. Normal visual acuity (VA). Myopia diagnosed at age 2½. No progression.
- A father and two daughters have bilateral high myopia (10 to 16D) with flat corneas, AL around 30 mm and a moderate visual loss due to posterior pole dystrophy. Myopia diagnosed at school start. Moderate progression
- A mother and two sons have bilateral high myopia (12 to 17 D), normal corneal curvature and AL between 27 and 30 mm. Normal VA. One of the sons had a retinal detachment in one eye at age 25. Myopia diagnosed around school start with progression also during adulthood.
- A family with five affected cases in three generations, the four with extreme myopia over −15D and AL over 30 mm of whom two have poor vision and the other two only a moderate reduced VA. A girl 13 years old has normal VA and only −10. Corneal curvature varies from 7.5 to 8.5 mm. All have very early onset with nearly no progression and no degenerative findings of the posterior poles.
Discussion and Conclusions: Hereditary high myopia represents several phenotypes characterized by differences in age-of onset, myopia progression, visual acuity, retinal degenerations and eye shape suggesting substantial genetic heterogeneity. Molecular genetic studies of multiple families should account for phenotype differences. The intrafamily concordance suggests only moderate influence from environment.
Symposium 2: Paper 2 A Genome Wide Association Study for Degenerative Myopia in a Japanese Cohort
Department of Ophthalmology and Visual Sciences, Kyoto University Graduate School of Medicine, Kyoto, Japan
Purpose: To identify genetic determinants associated with pathological myopia.
Methods: Two genome wide association studies (GWAS) on degenerative myopia were done. As an initial experiment, a genome-wide association study, analyzing 411,777 SNPs with 830 cases and 1,911 general population controls in a two-stage design (297 cases and 934 controls in the first stage and 533 cases and 977 controls in the second stage) was done by using Illumina HapMap550 chips. Additional 208 cases and 3,117 controls were also subjected to a GWAS. In this experiment Illumina HapMap610 chips were used as a platform.
Results: In the first GWAS, 22 SNPs that showed P-values smaller than 10–4 in the first stage were selected and tested for association in the second stage. The meta-analysis combining the first and second stages identified an SNP, rs577948, at chromosome 11q24.1, which was associated with the disease (P = 2.22×10−7 and OR of 1.37 with 95% confidence interval: 1.21–1.54) (PLos Genetics. 2009;5(9): e1000660). The data analysis of the second experiment is now underway.
Discussion and Conclusions: Although an SNP showing P = 2.22×10−7 and OR of 1.37 with 95% confidence interval: 1.21–1.54 was found in the first experiment, the second experiment may or may not reproduce the Results: Most likely, bigger sized GWAS is needed to identify SNPs that play a role in the development of pathologic myopia.
Symposium 2: Paper 3 Myopia Genetics - An Update
Terri L. Young
Duke University Center for Human Genetics, Durham, North Carolina, and Duke- National University of Singapore Graduate Medical School – Singapore, Singapore
This presentation is a review of current approaches in utilizing genomic information in genetics studies of myopia. Approaches using genomic convergence and biological pathway analyses will be highlighted as complementary methods to potentially improve outcomes in genome wide association studies. As we move towards integrative analyses in system biology, we need to think beyond our current genome wide association approaches and develop methodologies that will incorporate genomic information to enhance discovery. As more biological context is included in the analyses, the information content become richer and more relevant.
Symposium 2: Paper 4 Linkage and Association Analyses of High Grade Myopia in France
Purpose: Myopia, or nearsightedness, is a worldwide common type of refractive error. High grade myopia is one of the main causes for blindness. The identification of myopia genes will bring significant social and economical benefits due to myopia's increasing prevalence. The purpose of our study is to locate susceptible loci of high grade myopia using both linkage and association analyses In France.
Methods: High grade myopia is defined as refractive error less than −5D. The linkage study involves 233 individuals from 26 French families. Multipoint parametric and non parametric analyses were conducted with Genehunter and Merlin software. Association analysis consists of 192 high myopia cases. Whole genome genotyping using Affymetrix SNP 6.0 array was performed. The statistical analysis was performed by PLINK. The axial length information was treated as phenotype instead of the refractive error information. A general linear regression model was applied.
Results: The linkage study suggested a signal in chromosome 7p15 based on non parametric analysis. The association study showed 15 candidate SNPs across genome. A replication study involving 600 high grade myopia individuals was underway.
Discussion and Conclusions: Linkage analysis is an important method to identify genetic loci before 2005. However It requires responsible genes to have larger effects and the result normally requires further fine mapping. The genome-wide approach of using axial length as a quantitative trait may have the ability to reveal novel candidate genes and loci warranting further investigation and replication.
SYMPOSIUM 3: EPIDEMIOLOGY AND RISK FACTORS IN MYOPIA
Chairs: Seang-Mei Saw and Kathryn Rose
This symposium consisted of four presentations, covering distinct approaches to risk factors for myopia. Jane Gwiazda examined the balance between parental myopia and early (1 year of age) refractive status, showing that adolescents with 2 myopic parents were at risk of myopia, irrespective of their early refraction. In contrast, early refraction was a more significant determinant in children with no, or one, myopic parent. Seang-Mei Saw examined the determinants of early onset myopia in Singapore, finding that parental myopic status was a major factor, but that the environmental factors near work and outdoor activity had little effect, although as previously reported, outdoor activity appears to be a significant protective factor in older children. She also presented the unexpected finding that the prevalence of myopia was high in children in the first year of life, peaked at around 2-3 years and then declined. Kathryn Rose reported on the clustering of students with myopia by school and educational stream, particularly at the high school level. While major differences in the prevalence of myopia between schools and classes have been noted previously, here the differences appear to be driven, at least in part, by parental choices about educational pathways. All these factors and many more, contribute to the gamut of life-course influences on myopia, as discussed by Jugnoo Rahi. In addition to the conventional genetic and post-natal factors, low birth weight for gestational age, greater maternal age and maternal smoking were all associated with more myopia later in life. Which factors are associated with recent secular changes in the prevalence of myopia remains to be determined.
Symposium 3: Paper 1 The Influence of Children's Refractions at One Year on the Later Development of Myopia Varies by the Number of Myopic Parents
Jane Gwiazda and Li Deng
New England College of Optometry, Boston, Massachusetts (JG, LD)
Purpose: To investigate children's refractions at one year and parental refractive errors as risk factors for the development of myopia.
Methods: One hundred and sixty-five children had refractions at 1 year and 14/15 years, and also had refractions from both parents. The infants were refracted in the laboratory by non-cycloplegic near retinoscopy and the older children by non-cycloplegic distance retinoscopy. Parents were either refracted in the laboratory or their prescriptions were obtained from their eye care providers. Myopes were defined as having a spherical equivalent refraction < −0.50 D. Data were analyzed using odds ratios.
Results: The mean spherical equivalent refraction at 1 year was 0.92 +/- 0.84D. For children with a refraction at 1 year <1.0D, a higher proportion were myopic at age 14/15 years than for those with a refraction ≥ 1.0D at 1 year (42.4 versus 26.0%, OR=2.09, 95% CI: (1.07, 4.07)). For children with 0/1 myopic parent, there was a significant difference in the prevalence of myopia at 14/15 years by the 1-year refraction, with more myopic children in the 1-year lower Rx group compared to the higher Rx group (39.3 vs. 15.1%, OR=3.65, CI (1.47, 9.07)). For children with 2 myopic parents there was no significant difference in the prevalence of myopia at 14/15 years by the infancy refraction (48.4 vs. 55%, OR=0.767, CI (0.25, 2.37)).
Discussion and Conclusions: For children with 2 myopic parents, the infancy refraction does not appear to make a difference in whether they become myopic by age 15 years; approximately half are myopic by that age. However, for children with 0/1 myopic parent, having a negative or low positive refraction at 1 year increases the risk of being myopic at 14/15 years. The effect of season of birth and photoperiod on refractive errors in infancy and the later development of myopia also will be discussed.
Symposium 3: Paper 2 Educational Achievement and Time Outdoors: Major Predictors of the Prevalence of Myopia
Discipline of Orthoptics, University of Sydney, Sydney, New South Wales, Australia
Purpose: To examine the contribution of environmental and lifestyle factors on the development of myopia in school-aged children.
Methods: The Sydney Myopia Study (SMS) is a large randomly selected cross-sectional study of two age samples from 34 primary schools and 21 high schools. All Year 1 (mean age 6.7 years) and Year 7 (mean age 12.7 years) students were invited to take part and over 4,000 families gave informed consent for their child to participate. As part of a comprehensive ocular examination, cycloplegic (1% cyclopentolate) autorefraction was performed. Spherical equivalent (SE) was calculated (sphere +½ cylinder) for the right eye only. Details of lifestyle and environmental factors were ascertained by questionnaire.
Results: The SMS, in parallel with other epidemiological studies in school-aged children, has reported that time spent outdoors is protective for the development of myopia. In the SMS, this protective effect was seen even when children performed high levels of near-work. A number of studies have also noted an association between myopia and higher educational achievement. The SMS found that in the first year of high school, the prevalence of myopia varied widely across schools (3-60%). The two high schools with the highest prevalence of myopia were academically selective and measures of academic achievement were strongly correlated with the prevalence of myopia in the high schools (all correlations, r >0.78) but not in the primary schools. Mean time spent in near work within a school was correlated with both academic achievement (r = 0.78) and myopia (r = 0.69), while mean time spent outdoors was negatively correlated with the proportion of children within the school who had myopia (r= −0.69). The proportion of children enrolled in a school who were from outside the normal geographical enrolment area of that school was also correlated to the prevalence of myopia in the high schools (r = 0.61) but not primary schools.
Discussion and Conclusions: These findings emphasize the care that needs to be taken when sampling from school-based populations to establish a representative sample. Our findings suggest that the high prevalence of myopia located within some schools is a form of self-selection based on aspiration for high academic achievement through particular study habits involving high levels of close work, established prior to entry to high school. While we have been able to suggest a plausible biological mechanism for the preventive effects of time spent outdoors, the biological pathways that may mediate the effect of educational aspirations and near work are not clear.
Symposium 3: Paper 3 Early Onset Myopia in Singapore Chinese Children: Prevalence and Predictors
Seang-Mi Saw, Mohammed Dirani, Audrey Chia, Kit Ian, Björn Drobe, and Tien Yin Wong
National University of Singapore (S-MS, TYW), Singapore Eye Research Institute (SMS, MD, TYW), and Essilor International, Singapore (KI, BD)
Purpose: To determine the prevalence, risk factors for myopia and correlations with peripheral refraction in Singapore Chinese children aged 6 to 72 months in the Strabismus, Amblyopia and Refractive error in Singapore Children (STARS) study.
Methods: A population-based survey was conducted in the South-Western region of Singapore. Disproportionate random sampling by 6 month age groups of Chinese children aged 6 to 72 months was performed. Participants underwent cycloplegic refraction (3 drops of 1% cyclopentolate) using the table-mounted autorefractor Canon RK-F1 in children aged 30 months and above, hand-held Nikon Retinomax K-Plus 2 in children aged 30 months and below and retinoscopy, if reliable Retinomax readings could not be obtained. In 250 children > 40 months, an open field, infrared autorefractor (Grand Seiko Autorefractor / Keratometer WAM-5500, Grand Seiko Co. Ltd., Japan) was used to measure relative peripheral refraction at the 4 eccentricities (temporal 30°, temporal 15°, nasal 15°, nasal 30°). A questionnaire assessed risk factors such as parental myopia or near work.
Results: Of the 3009 children (participation rate=72.3%) who participated, right eye data from 2639 children who agreed to cycloplegic eye drops were included. The mean right eye spherical equivalent was +0.69 D (SD = 1.15). The overall prevalence of myopia (SE at least −0.5 D) was 11.0% and high myopia (SE at least −6.0 D) was 0.2%. Myopia rates were 15.8%, 14.9%, 20.2%, 8.6%, 7.6%, and 6.4% in children aged 6-11, 12-23, 24-35, 36-47, 48-59, and 60-72 months old. Children with two myopic parents were more likely to be myopic (adjusted OR=1.91; 95% CI 1.38 to 2.63). For each 1 cm increase in height, the SER was more myopic by 0.01 D. Neither near work nor outdoor activity was associated with preschool myopia. Myopic children had relative less myopic refraction at the temporal (mean = −2.22 D) and nasal 30° (mean = −1.71 D) compared to the central meridian (mean = −2.66 D) (p < 0.001).
Discussion and Conclusions: The prevalence of myopia in young Singapore Chinese aged 6 to 72 months is high and refraction at the periphery is relatively less myopic. Early-onset myopia may be determined primarily by parental myopia.
Symposium 3: Paper 4 Myopia Over the Life Course: Prevalence and Early Life Influences in the 1958 British Cohort
Jugnoo S. Rahi, Phillippa M. Cumberland, and Catherine S. Peckham
MRC Centre of Epidemiology for Child Health, Institute of Child Health, University College London (UCL), London, United Kingdom (JRS, PMC, CSP), Institute of Ophthalmology, UCL, London, United Kingdom (JRS), and Ulverscroft Vision Research Group, Institute of Child Health, University College London (UCL), London, United Kingdom (JRS, PMC)
Purpose: To investigate the hypothesis that the excessive growth of the eye in myopia is associated with general growth and thus influenced by early life biological and social factors; and that these associations underlie recent secular trends of increasing prevalence and severity of myopia.
Methods: Design: Cohort study. Participants: 2487 randomly selected 44 year old members of the 1958 British birth cohort (27% subsample). Methods: Diverse and detailed biological, social and lifestyle data have been collected by following members since birth, through a series of clinical examinations and/or face to face interviews carried out by trained examiners. At 44 years, cohort members underwent autorefraction using the Nikon Retinomax 2, under non-cycloplegic conditions. A lifecourse epidemiological approach, based on four sequential multivariable ‘life stage’ models (‘preconceptional’, ‘prenatal, perinatal and postnatal’, ‘childhood’, and ‘adult’) was used to examine the influence of early life biological, social and lifestyle factors, growth patterns and ‘eye-specific’ factors on adult myopia. Main outcome measures: Myopia severity (all, mild/moderate; (Spherical Equivalent −0.75 to −5.99 diopters (D)), severe; (- 6.00D or more extreme), versus emmetropia (-0.74D to +1.00 D)) and myopia onset (early, under 16 years, versus later).
Results: 1214 (49%, 95% CI 48.8 to 50.8) individuals were myopic: 979 (80.6%) late onset. Myopia was positively associated with low birth weight for gestational age as well as sex, greater maternal age, higher paternal occupational social class, and maternal smoking in early pregnancy. It was independently associated with proxy markers of near work and educational performance, with some differences by onset and severity. In adults, higher educational attainment and socio-economic status and greater height were associated with myopia.
Discussion and Conclusions: Trends in the key influences on child health and growth identified as novel putative risk factors in this study are consistent with global trends of increasing myopia: increasing births to older mothers, increasing rates of intra-uterine growth retardation and survival of affected children, increasing persistence of smoking in pregnancy and changing socio-economic status. Prospects for prevention of myopia will likely remain poor without a paradigm shift in myopia research with life course and genetic epidemiological approaches applied in tandem in large unselected populations.
TOPIC 2: NOVEL APPROACHES TO RISK FACTORS
SYMPOSIUM 4: OPTICAL AND ENVIRONMENTAL INFLUENCES ON MYOPIA AND HYPEROPIA DEVELOPMENT
Chairs: Earl Smith, III and Don Mutti
The primary focus of this symposium was on the potential influence of peripheral refractive error on central refractive development.
In a large parametric study in chickens, Liu demonstrated that optically imposed defocus had a greater effect on central refractive development when the periphery of the eye was defocused than when the focus of the central retina was selectively manipulated. Similarly, Troilo showed that when hyperopic defocus and myopic defocus are simultaneously imposed across the retina, refractive development in the marmoset is biased in the hyperopic direction. Both of these studies are in agreement with the idea that optically manipulating peripheral vision may be an effective means to influence foveal refractive development.
In agreement with this hypothesis, Santodomingo reported that orthokeratology, a central correction strategy that also effectively reduces the degree of peripheral hyperopia, is effective in slowing axial elongation in a small sample of children over 18 months. If uncorrected, the retinal periphery may exacerbate myopic development. This possibility was suggested by a longitudinal study of refractive development in children where Schmid found a significant correlation between the development of central myopia and retinal steepness, the primary determinant of the pattern of peripheral refraction. Specifically, Schmid found that children with steep temporal retinas and, presumably more relative peripheral hyperopia, were more likely to undergo a shift in refractive error toward myopia.
Although peripheral hyperopia has been implicated as a risk factor for myopia, Smith demonstrated that in monkeys the association between peripheral hyperopia and central myopia is not always casual in nature and that in addition to regulating central refraction, visual experience can independently influence eye shape and the pattern of peripheral refractions. The nature of this peripheral visual signal was explored by Berntsen who employed aberrometry to examine peripheral retinal image quality in myopic children. He found that image quality, which varied between and along the horizontal and vertical meridians, was largely dominated by the effects of radial astigmatism.
Lastly, the symposium touched on a different potential influence on refractive error. In a study of young adults, Mutti found that myopic individuals exhibited lower blood levels of vitamin D than emmetropes. Although this difference was not associated with differences in diet or the amount of time spent outdoors, the results suggest that vitamin D might be involved in the anti-myopia effects associated with a greater amount of time spent outdoors. Understanding these factors influencing refractive error will hopefully lead to more effective treatments to slow myopia progression or to prevent its onset.
Symposium 4: Paper 1 The Effect of 2-Zone Concentric Bifocal Spectacle Lenses on Emmetropization and Eye Shape
Yue (Maria) Liu and Christine F. Wildsoet
University of California Berkeley School of Optometry Center for Eye Disease, Berkeley, California (YL, CFW)
Purpose: To characterize the role of the peripheral versus central retina in guiding emmetropization using a novel lens design to present different defocus signals to the central and peripheral retina.
Methods: Four concentric bifocal lens designs ((i) +5 D center (+5C), (ii) +5 D periphery (+5P), (iii) −5 D center (-5C), (iv) −5 D peripheral (-5P), with plano in second zone in all designs were used to differentially expose the central and peripheral retina to defocus. Five central optical zone diameters, 2.5 to 6.5 mm in 1mm increments were tested, corresponding to central visual field projections of between ∼ 21 to 51 degrees. The lenses were fitted monocularly to 17 days old White-Leghorn chicks and worn for 5 days. High frequency ultrasonography and retinoscopy were performed at baseline and at the end of experiments.
Results: Increased hyperopia with reduced axial length and myopia with increased axial length were observed with +5 D and −5 D defocus respectively. For the 2-zone lenses, peripheral defocus had a greater effect than central defocus on both on-axis eye growth and refractions. All but the 6.5 mm +5P lens induced larger changes than the +5 D SV lens and +5C lenses with CZD less than 5.5 mm had little effect. The 2-zone −5 D lenses had less effect than the −5 D SV lens, and only the 6.5 mm CZD lens of the −5C series had a significant effect.
Discussion and Conclusions: For the four 2-zone lens designs tested, peripheral defocus had a greater effect than central defocus on both on-axis eye growth and refractions, with hyperopic overshoot seen in some plus 2-zone lens designs. The latter result argues against a simple weighted average of the defocus experience imposed by the two lens zones as the determinant of the response. An alternative model involving imposed changes in ocular spherical aberration also does not fully explain the results, implying that a more complex model is required. A significant negative correlation between changes in central refractive errors and relative peripheral refractive errors was observed, associated with significant interaction between lens design and CZD, implying that the peripheral defocus incorporated in the lenses not only influenced central refractive development but also peripheral refractive development and thus ocular shape. Our study lends support to the use of concentric designed multifocal lenses for the control of human myopia.
Symposium 4: Paper 2 The Effects of Multifocal Contact Lens Designs in Non-Human Primates
David Troilo, Alexandra Benavente-Perez, Ann K. Nour, and Nancy J. Coletta
State University of New York, College of Optometry, New York, New York (DT, ABP, AKN), and The New England College of Optometry, Boston, Massachusetts (NJC)
Studies with animals over more than three decades leave little doubt that retinal defocus carries specific visual information that is used to regulate the growth of the eye to compensate for the imposed defocus. This suggests that controlling visual experience may provide a means for controlling the development of refractive errors, particularly myopia. In support of this, optical treatments with bifocals and progressive lenses in humans show some reduction in the progression of myopia, however the results are modest. One reason that myopia in humans has been so difficult to control may be that most clinical studies are exclusively concerned with axial refractive state and do not consider the refractive state in the retinal periphery. Studies in human myopes have shown that there is typically more relative peripheral hyperopia in those eyes, and if the visual signal guiding eye growth is integrated across the retina this may help explain why myopia may progress despite correction. Indeed, many animal studies have shown that visual regulation of eye growth and refractive state can be locally controlled and the effects of imposed defocus can be restricted to regions of the retina by isolating the visual experience to that region. Optical treatments that correct axial myopia while reducing any peripheral hyperopia, or even providing peripheral myopia that may serve as a “stop” growth signal, may provide a viable optical therapy for some myopes. Recent studies in both animals and humans have supported this idea. In this presentation we will describe the eye growth responses to different multifocal lens designs that we are testing in marmoset monkeys. We have looked at a concentric multizone design that imposes simultaneous hyperopic and myopic defocus across the retina. In these studies the multizone lens treated eyes grew at a slower rate and became shorter and more hyperopic than controls, a response similar to what is seen in response to imposed myopic defocus from single vision lenses. We are currently examining, and will describe, annular and aspheric lens designs that restrict defocus to the peripheral retina while providing clear vision on-axis. Our results support the idea that contact lenses designed to bend the image shell to fit the curvature of the retina may be an effective treatment for preventing, or even reversing, the development of myopia.
Symposium 4: Paper 3 Association Between Retinal Steepness at the Posterior Pole and Myopic Shift in Children
CIBAVISION Corporation, Duluth, Georgia, Salus University, Elkins Park, Pennsylvania, and Vision CRC, Sydney, Queensland, Australia
Purpose: Retinal steepness at the posterior pole was shown to be associated with peripheral refraction, and there exists strong evidence that peripheral refraction influences refractive development. The purpose of this study was to investigate whether retinal steepness is associated with myopic shift in children.
Methods: 140 emmetropic or near-emmetropic children age 7-11 years were enrolled in the study. Central refraction was measured in right eyes as central sphere equivalent refraction (CSER) and central sphere refraction (CSR) with a Shin-Nippon NVision K5001 autorefractometer at baseline and after an average of 30 months. For the estimation of retinal steepness, eye length was measured axially with a custom-made optical low coherence interferometer and subtracted from eye length measured peripherally at 20° in the nasal, inferior, temporal and superior fields. Correlation between baseline retinal steepness and central refractive shift was evaluated with a Structural Equation Modeling analysis, also considering the effects of covariates such as gender and race.
Results: CSER at baseline measured +0.05±0.54 D (mean ± SD). Shifts in CSER and CSR, as standardized over a 30-month interval to account for individual differences in the follow-up period, were −0.23 ± 0.53 D and −0.21 ± 0.56 D, respectively. In spite of small refractive changes over the measurement period and great individual variability, a weak, but significant, correlation was observed between baseline retinal steepness in the temporal retina and myopic shift in CSER (r = 0.207, p = 0.049) and CSR (r = 0.211, p = 0.044), steeper retinas displaying greater myopic shifts. No significant correlation was observed in the other retinal locations. Myopic shift was correlated with axial elongation (r = 0.333 and 0.378 for CSER and CSR, p ≤ 0.001), but not with baseline refraction. Retinal steepness did not change significantly, except in the superior retina, where it became slightly steeper by −0.053 mm (p = 0.049, paired t-test).
Discussion and Conclusions: The significant correlation between temporal retinal steepness and central myopic shift, with the latter being independent on baseline refraction, supports the hypothesis that eye shape at the posterior pole is one of the factors influencing visually guided axial eye growth and may be a better predictor for myopia development or progression than baseline refraction.
Symposium 4: Paper 4 Effects of Vision on Eye Shape and Peripheral Refraction
Earl L. Smith, III, Li-Fang Hung, Juan Huang, and Ying Qiao-Grider
University of Houston College of Optometry, Houston, Texas (ELS, LFH, JH, YQG), and Vision CRC, Sydney, Australia (ELS)
Purpose: Evidence from humans and laboratory animals suggests that the pattern of peripheral refractive can influence central refractive development. Therefore, it is important to know what factors influence the pattern of peripheral refractions. The purpose of this series of investigations was to determine the effects of visual experience on peripheral refractions.
Methods: Infant monkeys were reared with full-field form deprivation (n = 8), full-field hyperopic defocus (n = 6), nasal-field form deprivation (n = 9), nasal-field defocus (-3 D, n = 8; +3 D, n = 7), or unrestricted vision (n = 7). The pattern of peripheral refractive errors was determined by cycloplegic retinoscopy at the start of the rearing period and periodically throughout the 4-5 month treatment period and during the 4-5 month recovery period. Axial length was assessed by A-scan ultrasonography and the shape of the eye was determined by magnetic resonance imaging.
Results: In addition to altering central refractive development, full-field form deprivation and hyperopic defocus altered the shape of the eye and the pattern of peripheral refractions. Specifically, with the development of central myopia, the treated eyes became less oblate in shape and exhibited relative peripheral hyperopia. Hemi-field manipulations produced regionally selective changes in ocular shape and refractive error. Upon restoring unrestricted vision, the animals showed systematic reductions in the magnitude of induced central and peripheral refractive errors, which were associated with alterations in the shape of the globe.
Conclusions: Because the effects of visual experience on ocular growth and refractive development are mediated by independent, locally acting mechanisms, in addition to regulating central refraction, visual experience can independently influence eye shape and the pattern of peripheral refractive errors.
Symposium 4: Paper 5 Peripheral Optics in Myopic Children
David A. Berntsen, Donald O. Mutti, and Karla Zadnik
The Ohio State University College of Optometry, Columbus, Ohio (DAB, DOM, KZ)
Purpose: The peripheral retina influences eye growth in animal models and a role in myopia progression has been proposed. Aberrometry was used to determine peripheral retinal image quality using a single-valued metric and relative peripheral refraction (RPR) in four retinal quadrants in myopic children.
Methods: Baseline data from 85 myopic children in the Study of Theories about Myopia Progression were analyzed. Habitual, photopic pupil size was measured. Cycloplegic measurements were made with a COAS aberrometer centrally, 30° nasally, temporally, and superiorly, and 20° inferiorly on the retina. Zernike polynomials were fitted through the 6th order using an analysis circle with diameter equal to habitual pupil size and were used to calculate the visual Strehl ratio using the optical transfer function (VSOTF). After reconstructing peripheral wavefronts, a mask eliminated data outside the habitual oval pupil. The VSOTF was “un-normalized” relative to the neural-weighted diffraction limited case because pupil size varied across children. The metric was calculated using higher-order aberrations (HOAs) only and HOAs + RPR (i.e., residual 2nd order terms after subtracting central 2nd order terms). Data analyses included repeated-measure ANOVAs with Tukey's post-hoc t-tests.
Results: The mean (± SD) age, spherical equivalent refractive error, and photopic pupil size were 9.8 ± 1.3 years, −1.95 ± 0.78 D, and 5.25 ± 0.80 mm, respectively. Image quality differed by retinal location (p < 0.0001) and was best centrally (114,487 ± 67,861). For HOAs only, image quality was next best 20° inferiorly on the retina (80,974 ± 41,295) and was poorest 30° nasally (61,345 ± 32,372), temporally (66,671 ± 39,675), and superiorly (64,279 ± 46,779). For HOAs + RPR, no difference was found between inferior (19,815 ± 20,260) and nasal locations (15,144 ± 15,558), which were worse than centrally. Image quality was poorest for temporal (5,306 ± 4,783) and superior retina (6,555 ± 6,935). Peripheral astigmatism was greater temporally and superiorly than inferiorly and nasally (p < 0.05). Horizontal relative peripheral hyperopia (30° nasal retina +0.56 ± 0.59 D; 30° temporal retina +0.61 ± 0.77 D) and vertical relative peripheral myopia (30° superior retina –0.36 ± 0.92 D; 20° inferior retina –0.48 ± 0.83 D) were found.
Discussion and Conclusions: Retinal image quality varies by retinal location and was best centrally. Image quality was poorest temporally and superiorly when considering RPR, which was largely due to peripheral astigmatism. Asymmetry between vertical and horizontal meridian RPR was found.
Symposium 4: Paper 6 Myopia Control With Orthokeratology Contact Lenses in Spain (Mcos): Design, Baseline Findings and 18 Month Refractive & Biometric Data
Jacinto Santodomingo-Rubido, Cesar Villa-Collar, Bernard Gilmartin, and Ramon Gutierrez-Ortega
Menicon Co., Ltd., Nagoya, Japan (JSR), Clinica Novovision, Madrid, Spain (CVC, RGO), and School of Life and Health Sciences, Aston University, Birmingham, United Kingdom (BG)
Purpose: To compare axial length growth between white myopic children wearing orthokeratology contact lenses (OK) and distance single-vision spectacles (SV) over a 2-year period. We outline the methodology adopted, baseline data and preliminary refractive and biometric observations following the first 18-months trial duration.
Methods: Subjects 6 to 12 years of age and with myopia of −0.75 to −4.00DS and astigmatism ≤1.00DC were prospectively allocated OK or SV correction. Measurements of axial length (Zeiss IOLMaster), anterior chamber depth, corneal topography, cycloplegic refraction and visual acuity were taken at 6-month intervals.
Results: Thirty-one children were fitted with OK and 30 with SV. Baseline refractive errors and biometric parameters were not statistically different between groups (p>0.05). Over the first 18-month trial period, axial length increased significantly over time in both study groups (p<0.0001), but the SV group experienced a greater axial elongation in comparison with the OK group (p=0.01). Both groups showed a small, but statistically significant change in anterior chamber depth over time (p<0.05), which was greater in the SV group in comparison to the OK group (p=0.03). Significant differences in refraction were found over time, between groups and for the time:group interaction with regard to the spherical (p<0.01), but not cylindrical components (p>0.05). As expected, the OK group experienced a significant corneal flattening in comparison to the SV group evidenced by the change in the flatter and steeper corneal powers (p<0.0001) and corneal shape factor (p<0.003).
Discussion and Conclusions: Orthokeratology lens wear attenuates axial elongation in comparison to distance single-vision spectacles in children.
Symposium 4: Paper 7 Nutrition, Vitamin D, and Refractive Error
Amanda R. Marks and Donald O. Mutti
The Ohio State University College of Optometry, Columbus, Ohio (ARM, DOM)
Purpose: Several cross-sectional studies have shown that myopes spend less time in outdoor activities and longitudinal data suggest that time outdoors may be protective against myopia onset. We evaluated whether cutaneously-derived vitamin D from outdoor exposure might play a role in this process.
Methods: Subjects provided 200μl of peripheral blood in addition to survey information about dietary intakes (Block Kids Food Frequency Questionnaire) and time spent in indoor or outdoor activity. The 22 subjects ranged in age from 13 to 25 years. Myopes (n = 14) were defined as having at least −0.75D of myopia in each principal meridian and non-myopes (n = 8) had +0.25D or more hyperopia in each principal meridian. Blood level of vitamin D was measured using mass spectrometry.
Results: Unadjusted blood levels of vitamin D were not significantly different between myopes (13.95 ± 3.75ng/ml) and non myopes (16.02 ± 5.11ng/ml, p = 0.29), nor were the hours spent outdoors (myopes = 12.9 ± 7.8 hours) (non-myopes = 13.6 ± 5.8 hours, p = 0.83). Five dietary variables showed significant negative correlations with blood vitamin D (total sugar, carbohydrate, folate/folic acid (food or total in the diet), and vitamin B6). In a multiple regression model, total sugar and folate from food remained significantly negatively associated with blood vitamin D. Two additional nutrients, theobromine and calcium, were positively associated with blood vitamin D after adjustment for total sugar and folate from food. Refractive error group and demographic variables such as age and gender were then added to this four-nutrient base model. Myopes had lower levels of blood vitamin D by 3.41ng/ml compared to non-myopes, adjusted for age and dietary intakes of total sugar, folate from food, theobromine, and calcium (p = 0.005 for refractive error group, model R-squared = 0.76). Gender, time outdoors, and dietary intake of vitamin D were not significant in this model.
Discussion and Conclusions: Adjusted for differences in dietary intakes, myopes appear to have a lower blood level of vitamin D than non-myopes. The lack of association between blood vitamin D and either time outdoors or dietary intake of vitamin D suggests that this difference may not be driven solely by environmental influences. However, no firm conclusions can be drawn about the role of time outdoors and vitamin D as they relate to myopia at this small sample size. Yet the significantly lower levels of blood vitamin D in myopes are, at a minimum, consistent with the hypothesis that cutaneously-derived vitamin D might play a role in the protective effect of time outdoors.
SYMPOSIUM 5: OUTDOOR, LIGHT AND MYOPIA - ANIMAL STUDIES
Chairs: Regan Ashby and Richard Stone
Howard Howland opened the symposium reviewing the extensive literature on the effects of light regimes on eye growth in laboratory animals. This work began in the 1950's with an incidental observation that constant light rearing increases overall eye size in chicks. This early work progressed to investigations involving other photoperiod regimens and studies of the hormone melatonin. More recently, endogenous rhythms in the retina have been identified; and the complexity of the photoperiod effects on overall eye anatomy has been recognized, including influences on both the vitreous chamber and the anterior segment.
Regan Ashby described how high illuminance lighting levels the reduced accelerated growth response of the chick eye to either minus lens wear or translucent diffusers and enhanced the growth suppression from plus lens wear. Based on pharmacological responses, it appears that the inhibition of deprivation myopia by light is mediated at least in part by dopamine, a retinal neurotransmitter previously implicated in refractive development. Yuval Cohen then indicated that the ocular growth effects of continuous lighting in chick are highly dependent upon the illumination level – not only vitreous chamber size but also altered anterior segment parameters. Rearing with higher intensity light resulted in progressively severe corneal flattening, with secondary hyperopia developing in response to extreme corneal flattening. In contrast, continuous but low intensity illumination permitted proper emmetropization.
Finally, Frances Rucker discussed the influences of chromatic and luminance temporal modulation on the development of refraction and ocular components in chicks not wearing lenses or goggles. Chromatic illumination flicker had different effects from purely luminance flicker on refraction and ocular components, including choroidal thickness, thus strengthening the notion that the eye combines luminance and chromatic contrasts to determine the sign of image defocus for the purpose of emmetropization.
As an overall conclusion from Symposium 5, properties of ambient illumination such as photoperiod or lighting intensity and certain luminance and chromatic signals can modulate refractive development, at least in chick.
Symposium 5: Paper 1 Light Regimes and Eye Growth in Animal Models: the Older
Howard C. Howland
Department of Neurobiology and Behavior, Cornell University, Ithaca, New York
The early literature on light regimes and eye growth began with studies of domestic fowl in the 1950s. The object of this research was to optimize the growth of poultry for the market. Incidental to the purpose of the research, it was found that constant light flattened the cornea, and resulted in angle closure glaucoma. Subsequent studies have related the abnormal growth in constant light to a failure of normal melatonin and dopamine rhythms.
Symposium 5: Paper 2 The Role of Light Intensity in Controlling Ocular Development in Chickens
Regan Ashby and Ian Morgan
ARC Centre of Excellence in Vision Science, Australian National University, Canberra, ACT, Australia (RA, IM), and Institute for Ophthalmic Research, Section of Neurobiology of the Eye, University of Tübingen, Tübingen, Germany (RA)
Purpose: To investigate the ability of high light levels to protect against the development of experimental myopia in chickens, and the role of dopamine in any protective effects.
Methods: (1) Chickens were fitted with translucent diffusers, −7 D or +7 D lenses for 5 days under either 500 lux or 15,000 lux. (2) Chicks wore diffusers for a period of four days under either 500 lux or 15,000 lux, with the high light group intravitreally injected daily with the D2 dopamine antagonist spiperone. (3) Chickens were form-deprived for 5 days, with the translucent diffusers removed daily for 15 min under one of three lighting conditions: 500 lux, 15,000 lux or ∼ 30,000 lux. (4) The effects of light intensity and light duration on dopamine release were assessed through measurements of vitreal DOPAC levels via HPLC analysis. Axial length and refraction were measured at the start and end of all treatments.
Results: 1) High illuminance levels reduced the rate of ocular growth normally seen in response to the fitting of negative lenses or translucent diffusers, and enhanced the growth suppression associated with plus lens-wear. 2) The protective effects of light against deprivation-myopia were abolished by the daily injection of spiperone. 3) The protective effect of light against the development of FDM, and the retinal release of dopamine, were greater with increasing illuminance levels. 4) Diurnal rhythms in the release of dopamine, melatonin and enkephalins were suppressed by six days of continuous illumination.
Discussion and Conclusions: Exposing chicks to high light levels retards the development of experimental myopia and reduces the rate of compensation for negative lenses, but enhances the rate of compensation for positive lenses. The retardation of deprivation myopia by light is mediated, in part, by dopamine, as the injection of a dopamine antagonist abolishes the protective effect of light. The protective effects of light, and the retinal release of dopamine, are greater with increasing illumination levels, while exposure to constant illumination eliminates the diurnal rhythm of dopamine release within 6 days.
Symposium 5: Paper 3 Light Intensity Modulates Corneal Power and Refraction in the Chick Eye Exposed to Continuous Light
Yuval Cohen, Michael Belkin, Isaac Avni, and Uri Polat
Goldschleger Eye Research Institute, Tel Aviv University, Tel Hashomer, Israel (YC, MB, UP), and Department of Ophthalmology, Assaf Harofeh Medical Center, Zerifin, Israel, affiliated to the Sackler Faculty of Medicine, Tel Aviv University, Israel (IA)
Purpose: Continuous exposure of chicks to light was shown to result in severe hyperopia accompanied by anterior segment changes, such as severe corneal flattening. Since rearing chicks in complete darkness results only in mild hyperopia and minor changes in corneal curvature, we hypothesized that light intensity may play a role in the development of refractive changes under continuous light illumination. To test this hypothesis, we examined the effects of rearing chicks under various continuous light intensities. More specifically, we investigated the refractive parameters of the chicks' eyes, avoiding light cycling effects on ocular development.
Methods: Thirty-eight chicks were reared under 24-h incandescent illumination, at three different light intensities: 10 000 lux (n = 13), 500 lux (n = 12), and 50 lux (n = 13). Their eyes underwent repeated retinoscopy, keratometry, and ultrasound biometry as well as caliper measurements of enucleated eyes.
Results: Both refraction and corneal refractive power were found to be correlated with light intensity. On day 90 after hatching, exposure to light intensities of 10 000, 500, and 50 lux resulted in hyperopia of +11.97 ± 3.7 (mean ± SD) +7.9 ± 4.08 and +0.63 ± 3.61 diopters (D), respectively. Under those intensities, corneal refractive power was 46.10 ± 3.62, 49.72 ± 4.16, and 56.88 ± 4.92 D, respectively. Axial length did not differ significantly among the groups. The vitreous chamber was significantly deeper in the high than in the low-intensity groups.
Discussion and Conclusions: During the early life of chicks exposed to continuous lighting, light intensity affects the vitreous chamber depth as well as the anterior segment parameters, most notably the cornea. The higher the intensity, the more severe was the corneal flattening observed and the hyperopia which developed, whereas continuous illumination at low intensity resulted in emmetropia. Thus, light intensity is an important factor that should be taken into account when studying refractive development.
Symposium 5: Paper 4 Refractive and Ocular Component Changes are Sensitive to the Relative Amount of Chromatic and Luminance Temporal Modulation
Frances J. Rucker and Josh Wallman
Department of Biomedical Science and Disease, The New England College of Optometry, Boston, Massachusetts (FJR), and Department of Biology, City College New York, New York, New York (JW)
Purpose: The chick eye alters its growth in response to changes in cone contrasts that simulate the effects of longitudinal chromatic aberration (Rucker and Wallman [Vision Res., 2009]). At ARVO we showed that luminance and equiluminant flicker have very different effects on emmetropization. We now explore whether the chick eye alters its growth in response to a combination of modulated luminance and color.
Methods: Chicks, not wearing lenses, were exposed daily (10am to 5pm) for three days on two consecutive weeks to 2 Hz sinusoidally modulated illumination (mean illuminance of 680 lux), either in–phase modulated luminance flicker (LUM), counterphase equiluminant flicker (EQUILUM), combined luminance and color flicker (LUM+EQUILUM) or No flicker (NF). After the three-day exposure, chicks were kept under normal lighting in a brooder for 4 days. Changes in the ocular components were measured with ultrasound and with a Hartinger Coincidence Refractometer.
Results: After the first three-day exposure LUM+EQUILUM flicker produced refractions (+0.65 D) that were intermediate to those of EQUILUM (-0.9D) and LUM (2.26 D) and NF (-0.45 D). Eye length changes over the three day period contributed to the refractions: LUM+EQUILUM (182 μm), EQUILUM (278 μm), LUM (148 μm), NF (144 μm). Choroidal thinning for LUM+EQUILUM (-17 μm) was similar to that of EQUILUM (10 μm) but less than that of LUM (-69 μm) and NF (-65 μm). During the 4 days in the brooder after exposure the eye length changes with LUM+EQILUM were again intermediate to those of EQUILUM and LUM. Daily rate of eye growth for LUM+EQUILUM (124 μm) was smaller than that of LUM (159 μm) and greater than EQUILUM (97 μm) and NF (103 μm). There was no difference in choroid thickness (LUM+EQUILUM: 50 μm; EQUILUM: 13 μm; LUM: 42 μm; NF: 36 μm).
Conclusions: Purely chromatic flickering illumination has very different effects from purely luminance flicker on refractions and ocular components; combined chromatic and luminance flicker has intermediate effects. These results strengthen the possibility that the eye combines luminance and chromatic contrasts to determine the sign of defocus in the interest of emmetropization.
TOPIC 3: SIGNALING EYE GROWTH: HOW COULD BASIC BIOLOGY BE TRANSLATED INTO CLINICAL INSIGHTS?
KEYNOTE LECTURE 2
Mechanisms of Retinal Adaptation to Spatial Stimuli and Defocus
University of Michigan, Department of Ophthalmology & Visual Sciences and Department of Molecular, Cellular & Developmental Biology, Ann Arbor, Michigan
The retina adapts its sensitivity depending on the statistics of the immediate environment. Two statistics that drive adaptation are the mean light level and the variance around the mean, also known as the contrast. Contrast adaptation occurs beyond the stage of photoreceptor glutamate release and thus arises within retinal circuitry. This talk will review recent advances in understanding the cellular mechanisms for contrast adaptation. Retinal ganglion cells adapt to contrast presented over their receptive field center. Adaptation is present in the excitatory synaptic input to ganglion cells and thus arises partly within the presynaptic bipolar cells. Additional adaptation arises at the level of ganglion cell spike generation through mechanisms that involve voltage-gated sodium and potassium channels. A slow form of adaptation evokes sustained membrane hyperpolarization in ganglion cells and depends on suppression of presynaptic glutamate release from bipolar cells. Ganglion cells adapt to contrast presented over their peripheral receptive field. The mechanism involves long-range signaling from amacrine cells, which synapse with both the ganglion cell and the presynaptic bipolar terminals. High spatial frequency stimuli presented over the receptive field periphery hyperpolarize the ganglion cell and reduce gain of the presynaptic bipolar input. Defocus of the image, as occurs in myopia, reduces contrast and will alter the receptive fields of retinal ganglion cells.
SYMPOSIUM 6: RETINAL IMAGE PROCESSING AND ERROR SIGNAL GENERATION FOR EYE GROWTH CONTROL
Chairs: Christine F. Wildsoet and Howard C. Howland
Neil Charman discussed focusing mechanisms and compared them in emmetropization and accommodation. Both of these processes require the determination of the sign of defocus, but involve different time constants. It is possible that they also give different weighting to defocus across the visual field, and perhaps also different weightings to the multitude of possible cues of defocus.
Melanie Campbell discussed monochromatic cues to the direction of defocus available to central (on axis) vision during normal emmetropization, lens-induced myopia (LIM) and recovery from LIM in chicks. It was speculated that asymmetries in the PSF, for example, introduced by astigmatism and higher order aberrations (HOA), may provide directional cues. The diurnal oscillation in refractive error may also provide a cue. In normally developing chicks, astigmatism and HOA decrease with age and thus also associated retinal blur, but more slowly than spherical refractive errors, while in the presence of imposed optical defocus, astigmatism, HOA and the diurnal oscillation in spherical refractive error all increase.
Janice Tarrant presented a method for determining accommodative errors and thus responses from wavefront data, based on the best image plane rather than the paraxial focus. Serving to emphasize the advantages of this approach, relevant data from two studies, one involving multifocal soft contact lenses and the other orthokeratology, were used to illustrate the following insights: there is generally little blur in the retinal image, differences in aberrations can account for differences in accommodative responses between emmetropes and myopes, pupil diameter significantly influences the location of the best image plane, and orthokeratology appears to induce a slowly developing change in pupil responses, a possible consequence of, and an adaptation to, associated changes in optical aberrations.
Frank Schaeffel address the topic of whether the retina can decode the sign of defocus and if so, where. He made two main points: (1) one of the retina's major jobs is information reduction and selection, as can be seen from the extreme convergence from photoreceptors to ganglion cells, and the more compressed response range for the latter cells, for example, in brightness encoding. Evidence that the system is optimized to extract differences and changes, and for “dynamic predictive coding” was discussed; (2) based on the lack of evidence that ganglion cells encode the sign of defocus in in-vitro studies, it was suggested that defocus information might not be transmitted to the visual cortex but used only for eye growth control; as an alternative explanation for the same negative result, the lack of fixational eye movements in such studies was considered, with acknowledgement that eye movements are of fundamental importance for feature detection.
Symposium 6: Paper 1 Challenging Introduction
W. Neil Charman
Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
Purpose: To provide an overview of the factors that might constrain the nature of the error signals mediating growth.
Methods: The general problem of maintaining an in-focus retinal image is considered, together with the possible tolerances in focus. The different demands and constraints on emmetropization and accommodation are compared and contrasted, and a comparison is drawn with man-made auto-focus systems. Cues to the sign of defocus (monochromatic and chromatic aberration, proximity and looming, binocular etc) are briefly reviewed. The question as to whether focus control is essentially foveal or at least partly peripheral is discussed in relation to the sensitivity of the peripheral retina to defocus and the spatial distribution of stimuli offered in real world environments. Some suggestions are made as to the optical characteristics that might be of prime importance in the accommodation and emmetropization processes.
Symposium 6: Paper 2 Keeping the World in Focus: How Might it be Achieved?
W. Neil Charman
Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
Although both accommodation and emmetropization are concerned with the production of a clear retinal images and have comparable accuracy, it is concluded that their mechanisms involve markedly different areas of retina, related to different visual needs. Accommodation is designed to produce a sharp focus of near objects at the fovea and uses a variety of cues: peripheral involvement would be detrimental when the object of interest was of small angular subtense and the rest of the visual field was at a different distance. In contrast, emmetropization may involve focus, and perhaps depend on oblique astigmatism, over a substantial area of visual field and may work best when this field is at a constant vergence, as in outdoor environments.
Symposium 6: Paper 3 Monochromatic Signals for Decoding
Melanie C. W. Campbell
Department of Physics and Astronomy and School of Optometry, University of Waterloo and Guelph-Waterloo Physics Institute, Waterloo, Ontario, Canada
Purpose: Defocus, astigmatism, higher order monochromatic aberrations (HOA) and chromatic aberration all contribute to the optical blur on the retina. Previous work has shown that chromatic and size signals are not necessary signals to emmetropization or accommodation. There are several monochromatic signals to the direction of defocus which could assist both emmetropization and accommodation. These include fourth order HOA and astigmatism. In emmetropization, the variation of either optical blur or object contrast over a period of time could also provide a monochromatic signal to the direction of defocus. Here, I will discuss to potential signals and our studies of their magnitude during normal emmetropization and in experimental myopia.
Methods: We have run a variety of experiments on the chick model of myopia in which rearing conditions are manipulated. We measure the defocus of the eye, HOA and astigmatism using a Hartmann- Shack device. We have also developed a new optical model of the eye which predicts the variation of HOA during eye growth which accompanies emmetropization. In this model, (where HOA and its associated linear blur on the retina is held constant), changes in HOA and resulting image quality on the retina during growth, were predicted using rates of growth in each of chick, monkey, and human. We have compared these predictions to the HOA measured in the chick, monkey and human eyes.
Results: Our model of eye growth predicts improvement in human optical quality between infant and adult. In chick and monkey, angular blur improves at a rate faster than that predicted by our model. Experimentally, blur due to astigmatism reduces in normal chick eyes once it exceeds a threshold value. In chick and monkey, HOA increases in response to lenses. Astigmatism in chicks increases in the presence of large optical blur. The amplitude of oscillation of JCC45 also appears to be higher in dark reared birds than in birds raised in a normal light dark cycle.
Discussion and Conclusions: These results suggest that monochromatic signals to the direction of defocus in chicks may only decrease if they are above threshold levels and that their levels may be higher in the presence of visual blur and in the dark. The decrease during emmetropization in linear retinal blur due to HOA in chick and monkey suggests that a signal from HOA would also decrease during normal growth but retinal sensitivity to this signal may increase with growth.
Symposium 6: Paper 4 The Accommodative Response: Why Measuring Aberrations Matters
Janice Tarrant and Christine F. Wildsoet
School of Optometry, University of California, Berkeley, Berkeley, California (JT, CFW)
Ocular spherical aberration changes with accommodation, from positive values in the relaxed state, to become more negative with increasing accommodation. Because of the presence of spherical aberration the best image plane of the eye is not necessarily the paraxial image plane. For an optical system with spherical aberration alone, the best geometric focus (described by ray tracing) is located three-quarters of the way between the paraxial and the marginal foci, whereas including the effects of diffraction the best image plane (determined by the point spread function) is half way between the two. There is no evidence that the eye alters its accommodative state to bring the best geometric focus onto the retina, on the contrary it appears to choose the best image plane.
Data from two studies illustrates the insights to be gained from using a wavefront sensor to measure accommodative responses. The first study assessed the effect of multifocal soft contact lenses on the ocular aberrations and accommodative responses of young adult emmetropes and myopes. The second study evaluated the long-term effects of orthokeratology on the ocular aberrations and accommodative responses of young adult myopes. For both of these studies a neural sharpness optical quality metric was used to determine the best image plane and the accommodative error was calculated relative to this plane. These accommodative responses were compared to the results calculated by Seidel defocus (the paraxial image plane).
The results of these accommodation studies demonstrated the following:
- there was very little blur in the retinal image,
- aberrations could explain the differences in accommodative responses between emmetropes and myopes,
- pupil diameter influenced the best image plane,
- the changes in aberrations induced by orthokeratology appeared to result in a slowly developing, presumably adaptive change in pupillary responses.
Symposium 6: Paper 5 If Retinal Ganglion Cells Can't Detect the Sign of Defocus, so What Retinal Cells do?
Frank Schaeffel and Erich Diedrich
Section of Neurobiology of the Eye, Ophthalmic Research Institute, Tübingen, Germany (FS, ED)
Purpose: Because it has been shown in chicks that glucagon amacrine cells express the transcription factor ZENK in correlation with the sign of imposed defocus, it was studied whether the information on sign of defocus is transmitted to ganglion cells.
Methods: Using a microelectrode array, spikes of up to 60 ganglion cells were recorded from the isolated chicken retina. Optical stimulation of the retina occurred via a CRT monitor and a 6 mm lens. Stimuli were phase-reversing checkerboards with varying field sizes and contrast. Trial lenses could be inserted in the projection beam to impose defined amounts of defocus.
Results: The numbers of spikes following phase reversal dropped with increasing defocus, with no differences when positive or negative lenses were used. They were well predicted by the MTF of a defocused optical system. This result suggests that ganglion cells do not encode the sign of defocus in vitro. Furthermore, two clusters of ganglion cells were observed, based on the linearity of responses with changing contrast. In general, spatial “visual performance” (contrast sensitivity and spatial resolution) was surprisingly similar in alert chicks and in retinas in vitro.
Discussion and Conclusions: Previous experiments have shown that the regulation of ZENK is no longer controlled by the sign of defocus, if chicks were anesthetized while they were wearing lenses (eyes were kept open, in lab environment). The major difference to alert chicks was the absence of eye movements. Also in the MEA recordings, the projected stimuli were stationary. At present, there are still two options (1) the sign of defocus information is generated at the level of amacrine cells (in alert animals) but not transmitted to the ganglion cells or (2) it is in fact transmitted to ganglion cells, but cannot be detected in vitro because it requires at least fixational eye movements to be generated. To resolve this question, future experiments require presentation of non-stationary stimuli, preferably copying the retinal slip that occurs with normal eye movements.
SYMPOSIUM 7: RETINAL SIGNALING IN MYOPIA AND HYPEROPIA: BIOCHEMISTRY & PHARMACOLOGY
Chairs: Andy Fischer, Bill Stell, and Andreas Reichenbach
The Symposium was focused upon several different aspects of (intra-) retinal signaling in myopia and hyperopia. Prof. Stell opened with data from chicks, prompting the conclusions that (i) in birds the optokinetic response (OKR) is generated by bipolar-amacrine cell circuits, upstream from the displaced retinal ganglion cells (Dogiel cells), and (ii) bipolar-amacrine cell circuits having similar spatial and possibly temporal tuning properties are involved in OKR contrast sensitivity and myopia-prevention.
Ritchie reported that RGE mutant chickens (lacking the phototransduction-related second messenger, SYMBOL-transducin or GNB3) displayed vision-guided ocular growth despite a significant reduction in visual acuity resulting from impaired activity in photoreceptors and ON-bipolar cells. These studies suggest that normal photoreceptor and ON-bipolar cell functions are not required for emmetropization.
Penha highlighted the involvement of insulin receptor and candidate down-stream second messenger signaling (MAP-kinase MEK-Erk1/2 and PI3K/pAkt) in the control of normal and myopic eye growth. Evidence was provided that small-molecule inhibitors of these pathways may be useful for inhibiting form-deprivation myopia. Prof. Fischer showed that injections of a combination of IGF1 and FGF2 (but of neither substance alone) induced rapid, excessive eye growth and extreme myopia in chicks. He provided evidence that these extreme changes resulted from a combination of posterior chamber elongation, elevated intraocular pressure, increased lens thickness, increase corneal curvature, and decreased anterior chamber depth.
Reichenbach presented data showing that in the mammalian retina, Müller (glial) cells can sense and respond to mechanical tissue stretch; this involves the production of bFGF, which had been shown by others to be neuroprotective and inhibit excessive eye growth, and thus may suggest a role of Müller cells as ‘emergency brakes’ in cases of retinal stretching by excessive eye growth.
Stone closed the Symposium by presenting Affimetrix gene-chip data from chick retinas after positive and negative spectacle lens wear. These data prompted the conclusions that (i) the genes down- or up-regulated after induction of myopia and hyperopia are different, rather than oppositely regulated, and (ii) the initial responses appear to differ from those maintained after establishment of the perturbed eye-growth patterns.
Taken together, the Symposium provided novel and intriguing data and ideas about retinal signaling in normal and perturbed eye growth.
Symposium 7: Paper 1 Retinal Signaling in Myopia and Hyperopia: Spatiotemporal Tuning and Amacrine Cell Circuits
William K. Stell, Stephan Bonfield, Giselle DeVetten, David LeBaron, Qing Shi, Sherri Tran, Floria Tse, and Katrina L. Schmid
University of Calgary Faculty of Medicine, Calgary, Alberta, Canada (WKS, SB, GD, DL, QS, ST, FT) and IHBI, Queensland University of Technology, Brisbane, Queensland, Australia (KS)
Purpose: Retinal signaling in myopia and hyperopia involves spatiotemporal analysis of visual stimuli and release of chemical messengers from retinal neurons, in particular amacrine cells (ACs), driven by local circuits tuned to image changes in space and time. Here we consider the hypothesis that the spatiotemporal tuning properties of myopia-preventing ACs, and those of dsRGCs, are due to processing in the same pre-RGC circuits.
Methods: Subjects were White leghorn cockerels, age P5-P15 (n'6 per condition). Exp. 1: Chicks were form-deprived (FD) monocularly for 5 days. FD was interrupted daily for 2 hr by viewing high-contrast square-wave gratings, spatial frequency 0.03-10 c/d, through a lens-cone device, followed by returning to FD; controls were FD, open viewing, or uniform grey during the test period. Myopia-prevention by the gratings was assessed at the end by refraction, A-scan ultrasound, eye size and weight. Exp. 2: Contrast-sensitivity (CS) of the optokinetic response (OKR) was measured in OptoMotry (Cerebral Mechanics), using vertical sine-wave gratings of spatial frequency (SF)=0.03-2.0 c/d, drifting horizontally at velocity (V)= 3-48 d/s. Luminance was photopic, 10-50 cd/m2, in both Experiments.
Results: Exp. 1: FD-induced myopia and axial elongation were inhibited strongly by interrupting FD for 2 hr/day with gratings of SF=0.1-1.0 c/d, less so at SF=3.0 c/d, and not at all at SF=0.03 or 10.0 c/d. Vertical, horizontal, and 45o oblique 1.0 c/d gratings were equally effective. Exp. 2: At the optimal drift velocity, V=12 d/s, the CS vs. SF function was inverted U-shape, with CS maximal at SF=0.5 c/d and declining sharply above SF=0.8-1.0 c/d to a 100% contrast cut-off (“Acuity”) at SF=1.3 c/d.
Discussion and Conclusions: 1. In birds, the OKR is mediated in the retina by displaced RGCs (Dogiel cells), and thus reveals their spatiotemporal properties. At the optimal SF (0.5 c/d), one bar (half-cycle) of the grating subtends ∼100-150 μm on the retina. Since this is much smaller than the dendritic field diameters of displaced RGCs (400-500 μm), the spatial resolution of these dsRGCs must be determined by the spatial scale of pre-RGC (BC-AC) circuits. 2. The similarity in spatial scale of myopia-prevention and OKR contrast sensitivity suggests that the same upstream (BC/narrow-field AC) circuits could mediate both of these functions. However, while 3 c/d gratings were clearly effective in preventing myopia, they did not elicit an OKR.
Symposium 7: Paper 2 Vision-Guided Ocular Growth in RGE Mutant Chickens with Diminished Visual Acuity
Eric R. Ritchey, Chris Zelinka, and Andy J. Fischer
College of Optometry (ERR) and Department of Neuroscience (CZ, AF), The Ohio State University, Columbus, Ohio
It is well established that vision-guided ocular growth is regulated by the retina in multiple species. This growth can be modulated in early postnatal development by form deprivation or optical defocus. Therefore, emmetropization is thought to require retinal processing of image quality. We sought to determine whether a mutant model with reduced visual acuity, the Retinopathy, Globe Enlarged (RGE) chicken, responds to form-deprivation or lens-imposed defocus in a manner comparable to wildtype (WT) animals. The RGE phenotype results from a single codon deletion and, consequently, a complete loss of GNB3 protein from photoreceptors and ON-bipolar cells. Prior to 45 days of age, the RGE mutant retina appears healthy and eyes show normal refractive development. Ocular biometrics (a-scan ultrasonography and ocular pictographs), immunohistochemistry and qPCR were utilized to examine ocular growth, up- or downregulation of Early Growth Response Gene 1 (Egr1) and retinal levels of proglucagon mRNA. We found that young (<P30) RGE chicks have greatly reduced spatial frequency sensitivity as measured by opticokinetic responses. RGE chicks under form-deprivation show increases in axial length and changes in Egr1 expression similar to wildtype controls. RGE chicks exposed to hyperopic defocus show increases in axial length and decreases in retinal glucagon levels. RGE chickens exposed to brief periods of myopic defocus show increased retinal levels of glucagon mRNA. We propose that the RGE chicken, despite a congenital reduction in visual acuity, respond to visually-guided ocular growth stimuli in a manner similar to wildtype animals and that the loss of GNB3 from photoreceptors and ON-bipolar cells does not impact vision-guided ocular growth.
Symposium 7: Paper 3 Insulin Receptor Signaling During Eye Growth
Alexandra Marchã Penha, Eva Burkhardt, and Marita Feldkämper
Institute for Ophthalmic Research, University of Tübingen, Tübingen, Germany
Purpose: Intravitreal insulin injections were shown to induce myopia in chickens. This effect was much enhanced when spectacle lenses were worn in addition. Stimulation of the insulin receptor results in the activation of two major pathways: a) mitogen-activated protein (MAP) kinase cascade and b) the phosphatidylinositol 3-kinase (PI3-kinase) pathway. The objective of this study was to identify which pathway is activated by insulin injections and to investigate whether inhibition of these pathways might influence eye growth regulation.
Methods: Eight days old chickens were treated with plus 7D lenses, minus 7D lenses or no lenses for 4 days. In addition, they were either intravitreally injected (12.5 μl) with insulin (0.05 mM) in one eye and saline in the contralateral eye, or with the PI3-kinase inhibitor LY294002 (0.05 mM) and LY 294002 plus insulin in the contralateral eye, or with the MAP-kinase inhibitor U0126 (0.05 mM) and U0126 plus insulin in the contralateral eye, respectively (n=6 per group). Chicks were injected every other day. Refractive state and axial length were measured at the beginning of the experiment and 4 days later.
Results: Insulin injections induced significant amounts of relative myopia in plus lens treated eyes and further enhanced myopia development during minus lens treatment. These changes were correlated with changes in axial length. LY294002 injected eyes were not different from saline injected eyes. Whereas insulin further enhanced eye growth in minus lens treated chicks, it had no significant additional effect in combination with LY294002. On the contrary, U0126 alone inhibited the expected hyperopia in plus lens treated animals. In combination with insulin, U0126 inhibited hyperopia development in plus lens treated animals and induced a hyperopic shift (1.5D) in control (no lens) animals.
Discussion and Conclusions: Neither the inhibition of the MAP-kinase nor of the PI3-kinase pathway influenced refractive development in minus lens treated animals. Since the MAP-kinase inhibitor influenced refractive development when plus or no lenses were worn and since it inhibited or reversed the effect of insulin in control and plus lens treated chicks, the MAPK (MEK-Erk1/2) pathway may be involved in normal eye growth and eye growth induced by negative lenses.
Symposium 7: Paper 4 Rapid Induction of Excessive Eye Growth and Extreme Myopia in Chicks by the Combination of IGF1 and FGF2
Andy J. Fischer, Eric R. Ritchey, and Chris Zelinka
Department of Neuroscience (AF, CZ), and College of Optometry (ERR), The Ohio State University, Columbus, Ohio
Recent reports have indicated that intraocular injections of insulin enhance the ocular elongation that results from form-deprivation of chicks (Zhu & Wallman 2009; Feldkaemper et al., 2009). However, insulin did not affected growth and refractive development in eyes with unrestricted vision. It remains unknown whether Insulin-like growth factors (IGF) influence ocular growth. Through the course of studies into the combined effects of IGF1 and fibroblast growth factor 2 (FGF2) upon retinal glia, we observed that treated eyes appeared larger than control eyes. Accordingly, the purpose of this study was to investigate whether the combination of IGF1 and FGF2 influenced the growth of eyes with unrestricted vision. Consecutive daily injections of IGF1 and FGF2 resulted in extreme myopia; more than 20 diopters of refractive error. In addition, treatment with IGF1 and FGF2 resulted in significant increases in axial length, posterior chamber depth, and corneal curvature, and a significant decrease in posterior chamber depth coupled with angle closure. Histological examination revealed dramatic changes to the lens including disorganization of the lens epithelium. In treated eyes, there was increased proliferation of cells within the equatorial zone of the lens epithelium and within the zonules that attached to the lens. Within the retina, IGF1 and FGF2 stimulated proliferation of microglia and a novel type of glial cells that has been recently described (Fischer et al., 2010; Rompani and Cepko, 2010). With lower doses of IGF1 combined with FGF2 there was no indication of cell death within the retina. By contrast, elevated doses of IGF1 combined with FGF2 damaged retinal neurons, particularly ganglion cells. Injections of IGF1 or FGF2 alone had no effects upon ocular size or the refractive state of the eye. We conclude that IGF1 and FGF2 act synergistically to rapidly induce extreme myopia, resulting primarily from increased posterior chamber depth and decreased anterior chamber depth. We propose that treatment with IGF1 and FGF2 may elevate intraocular pressure (IOP) through acute angle closure, and the elevated IOP, along with posterior chamber growth, may promote axial elongation.
Symposium 7: Paper 5 Retinal Glial (Müller) Cells Can Sense and Respond to Mechanical Stretch of the Retina
Niclas Lindqvist, Qing Liu, Joachim Zajadacz, Kristian Franze, and Andreas Reichenbach
Paul Flechsig Institute of Brain Research, University of Leipzig (NL, QL, KF, AR), Leibniz Institute of Surface Modification, Leipzig, Germany (JZ), and Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, United Kingdom (KF)
Purpose: If a degenerative axial myopia results from excessive ocular growth, the retina is over-stretched which causes tractional retinal detachment or splitting of retinal layers (retinoschisis). In less severe cases of axial myopia, however, the structural integrity of the retina is strikingly well-maintained if one considers its fragility. This study is devoted to the question whether there are cells in the retina which are sensitive to mechanical stress, and which may respond to mechanical stress by cellular reactions suitable to interfere with stress-induced retinal damage.
Methods: To monitor calcium-levels in Müller cells during retinal stretch, we used adult guinea pig retinae. We designed a device to stretch the retina at right angles to its surface. The retina was hold in place by negative pressure applied through two hollow metallic tubes. One of the tubes was fixed to the chamber and the other one to a micrometer-stepping motor. The calcium indicator dye, X-rhod-1, selectively stained the Müller cells and was used to monitor stretch-induced calcium rises in the Müller cells. In another series of experiments, adult Long-Evans rat retinae were used for immunohistochemical analysis after stretch.
Results: During retinal stretch the X-rhod-1 fluorescence in Müller cells increased, which indicated increased intracellular calcium levels. When retinae were kept in a stretched position, the fluorescence subsequently declined and reached basal levels after approximately 100 s. After stretch, Müller cells showed a fast activation of extracellular-signal-regulated kinase (after 15 min), and an upregulation of transcription factor c-Fos (after 1 h) and basic fibroblast growth factor (after 3 h).
Discussion and Conclusions: We show that Müller glial cells respond to retinal stretch both with fast changes, as evidenced by transient intracellular calcium increases, as well as with slower changes in protein expression. bFGF derived from Müller cells may provide protection of retinal neurons, including photoreceptors. In addition, during induction of eye enlargement by form-deprivation, exogenously added bFGF was shown to inhibit further growth of the eye. Thus, Müller cell-derived bFGF could be part of an injury-induced system aiming to limit damage to retinal cells after acute stretch and/or to limit axial elongation of the eye.
Symposium 7: Paper 6 Retinal Regulation of Eye Growth: Clues from Retinal Gene Expression After Spectacle Lens Wear in Chick
Richard A. Stone, Alice M. McGlinn, John W. Tobias, Donald A. Baldwin, and Tejvir S. Khurana
Departments of Ophthalmology (RAS, AMM), Pathology and Laboratory Medicine (JWT, DAB) and Physiology (TSK), University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
Purpose: To evaluate changes in retinal gene expression following plus or minus spectacle lens wear at two times: the earliest time (6 hours) when biochemical changes are evident in sclera and at a later time (3 days) when altered ocular form is established following image defocus.
Methods: White leghorn chicks were reared with either a +15 or – 15 diopter lens over one eye for either 6 hours or 3 days. After the chicks were killed, isolated retinal/RPE RNA was used to prepare labeled targets for Affymetrix Chicken GeneChips. Following hybridization to the microarrays, the normalized data were evaluated by analysis of variance to compare gene expression in the lens wearing eye to that in the contralateral control eye. Differentially expressed genes were identified using a false discovery rate of 10%, as a correction for the multiple comparisons inherent in microarray Methods: Real-time quantitative reverse transcription-polymerase chain reaction (qPCR) was used to validate selected genes.
Results: Low fold-changes, generally below 2, characterized altered gene expression in these conditions. While very few genes were differentially expressed by plus lens wear, well over 1000 genes were differentially expressed in each of the minus lens conditions. Common genes between the plus and minus lens conditions changed in the same directions. The altered retinal/RPE gene expression at 6 hours of lens wearing differed from that after 3 days, particularly for minus lens wear. Patterns of altered expression of specific genes will be discussed.
Discussion and Conclusions: As with goggle wear, low fold-changes characterize the altered retinal/RPE gene expression following spectacle lens wear in chick. The changes are different, not opposite, following plus or minus lens wear under the conditions studied here. Based on this retinal transcriptome analysis, the retinal mechanisms contributing to the initial responses seem different from those active once perturbed eye growth patterns are well established.
KEYNOTE LECTURE 3
Photoreceptor Activity Patterns and the Cause and Prevention of Myopia
Jay Neitz and Maureen Neitz
Department of Ophthalmology, The University of Washington Medical School, Seattle, Washington
Myopia has a major genetic component, yet attempts to identify specific genes associated with simple myopia have failed. It also has a powerful environmental component as is evident from the epidemic increases in the incidence of myopia in Asian countries in the last two decades, yet the recent environmental changes that are responsible for the upsurge and the mechanism of myopia have remained mysterious. During emmetropization the developmental process in which eye growth is regulated by visual experience, axial length increases to match the eye's optics and to compensate for genetic variation in eye size, corneal curvature, and lens power. Myopia occurs when the eye becomes overly elongated because of an abnormality in the emmetropization process. Visual signals that guide emmetropization are initiated by light absorption in photopigments in the long- (L) and middle-wavelength (M) cone photoreceptors. There are an extraordinary number of non-synonymous mutations in the cone opsin genes, OPN1LW and OPN1MW. We have discovered that alleles of these genes are the single major genetic factor underlying simple myopia. This discovery illuminates a mechanism whereby both the genetic component and the progression of refractive error mediated by visual experience operate through a common pathway. This suggests that myopia in children can be prevented by controlling their visual experiences. To test this we carried out a small study in which children wore special eyeglasses containing one experimental and one control lens for three months. Both lenses had the individual's optimal correction. The experimental lens had a colored filter designed to equalize differences in the activities of the L and M cone submosaics. Eyes wearing the experimental treatment lens grew 10 times slower than eyes wearing the control lens (p=0.001) making this a promising method for preventing myopia.
SYMPOSIUM 8: PHARMACOLOGICAL INTERVENTIONS OF MYOPIA DEVELOPMENT, SCLERAL METABOLISM
Chairs: Michael Frost and Alex Gentle
Alex Gentle reviewed scleral metabolic and structural changes in myopia, then went on to present an argument, based on data from human and animal models, supporting the use of TGF-beta to stabilize the mechanical properties of the sclera in high myopes.
Klaus Trier showed that manipulation of adenosine signaling in the sclera affected scleral structure and metabolism in animal models. His data from human clinical trials supported this thesis as dietary supplementation with 7-methylxanthine slowed the progression of myopia, while withdrawal of therapy resulted in no regression of this effect.
Jody Summers Rada reported that TGFBIp, a causative factor in a variety of corneal dystrophies, was capable of inhibiting interaction between scleral fibroblasts and their surrounding matrix, and proposed a mechanism whereby TGFBIp could impact scleral viscoelastic properties.
Elena Lomdina described studies in rabbits utilising photosensitiser compounds, activated by UVA radiation, to crosslink scleral collagen and reinforce the sclera.
Sally McFadden showed that a variant of this process, applying a photosensitiser reactive to visible wavelengths of light, could also constrain ocular growth rate. It was argued that such interventions show potential for scleral stabilization in both progressive high myopes and simple myopes.
Symposium 8: Paper 1 Overview of Recent Advances in Our Understanding of Scleral Remodelling in Myopia
Neville A. McBrien and Alex Gentle
Department of Optometry & Vision Sciences, The University of Melbourne, Parkville, Victoria, Australia (NAB, AG)
Purpose: Recent studies in human populations with myopia have continued to implicate the genes of scleral matrix structural components and their enzymatic regulators in the process of myopia development, particularly those of matrix proteoglycans. Despite increasingly strong evidence that TGF-beta is not a principle factor in the retinoscleral signaling cascade presumed to drive myopia development, human studies support the outcomes of animal studies in reinforcing that TGF-beta is a key intrascleral regulator of remodeling. This presentation will collate recent reports from human studies and present data from animal studies to demonstrate the link between scleral remodeling and TGF-beta during the development of myopia.
Methods: Form-deprivation myopia was induced for short periods in young tree shrews and the scleral mRNA expression patterns of TGF-beta isoforms were determined. Scleral fibroblasts were also cultured under the influence of TGF-beta and expression patterns of scleral matrix components determined from assay of both mRNA and radiolabeled scleral precursors.
Results: TGF-beta expression in the sclera was reduced in a matter of hours, following the induction of myopia development. TGF-beta was shown to have the capacity to regulate the expression of various components of scleral proteglycans in a fashion consistent with that previously found in myopic eyes. However, although TGF-beta regulated proteoglycan production in a dose-response fashion, individual proteoglycan components responded differently to a given concentration of TGF-beta.
Discussion and Conclusions: Despite the fact that a number of candidate genes have been identified as potential targets for pharmacological, and other, interventions in myopia control, TGF-beta remains a prime candidate for intervention given its central role in the control of scleral homeostasis.
Symposium 8: Paper 2 Adenosine Signaling Modulation in Eye Growth Control and Its Potential for Myopia Prevention
Klaus Trier, Dongmei Cui, and Søren Munk Ribel-Madsen
Trier Research Laboratories, Hellerup, Denmark (KT, SMRM), State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China (DC)
Purpose: To give a review of the experimental and clinical results regarding the role of adenosine receptors in the development of myopia.
Methods: Biochemical analysis, electron microscopy, confocal fluorescence microscopy, western blot, form deprivation in guinea pigs, clinical trial.
Results: Adenosine receptors (ADOR) of all subtypes are localized in the retina, choroid and sclera of guinea pigs, and in human retinal pigment epithelium cells and scleral fibroblasts. In guinea pigs with form deprivation myopia, a decrease in retinal protein expression of ADORA1 and an increase in expression of ADORA2B is found. Long-term treatment of rabbits with the non-selective adenosine antagonist 7-methylxanthine (7-mx) increases the content of collagen and the thickness of collagen fibrils in posterior sclera. Myopia, axial elongation, thinning of the posterior sclera, and thinning of the median collagen fibril diameter in the posterior sclera normally found in guinea pigs subjected to visual deprivation are prevented by treatment with 7-mx. Results from a 36-months clinical trial suggest that systemic treatment with 7-methylxanthine reduces the axial eye growth rate and myopia progression in myopic children aged 8-13 years.
Discussion and Conclusions: ADORs are known to modulate muscarinic acetylcholine and dopamine receptors, which are believed to play a role in the control of eye growth. Nevertheless, the role of ADORs in myopia have not previously been studied. The presented experimental and clinical results seem to corroborate that ADORs are indeed involved in the control of eye growth, and that development of myopia may be prevented by adenosine antagonists such as 7-mx.
Symposium 8: Paper 3 Manipulation of TGFBIp in the Sclera
Jody Summers Rada and Lilian Shelton
Department of Cell Biology, University of Oklahoma Health Science Center, Oklahoma City, Oklahoma (JSR, LS)
Purpose: The transforming growth factor beta induced protein (TGFBIp) is a 72 kDa extracellular protein, initially identified in an adenocarcinoma cell line where it was found to be up-regulated upon addition of transforming growth factor beta (TGF-β). Mutations of the TGFBI gene and TGFBIp result in several corneal dystrophies in humans due to the accumulation of abnormal protein aggregates in the corneal stroma. Elevated TGFBIp expression levels are generally observed in areas of active growth and high levels of TGFBIp have been found in skin, bone, kidney, cornea, and most recently, in the ocular choroid and sclera. TGFBIp is thought to function as a cell adhesion protein partly because of structural elements which are known to possess cell binding properties and partly because of the presence of the integrin-binding RGD motif.
Methods: TGFBI/TGFBIp expression was evaluated by RT-PCR and immunoblotting of human sclera fibroblast (HSF) cell lysates and culture supernatants. Fluid-phase cell attachment assays were used to investigate the effect of recombinant TGFBIp (rTGFBIp) on cell attachment to collagen type I using HSFs, human foreskin fibroblasts (HFFs), and human corneal stroma fibroblasts (HCFs). Binding assays using biotinylated rTGFBIp were used to assess TGFBIp binding to the HSF surface. Flow cytometry and immunocytochemistry were used to determine both αvß3 and αvß5 expression and localization to the HSF cell surface.
Results: We have shown that TGFBIp binds to the cell surface of human scleral fibroblasts via the integrin receptors αvß3 and αvß5, with an IC50 of 0.03nM, similar to that of other RGD- containing ligands for integrin receptors. Using in vitro cell based functional assays, we have determined that TGFBIp inhibits the attachment of human sclera fibroblasts to collagen type I, most likely by triggering downstream signaling events via integrin receptors that result in an anti-adhesive phenotype. TGFBIp did not inhibit the attachment of human corneal fibroblasts or human foreskin fibroblasts to collagen, suggesting that the effect of TGFBIp on cell attachment is relatively scleral cell specific.
Discussion and Conclusions: Together, these data suggest that TGFBIp may alter scleral fibroblast/collagen interactions resulting in increased scleral distensibility. An understanding of the molecular regulation of TGFBIp may aid in the development of therapeutic agents capable of increasing or decreasing TGFBIp expression by scleral fibroblasts to control ocular elongation.
Symposium 8: Paper 4 Manipulation of Scleral Biomechanics for the Treatment of Progressive Myopia
Elena Iomdina, Elena Tarutta, Natalya Ignatieva, Nikita Danilov, and Gregor Wollensak
Moscow Helmholtz Research Institute of Eye Diseases, Moscow, Russian Federation (EI, ET), Moscow State University named M.V. Lomonosov, Moscow, Russian Federation (NI, ND), and Martin-Luther-University, Halle, Germany (GW)
Purpose: Scleroplasty with various grafts is used to improve the biomechanical state of the sclera in progressive myopia. However, in many cases surgeries do not stop the condition from progressing. Our goal is to develop new methods of improving biomechanical stability of the sclera by way of increasing the cross-linking level of scleral collagen structures.
Methods: Two types of experiments were performed: 1) sclera strengthening by UVA radiation combined with riboflavin treatment (12 eyes of Chinchilla rabbits). We used two diodes (370 nm, Roithner Lasertechnik) to expose a limited area of equatorial sclera surface to UVA for 30 minutes; 2) sub-tenon injections of cross-linking agents (0.15 ml of 0.1 M solution of glyceraldehide, GA, or treose, TO) administered under epibulbar anesthesia. GA or TO solution was injected on the scleral surface in the superior-anterior quadrant using a needle bent to match the shape of the eye. 18 rabbits received 5-7 injections with the interval of 2-3 days between them. Scleral samples of the eyes of experimental groups, enucleated 1 day, 3-4 and 6-9 months after treatment, were biomechanically tested using the biomaterial tester MINIMAT 2000 (Rheometric Scientific). Breaking load, ultimate stress (ς), Young′s modulus (E) and ultimate strain (ε) of the sample were determined. Intact fellow eyes served as control.
Results: 6-9 months after UVA treatment, the ultimate stress of the sclera of treated area was more than 3 times as high as the ς of the sclera in the respective intact area. E, despite considerable individual scatter, is averagely 5 times as high as the respective parameter in controls, ε showed no significant difference from the initial level over the 3-4 month follow-up period (largely due to substantial scattering of data), but demonstrated a statistically significant 1.8-fold fall by the end of the 9-10 months' follow-up. At this time, the sclera strengthening effect of GA injections is more substantial: the ultimate stress is 3.5 times as high as the control, the elasticity modulus 5.5 times as high, and the extensibility (ε) 1.6 times as low as the initial value. The sclera strengthening effect of TO (a less active but safer agent) was also significant.
Discussion and Conclusions: Both UVA treatment and GA/TO injections change the inner structure of the sclera. However, while GA and TO injections are more convenient, less traumatic and technically simpler methods of sclera strengthening than UVA, the clinical use of injections appears to be more promising. Yet, in certain cases (such as posterior pole staphyloma), the application of UVA and riboflavin may be more advisable.
Symposium 8: Paper 5 The Effect of Scleral Cross-Linking on Emmetropisation and Eye Shape
Sally A. McFadden, Marco Coassin, Matthew S. Mattson, Julie A. Kornfield, and Dan M. Schwartz
School of Psychology, The University of Newcastle, Newcastle, New South Wales, Australia (SAM), Department of Ophthalmology, School of Medicine, University of California, San Francisco, San Francisco, California (MC, DMS), University of Rome “Campus Bio-Medico”, Rome, Italy (MC), and Department of Chemical Engineering, California Institute of Technology, Pasadena, California (MSM, JAK)
Purpose: Changes in scleral extracellular matrix in the myopic mammalian eye are believed to affect its viscoelasticity and underlie the ocular elongation associated with progressive myopia. Collagen cross-linking agents can strengthen the sclera but involve UV light which can induce severe toxicity to the retina. We developed a non-toxic cross-linking method which completely halts the normal posterior elongation of the eye when subjected to form deprivation. Since peripheral optical blur has been proposed to guide ocular growth on-axis, we studied the changes in eye shape during normal growth after modification of the peripheral sclera by cross-linking.
Methods: Guinea pigs were surgically treated at 6 days of age with either the cross-linking agents injected sub-conjunctivally, posterior to the limbus covering 2/3 of the globe of the right eye (n=7) or given sham surgery (vehicle only, n=8). The posterior pole remained untreated. In both groups, cross-linking activation was delivered by 360 degree irradiation of the treated sclera with green light for 5 mins. Optical parameters were measured the day prior to surgery and every week for 5 weeks using retinoscopy and high frequency A-scan ultrasound. Eyes were enucleated at 41 days of age for shape analysis from frozen sections.
Results: The cross-linking treatment significantly modified ocular shape in the periphery by accentuating the normal prolate shape of the eye. Relative to sham-treatment, cross-linked eyes had reduced equatorial width by 300 μm and reduced distances from the center of the lens to the retina throughout the treated zones. Despite these significant peripheral changes, cross-linking did not affect normal emmetropisation on-axis (change of −4.3D in cross-linked compared to-4.6D in sham-treated eyes over 35 days), although relative to its untreated eye, at 41 days cross-linked eyes were slightly more myopic than shams (difference of −1.8D compared to 0.1D respectively). At 41 days, eyes with the cross-linked sclera were on average 100 μm longer than their untreated fellow eyes arising from on-axis increases in the depth of the anterior chamber and thickness of the lens. In contrast, the depth of the vitreous chamber on-axis and the distance from the center of the lens to the retina about the posterior pole were unaffected by the cross-linking treatment of the peripheral sclera.
Discussion and Conclusions: Cross-linking of the anterior 2/3 of the sclera significantly altered the shape of the eye reducing the equatorial diameter, but without affecting normal growth about the posterior pole. It suggests that cross-linking can effectively constrain ocular growth in a local region. In the face of perturbation in growth of the peripheral sclera, the mammalian eye is able to coordinate the growth of both optical and scleral factors to maintain emmetropization.
SYMPOSIUM 9: RPE - CHOROIDAL - SCLERAL SIGNALING
Chairs: Xiaoying Zhu and Jody Summers-Rada
Visually guided ocular growth requires a signaling cascade which links retinal image processing to sclera growth and remodeling. The papers in this symposium describe unique properties of the RPE and choroid that may play roles in locally controlled ocular growth regulation.
Debora Nickla (New England College of Optometry, Boston, MA) provides evidence that acetylcholine may mediate choroidal thinning through stimulation of non-vascular smooth muscle in the choroid while prostaglandins may mediate choroidal thickening through changes in uveoscleral outflow.
Christine Wildsoet (University of California Berkeley) has demonstrated that induced retinal defocus alters the expression in the RPE of a variety of growth factors including TGF-β, which have the potential to mediate downstream changes in the choroid and sclera and in some cases, may be linked to myopia-related pathologies.
Jody Summers Rada (University of Oklahoma) suggests that choroidal expression of hyaluronic acid synthase 2 (HAS2) stimulates the synthesis and accumulation of hyaluronan within the choroid which results in choroidal thickening observed during recovery from induced myopia.
Finally, Falk Schroedl (Paracelsus University Salzburg, Austria) describes the neurochemical coding of the intrinsic choroidal neurons and provides evidence that they receive input from multiple autonomic pathways and possibly also from other intrinsic choroidal neurons. Still, the neuronal control of choroidal thickness is poorly understood.
Symposium 9: Paper 1 A Role for Muscarinic Agonists in the Choroidal Responses to Defocus in Chickens
Debora L. Nickla, Xiaoying Zhu, and Josh Wallman
The New England College of Optometry, Boston, Massachusetts (DLN), and The City College of CUNY, New York, New York (XZ, JW)
Purpose: In chicks, muscarinic antagonists inhibit the development of experimentally induced axial myopia, and transiently increase choroidal thickness. We have recently presented evidence that the agonists carbachol and oxotremorine cause significant choroidal thinning, which may be linked to increased ocular elongation. Now, we examine two other muscarinic agonists, pilocarpine and arecaidine. Furthermore, to test the hypothesis that increased uveoscleral outflow might thicken the choroid (fluid from the anterior chamber can move to the choroid), we treated eyes with the prostaglandin PGF2α.
Methods: In vivo: Eyes of chickens 2-3 weeks old were injected with drugs (pilocarpine (M1/M3): dose=50 μg, n=9; arecaidine (M2): dose=80 μg, n=6; PGF2α, dose=0.8 μg; n=14) dissolved in 20 μl saline, or saline alone (n=32) as a control. Ocular dimensions were measured repeatedly using high-frequency A-scan ultrasonography before, and during the 48 hours after, the injections. In vitro: Paired eyecups without retinas were cultured either with PGF22α (4 μg/ml; n=11), or plain medium for 24 hours, then put into plain medium for 24 hours. Choroidal thickness was measured at the start and at 1, 3 and 24 hours later. Scleral glycosaminoglycan (GAG) synthesis was measured after 48 hours.
Results: In vivo: Arecaidine had no effect at 3 hours, but caused significant choroidal thinning by 24 hours (-46 μm vs 3 μm; p<0.005); this thinning was similar to that caused by both oxotremorine and carbachol (Nickla et al., ARVO 2010). By contrast, choroids of eyes treated with pilocarpine significantly thickened at 3 hours (drug vs. saline: 66 μm vs. 11 μm; p<0.05), and returned to normal by 24 hours. The prostaglandin PGF22α also resulted in significant choroidal thickening by 1 hour (63 vs. 31 μm; p<0.05), which was gone by 3 hours. In vitro: PGF22α did not have any effect on the choroid at any time, however, it reduced scleral GAG synthesis by 44% (p<0.05).
Conclusions: The muscarinic agonist arecaidine, but not pilocarpine, caused thinning of the choroid as did oxotremorine and carbachol, supporting a role for acetylcholine (possibly acting via M2 or M3 receptors) in the choroidal responses to defocus. We speculate that this thinning may be due partly to stimulation of the non-vascular smooth muscle of the choroid. We are intrigued by the possibility that the transient choroidal thickening caused by the prostaglandin PGF22α in vivo may be a manifestation of prostaglandins increasing uveoscleral outflow; the lack of thickening in vitro is consistent with this interpretation.
Symposium 9: Paper 2 The Retinal Pigment Epithelium as a Signal Relay Between Retina, Choroid and Sclera
Christine F. Wildsoet
Center for Eye Disease & Development, University of California, Berkeley, Berkeley, California
Purpose: On-going research based on the hypotheses that the retinal pigment epithelium (RPE) plays a critical role in transferring ocular growth modulatory signals from retina to sclera makes use of the chick as an in vivo animal model as well as RPE cell cultures.
Methods: RPE is isolated from enucleated eyes post-sacrifice of chicks made myopic with monocular defocusing lenses, with ocular changes tracked using retinoscopy and A-scan ultrasonography for refractive errors (RE) and axial ocular dimensions respectively. In some studies to be discussed, animals also underwent myopia-inhibiting drug treatments. Additional pharmacological studies made use of RPE cell cultures and drugs known to inhibit myopia in vivo. Gene microarray, real time PCR, Western blots and immuno-histochemistry techniques were applied.
Results: Many RPE genes are affected by optical defocus, with differences in expression related to the sign of imposed defocus, retinal region and duration of treatment observed in one of more genes. For example, among the genes identified to have altered expression with both gene microarray and real time PCR testing in RPE from highly myopic eyes were BMP2, BMP7, DRD4, RARB, and RRH (down- regulated), and NOG, PDGFA and FIGF (up-regulated). Apomorphine, an antimyopia drug, was shown to promote secretion of TGFSYMBOL from the basal side of cultured RPE. Discussion and Conclusions: RPE cell culture data fit with a model for eye growth regulation that involves secretion of growth factors including TGFSYMBOL, which has been implicated in scleral growth by others. Some of the genes showing differential expression in response to myopia-inducing treatments could plausibly be involved in ocular growth regulation, although functional changes in RPE secondary to myopic growth may underlie some of the sustained gene expression changes. The significance of data from other research laboratories for the proposed model will also be considered in this presentation.
Symposium 9: Paper 3 Molecular Regulation of Choroidal Accommodation
Jody Summers Rada
Department of Cell Biology, University of Oklahoma Health Science Center, Oklahoma City, Oklahoma
Purpose: Several studies have convincingly shown that chicks and primates have the ability to compensate for imposed defocus by changing their rate of vitreous chamber elongation. In chicks, and to a lesser extent in primates, this compensation involves immediate changes in choroidal thickness (choroidal accommodation). The structural changes associated with choroidal thickening and the regulation of these changes is largely unknown. The present study was designed to identify gene expression changes in choroids from eyes during the process of recovery from induced myopia in order to better understand the nature of the visually guided choroidal response.
Methods: Form–deprivation myopia was induced in the right eyes of 2 day-old chicks by the application of translucent occluders. Following 10 days of deprivation, occluders were removed and chicks were provided unrestricted vision for an additional 1– 20 days (recovery). Microarray and qRT-PCR analyses were carried out on mRNA isolated from choroids of control eyes and eyes following 0 - 15 days of recovery. Paraffin sections were obtained from the posterior poles of treated and control eyes and were used for localization of hylauronic acid (HA) and retinaldehyde dehydrogenase 2 (RALDH2). Analyses of HA size and concentration were carried out using size exclusion chromatography-multiangle laser light scattering (SEC-MALLS).
Results: Hyaluronan synthase 2 (HAS2) and RALDH2 mRNA pools are rapidly upregulated in recovering choroids. HAS2 gene expression increased significantly after six hours of unrestricted vision (↑7 fold) and peaked at 24 hours (↑9 fold). In untreated eyes, HA was localized to perivascular sheaths of larger choroidal blood vessels, however following 4 – 15 days of recovery, intense labeling for HA was detected throughout the thickened choroidal stroma. Analyses of choroidal HA by SEC-MALLS indicated that HA concentration was significantly increased following 4 −8 days of recovery (↑3.5 fold ). Choroidal RALDH2 mRNA pools were significantly elevated following 12 and 24 hrs of recovery (↑60% and ↑188%, respectively) and returned to control levels by four days of recovery. RALDH2 was localized in recovering eyes to the outer third of the choroid, adjacent to the sclera, while RALDH2 was nearly undetectable in contralateral control eyes.
Discussion and Conclusions: Both HAS2 and RALDH2 mRNA pools are upregulated within 24 hrs of recovery. Increased HAS2 expression leads to significant HA accumulation in the choroidal stroma and is likely to be responsible for the stromal swelling observed during the recovery from myopia. Based on the similar temporal changes observed for choroidal HAS2 and RALDH2 expression, we speculate that HAS2 and RALDH2 upregulation represent two independent choroidal responses to myopic defocus.
Symposium 9: Paper 4 Neuronal Control of Choroidal Accommodation: A Morphological Perspective
Paracelsus University Salzburg, Salzburg, Austria
Purpose: The choroid is supplied with a dense sympathetic (superior cervical ganglion) as well as parasympathetic (ciliary and pterygopalatine ganglion, PPG) and primary afferent (sensory; trigeminal ganglion) innervation. Besides this extrinsic innervation, some though not all species possess an intrinsic choroidal innervation, mediated by ganglia and neurons within the choroid, the intrinsic choroidal neurons (ICN's). Targets of this intrinsic innervation are vascular and non-vascular smooth muscle cells. Here, we summarize the data obtained so far in birds with focus on the chicken, discuss their implementation in extrinsic circuits of the autonomic nervous system (mainly the PPG) and their impact on choroidal accommodation.
Methods: Up to date, immunohistochemistry and cytochemistry at the light- and ultrastructural level only reveals answers about ICN, any functional data are still lacking.
Results: Immunohistochemistry revealed that ICN's are apposed by sympathetic, parasympathetic and also primary afferent nerve fibers, and possibly also receive contacts from other intrinsic neurons. The majority of avian ICN's are positive for vasoactive intestinal polypeptide (VIP), galanin (GAL) and neuronal nitric oxide (nNOS), but lack choline acetyl-transferase and somatostatin. A similar chemical coding (VIP/GAL/nNOS) is found in 50% of the neurons in the PPG. Lesion studies on the PPG pathway, however, revealed no influence on compensatory response to myopic defocus. A role for the PPG in these responses however cannot be excluded because of possible sympathetic and parasympathetic interganglionic pathways.
Discussion and Conclusions: The innervation pattern in and especially to the avian choroid is more complex than expected. The neuronal control of choroidal thickness (via blood vessels or non-vascular smooth muscle cells) still is an equation with too many unknown parameters.
KEYNOTE LECTURE 4
Chew Sek-Jin Memorial Lecture: The Unresolved Questions of Myopia: Animal Models and Humans
Thomas T. Norton
Department of Physiological Optics, University of Alabama at Birmingham, Birmingham, Alabama
After more than three decades of research on animal models and the recent increase in human clinical and genetic studies, we have learned important facts but still have some distance to go before we will understand the causes of human myopia and be able to apply effective treatments to slow or prevent myopia development. The most important finding has been that there is, unquestionably, an emmetropization mechanism in animals and humans that uses visual signals to match the axial length of eyes to their own focal plane. Not only has this mechanism been demonstrated in a wide range of animal species at many different ages, but there is increasing evidence that the development and course of myopia progression in children can be affected by environmental factors (outdoor activity, muscarinic antagonists, peripheral refraction, lenses, etc.) as well as by inherited factors.
What are the important unresolved questions? There may be as many questions as there are investigators. Some include: Is the emmetropization mechanism damaged or defective in children who develop myopia? Do environmental stimuli interact with the emmetropization mechanism to cause eyes to elongate into myopia? Can genetic factors interact with the emmetropization mechanism to produce myopia in some children? At the cell-signaling level, what constitutes the “go” and “stop” signals in retina, RPE and choroid? Do genetic factors involved with juvenile-onset myopia include changes in the coding regions, and/or in the promoter/repressor regions? Can we find acceptable optical and/or pharmacological treatments that will stop myopia progression? Some of these may be answered by continued research along current lines. Others may require new strategies.
SYMPOSIUM 10: THE ORIGINS OF THE MYOPIC CASCADE: CURRENT ADVANCES GLEANED FROM SMALL ANIMAL MODELS
Chairs: Veluchamy Barathi, Liqin Jiang, and Sally A. McFadden
In humans and animals, myopia occurs when vision is disrupted implicating retinal signals as the origin of the myopic cascade. This symposium asked what changes occur in the retina in response to blur exposure.
Sally McFadden first asked the critical question of whether both signs of defocus are locally controlled within the mammalian eye. She reported that in guinea pigs, myopia still occurs when the optic nerve is cut, but the eye cannot inhibit its ocular growth; and that myopia can be induced in most, but not all, hemi-sectors when the eye is partially form-deprived; but may not be able to selectively inhibit its growth in a local region.
Wallace Foulds suggested that the chick eye may be able to use the relative wavelength distribution of light on the photoreceptors to guide the direction of its growth, with growth inhibition arising from a preponderance of exposure to blue light, and showed that outdoor light also had a relative blue bias.
Eun-Jin Lee presented the extraordinary finding that brief blur exposure causes horizontal cells to remodel in the guinea pig retina, possibly making new synapses with cone photoreceptors. This demonstrates for the first time that the visual blur stimulation that induces myopia also causes early morphological, possibly adaptive, changes in mammalian retina.
Finally, Xiangtian Zhou reported that one underlying retinal pathway for myopia may involve a functional antagonism between adenosine A2A and dopamine D2 receptors in the retina, since myopia induced in adenosine A2A receptor knock-out mice is inhibited if the dopamine D2 receptor is pharmacologically blocked. Taken together, there is little doubt that the retina undergoes multiple significant changes associated with myopic growth, but in mammalian retina, the inhibition of that growth may be through a separate pathway.
Symposium 10: Paper 1 Location of Signals Which Control Ocular Growth in the Mammalian Eye
Sally A. McFadden, Guang Zeng, Hannah Bowrey, Amelia Leotta, and Christine F. Wildsoet
School of Psychology, The University of Newcastle, Newcastle, New South Wales, Australia (SAM, GZ, HB, AL), and School of Optometry, University of California, Berkeley, Berkeley, California (CFW)
Purpose: It is often argued that signals for myopia reside in the retina because myopia still develops after the eye is disconnected from the brain, and partial myopia can be induced in the corresponding part of the eye. We studied these fundamental issues in the mammalian eye. First, we asked if section of the optic nerve in guinea pigs affects myopic and hyperopic growth using lenses and diffusers. Second we asked if myopia and hyperopia can be locally induced in the mammalian eye. We will present a summary of some of our findings on these two related questions.
Methods: A. Optic nerve section (ONS) or sham surgery was undertaken at P5 in 56 guinea pigs which wore either a +4D, −4D lens or were form deprived with a diffuser or had ONS, but did not wear a lens. Lenses were worn from P8 on the surgically–treated eyes for 2 weeks, and ocular measures were taken before and after surgery, and before, and after lens wear; and at several weeks after recovery in which lenses were removed. B. In a second study, 37 guinea pigs were monocularly form deprived in the nasal, temporal, superior or inferior visual field from P7-P14. Refractive error in cyclopleged eyes, and eye shape from frozen sections was ascertained at P14.
Results: A. Eyes become myopic and elongated from wearing −4D lenses and diffusers after ONS, but were unable to detect myopic defocus from plus lens-wear; showing nearly identical and excessive myopia in all 3 conditions within 3 days of surgery. No such change was observed from ONS alone. Inhibition of ocular growth from plus lens wear was disabled by ONS. Therefore, the associated signal either relies on the integrity of the retinal ganglion cells or on information beyond the retina. B. In the second study, we found that local myopia was perfectly induced in nasal or temporal retina. However, both dorsal and ventral retina did not show such local control. Furthermore, the superior visual field (which observes the sky) was highly resistant to developing myopia from form deprivation.
Discussion and Conclusions: In the mammalian eye, not all myopia-inducing signals are equally controlled in all parts of the retina, and indeed, it is possible that an important inhibitory growth signal may reside outside of the retina. These data question the belief that myopia and its inhibition are controlled by a unitary retinal signal.
Symposium 10: Paper 2 Outer Segment Photon Catch Distribution and Myopia
Wallace S. Foulds, Chi D. Luu, and Amutha V. Barathi
Singapore Eye Research Institute, Singapore (WSF, AVB), University of Glasgow, Scotland, United Kingdom (WSF), and Centre for Eye Research Australia, University of Melbourne, Melbourne, Victoria, Australia (CDL)
Purpose: To test the hypothesis that the degree of vergence of light traversing the retina allows it to determine its magnitude and sign on the basis of the differential distribution of photon density and photon catch along the length of the photoreceptor outer segments (OS). We have investigated the effect of rearing chicks in broadband light with a preponderance of red or of blue wavelengths to see if the pattern of eye growth and refractive development is influenced by the chromaticity of light in which chicks are raised.
Methods: Day old chicks were raised for 14 or 28 days in a light-tight enclosure lit by banks of red, blue or white emitting LEDs with a 12hour on/12 hour off periodicity. The enclosure was lined with alternating black and white vertical stripes with a spatial frequency of 4-8 cycles/degree and had a temperature controlled air supply and remote provision of food and water together with remote cleaning. Chicks were monitored by CCTV. The chromatic content of indoor and outdoor scenes was also determined to see if chromaticity might be a risk factor for myopia or its prevention.
Results: Chicks raised in white light (with a slight preponderance of blue) were mildly hyperopic at 14 days (+1.6 ±0.24D ). Chicks raised in light with 60% blue wavelengths and 40% green were hyperopic at 14 days and more hyperopic at 28 days (+2.97± 0.34D at 14d; +4.50± 0.21D at 28d). Chicks raised in 70% red light, 5% green and 20% blue were myopic at 14d and more myopic at 28d (-1.9 ± 0.59D at 14d; −2.63 ± 0.40D at 28D).
Discussion and Conclusions: Wideband chromatic lighting has an advantage over narrowband near monochromatic light for studying the effects of chromaticity on eye growth and refraction. Monochromatic light fails to induce a differential distribution of photons along the OS and has been shown not to affect refractive development in the chick. Indoor lighting has a chromatic spectrum resembling that inducing myopia in the chick. Bright outdoor scenes have a chromatic spectrum resembling that inducing hyperopia. The effects of chromaticity on refractive development although small are continuous, eventually capable of inducing high degrees of ametropia, unlike lens induced defocus the effect of which ceases once the eye has adapted to the defocus.
Symposium 10: Paper 3 Cellular Remodelling in the Mammalian Myopic Retina
Eun-Jin Lee, Guang Zeng, Norberto M. Grzywacz, and Sally A. McFadden
Department of Biomedical Engineering, University of Southern California, Los Angeles, California (EJL, NMG), and School of Psychology, The University of Newcastle, Newcastle, New South Wales, Australia (GZ, SAM)
Purpose: Retinal signals initiate a cascade of events which lead to excessive ocular elongation and myopia. We studied blur induced changes in the outer plexiform layer of the retina since we had previously found that light manipulation can initiate neuronal plasticity in early retinal processing. We report here our findings of morphological changes in horizontal cells (HC) in retinas from guinea pig eyes exposed to myopia-inducing blur.
Methods: Classical changes in refractive error and ocular growth were induced in young guinea pig eyes using minus lenses (n=60), plus lenses (n=20), and recovery from minus lens wear (n=20). Retinas were also studied in control age-matched untreated eyes. Lenses were worn on one eye from 6 days of age for either 6 or 12 days under a 12hr/12hr light/dark cycle. At P13 or P18, refractive error was measured in cyclopleged eyes and ocular length measured with ultrasound. To observe the morphology of retinal neurons, immunocytochemistry included: antibodies to calbindin to study HC and their dendritic processes; Neurofilament-H to identify HC type; Bassoon and Ribeye to study synaptic properties, and cone opsins to study HC sprout terminations. Cell apotosis was studied using TUNEL. Images were analyzed using confocal microscopy.
Results: We observed morphological changes in horizontal cells in guinea pig eyes which had induced myopic eye growth. Specifically, HC processes emerged from Type B HCs in the Outer Plexiform Layer (OPL) and ramified abnormally in the outer nuclear layer (ONL). We term this HC sprouting. We did not observe aberrant processes in other neuronal types, including rod bipolar cells and ON bipolar cells. HC sprouting processes contained elements of synaptic apparatus and appeared to make ectopic contacts with cones. In contrast, eyes wearing a +4D lens, and in fellow non-lens wearing eyes and in age-matched normal animals; HC processes ramified normally in the OPL. HC sprouting processes disappeared after 5 days of recovery from myopia, by which time ocular length had also returned to normal.
Discussion and Conclusions: Our finding that horizontal cells sprout as a consequence of brief exposure to visual defocus, and the tantalizing finding that this sprouting seems to be sensitive to the sign of defocus or the direction of ocular elongation, provides a probe to uncover not only the possible consequence of this unique plasticity, but yields insight into the retinal signal(s) which accompany myopia.
Symposium 10: Paper 4 Opposite Modulation of Visual Growth and Refraction By the Dopamine D2 Receptor and Adenosine A2A Receptor Activities During Postnatal Development
Xiangtian Zhou, Qu Li, Yinlin Zhu, Qinzhu Huang, Jianhong An, Yuan Li, Jiangfan Chen, and Jia Qu
School of Ophthalmology and Optometry, Wenzhou Medical College, Wenzhou, Zhejiang, China (YZ, QL, QH, JA,YL, JQ), and Department of Neurology, Boston University School of Medicine, Boston, Massachusetts (JC)
Purpose: Dopaminergic activity in the eye has been shown to modulate development of form-deprivation myopia. Furthermore, activation of adenosine A2A receptors can antagonize dopamine D2 receptor function in the brain. In this study, we investigated the possible opposite modulation of refractive development by the adenosine A2A and dopamine D2 receptors using combined genetic knockout (KO) and pharmacological approaches.
Methods: We evaluated ocular growth and refractive development in dopamine D2 receptor KO mice, adenosine A2A receptor KO mice and their corresponding wild-type littermates from postnatal 4 −14 weeks. Refraction was measured using eccentric infrared photorefraction. Corneal radius of curvature was evaluated by a keratometer with a + 20.0D aspherical lens mounted before it. Ocular dimensions were measured by a custom-designed optical coherence tomography which we designed. Furthermore, we studied the antagonistic interaction between A2A and D2 receptors in the control of refractive development by intraperitoneal injection of the dopamine D2 antagonist sulpiride into A2AR KO mice from P35 to P49.
Results: During postnatal development (P28 to P56), D2R KO mice displayed significantly more hyperopia than that of WT littermates at the age of P28, P42 and P63. Parallel with their hyperopic refraction, the anterior chamber depth of D2R KO mice was significantly shorter than that of WT littermates during postnatal development. By contrast, A2AR KO mice displayed significantly more myopia than that of WT littermates at the age of P28. This myopic refraction in A2AR KO mice was associated with increased vitreous chamber depth compared to WT littermates. Furthermore, sulpiride treatment reversed the changes in refraction and axial length compared to vehicle-injected mice at P49.
Discussion and Conclusions: The D2R KO mice developed relatively more hyperopia while the A2AR KO mice developed relatively more myopia during the first two months of postnatal development. Pharmacological blockade of the D2R reversed the myopic phenotype resulting from A2AR gene deletion during postnatal development. Thus, dopamine D2 receptors and adenosine A2A receptors exert opposite effects on refractive development and ocular growth during postnatal development. The antagonistic interaction of the A2AR and D2R in the modulation of refractive error suggests a fine-tuning mechanism of eye growth.
TOPIC 4: WHERE ARE GENETIC AND PROTEOMIC APPROACHES LEADING?
SYMPOSIUM 11: GENOME-WIDE STUDIES IN MYOPIA
Chairs: Jeremy Guggenheim and Chris Hammond
Genome-wide association studies (GWAS) have captured the attention of geneticists in recent years, as they represent the culmination of decades of research aiming to pinpoint common disease-predisposing genetic variants in human populations. Thus, they nicely complement the well-established linkage analysis approach for identifying rare disease-predisposing variants in isolated pedigrees that show a clear Mendelian inheritance pattern.
Virginie Verhoeven, representing the Rotterdam Study ophthalmic research group led by Caroline Klaver, reported the results of their refractive error GWAS. They identified a variant on Chromosome 15q24 close to the GJD2 gene, which conferred an approximately 1.8x risk of developing myopia (P=2x10E-14). Since the variant is intergenic, it was speculated that it may function by regulating the expression of GJD2, or one or more nearby genes.
Cathy Williams, representing the ALSPAC study group in the UK, reported preliminary findings from a GWAS of childhood refractive error. Variants within the COL4A1 gene on chromosome 13 (P=2x10E-6) and within an intergenic region at the MYP3 locus on chromosome 12q21-23 (P=6x10E-8) conferred similar levels of risk for myopia as the GJD2-associated variant. However, these and the other findings presented await replication in independent cohorts.
Robert Wojciechowski, representing the National Human Genome Research Institute's ophthalmic research group in the United States, led by Joan Bailey-Wilson, described how gene-environment interactions influencing myopia development could now be assessed, genome-wide, at the molecular level. Indeed, the most highly-significant GWAS results were found when models included interaction terms, such as gene x age and gene x education level. The most promising regions were located on chromosomes 12q13.3, 10q22.3 and 19p13.2.
Pirro Hysi, representing the Twin Research and Genetic Epidemiology ophthalmic research group in the UK, led by Christopher Hammond, began by describing a GWAS for refractive error carried out on dizygotic twins, in which a variant on chromosome 15q25 (distinct from the Rotterdam Study's GJD2-associated variant) had been identified (P=2x10E-9). Additional variants were being sought by considering the networks and pathways through which groups of genes act or interact, and this had resulted in the identification of novel variants that had failed to reach genome-wide significance in the standard, one-variant-at-a-time analyses.
Margarida Lopes, also from the Twin Research and Genetic Epidemiology group in the UK, presented findings from the first GWAS for astigmatism. Using a genetic analysis method in which astigmatism was treated as a quantitative trait, but which was robust to the highly non-normal frequency distribution of astigmatism – and employing a sample size of over 20,000 participants – the top hit implicated the gene COL13A1 (P=1x10E-5).
Thus, in summary, it appears that, like most other complex diseases/disorders, the commonly-occurring genetic variants that are responsible for causing the bulk of the risk of myopia or astigmatism in the general population, have modest effect sizes (i.e. increasing the risk of the disorder by less than 2-fold) and are numerous. However, the identification of the genes involved, the pathways through which they act, and their interaction with environmental risk factors looks likely to offer new directions for elucidating the aetiology of refractive errors.
Symposium 11: Paper 1 A Genome-Wide Association Study for Myopia in the Avon Longitudinal Study of Parents and Children (ALSPAC)
Cathy Williams, George McMahon, Kate Northstone, Jeremy Guggenheim, and Beate St. Pourcain
Centre for Child and Adolescent Health, University of Bristol, Bristol, United Kingdom (CW), Cardiff School of Optometry and Vision Science, Cardiff, Wales, United Kingdom (GM, JG), and Department of Social Medicine, University of Bristol, Bristol, United Kingdom (KN, BSP)
Purpose: To examine potential genetic determinants of refractive error at age 15 in the ALSPAC cohort.
Methods: The Avon Longitudinal Study of Parents and Children (ALSPAC) was designed to investigate genetic and environmental factors during pregnancy or childhood that affected the development, health or well-being of the child. All pregnant women living in the Bristol area of the UK with an expected delivery date between 01/04/1991 and 31/12/1992 were eligible for inclusion. Participants in ALSPAC underwent non-cycloplegic autorefraction and ocular biometry (IOLMaster axial length measurement) at age 15 in a research clinic. Quality-checked GWAS data (310k Illumina chip) were available for >1,000 participants with axial length and >2,000 participants with autorefraction measures. Analysis was carried out with PLINK assuming an additive genetic model.
Results: No directly genotyped SNP reached genome-wide significance (taken as P<5 × 10-8). Suggestive evidence for association (P<10-6) with axial length was observed a for a SNP for at the MYP6 locus on chromosome 22q12.
Discussion and Conclusions: Follow-up analyses using imputed genotypes is on-going. Replication will be sought in independent subject cohorts, especially since the axial length analysis is underpowered to identify genes of even moderate effect size. Our results are consistent with studies suggesting that the genetic aetiology of myopia is complex.
Symposium 11: Paper 2 Genome-Wide Association Study Identifies a Locus on Chromosome 15Q14 for Refractive Errors and Myopia in the General Population
Caroline C. W. Klaver, Virginie J. M. Verhoeven, Abbas M. Solouki, Cornelia M. van Duijn, Annemieke J. M. H. Verkerk, M. Kamran Ikram, Pirro G. Hysi, Dominiek D. G. Despriet, Leonieke M. van Koolwijk, Lintje Ho, Wishal Ramdas, Monika Czudowska, Robert W. A. M. Kuijpers, Najaf Amin, Maksim Struchalin, Yurii S. Aulchenko, Gabriel van Rij, Frans C.C. Riemslag, Terri L. Young, David A. Mackey, Timothy D. Spector, Theo G. M. F. Gorgels, J. J. M. Willemse-Assink, Aaron Isaacs, R. Kramer, Sigrid M. A. Swagemakers, Arthur A. B. Bergen, Andy A. L. J. van Oosterhout, Ben A. Oostra, Fernando Rivadeneira, Andre G. Uitterlinden, Albert Hofman, Paulus T. V. M. de Jong, Christopher J. Hammond, and Johannes R.Vingerling
Department of Ophthalmology, Erasmus Medical Center, Rotterdam, the Netherlands (CCWK, AMS, VJMV, MKI, DDGD, LMvKSW, LH, WR, MC, RWAMK, GvR, JRV), Department of Epidemiology, Erasmus Medical Center, Rotterdam, the Netherlands (CCWK, VJMV, AMS, CMvD, MKI, DDGD, LH, WR, MC, NA, MS, YSA, AI, AALJvO, FR, AGU, AH, PTVMdJ, JRV), Department of Bioinformatics, Erasmus Medical Center, Rotterdam, the Netherlands (AJMHV, SMAS), Department of Neurology, Erasmus Medical Center, Rotterdam, the Netherlands (MKI), Department of Twin Research and Genetic Epidemiology, King's College London School of Medicine, London, United Kingdom (PGH, TDS, CJH), The Rotterdam Eye Hospital, Rotterdam, the Netherlands(LMVK), Bartiméus, Institute for the Visually Impaired, Zeist, the Netherlands (FCCR), Center for Human Genetics, Duke University, Durham, North Carolina (TLY), Lions Eye Institute, University of Western Australia, Centre for Ophthalmology and Visual Science, Perth, ACT, Australia (DAM), Department of Clinical and Molecular Ophthalmogenetics, Netherlands Institute of Neurosciences (NIN), An Institute of the Royal Netherlands Academy of Arts and Sciences (KNAW), Amsterdam, the Netherlands (TGMFG, AABB, PTVMdJ), Department of Ophthalmology, Amphia Hospital, Breda, the Netherlands (JJMWA), Department of Ophthalmology, Fransiscus Hospital, Roosendaal, the Netherlands (RK), Department of Genetics, Erasmus Medical Center, Rotterdam, the Netherlands (SMAS), The Cancer Genomics Center, the Netherlands (SMAS), Department of Clinical Genetics, Academic Medical Center, Amsterdam, the Netherlands (AABB), Department of Ophthalmology, Academic Medical Center, Amsterdam, the Netherlands (AABB), Department of Clinical Genetics, Erasmus Medical Center, Rotterdam, the Netherlands (AALJvO, BAO), and Department of Internal Medicine and Clinical Chemistry, Erasmus Medical Center, Rotterdam, the Netherlands (FR, AGU)
Purpose: Myopia is highly heritable, nevertheless identification of susceptibility genes has been challenging. We aimed to assess genetic risk factors for this trait in the general population.
Methods: We conducted a genome-wide association study testing 2.5 million single nucleotide polymorphisms (SNP) for association with refractive error in 5,328 unrelated individuals of a Dutch population-based study using a quantitative trait loci approach. Refractive error was measured with Topcon RM-A2000 autorefractor, and analyzed as spherical equivalent. We replicated findings in four independent Caucasian cohorts (10,280 persons).
Results: We identified a significant association with a locus on chromosome 15q14. The association with the most significant SNP was P=2.21x10-14. The minor allele of this variant increased the risk of myopia [1.83 (95% CI 1.42, 2.36) for myopia versus hyperopia]. The associated region lies proximal to genes which are highly expressed in the retina, and appears to harbor regulatory elements which may influence transcription of these genes.
Discussion and Conclusions: Our data suggest that common variants at chromosome 15q14 influence susceptibility for refractive errors in the general population.
Symposium 11: Paper 3 Astigmatism Genome-Wide Association Studies
Margarida C. Lopes, Toby Andrew, Tim D. Spector, and Christopher J. Hammond
King's College London, London, United Kingdom (MCL, TA, TDS, CJH)
Purpose: Astigmatism is a complex trait, likely to be influenced by both genetic and environmental factors. Recent large twin studies of refractive error have found a high heritability of approximately 60% where dominant effects explained most of the phenotypical variance. We conducted the first genome-wide association study (GWAS) and meta-analysis of astigmatism in order to identify genetic loci that might be associated with this trait.
Methods: GWAS was conducted, initially in 2341 twin subjects (1172 DZ) with the Illumina 317k SNP chip at the Sanger Centre, and subsequently, for replication, in 1749 independent UK twins (1170 DZ) with the Illumina 610k SNP chip at CIDR using polygenic models. Subsequently, the two different data sets were meta-analysed and then mega-analysed resulting in a total of 4270 twin subjects (2671 DZ) analysed for 627,116 SNPs. Characterisation of astigmatism susceptibility genes was performed in silico.
Results: The 317k GWAS identified SNP associations (p<1.05x10-5) with astigmatism in genes AC011592.5 (SNP rs2727385), DACH1 (SNP rs7328290) and COL13A1 (SNP rs2642609). After completing the meta-analysis and mega-analysis the rs2642609 SNP showed strongest association with p-values of 1.23x10-5 and 6.25x10-5 respectively. In silico analysis has shown that this SNP falls in a 24Kb linkage disequilibrium block with low recombination rate that overlaps the promoter and first exon.
Discussion and Conclusions: COL13A1 is found to be widely expressed in ocular tissues including the cornea of adult human tissues. The transcripts for this gene are subject to complex and extensive splicing events involving almost all exons, explaining the 19 different isoforms. COL13A1 is regulated by the complex VitD3-VDR-RXR. Retinoic acid signaling pathways are complex and play an important role in eye development, including the cornea. Although the result was not genome-wide significant, identification of COL13A1 as a candidate gene may provide new insights into astigmatism and advance understanding of refractive error, which affects a considerable part of the world population.
Symposium 11: Paper 4 Interaction Effects in Genome-Wide Association Studies With Examples From the Framingham Eye Study
Robert Wojciechowski and Joan E. Bailey-Wilson
Statistical Genetics Section, Inherited Disease Research Branch, National Human Genome Research Institute (NIH), Baltimore, Maryland (RW, JEB-W)
Purpose: Both genetic and environmental factors play crucial roles in ocular refractive development. In order to assess the main genetic and gene-environment interaction effects on refraction, we carried out whole-genome association analyses of refractive error in the Framingham Eye Study.
Methods: Participants from the parents and offspring cohorts of the Framingham Eye Study were examined between 1973 and 1991. Both refraction and genotype data were available for 3297 individuals in 1112 families at the time of analysis. Genotyping was carried out at ∼550K SNPs using Affymetrix microarray chips. Whole-genome association analyses for mean spherical equivalent (SE) refraction were performed in R using linear regression models with generalized estimating equations, clustering on 2042 nuclear pedigrees. Analyses were carried out assuming an additive genetic model. Covariates included age, sex and years of education. Separate analyses that included a genotype-education interaction term were also carried out.
Results: Age and education were statistically significantly correlated with SE (both p<0.001 in all models). Association analyses using non-interaction models yielded a minimum p=10e-7.54 at 16q23.2. Models that included interaction terms yielded more highly significant results; the most significant main and interaction effects were seen for markers at 12q13.3, 10q22.3 and 19p13.2.
Discussion and Conclusions: In a whole genome analysis of a population-based sample, we identified several SNPs that were statistically associated with SE. Our results also indicate that properly accounting for gene-environment interaction may be important in associations studies of myopia and refractive error.
Symposium 11: Paper 5 Where Next- What Do We Do Now With Myopia GWAs Analyses?
Pirro G. Hysi
Twin Research and Genetic Epidemiology Department, King's College London, London, United Kingdom
Purpose: Whole genome association analyses (GWA) have caused a revolution in the ways etiologies of complex diseases are investigated. Ophthalmic research is catching up fast and first GWA results have already become available informing about inheritable risk factors associated with many disorders, including refractive error and myopia. As more similar results are likely to become available in the future, it is important to formulate research strategies that would translate our improved theoretical knowledge of genetic risks into better care for the patients. The purpose of this presentation is to show methodological examples of how GWA results can generate clinically relevant information in the context of refractive error.
Methods: A variety of methodologies are used to illustrate translational opportunities afforded by GWA. Functional analysis of polymorphisms, pathway analysis, epistatic statistical analysis and system biology approaches results applied on the first genes associated with refractive error show the potential of using genetic association knowledge to further understanding of clinical disease.
Results: An interesting web of interacting genes and proteins can be reconstructed starting from statistical association between genetic polymorphisms and phenotypes. Several pathways appear to associate themselves with development of refractive error.
Discussion and Conclusions: GWA results are a valuable starting point in the translational research. Identification of pathways and interactions between genes and their protein products, subject to experimental validation, offers promising possibilities for therapeutic intervention and better patient care.
SYMPOSIUM 12: PROTEOMIC AND GENETIC SCREENING IN MYOPIA
Chairs: Ruth Schippert and Chi-Ho To
Since it is known that the retina is able to detect the sign of defocus, the question of how the signal for accelerated or reduced eye growth is transmitted through the RPE and the choroid towards the sclera, is open. The biochemical pathways underlying the distinctive changes in the different tissues need to be determined if we want to interfere pharmacologically with the regulation of eye growth in the future.
Ruth Schippert summarized those microarray analyses that have already been done in this field and emphasized the need to look at mRNA expression changes in single cell types rather than in complex tissues such as the retina or even in samples comprised of different tissues.
Veluchamy Barathi gave an overview about the mRNA expression changes in myopic mouse sclera, muscarinic receptor knock-out mouse sclera and the influence of muscarinic receptor agonists and antagonists on the expression of extracellular matrix proteins in scleral fibroblasts.
Thomas Norton identified several proteins associated with cell-extracellular matrix interactions with Difference Gel Electrophoresis (DIGE) and mass spectrometry that are downregulated in myopic tree shrew sclera, providing a possible explanation for the increased viscoelasticity in myopic sclera.
Using similar proteomic technology, Chi-Ho To described the dynamic change of a new candidate protein - apolipoprotein A1 (ApoA1) which is transiently down-regulated during normal as well as myopic growth. Increasing ApoA1 level in the chick retina could retard the accelerated eye growth in myopic chicks. Apparently, innate cAMP changes are involved in modulating ApoA1 expression which in turn controls eye growth.
Symposium 12: Paper 1 Gene Expression Profile in Mouse Model of Experimental Myopia
Veluchamy A. Barathi, J. L. Kwan, W. Lim, Sung R. Weon, T. S. W. Queenie, J. Wess, and Roger W. Beuerman
Singapore Eye Research Institute, Singapore (VAB, LK, WL, SRL, TSWQ, RWB), Yong Loo Lin School of Medicine, National University of Singapore, Singapore (RWB), DUKE-NUS Graduate Medical School, Singapore (RWB), and National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland (JW)
Purpose: To investigate the gene expression profile in mouse sclera during eye development and with induction of experimental myopia.
Methods: On post-natal day 10, negative 10D spectacle lenses were placed over the right eyes of M1-M5 mutant and wild type mice (n = 24 mice from each strain). Refraction was measured by automated infrared photo-refraction and axial length was measured by AC-Master, OLCI at 2, 4, 6 weeks after induction. Naive mouse sclera at P7, P14, P21, P28, P42, P56 and mouse sclera with and without myopia was subjected to expressions array analysis (Affymetrix). The microarray data (cel files) were imported into Partek Genomic Suite 6.5 beta and normalized using RMA. The variability of all samples was assessed using PCA plot and a Venn diagram was generated to compare the differentially expressed genes found among the groups. ANOVA analysis (P<0.05) was performed on the data and a set of genes was selected using a 2-fold change threshold. The set of genes was then further grouped into biological process, cellular component and molecular function using Gene Ontology (GO) enrichment. The GO enrichment score for each functional group is calculated using Chi-square test and a bar chart was generated. In addition, a forest plot showing the gene expression of each functional group was also generated. After induction of myopia, mice were treated with sub/conjunctival injection of 12 μl (100 μM) atropine for 4 weeks. Cultured scleral fibroblasts were tested with atropine, carbachol, himbacine and 4-DAMP (0.1, 1.0, 5.0 and 10 μM) for 5 days. Extracted RNA was used for real-time PCR and protein was used for Western blot analysis.
Results: Week 1 versus Week 8 had the highest number of differential genes while Week 3 versus Week 8 and Week 1 versus 3 had similar number of differentially genes. 9 genes were found in all the gene lists. While 288 genes were found in both Week 1 versus Week 8 and Week 1 versus Week 3, 191 genes were found in both Week 1 versus Week 8 and Week 3 versus Week 8. 52 genes that were shown to have significant differential expression between week 1 and week 8 mouse sclera, gene expression was validated with qPCR. Mouse 18s rRNA gene was used as an internal standard control due to its constant expression level across the age group and other housekeeping genes' expression levels were significantly different across the age group. Micro-array studies of mouse sclera showed the significant up-regulation of extra-cellular matrix (ECM) related genes compared to control at 6 weeks after induction. ECM gene levels in cultured scleral fibroblasts were down regulated after atropine, himbacine, 4-DAMP treatment, which also blocked the progression of experimental myopia and up regulated after carbachol treatment.
Conclusions: Out of the 52 genes, there were 22 up-regulated genes and 30 down regulated genes at P56. They were components of extracellular matrix and regulators of cell proliferation and cell death and were analyzed in order to elucidate the pathophysiology of sclera. Identification of genes expressed in the experimental myopic sclera contributes to our understanding of scleral biology, and potentially provides positional candidate genes for scleral disorders such as high myopia.
Symposium 12: Paper 2 Microarray Analysis and Myopia: Recent Findings and Future Possibilities
City College of the City University of New York, New York
Purpose: This talk will give an introduction about the principle of microarray analysis techniques, a summary of outcomes from several studies related to myopia and a brief introduction to a new method, the microwestern-array.
Methods: Literature-Research/Summary Talk.
Results: A number of microarray analyses, aiming to identify novel target genes that might be involved in the regulation of eye growth, have been carried out during the last 6 years. A variety of animal models, tissues, treatments and treatment durations have provided a large amount of data, which has been problematic to interpret. Although several genes that had not previously been related to eye growth were identified in each study, there was little overlap in different studies among the large number of genes tested in each microarray (usually several thousands). Nevertheless, some genes were found by more than one study to change their mRNA expression pattern in response to experimentally altered visual experience, e.g. bone morphogenetic protein-2 and vasoactive intestinal polypeptide. Validation of the data obtained by microarray analysis was mostly achieved by measuring the same samples with real-time PCR. However, the question remains of whether these changes in mRNA levels reflect changes in protein levels,. A recently published screening method for proteins, the “microwestern array” (Ciaccio et al. Nature Methods, Feb.2010) might prove to be useful in this respect.
Discussion and Conclusions: Largely because of differences in the species of animals and the visual manipulations used, as well as different methods of analysis, one cannot yet draw the big picture of the biochemical signaling cascades presumed to underlie visual control of eye growth. In order to solve the problem of the comparability across studies, the publication of raw data of experiments in publicly available databases (e.g. NCBI′s Gene Expression Omnibus (GEO)) would facilitate comparison of gene expression levels from different studies, using different manipulations (e.g. form-deprivation and the wearing of positive and negative lenses), thereby yielding a more global view on gene expression than can be obtained from a single study. The rapid advances in large-scale screening methods and new technologies raise the hope that these methodologies will further increase our knowledge about the molecular basis of myopia.
Symposium 12: Paper 3 Protein Expression Patterns in Tree Shrew Sclera During Minus Lens Compensation and Recovery
Michael R. Frost and Thomas T. Norton
University of Alabama, Birmingham, Birmingham, Alabama (MRF, TTN)
Purpose: During minus lens compensation (lens-induced myopia), the viscoelasticity of the treated sclera (creep rate) parallels the axial elongation rate, which rises initially and then returns to normal as the eye completes its compensation for the lens. During recovery from induced myopia, the creep rate rapidly drops below normal, slowing the axial elongation rate. Underlying these changes is a regulated remodeling of the sclera. Difference Gel Electrophoresis (DIGE) was used to identify scleral proteins that are involved in this emmetropization process.
Methods: Two groups of 5 tree shrews wore a monocular 5 D lens, starting 24 days after natural eye opening. The compensation group wore the lens for 4 days. The recovery group wore the lens for 11 days, compensating fully, and then recovered for 4 days without the lens. Two age-matched normal groups (n=5) were also examined. Scleral proteins were isolated and resolved by DIGE to discover proteins that were differentially represented between treated, control, and normal eyes during both lens compensation and recovery. Proteins of interest were identified by mass spectrometry.
Results: After four days of lens compensation there was a general down-regulation of proteins involved in cell adhesion and mobility, both cell-cell and cell-ECM interaction. Also reduced was the level of several ECM components and proteins involved in cytoskeletal organization and biogenesis, primarily actin remodeling and proteins that interact with actin. Also down-regulated were small GTPase-mediated signal transduction proteins and factors that regulate transcription. Few proteins were found to be up-regulated during lens compensation. After 4 days of recovery, there was a continued down-regulation of many of the cytoskeletal, ECM, and signal transduction proteins identified during lens compensation, while several stress response proteins and some ECM constituents were up-regulated (in contrast to the slight down-regulation observed during compensation).
Discussion and Conclusions: These results suggest that a major effect the retinal “go” signal in the sclera is to down-regulate cell-ECM interactions. Along with collagen loss at the lamellae edges, this may bring about the increased viscoelasticity that results in faster axial elongation. At the protein level, it seems that recovery is generally not just the inverse of minus lens compensation.
Symposium 12: Paper 4 Camp Modulates Apolipoprotein A1 Expression During Eye Growth: A Proteomic Approach
Chi-Ho To, Rachel K. M. Chun, Chun Lung Wong, and King Kit Li
Laboratory of Experimental Optometry, Centre for Myopia Research, School of Optometry, The Hong Kong Polytechnic University, Hong Kong, P. R. China (CHT, RKMC, CLW, KKL), and State Key Lab of Ophthalmology, Zhongshan Ophthalmic Center, P. R. China (CHT)
Purpose: This study aimed to investigate the roles of apolipoprotein A1 (ApoA1) and cyclic adenosine monophosphate (cAMP) on eye growth in chicks.
Methods: White leghorn chicks (Gallus gallus domesticus) at the age of 2 days after hatchling worn negative lenses (-10D) or translucent diffusers over the right eyes via Velcro rings for 3 days. Plano lenses were applied on the left eyes as control. Ocular dimensions and refractive errors were measured before and after the treatment by using high frequency A-scan ultrasound system and retinoscopy respectively. After the treatment, retinas were extracted and homogenized in lysis buffer (7 M urea, 2 M thiourea, 40 mM Tris, 0.2% (w/v) Biolytes, 1% (w/v) DTT, 2% (w/v) CHAPS, 1% (v/v) ASB14 and 1% (v/v) Protease Inhibitor Cocktail). Lysed retinas were then labeled using CyDye Fluor minimal dyes. Afterwards, retinal proteins were separated under isoelectric focusing and second dimension of electrophoresis. The labeled proteins were visualized and differential protein expressions between myopic and control retinas were analyzed using a nano-liquid chromatography with tandem mass spectrometry (LC-MS/MS). In another set of experiment, eight-day-old chicks wearing negative lenses (-10D) over both eyes were injected with 8-Bromo-cAMP (8-Br-cAMP) in one eye, saline in another eye as control for 4 consecutive days. Ocular dimensions and refractive errors were measured. Retinas were then extracted after four days of intravitreal injections to measure the ApoA1 expressions using Western blotting.
Results: Both the right eyes of the chicks became myopic with an increase in axial length after deprivation using −10D lenses or diffusers for three days. There was a down-regulation of ApoA1 in myopic retinas of LIM (-1.47 fold) and FDM (-1.98 fold) significantly (p<0.05, paired Student's t-test). More importantly, ApoA1 was the only common retinal protein showing down-regulation in both LIM and FDM. On the other hand, intravitreal injection of 1mM 8-Br-cAMP inhibited LIM significantly (1.56D±1.07 vs −10.41D±1.32; treated vs control, mean spherical equivalent±SEM, n=9, p<0.001). It acted through the inhibition of elongation of vitreous chamber depth. It also slowed down the thinning of choroid under LIM. Besides, cAMP analog injections increased retinal ApoA1 expressions significantly (p<0.01).
Discussion and Conclusions: ApoA1 may act as a key protein involved in myopia development. Moreover, the potent role of cAMP in inhibiting the myopia development with an increase in retinal ApoA1 was demonstrated. These findings indicated that an increase in retinal cAMP level and ApoA1 expressions may play an crucial role in mediating ocular growth. Since ApoA1 have been suggested as a “STOP” signal to myopia, the interaction between cAMP and ApoA1 in manipulating ocular growth is an important direction for further exploration.
TOPIC 5: HOW DOES VISUAL FUNCTION CONTRIBUTE TO AND INTERACT WITH AMETROPIA?
SYMPOSIUM 13: ACCOMMODATION, BINOCULAR VISION, ABERRATIONS AND MYOPIA
Chairs: Jane Gwiazda and Susana Marcos
Whether accommodation and aberrations are casually related to the development of myopia is still being debated, with conflicting evidence in the literature. The talks in this symposium presented some data relevant to this topic.
Gambra reported results from five subjects showing how aberrations can influence accommodation. Aberrations were manipulated with an adaptive-optics deformable mirror and various conditions were tested. Accommodative lag was found to increase when positive spherical aberration and coma were introduced, confirming the association of aberrations and accommodation. Additional data are needed to establish an association with myopia.
Anderson reported data from a study of accommodation related to age. Accommodation was objectively measured with an open field autorefractor in 140 subjects aged 3 to 40 years. The main findings were that accommodative lag decreased with age for all demands, latencies decreased with increasing age, and microfluctuations increased with accommodative demand and decreased with age. These changes in accommodation with age may or may not be related to changes in refraction.
Collins reported on short-term changes in axial length with accommodation and convergence. Axial length was found to be unaffected by 15 minutes of convergence, but did increase slightly but significantly with accommodative tasks. While no refractive group differences were found during accommodation, early-onset and progressing myopes had the largest increase in axial length immediately after accommodation.
Additional studies, especially longitudinal in nature, are needed to determine the temporal association and any causal connection between accommodation, aberrations, and myopia.
Symposium 13: Paper 1 Influence of Aberrations on the Accommodative Response
Enrique Gambra, Lucie Sawides, Carlos Dorronsoro, and Susana Marcos
Instituto de Optica Madrid, Madrid, Spain (EG, LS, CD, SM)
Purpose: In this study, we address the influence of ocular aberrations in the accommodative response, in particular the accommodative lag and fluctuations of accommodation.
Methods: We evaluated the accommodative response to a monocular stimulus changing in vergence from 0 to 6 D (which was moved following a staircase function) under natural, corrected, and induced optical aberrations. The aberrations were manipulated using an adaptive-optics (AO) electromagnetic deformable mirror. The accommodative response of the eye (through the mirror) and its fluctuations were measured on 5 subjects using a Hartmann–Shack wavefront sensor operating at 12.8 Hz. Five conditions were tested: (1) natural aberrations, (2) AO correction of the unaccommodated state and induction (over 6-mm pupils) of (3) +1 μm and (4) −1 μm of spherical aberration and (5) −2 μm of vertical coma.
Results: Four subjects showed a better accommodative response with corrected aberrations than with their natural aberrations. The induction of negative spherical aberration also produced a better accommodative response in the same subjects. Accommodative lag increased in all subjects when positive spherical aberration and coma were induced. Fluctuations of the accommodative response (computed during each 1-D period of steady accommodation) increased with accommodative response and when high-order aberrations were induced. The largest fluctuations occurred for induced negative spherical aberration and the smallest for natural and corrected aberrations.
Discussion and Conclusions: The study demonstrates that the presence of larger amounts of high-order aberrations produces an increase in accommodative lag. This result could suggest that the increased accommodative lag found in myopes (Mutti et al, 2006) may be associated with a larger amount of high-order aberrations in myopes (He et al, 2002; Marcos et al, 2000; Paquin et al, 2002), and therefore be a consequence rather than a preceding factor in myopia development (Mutti et al, 2006). Whether increased amounts of aberrations may trigger myopia development has also been a matter of debate (Collins et al, 1995; Thorn et al, 2008). Recent studies on animal models (Garcia de la Cera et al, 2007) suggest that increased aberrations may be rather a result of the structural properties of myopic eyes, rather than a cause of myopia.
Symposium 13: Paper 2 Changes in Accommodation From Preschool to Pre-Presbyopia
Heather A. Anderson
University of Houston College of Optometry, Houston, Texas
Purpose: The relationship between accommodation and myopia has long been of interest. Since it is known that myopia onset is related to age, it is critical to understand the relationship between accommodation and age throughout childhood. This study objectively measured accommodation to identify age-related changes from preschool to pre-presbyobia.
Methods: One-hundred-forty subjects (3–40 yrs) participated in 1 or more measures of accommodation. Static measures of accommodation were taken with the Grand Seiko autorefractor as subjects viewed a target at 33 cm through minus lenses of increasing power until responses showed no further increase in accommodation. Measurements were referenced to the corneal plane and the maximum response identified as accommodative amplitude (n=140). Accommodative lag was calculated for the first 5 demands tested for all subjects who were emmetropic or wore contact lenses (n=101). Accommodation was recorded with dynamic infrared photorefraction as subjects viewed a target alternating from distance to near demands of 2, 3, 4, & 5D. Latencies, peak velocities, and the magnitude of accommodative microfluctuations were calculated from the responses (n=41).
Results: Accommodative amplitude descreased curvilinearly as a function of age (y = 7.33-0.0035*(Age-3)2, p<0.001). Tangent analysis indicated amplitude remains relatively stable (∼7D) between ages 3–20. Accommodative lag decreased linearly with age from 3-20 yrs for the first 4 demands tested (p ≤ 0.013) and approached significance for the 5th demand (p=0.053). Mean accommodative and disaccommodative latencies decreased linearly with age (p<0.001). The magnitude of microfluctuations for sustained accommodation varied quadratically with age, with subjects in the 1st decade of life having the largest fluctuations for all stimulus demands (p<0.05). Accommodative peak velocities were fastest in subjects in their first 2 decades of life as compared to subjects in their 3rd and 4th decades of life; however, disaccommodative peak velocities showed no significant age differences.
Discussion and Conclusions: These findings indicate that accommodative behavior is changing through the school years. In general, accommodative accuracy improves, microfluctuations decrease, and peak velocities slow down as children age and eventually reach pre-presbyopia.
Symposium 13: Paper 3 Accommodation, Convergence and Short Term Axial Length Changes
Michael J. Collins, Scott A. Read, Emily C. Woodman, and Shiow-Huoy Cheong
Contact Lens and Visual Optics Laboratory, School of Optometry, Queensland University of Technology, Brisbane, Queensland, Australia (MJC, SAR, ECW, SHC)
Purpose: To study the short-term effects of accommodation and convergence on axial length in the human eye.
Methods: With a group of young myopes and emmetropes, the Lenstar LS900 was used to measure axial length during brief periods of accommodation (0, 3 and 6 D) and on a separate cohort, the IOL Master was used to measure axial length before and after a prolonged accommodation task (30 min of 5 D). The change in lens thickness measured by the Lenstar during accommodation was used to correct the average ocular refractive index to convert from optical path length to geometric axial length. A study of the effect of sustained convergence (with relaxed accommodation) on axial length in another group of young emmetropes was also undertaken with the IOL Master utilising 8 or 16 Δ BO prism.
Results: Small but significant increases in axial length were evident during (ANOVA p<0.001) and to a lesser extent, immediately after (ANOVA p<0.001) the accommodation tasks. After accounting for the increased lens thickness during accommodation with the Lenstar, the increase in axial length was smaller, but still statistically significant. The study of the effect of convergence showed no significant changes (p>0.6) in axial length in young emmetropes with 8 or 16 Δ BO prism.
Discussion and Conclusions: Consistent with previous studies, we found a small increase in axial length during accommodation. However, we did not find a significant difference between myopes and emmetropes during the brief period of accommodation, but did find that immediately after the prolonged accommodation task, the largest axial elongation was apparent in the early onset and progressing myope sub-groups. The influence of longer periods of accommodation, the time course of recovery, and the relative differences between refractive error groups is an area worthy of further study.
SYMPOSIUM 14: VISUAL FUNCTION IN AMETROPIA
Chairs: Michael Collins and W. Neil Charman
This session commenced with an introduction from Neil Charman who outlined some of the possible mechanisms through which visual function could vary as a result of ametropia. He proposed that the factors to be considered could be broadly grouped as optical, neural and biomechanical.
Rossi described how adaptive optics correction of the eye allows analysis of the visual resolution of myopes after correction of the total optical aberrations. He reported that while myopes do show reduced visual acuity at the fovea, this reduction is not apparently due to increased cone spacing or to greater levels of higher-order aberrations, suggesting an underlying neural deficit.
Mallen then described a study demonstrating that blur adaptation occurs in the parafoveal areas of the visual field, in a similar way to the fovea and presumably through a neural mechanism. While myopes showed greater adaptation effects than emmetropes, this difference did not reach significance.
Short-term change of axial length in response to blur was the topic of Read's presentation. He showed that the distance to the RPE apparently increased in response to one hour of negative defocus and diffuser blur, but shortened in response to positive defocus, as seen in many other animal species: this appeared to occur as a result of changes in choroidal thickness.
Seidel discussed his results of a series of experiments investigating accommodation microfluctuations and blur thresholds for foveal and peripheral stimuli in both myopes and emmetropes. Myopes showed greater levels of microfluctuations and increased blur thresholds for foveal and peripheral stimuli, suggesting a loss of image quality or resolution capacity in the myopic eyes.
It is clear that improvements in instrumentation are helping to give new insights into the subtle differences in the visual performance of different refractive groups and the associated changes in their visual systems.
Symposium 14: Paper 1 Brief Introduction
W. Neil Charman
University of Manchester, Manchester, United Kingdom
Symposium 14: Paper 2 Factors Influencing Visual Resolution in Myopia After Adaptive Optics Correction of High Order Aberrations
Ethan A. Rossi, Kaccie Y. Li, Pinky Weiser, Janice Tarrant, and Austin Roorda
School of Optometry, University of California, Berkeley, Berkeley, California (EAR, KYL, PW, JT, AR)
We previously showed that myopic observers do not benefit to the same extent as emmetropic observers in a visual acuity (VA) task after the optical aberrations of the eye are corrected with adaptive optics (AO). We measured AO-corrected visual acuity in a group of low myopes and compared them to a group of emmetropes; all subjects had VA of 20/20 or better with best spectacle correction only. AO-corrected minimum angle of resolution was 0.61 arcmin (SEM = 0.02) for the myopes and 0.49 arcmin (SEM = 0.03) for the emmetropes; the difference between groups was significant (p =0.0017). The effect was greater (p =0.00013) after accounting for spectacle magnification and axial length, with myopes and emmetropes able to resolve critical features on the retina with a mean size of 2.87 microns (SEM = 0.07) and 2.25 microns (SEM = 0.1), respectively. This study showed that both emmetropes and low myopes will benefit from AO-correction in a VA task, but on average, myopes never reach the performance levels found for normal observers. Optical aberrations do not limit VA in low myopia after AO-correction, as no difference was observed in the high-order aberrations of each group. This suggested that retinal and/or cortical factors must limit VA in low myopes after AO-correction. Retinal stretching has often been suggested as a possible cause of the visual deficit observed in axial myopes, with the hypothesis being that retinal stretching caused by increased axial length increases the spacing between photoreceptors in the central fovea, limiting VA. Li and Roorda recently evaluated the relation between foveal cone density and eye length in several myopic and emmetropic eyes and found a significant decrease in retinal density (P < 0.05) with increasing axial length at 0.30 mm eccentricity but not closer. However, more myopic eyes generally had higher angular density than shorter eyes at the center of the fovea. This suggests that the observed VA deficit in myopia is not due to increased photoreceptor spacing at the center of the fovea. Taken together, these results suggest that the visual deficit observed in myopia may be cortical in nature, perhaps representing a sub-clinical form of amblyopia.
Symposium 14: Paper 3 Blur Adaptation Away From the Fovea – IS IT Possible?
Edward A. H. Mallen, Kiren Hussain, Alex Mankowska, and Matthew Cufflin
University of Bradford, Bradford, United Kingdom (EAHM, KH, AM, MC)
Purpose: Adaptation to image blur, as measured by an improvement in vision under sustained defocus, is well-established at the fovea. This project aims to demonstrate the ability of the human visual system to adapt to blur in parafoveal areas of the visual field.
Methods: Twenty-one participants (11 emmetropes, mean refraction +0.11 ± 0.36 DS; 10 myopes, mean refraction −3.03 ± 1.95 DS) underwent a period of blur adaptation (45 minutes watching a DVD via +1.00 DS of refractive blur). Baseline clear, pre-blur adaptation and post-blur adaptation measures of visual acuity (VA) were made using a 4-AFC PEST algorithm (Freiburg Visual Acuity Test; FrACT) at fixation, and out to 10 degrees in the nasal visual field in 2 degree increments.
Results: The FrACT program produced repeatable measures of VA at fixation and at parafoveal locations. At fixation, induced blur caused a reduction in VA to 0.43 and 0.44 logMAR for emmetropes and myopes respectively. VA improved to 0.40 and 0.36 logMAR at fixation for emmetropes and myopes following adaptation. Improvements in parafoveal acuity were variable, but a general improvement was seen across all eccentricities (for example, mean acuity across emmetropes and myopes improved from 0.83 to 0.77 logMAR at 10 degrees eccentricity following adaptation).
Discussion and Conclusions: Exposure to blur produced an improvement in VA under defocus at fixation, and at parafoveal retinal locations in emmetropic and myopic participants. There was a trend for myopes to show greater adaptive effects than emmetropes, but this difference did not reach statistical significance. This work has demonstrated that parafoveal regions of the visual field are amenable to blur adaptation effects. We therefore conclude that the well-documented blur adaptation mechanisms that exist at fixation are also present to some degree within 10 degrees of the fovea. This finding has potential implications for adaptation to off-axis errors induced by myopia correction modalities.
Symposium 14: Paper 4 Defocus and Short Term Axial Length Changes in Humans
Scott A. Read, Michael J. Collins, and Beata Sander
Queensland University of Technology, Brisbane, Queensland, Australia (SAR, MJC, BS)
Purpose: To investigate the influence of a short period of defocus upon ocular biometrics in young adult subjects.
Methods: Twenty eight young adult subjects (mean age 25± 3 years) had eye biometrics measured before and then after 60 minutes of exposure to monocular (right eye) imposed spectacle lens defocus. Four different defocus conditions were tested: myopic defocus (+3.00 D), hyperopic defocus (-3.00 D), diffuse defocus (0.2 density Bangerter filter) and no defocus. Each condition was tested on a separate day, with the order of testing randomized.
Results: Significant changes in axial length were observed following exposure to defocus (repeated measures ANOVA p<0.0001). A significant axial elongation was observed following 60 minutes of hyperopic defocus (mean change +8 ± 14 SYMBOLm, p=0.03), and a significant decrease in axial length observed following the myopic defocus condition (mean change −13 ± 14 SYMBOLm, p=0.0001). A small increase in eye length that bordered on significance was also observed with the diffuse defocus condition (mean change +6 ± 13 SYMBOLm, p=0.053). No significant changes in axial length were observed in the fellow (non-defocused) for any of the conditions (p>0.05). Anterior eye biometrics (corneal thickness, anterior chamber depth and lens thickness) showed no significant change with defocus (p>0.05).
Discussion and Conclusions: Small, but statistically significant changes in eye length occur following 60 minutes of monocular defocus. The direction of the observed eye length changes appears dependent upon the sign of imposed defocus. These findings in human subjects, suggests a similar mechanism of short term ocular response to defocus as observed in other animal species.
Symposium 14: Paper 5 Object Spatial Profile, Blur Perception and Accommodation Thresholds in Emmetropia and Myopia
Dirk Seidel, Mhairi Day, Lorraine Duffy, Lyle S. Gray, and Niall C. Strang
Department of Vision Sciences, Glasgow Caledonian University, Glasgow, Scotland, United Kingdom (DS, MD, LD, LSG, NCS)
Purpose: To investigate the minimum blur thresholds required to elicit accommodation responses for a range of stimulus configurations and different retinal locations in emmetropia and myopia.
Methods: Emmetropic and myopic subjects viewed a range of stimuli placed in a Badal optical system under different experimental conditions: Experiment 1 investi-gated the variability of the accommodation response (microfluctuations) for stationary high-contrast sine and square wave gratings with spatial frequen-cies ranging from 0.5-32cpd. Experiment 2 assessed the foveal accommoda-tion blur threshold for a high contrast 6/9 letter and a 4cpd sine wave grating. Targets were placed at the subject's open-loop accommodation level and stimulus vergence was varied sinusoidally (0.5 Hz) between 0Dand 2.00D. Accommodation responses were recorded continuously using a modified infra-red autorefractor and power spectra were obtained from FFT analysis. Spectra for a particular stimulus condition were averaged to reduce noise and the power in the bins for 0.4-0.6Hz was summed. The total power from these three bins was then compared to the power obtained from a stationary target (0Hz), so that the foveal accommodation blur threshold could be determined. Experiment 3 assessed peripheral (2-8deg) accommodation blur thresholds for a circular annulus containing a 4cpd sine wave grating.
Results: In all viewing conditions the variability of the accommodation response (microfluctuations) was greater in the myopic group compared to the emmetropic group. The fluctuations were found to be smallest for square wave gratings and mid spatial frequency (4cpd) sine wave gratings while they increased for high and low spatial frequencies. The foveal accommodation blur threshold was found to be greater in the myopic group compared to emmetropes for a letter target, but not a 4cpd sine wave grating. Peripheral accommodation blur thresholds for sine wave gratings were found to be greater in the myopic group compared to emmetropes.
Discussion and Conclusions: Accommodation microfluctuations monitor the contrast gradient of the cortical image. Increased foveal and peripheral accommodation blur thresholds found in myopes are the consequence of a reduction in the slope of the contrast gradient. This could be the result of reduced retinal image quality or limited resolution due to changes in eye shape.
TOPIC 6: DOES EYE SHAPE MATTER?
SYMPOSIUM 15: OFF-AXIS OPTICS AND OFF-AXIS ERROR SIGNALS, LOCAL COMPENSATION OF REFRACTIVE ERRORS
Chairs: Pablo Artal, David Atchison and Juan Tabernero
This was the first of two symposia considering the possible involvement of eye shape and peripheral refraction in the development of myopia, under the Topic 6 heading “Does eye shape matter?”
We are familiar with the concept of myopic eyes having prolate shapes, but David Atchison explained that when the retina shape alone is considered then few myopic adult retinas can be considered in these terms, but they are generally less oblate than emmetropic retinas. The increases in length, height and width of the retina, as the amount of myopia increases, are in the approximate ratio 3: 2: 1.
Juan Tabernero described the adaptation of a Photorefractor that can quickly scan and acquire measurements of peripheral refraction across the horizontal meridian. It provided similar results to scanning Hartmann-Shack systems and was used to identify different refraction patterns in emmetropes.
Arthur Ho described horizontal peripheral refraction measurements for myopes with a new design of contact lens. This lens induced more myopic/less hypermetropic peripheral refraction than a control design for a range of accommodation stimuli, but the design will need some adjustment to give consistently relative myopic refractions.
Linda Lundström found that optical defocus as small as 1D could have considerable effects on peripheral detection acuity and a low contrast resolution task. Positive (myopic) defocus had greater effect than negative defocus, an effect that, interestingly, seemed larger for myopic than for emmetropic subjects.
Symposium 15: Paper 1 Retinal Shapes in Young Adult Emmetropic and Myopic Eyes
David A. Atchison
Visual and Ophthalmic Optics laboratory, School of Optometry & Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Queensland, Australia
Purpose: Our magnetic resonance imaging work investigated the shapes of the retinas of young adult emmetropic and myopic eyes. MethodsNon-rotationally symmetrical ellipsoids were fitted to the retinal surfaces of 21 emmetropic and 66 myopic eyes using transverse axial (horizontal) and sagittal images.
Results: Shapes varied considerably between subjects with similar refractive errors. For nearly all emmetropic eyes, the shapes were oblate (steepening away from the vertex), which means that the axial dimensions of the ellipsoids were smaller than both the vertical and horizontal dimensions. As myopia increased all ellipsoid dimensions increased, but the axial dimension increased more than the vertical dimension, and this in turn increased more than the horizontal dimension (increases in approximate ratios 3:2:1). The difference in the increase of these dimensions means that as the degree of myopia increased the retinal shape became less oblateness, but few myopic retinas were prolate. The ellipsoids were tilted about the vertical axis by 11° ± 13° and their centers were decentered.
Discussion and Conclusions: Both emmetropic and myopic retinas are oblate in shape, but myopic retinas less so.
Symposium 15: Paper 2 Peripheral Refraction: New Methods to Measure Fast and Comfortably
Juan Tabernero and Frank Schaeffel
Section of Neurobiology of the Eye, Institute for Ophthalmic Research, Tübingen, Germany (JT, FS), and Laboratorio de Óptica, Universidad de Murcia, Murcia, Spain (JT)
Purpose: To present the new scanning photorefractor to measure peripheral refraction. Some new experiments where the instrument is applied will be reviewed.
Methods: The new instrument scans the peripheral refraction (±45° horizontally; spatial resolution < 1°) in about 3 seconds, projecting light in the peripheral retina with a motorized infrared mirror. The subject fixates to a single central stimulus, shortening the measurement time and providing large reproducibility. A new scanning Hartmann-Shack wavefront sensor developed at the optics lab in Murcia was used to test the instrument. Different experiments with the new photorefractor were recently performed. Potential changes in peripheral refraction as a function of accommodation were analyzed as well as the variability of the different shapes of peripheral refraction. Also, the instrument (installed at the Tubingen eye-clinic) was used to assess changes in peripheral refraction after cataract surgery when an intraocular lens is implanted in the eye.
Results: The comparison of the peripheral photorefractor with the scanning Hartmann-Shack provided good agreement. In the accommodation experiment, for a group of 10 emmetropes, we found little differences in peripheral refraction as a function of accommodation. However, we observed significant variations in the shape of the profiles of the different subjects. This was later confirmed in a population of 43 nearly emmetropes subjects (spherical equivalent ≤ 2.5 D). The profiles were classified according to 4 different models, “flat” (nearly constant refraction as a function of eccentricity), “boxed” (a constant refraction over a central area followed by a linear increase starting at a certain eccentricity angle), “parabollic” change and “linear” change as a function of eccentricity. In addition, these data were compared to the peripheral refractions of 20 pseudophakic subjects where, in average, more relative peripheral myopia was found with respect to a normal population (around 2 D at 40 degrees).
Discussion and Conclusions: The new photorefractor might be useful for a wide range of experiments in myopia research. In particular, if optical interventions affecting peripheral refraction became more and more common, it would be relevant to identify those segments of population (according to the peripheral refraction shapes) that would likely obtain higher benefits.
Symposium 15: Paper 3 Influence of Accommodation on Peripheral Refraction: Effect of a Novel Optical Design Contact Lens for Manipulating Peripheral Defocus
Arthur Ho, Percy Lazon de la Jara, Aldo Martinez, Judy Kwan, Cathleen Fedtke, Brien Holden, and Padmaja Sankaridurg
The Brien Holden Vision Institute, Sydney, New South Wales, Australia (AH, PLdlJ, JK, CF, BH, PS), The Vision Cooperative Research Centre, Sydney, New South Wales, Australia (AH, CF, BH), The School of Optometry and Vision Science, The University of New South Wales, Sydney, New South Wales, Australia (AH, PLdlJ, AM, CF, BH, PS), and Asia Center of Excellence, CIBA Vision, Singapore (AM)
Purpose: To evaluate and compare the effect of a novel contact lens (CL) design and a conventional single vision CL on peripheral refraction (PR) at distance and various levels of accommodation.
Methods: Fourteen myopic participants (Age 19–32; Mean Sphere −0.625D– −3.875D) wore a single vision CL (O2Optix [control]) and a novel peripheral power design CL (CIBA Vision, Lotrafilcon B [test]). Powers of all lenses were matched to correct refractive error (RE). Non-cycloplegic central and PR were measured using a modified Shin Nippon NVision auto-refractor at central (0°), 20°, 30° and 40° eccentricities in the nasal and temporal visual fields and at target distances of 21, 30, 40 and 200 cm in the right eye with CLs. Results were represented by the power vector method and averaged over 5 repeats. Image shell position (ISP) shift and vertical astigmatism (J180) were analysed using linear mixed model with accommodation, RE and linear and quadratic terms of eccentricity as predictors.
Results: Both CL designs had significant nasal-temporal asymmetry and curvature in ISP and J180. The average peripheral ISP was behind the retina for all target distances although at nasal 40° field, it was in front. Overall, the test CL induced relatively more myopic defocus in PR increasing up to ∼-1 D at the 40° fields (p=0.002). This test CL induced defocus in PR did not change with accommodation, however, the test CL PR increased more in asymmetry with accommodation than the control (p=0.03). Difference in tilt and curvature of PR between test and control CL were related to RE (p<0.001). Accommodative lag did not differ between test and control CL.
Discussion and Conclusions: Given the appropriate optical design, it is feasible to manipulate the mean sphere PR of an individual with a CL. To place the ISP in front of the retina for distance and near focus, optical designs aiming to control peripheral hyperopic defocus will need substantial amounts of relative positive peripheral power. Observations on the J180 results suggest myopes and emmetropes may differ in their anterior segment optics as well as their accommodative characteristics.
Symposium 15: Paper 4 Correcting Peripheral Optics: Impact on Vision
Royal Institute of Technology, Biomedical and X-Ray Physics, Department of Applied Physics, Stockholm, Sweden
Purpose: Altering the image quality on the off-axis retina can be beneficial for reducing myopia progression, but will also affect our everyday peripheral visual perception. Even though retinal sampling poses a fundamental limit, optical correction can improve off-axis vision. This presentation is an overview of how different aspects of peripheral vision depend on optical blur.
Methods: The peripheral optical quality has been manipulated by trial lenses and by an adaptive optics system to measure acuity thresholds in certain peripheral angles, typically around 20° off-axis. Psychophysical routines based on forced choice have been used to handle the challenging task of evaluating off-axis visual performance. The sensitivity to optical blur has been studied for a wide range of peripheral visual tasks, including detection acuity of stationary and drifting gratings as well as resolution acuity of gratings and letters, at different contrast levels.
Results: In total around 20 subjects have been studied, all showing similar Results: In general, the different detection acuities as well as low contrast resolution vary with optical blur with as much as 0.25 logMAR per diopter of defocus. High contrast resolution, however, has low sensitivity to optical blur; some subjects had approximately the same threshold-value over several diopters of defocus and aberration correction did not have any significant effect. An exception was some subjects with central visual field loss, who achieved improved high contrast resolution with peripheral correction. Additionally, an asymmetric behavior with lower sensitivity to defocus by negative, than by positive, lenses has been found. Interestingly, there are indications that this asymmetry might be larger for myopic subjects.
Discussion and Conclusions: Peripheral optical corrections give visual benefits and optical defocus as low as one diopter has a large impact on most peripheral visual tasks, with high contrast resolution being the exception. Further investigations are needed to understand the asymmetric sensitivity to defocus.
SYMPOSIUM 16: SPECTACLE OR CONTACT LENS DESIGN TO REDUCE MYOPIA PROGRESSION
Chairs: Anne Seidemann and Dietmar Uttenweiler
This symposium summarized the different approaches aimed at the reduction of myopia progression by designing new lenses and studying their effects. These new special lenses induce relative peripheral myopia in the eye by their increasing radial power profile. This is assumed to reduce myopia progression since recent findings propose: “On the one hand, the peripheral retina can contribute to emmetropizing responses and to ametropias produced by an abnormal visual experience. On the other hand, unrestricted central vision is not sufficient to ensure normal refractive development, and the fovea is not essential for emmetropizing responses”.
For spectacle lenses Anne Seidemann and Björn Drobe discussed the conflicting aspects of wearer comfort and potential positive effect on refractive development. While normal spectacle lenses aim to provide best image quality with minimal aberrations for the entire field of view taking into account eye movements, the new special spectacle lenses with positive peripheral power profiles induce astigmatic errors as well as distortions and thus decline the wearer's comfort. Therefore, a compromise between positive peripheral power profiles, aberrations over the entire field, wearer's comfort and eye movements for designing these special spectacle lenses has to be found as concluded by Anne Seidemann.
In this context the eye-head coordination was discussed by Björn Drobe. In a study with 169 Singaporean children it turned out that these children are mostly eyemovers. This leads to the paradox of efficiency and free eye movement. Drobe suggests that either the amount of peripheral correction should be adjusted according to the eye-head coordination or that the peripheral focal plane could also be influenced by longitudinal chromatic aberration, or by using spectacle lenses similar to Fresnel lenses with central foveal correction and special peripheral concentric structures.
Padmaja Sankaridurg and Brien Holden showed that new results from the Vision CRC myopia control studies with special lenses are promising for a new generation of spectacle lens and contact lens designs. Using conventional single vision and new special spectacle lens designs with increasing positive power Padmaja Sankaridurg showed that higher base curve designs reduce relative hyperopia more effectively than designs with lower base curve by measuring central and peripheral refractive errors. The most effective lens was found to be the one with the new special lens design with high base curve: peripheral hyperopia is reduced over all measured angles. To quantify the efficiency of these designs in controlling myopia progression clinical trials of at least 12 months need to be carried out according to Padmaja Sankaridurg.
Brien Holden presented the results of a study with a special contact lens designed to correct foveal vision and to reduce relative peripheral hyperopia. A reduction in myopia progression by 0.27 D after 12 months of wear was found when compared to myopia progression with normal spectacle lenses in Chinese 7 to 14 years old children upon adjusting the measured refractive progression for type of lens, parental myopia, gender, age, compliance and baseline spherical equivalent values. According to Brien Holden these results are promising with regard to a new generation of contact lenses aimed at myopia control, however longer experiences with special contact lenses aiming myopia control were needed.
Carly Lam explained that a significant effect on retarding myopia progression was also found for another special contact lens design (Defocus Incorporated Soft Contact Lens) tested in a group of 220 Hong Kong Chinese children aged between 8 and 13. After 2 years of wearing special contact lenses myopia progression in 65 subjects finishing the study so far was found to be 0.31 D less than in the control group with single vision contact lenses. Additionally, the axial length data measured in the subjects was found to be consistent with the refractive findings.
Symposium 16: Paper 1 Spectacle or Contact Lens Design to Reduce Myopia Progression
Anne Seidemann and Dietmar Uttenweiler
Rodenstock GmbH, Corporate Research & Development/Research Optics, Munich, Germany
New approaches to inhibit myopia progression are spectacle and contact lens designs that impose relative peripheral myopia which is assumed to inhibit eye growth. Concomitant, the area of clear vision important for best foveal image quality is reduced. This symposium showed the large interest of academic as well as industrial research groups and various results of newly designed and tested lenses were discussed. While some of the effects imposed by the lenses are small, and wearers comfort in some of the presented lenses is significantly affected other approaches for designing lenses promise good adaptation and improved inhibitory effects on myopia progression in the future.
Symposium 16: Paper 2 Impact of Spectacle Lenses on Peripheral Refractive Errors
Padmaja Sankaridurg, Les Donovan, Saulius Varnas, Arthur Ho, Judy Kwan, Cathleen Fedtke, Xiang Chen, Jian Ge, Earl Smith, III, and Brien Holden
Brien Holden Vision Institute, Sydney, New South Wales, Australia (PS. LD, AH, JK, CF, BH), Vision Cooperative Research Centre, Sydney, New South Wales, Australia (PS. LD, AH, JK, CF, BH), Carl Zeiss Vision, Adelaide, South Australia, Australia (SV), Zhongshan Ophthalmic Centre, Guangzhou, P. R. China (XC, JG), College of Optometry, University of Houston (ES)
Purpose: To assess the effect of standard single vision and novel spectacle lens designs on relative peripheral refractive errors.
Methods: As part of the Vision CRC myopia control studies, Chinese children with bilateral myopia, aged 6 to 12 yrs were fitted with either single vision lenses (SVL) on 3D base curve (BC), novel lenses designed to reduce peripheral hyperopic defocus on 3D BC, SVL on 8D BC and novel lenses on 8D BC. Central and peripheral refractive errors (nasal and temporal visual field at 20, 30 and 40°) were measured using a modified Shin Nippon autorefractor with and without spectacles. Relative peripheral refractive errors with and without intervention was determined. Results were represented by the power vector method and averaged over 5 repeats per eye. The relative peripheral refractive errors (RPRE) with and without intervention were determined.
Results: On an average, all eyes had peripheral hyperopic defocus without intervention. With control SVL on 3D BC, there was an increase in relative peripheral hyperopic defocus at all field angles measured (max of 0.72D observed at 40° nasal field). In comparison, novel lenses on 3D BC did not affect peripheral hyperopia in the temporal field but increased hyperopic defocus in the nasal field (0.36D at 40°). Single vision lenses on 8DBC reduced peripheral hyperopic defocus at 20° in both nasal and temporal fields, but increased peripheral hyperopia for far angles(0.45D and 0.22Dat 40° nasal and temporal fields). In contrast, novel lenses on 8D BC reduced peripheral hyperopic defocus at all angles (at 40°nasal field 0.53D reduction).
Discussion and Conclusions: The results are promising for a new generation of spectacle lens designs that can manipulate peripheral refractive errors. Participants need to be followed in clinical trials for a period of at least 12 months to determine the efficacy of these designs in controlling the progression of myopia.
Symposium 16: Paper 3 Challenges in Spectacle Lens Design for Myopic Children
Essilor International, Singapore
Purpose: To discuss possible improvements for spectacle lenses to slow myopia progression in children based on their eye-head coordination.
Methods: Horizontal eye-head coordination, i.e. the relative amount of eye and head movements to fixate a peripheral target, has been measured in 169 Singaporean children by means of a VPS (Vision Print System, Essilor, France). Children were aged from 6 to 14 and were mainly of Chinese ethnicity (87%).
Results: Results were expressed in terms of eye-head gain (EHG, ratio between the angle of head movement and eccentricity of the target). Average EHG was 0.17±0.25. For 67% of the children, EHG was lower than 0.1, for 77% less than 0.3.
Discussion and Conclusions: Singaporean children showed to be essentially eye-movers. In terms of ophthalmic lens design, this implies lenses with large fields of vision. Lenses with peripheral correction, that are newly used to slow myopia progression, will therefore have to deal with a paradox between efficiency (amount of peripheral correction) and free eye-movements. A possible way to manage this paradox could be by adjusting the amount of peripheral correction according to the eye-head coordination of the child. Another solution could be to provide peripheral correction through colored filters, rather than through dioptric power, by making use of the longitudinal chromatic aberration of the eye. Finally, the superimposition of central and peripheral correction within the pupil of the eye through alternative Fresnel optics could also provide an acceptable compromise.
Symposium 16: Paper 4 Impact of Novel Contact Lenses on Progression of Myopia
Brien Holden, Padmaja Sankaridurg, Arthur Ho, Percy Lazon de la Jara, Judy Kwan, Xiang Chen, Earl Smith, III, and Jian Ge
Brien Holden Vision Institute, Sydney, New South Wales, Australia (BH, PS, AH, PLdlJ, JK), Vision Cooperative Research Centre, Sydney, New South Wales, Australia Australia (BH, PS, AH, PLdlJ, JK), Zhongshan Ophthalmic Centre, Guangzhou, P.R. China (XC, JG), College of Optometry, University of Houston (ES)
Purpose: To determine if a contact lens designed to fully correct central vision but reduce relative peripheral hyperopia (AMCL) would reduce the rate of progress of myopia.
Methods: Rates of progress of myopia over 12 months of Chinese children with baseline myopia between sphere −0.75 to −3.50D and cylinder '0.50D, and aged 7 to 14 yrs, wearing AMCL (n=45) were compared to children (n=40) wearing normal sphero-cylindrical spectacles (SPL). Change in spherical equivalent refractive error (SphE) measured with cycloplegic auto-refraction and axial length (AL) at 6 and 12 months were the outcome measures. Myopia progression between groups was compared using linear mixed models and if significant, post-hoc multiple comparisons with Bonferroni corrections were performed.
Results: At 12months, progression of myopia with AMCL was significantly less, −0.54±0.37D, than with SPL,-0.84±0.47D (p<0.01). Similarly, AL increase was less with AMCL, 0.24±0.17mm, compared to SPL, 0.39±0.19mm (p<0.01). Upon adjusting for type of lens, parental myopia, gender, age, compliance and baseline SphE values, estimated progression in SphE was −0.58D with AMCL compared with −0.85D for SPL and for AL, 0.28mm with AMCL compared with 0.39mm with SPL.
Discussion and Conclusions: After 12 months of wear, progression of myopia with a contact lens designed to maintain clear central vision but reduce relative peripheral hyperopia was 36% less for spherical equivalent and 38% less for axial length than that with standard sphero-cylindrical spectacles. Longer experience with wear of such contact lenses is needed, however the data are promising with regard to a new generation of contact lenses aimed at myopia control.
Symposium 16: Paper 5 Randomized Clinical Trial of Myopia Control in Myopic Schoolchildren Using the Defocus Incorporated Soft Contact (DISC) Lens
Carly S. Y. Lam, Wing Chun Tang, Ying Yung Tang, Dennis Y Tse, and Chi-Ho To
Centre for Myopia Research, School of Optometry, The Hong Kong Polytechnic University (CSYL, WCT, YYT, DYT, CHT)
Purpose: To determine whether wearing of a special designed ‘Defocus Incorporated Soft Contact’ (DISC) lens reduced the progression of myopia in Hong Kong schoolchildren over 2 years.
Methods: Two hundred and twenty one healthy myopic (-1D to −5D with astigmatism less than 1D) Hong Kong Chinese schoolchildren aged between 8 to 13 years were recruited. They had no prior use of bifocal or progressive lenses and no contact lens experience. The subjects were randomly allocated to wear either the DISC contact lenses (treatment group) or the single vision (SV) contact lenses (control group). Their refractive error and related ocular parameters (e.g. axial length) were measured every 6 months for 2 years. Both the subjects and the optometrist who performed eye data measurement were masked. Cycloplegic objective refraction and axial length were measured by using Shin-Nippon NVision-K 5001 autorefractor and IOL Master respectively. The changes in spherical equivalent refractive error and axial length between two groups in 2 years were compared by using unpaired t-test.
Results: So far 65 subjects had worn contact lenses for 2 years and completed the study. In total there are 141 subjects still enrolled in the project, and 80 subjects quitted the study. After 2-year contact lens wear, data from the right eyes showed that the control group (n= 32) had more myopia progression (mean differences: −0.35D) than the treatment group (n= 33) (p < 0.01). Axial length data was consistent with the refractive findings, the children wearing SV lenses showed significantly more axial elongation in their eyes than those wearing the DISC lenses (mean difference = 0.16mm, p < 0.01).
Discussion and Conclusions: The DISC lens showed significant effect on retarding myopia progression in schoolchildren.
TOPIC 7: WHY AMETROPIA AT ALL?
SYMPOSIUM 17: FREE SESSION - IDEAS ON WHY WE MAY BECOME MYOPIC OR HYPEROPIC
Chairs: David Troilo, Tom Norton, and Josh Wallman
Ian Flitcroft suggested that, rather than considering refraction as an end-point, it should be considered as a regulated growth process from embryogenesis to adulthood. Data on the distribution of refractions shows a significant decrease in variability from birth to early childhood, indicative of optical regulation of growth. Variability later increases with refractive distributions showing reduced kurtosis, increased variance and increased skew; all indicators of a failure of regulated growth. This implies that persistent or late-onset refractive errors are the result of a failure of regulation. Studies from twins that are often cited as genetic evidence for myopia in fact show that as the degree of myopia increases, the variability and inter-twin discordance in monozygotic twins also increases, again markers of dysregulation. This suggests that it is not myopia or a particular refraction, per se, that is the inherited variable but rather the ability, or inability, to properly regulate growth in a given environment.
Tom Norton suggested that, to achieve and maintain emmetropia, the emmetropization mechanism modulates the genetically programmed elongation rate of the eye, increasing it to reduce hyperopia and decreasing it to prevent myopia. In infancy, this mechanism is generally successful in correcting mismatches between the genetically determined focal plane and the axial length. With increasing age, tree shrew data suggest that the emmetropization mechanism may lose the ability to use myopia to prevent elongation whereas hyperopia continues to be effective in increasing elongation. These factors may contribute to myopia susceptibility.
Howard Howland reported that optical oblique astigmatism is found in all simple optical systems including the human eye. Its magnitude increases parabolically with the distance from the optic axis and its cylinder axis has circular symmetry about the optic axis. At 25 degrees from the optic axis of the human eye its magnitude is on the order of 2 diopters. It thus offers an excellent cue to the sign of defocus in the peripheral retina and hence may provide a signal of the magnitude and sign of defocus in the peripheral retina for the emmetropization of the eye.
Symposium 17: Paper 1 An Inverse Theory of Myopia: What We Don'T Yet Know About Refractive Development
Children's University Hospital, Dublin, Ireland
Discussant: Donald O. Mutti
Decades of study have shown genetic and environmental influences on myopia development but the identification of causative genes has lagged behind that of every other significant ocular abnormality. Similarly no environmental manipulations have been found to produce meaningful alterations in ocular growth. A grand unification theory of myopia seems as distant as ever.
One possible reason for this is that we have focused too much on myopia as an endpoint (or at best at the rate of change of myopia over the course of a study). Reducing refraction to a single parameter in the form of spherical equivalent is an appealing but dangerous over-simplification. Refractive development is a process commencing with the programmed embryogenesis of the structures of the eye, post-natal ocular growth, homeostatic regulation of that growth and disruptive influences on homeostasis. Final refractive state is therefore the end point of a long and complicated journey. The same final end point can have been achieved as the result of a wide range of different influences. As a result finding a direct causal link between a single factor (be that genetic or environmental) and final refraction, an approach which has been the mainstay of epidemiological and genetic research, is highly improbable or indeed probably unachievable.
In this presentation I shall map out the scope of the factors that can influence refractive development from embryogenesis to adulthood to demonstrate what facets of ocular growth and development will need to be incorporated into a comprehensive theory of refractive development.
Symposium 17: Paper 2 How Might Genetic and Environmental Factors Interact to Produce Refractive Error in 'Normal' Eyes?
John T. Siegwart, Jr. and Thomas T. Norton
Department of Vision Sciences, University of Alabama, Birmingham, Birmingham, Alabama (JTS, TTN)
Discussant: Jane Gwiazda
It is clear from many studies that both genetics and the visual environment play a role in whether children's eyes develop myopia. Perhaps the task faced by the emmetropization mechanism differs, depending on whether genetics alone would produce a hyperopic eye or a myopic eye. In the case where genetics alone would produce a hyperopic eye (axial length shorter than the focal plane) the emmetropization mechanism uses hyperopia to cause eyes to elongate to emmetropia. In animals, the nearly universal success of applied hyperopia (minus lens) to produce axial elongation suggests that this task is relatively easily achieved. For eyes whose genetics would produce a myopic eye (axial length longer than the focal plane), the emmetropization mechanism must use myopia to restrain axial elongation. Thus, the key to avoiding human myopia may be the ability of the emmetropization mechanism to use myopia to restrain axial elongation. In young tree shrew eyes with applied positive lenses (which make the eyes myopic), this task appears relatively easy achieve: the axial elongation rate is slowed and eyes achieve near-emmetropia. In contrast, in older tree shrews, and possibly in older children, the ability to use myopia to slow the axial elongation rate is reduced. In tree shrews, “it is easier to ‘go’ than it is to ‘slow’.”
The ability to increase elongation in response to hyperopic refractive error persists into young adulthood. This is good for a genetically-short eye that needs to push its elongation rate to maintain emmetropia and overcome genetic tendency for the eye to remain hyperopic. In contrast, the ability of the older juvenile tree shrew eye to slow elongation in response to myopic refractive error appears to diminish after the rapid infantile growth phase. This is bad for a genetically-long eye in which the emmetropization mechanism needs to restrain the elongation rate to maintain emmetropia.
Thus, normal variability in the genetic mismatch between optical power (cornea, lens) and axial length (scleral shell) creates very different tasks for the emmetropization mechanism. An asymmetry in the ability of older mammalian eyes to respond to myopia, compared to hyperopia may contribute to myopia susceptibility.
Symposium 17: Paper 3 A Possible Role for Peripheral Astigmatism in the Emmetropization of the Eye
Howard C. Howland
Department of Neurobiology and Behavior, Cornell University, Ithaca, New York
Discussant: W. Neil Charman
Purpose: To investigate a possible role for peripheral astigmatism in the emmetropization of the eye.
Methods: A PowerRefractor was used to measure human off-axis astigmatism in a population of young adults. The measurements were fit with a parabolic function and the constants of the function computed. Conditions necessary for estimating the sign and magnitude of the astigmatism in the peripheral retina were investigated.
Results: The magnitude, C, of human off-axis astigmatism was found to be C = k * α2, where k = 3.28E-3 [Diopters/degree2]. Thus at 25° from the (nominal) optic axis of the eye the off-axis astigmatism is 2.05 D. It was found from a search of the literature that many receptive fields of primate retinal cells have an elliptical shape, suitable for the measurement of the sign and magnitude of peripheral off-axis astigmatism.
Discussion and Conclusions: It is possible that the magnitude and sign of the off-axis astigmatism is estimated by the peripheral primate retina and used to control emmetropizing growth of the eye.