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Optometry & Vision Science:
doi: 10.1097/OPX.0000000000000115
OVS Announces

OVS Announces

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IN THIS ISSUE:

• Signal Pathways in Myopia Development in Chicks
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In animals, hyperopic defocus or form deprivation results in myopia by causing choroidal thinning and axial elongation with signaling through the RPE, choroid, and sclera. But what are the transmitters involved in myopia for choroidal changes and axial elongation? The authors’ experiments with chicks attempt to clarify the roles of dopamine pathways in this signaling process. (p. 1167)

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Editor’s Choice open access

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• Myopic Defocus Is Integrated Locally
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Our authors studied how visual signals that slow eye growth are integrated across the retina in infant monkeys. Restricting the effects of positive treatment lenses to the nasal visual field produced compensating hyperopic changes that were selective for the treated hemi-retina. As with form deprivation and hyperopic defocus, the effects of myopic defocus are mediated by mechanisms that integrate visual signals in a local regionally selective manner in primates. This agrees with the hypothesis that peripheral vision can influence eye shape independent of the central visual experience. (p. 1176)

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• Hyperopic Blur Influences Ocular Diurnal Rhythms
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Previously, our authors have shown that small changes of choroidal thickness can occur in humans as a result of defocus. These are clinically insignificant for refractive error shifts but reveal the existence of important pathways for choroidal and axial length response to blur in humans. Here, the authors discovered that the introduction of monocular hyperopic defocus resulted in a significant increase in the amplitude of the diurnal change in axial length and choroidal thickness but returned to normal the following day after removal of the blur stimulus. (p. 1187)

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• Bright Light Induces Choroidal Thickening in Chicken
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Bright light is a potent inhibitor of myopia development in animal models. Here, the authors found that bright light stimulates choroidal thickening in chicken, although the response is smaller than with experimentally imposed myopic defocus and occurs with some time delay. It suggests that choroidal thickening is also involved in the myopia inhibition by bright light. (p. 1199)

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• Multifocal Contact Lens Myopia Control
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Previous studies have reported that soft bifocal/multifocal contact lenses can assist myopia control. Here, the authors used a commercially available contact lens and found that the myopia control effect extends beyond the first year. The multifocal contact lenses cut myopia progression in half and slowed the growth of the eye by 29%for 2 years compared with a historical control group of single-vision soft contact lens wearers. The authors feel that it makes sense that practitioners consider off-label use of soft multifocal contact lenses for myopia control in children. (p. 1207)

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• Peripheral Defocus at Distance and Near with Spherical and Multifocal Contact Lenses
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Peripheral myopic defocus is thought to slow the progression of myopia. The authors determined the effect of spherical and center-distance multifocal soft contact lenses on peripheral defocus when looking at both distance and near. Whereas peripheral hyperopic defocus was present at distance when wearing spherical lenses, multifocal lenses caused myopic peripheral defocus or reduced hyperopic defocus whether looking at distance or near. The reductions in peripheral hyperopia with the multifocal contact lenses may explain the reduction in myopia progression reported by studies using multifocal contact lens designs. (p. 1215)

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• Orthokeratology Slows Myopia in Targeted Children
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Several treatment options have been used in the past with some success in reducing myopia progression. More specifically, recent studies have reported that orthokeratology can significantly educe axial length growth by up to 50%. But which children are the best candidates for this? Using multivariate analyses, our authors find that orthokeratology is most effective in younger children with lesser corneal power. (p. 1225)

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• Does Manipulation of OK Lenses Modify Peripheral Refraction?
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Peripheral refraction is thought to be involved in the success of orthokeratology (OK) in slowing axial length growth and, hence, myopia progression. Our authors asked if changing two OK lens parameters, optic zone diameter (standard 6 mm and modified 5 mm) and peripheral tangent curve (standard 1/4 peripheral tangent and modified 1/2 peripheral tangent), significantly impacted peripheral refraction. The lack of impact of changing these parameters leads them to suggest that there may be difficulty individualizing myopia control with OK lenses. (p. 1237)

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• Orthokeratology Induces Nonuniform Corneal Shape Changes
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The authors evaluated sectoral corneal topographic changes after 2 weeks of overnight spherical orthokeratology (OK) lens wear. They demonstrated typical central corneal flattening and paracentral corneal steepening. However, corneal changes in the central and paracentral regions (nasal, superior, temporal, and inferior sectors) were not uniform and may be related to OK lens decentration that could impact the success of myopia control. (p. 1249)

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• Age and Refractive Error Impact Corneal Shape in Chinese Eyes
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Myopia and astigmatism are highly prevalent in Hong Kong Chinese. But how does this relate to corneal shape? Our authors found that, in participants between the ages of 10 and 45 years of age, both age and refractive error were closely related to corneal shape. Participants with myopic astigmatism had more prolate (peripheral flattening) corneas in all age groups. They feel that these differences with age and refractive error should be part of properly designed corneal shape change studies. By implication, their data seem relevant to treatment studies (e.g., orthokeratology) where peripheral refractive error, resulting from corneal shape, is relevant. (p. 1259)

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• Astigmatism: A Risk Factor for Myopia Development?
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Many Native American children have significant levels of refractive astigmatism. The authors used a longitudinal study to determine how this might impact emmetropization and myopia development in almost 800 Tohono O’odham Native American children (aged 3 through 18 years). Their finding of greater shift in spherical equivalent power toward myopia with age for those who were hyperopic at baseline is consistent with continued emmetropization in the school years. Astigmatism-related degradation of image quality creates complex cues to emmetropization, resulting in increased rates of myopia onset. (p. 1267)

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• Dual Treatment of Myopia Progression After 1 Year
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Custom-designed contact lenses (designed to alter spherical aberration to aid accommodation) and vision training were used together as a dual treatment of myopia. In the authors’ study, group age, lag of accommodation, and AC/A ratio were significantly associated with myopia progression. Despite some interim effect at 12 months, there were no significant treatment effects at 24 months for the almost 100 participants still in the study. This may suggest that younger subjects might be more amenable to treatment because an interaction between age and contact lens treatment was observed. (p. 1274)

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• Myopia Development, Spherical Aberration, Defocus, and Image Contrast
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Animal development research has shown that hyperopic defocus leads to eye elongation, but myopic defocus does not. Our authors suggest that retinal image contrast may be the sign of defocus needed for the eye to control its own growth. Optical modeling of retinal image contrast depends on both the magnitude and the sign of defocus and is relative to the sign of the spherical aberration. (p. 1284)

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• Poor Retinal Image Quality During Accommodation in Myopes
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Our authors show that image quality and accommodative lag is task dependent with better image quality for visually demanding tasks such as visual acuity testing compared to naturalistic tasks (e.g., reading or movie watching). Myopes showed more reduced retinal image contrast than emmetropes. This is consistent with theories of myopia progression that point to image contrast as an inhibitory signal for ocular growth. (p. 1292)

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• Vision Performance with Corrected Peripheral Refraction
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Special lenses were made to correct peripheral refraction for a myope along the horizontal visual field. With extensive and time-consuming measures, the authors show that lenses were able to give near optimum peripheral visual performance to at least 30 degrees from fixation. However, the benefit of such lenses was only documented when there was considerable relative peripheral refraction on the order of 2 diopters. (p. 1304)

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• Something Strange About Ciliary Muscle in Anisometropia?
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Patients with anisometropia followed the previously reported trends for ciliary muscle thickness and myopic refractive error. But strangely, when ciliary muscle dimensions were compared between the longer more myopic eye and the shorter more hyperopic eye, no differences were found. The authors suggest that the ciliary muscle might not always increase in thickness with axial eye growth in mild to moderate anisometropia. (p. 1312)

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• High Myopia Risk and Gene Involvement in Chinese
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Recently, polymorphism in the Lumican gene has been reported by some, but not others, to be associated with high myopia. The authors’ meta-analysis of five eligible case-control studies, involving almost 1000 high myopia patients and more than 600 control participants, showed that the single nucleotide polymorphism (rs3759223, C→T) in the Lumican gene confers individual susceptibility to high myopia in the Chinese population. (p. 1321)

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• Two Distinct Kinds of High Myopia in Chinese
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Surprisingly, early (onset before primary school)- and late-onset high myopia in Chinese cohorts exhibit quite different electroretinography (ERG). Early-onset high myopia is associated with abnormal ERGs (especially the cone b-wave), and late-onset high myopia participants have normal ERGs. This discovery supports the existence of two kinds of high myopia and suggests early photoreceptor dysfunction in the early-onset high myopia type. The authors feel that early-onset high myopia may be genetic, whereas late-onset high myopia may be more environmentally and genetically determined. (p. 1327)

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• Has Myopia Prevalence Increased in Clinic Populations During the Past Century?
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Given the high impact of refractive error on health care resources, it is important to be aware of any prevalence changes with age and time. In a large clinic population, prevalence trends for refractive errors are examined across a wide age range. Myopia, hyperopia, astigmatism, and anisometropia show characteristic changes with age. By comparing the authors’ study to other studies in clinic populations, they conclude that there has been a dramatic increase in the prevalence of myopia during the past century in clinic populations that are predominantly white. (p. 1331)

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• History of Myopia Biometry by Correcting Four Classical Studies of the Past 100 Years
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The data sets measured by Stenström (1946), Sorsby (1957), Zeeman (1911), and Awerbach (1900) are of great historical interest, but each has issues that need to be addressed to allow practical comparisons. These issues range from only publishing statistical descriptors instead of the numerical data (Stenström) to assuming an equivalent refractive index of the crystalline lens that was constant with age (Sorsby) and calculation errors (Awerbach and Zeeman). Data from these four historical publications have been corrected and reconstructed by our authors using only subjects with ages ranging between 20 and 35 years and refraction within ±8 diopters. This data set may be used in studies on the evolution of ocular biometry, with appropriate acknowledgement of the remaining data limitations. (p. 1342)

Copyright © 2013 American Academy of Optometry

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