TRADITIONAL EFFERENT THERAPY
Traditional evidence-based therapy for efferent visual disorders, as used by ophthalmologists, orthoptists, and optometrists, is directed at improving visual acuity, ocular alignment, or both. Therapies that improve visual acuity include refraction and amblyopia treatment, such as patching or atropine penalization. Therapies that improve symptoms of ocular misalignment include prisms and strabismus surgery.
Vision therapy is a term without a uniform definition that typically refers to nonsurgical, nonpharmacologic methods used by a subset of optometrists and occupational therapists directed at improving visual perception and processing. Optometric vision therapy has been applied to a broad spectrum of visual and nonvisual functions and disorders, such as convergence, reading, dyslexia, attention-deficit hyperactivity disorder (ADHD), sport performance, and concussion (1). According to the American Optometric Association, optometric vision therapy is “a sequence of neurosensory and neuromuscular activities individually prescribed and monitored by the doctor to develop, rehabilitate and enhance visual skills and processing” through use of “lenses, prisms, filters, occluders, specialized instruments, and computer programs” (2). The primary intervention is ocular motor exercises (e.g., repetitive eye movements) directed at improving perception and processing and visual comfort and efficiency. Optometric vision therapies typically consist of in-office sessions complemented by a home-based exercise program.
Not all optometrists practice vision therapy. Special certification is provided in behavioral and functional aspects of vision by the College of Optometrists in Vision Development (1,3). The broad scope and lack of definition specificity of vision therapy do not readily lend it to generalized determination of scientific efficacy. Lack of clarity also arises from similar terms applied to overlapping therapeutic approaches variably termed visual integration vision therapy, functional optometry, neuro-optometry, nonstrabismic vision therapy, and behavioral optometry. All of these factors have resulted in considerable controversy surrounding the potential efficacy, or lack thereof, of optometric behavioral vision therapy.
A critical optometric review of optometric behavioral vision therapy published in 2009 described clinical scenarios to which such therapy has typically been applied (1). These include: 1) accommodation and vergence disorders; 2) the underachieving child with disorders such as dyslexia or ADHD that may result in learning impairments; 3) near binocular vision and postural disorders with treatment attempts by yoked prisms; 4) near vision stress with treatment attempts by low-plus prescriptions; 5) behavioral approaches to attempt to treat strabismus and amblyopia; 6) central and peripheral awareness training; 7) sports vision therapy for performance improvement; and 8) neurological disorders and neurorehabilitation after brain trauma or stroke (1). This review will focus primarily on published data regarding convergence, reading, dyslexia, and ADHD.
Vergence denotes simultaneous eye movements in opposite directions often used to maintain single binocular vision at variable distances of visual fixation. Vergence eye movements include convergence (adduction of both eyes to focus on a near target) and divergence (abduction of both eyes to focus on a distant target). Convergence can be induced by visual blur (accommodative vergence), retinal disparity (fusional vergence), or both. Convergence is a component of the near triad that includes accommodation and pupillary miosis.
Convergence insufficiency (CI) is a disorder of the binocular visual system characterized by reduced ability of the eyes to converge on a near target. Common symptoms include asthenopia, binocular diplopia, or visual blur with near visual tasks. Supportive examination signs include increased near point of convergence (greater than 10 cm), reduced convergence amplitudes (<15 prism diopters), and an exodeviation of the eyes greater at near vs distance fixation.
The term “vision therapy” as used by behavioral optometrists for the treatment of CI has no uniform definition. Most of the treatments of CI in the recent optometric literature referred to as “vision therapy” are standard orthoptic exercises directed at improving fusional convergence, accommodative convergence, or both through the controlled manipulation of vergence demand, target proximity, and target blur (4–6). Many of these treatments consist of having the patient maintain convergence on an approaching target until the patient appreciates diplopia (the so-called break point). The classic CI exercise is the “pencil push-up” in which the patient converges on an approaching pencil tip. A detailed target is often placed on the pencil tip to stimulate accommodation and fusion. Fusional convergence can be further stimulated by having the patient perform pencil push-ups while looking through a base-out prism. “Tonic convergence exercises” require the maintenance of convergence on a near target for at least 30–40 seconds (7). “Jump convergence exercises” entail the rapid alternation of fixation between a distance and a near target. Stereogram exercises require the patient to maintain single binocular vision as vectorgram targets stimulate variable degrees of fusional convergence. The specific convergence exercises and the duration and frequency of these ocular motor tasks vary between studies.
Randomized clinical trials show efficacy of vergence therapy for CI in adults and children, with improvement in both convergence amplitudes and asthenopic symptoms (8–12).
A study of 60 adult men randomized to office and home-based combined therapy, home-based therapy, or no vision therapy for 24 weeks showed a 62% success rate of therapy for the group receiving combined office and home-based treatment, compared with 30% for home-based treatment only, and 10% in the untreated group (8). Limitations of this study included lack of masking and the possibility of a placebo effect (Hawthorne effect) between groups as a result of the difference in attention paid to subjects according to the amount of therapy received (13).
Two studies (one in 47 children, one in 46 young adults) by the Convergence Insufficiency Treatment Trial (CITT) study group randomized subjects to office-based vision therapy and orthoptics, office-based placebo vision therapy and orthoptics, or home-based pencil push-ups (9,10). The office-based vision therapy and orthoptics group was treated with multiple convergence and accommodative exercises administered by a trained therapist during a weekly 60-minute office visit and additional exercises to be performed at home (9,10). The office-based placebo vision therapy and orthoptics group received similar weekly office visits and home assignments. However, the exercises consisted of multiple “sham” therapies that did not stimulate vergence or accommodation (i.e., monocular activities with a plano lens). The primary outcome measure was symptom score on the Convergence Insufficiency Symptom Survey after 12 weeks of treatment. Secondary outcome measures included near point of convergence and positive fusional vergence amplitudes at near. In the study of children, the office-based treatment group had the largest improvement in CI symptoms, near point of convergence, and vergence amplitudes (9). In the study of young adults, all 3 groups had symptom improvement (42% in the office-based treatment group, 31% in the office-based placebo group, and 20% in the home-based pencil push-up group) and only the office-based treatment group showed improvement in secondary outcome measures (10). The conclusion by the CITT study group was that office-based therapy is superior to home-based therapy for CI treatment. However, an accompanying editorial pointed out that the pencil push-up regimen used in the study was less intensive than the office-based treatment regimen (5). Therefore, the only conclusion to be drawn from the CITT study is that intensive office-based treatment is more efficacious than a specific home-based program of minimal intensity (5). A subsequent survey of the Pediatric Eye Disease Investigator Group by the CITT study group showed that home-based pencil push-ups were often prescribed by the pediatric ophthalmologic community at a dosage similar to that used in the study (15 minutes per day, 5 days per week) (14). Therefore, although the home-based pencil push-up group had a less intensive treatment regimen, this regimen appeared to be the predominant treatment prescribed by most pediatric ophthalmologists.
In 2009, the CITT study group performed a larger (n = 221) study in children using the same primary and secondary outcome measures, with subjects randomized to one of 4 arms: home-based pencil push-ups, home-based computer vergence and accommodative therapy including pencil push-ups, office-based vergence and accommodative therapy with home reinforcement, and office-based placebo therapy (11). The home-based computer vergence and accommodative therapy with pencil push-ups group provided a more intensive home treatment protocol than in the previous CITT studies discussed above. After 12 weeks of therapy, primary and secondary outcome measures were statistically significantly improved for the office-based treatment group, as compared to the other groups (11,15). CI symptoms were improved in 73% of the office-based treatment group, 43% in the home-based pencil push-up group, 33% of the home-based computer vergence and accommodative therapy with pencil push-up group, and 35% of the office-based placebo group. Most patients in all groups (including the office-based placebo group) who were asymptomatic after 12 weeks of treatment remained asymptomatic one year later (16). Again, an accompanying editorial (17) argued that the home-based therapy arms received less therapist contact and treatment time compared with the office-based treatment group (i.e., ≤100 min/wk for the home-based treatment groups compared with 135 min/wk for the office-based treatment group). Therefore, this study still did not answer the question of whether office-based therapy was more efficacious than home-based therapy of similar intensity (17). The CITT study group rebuttal stated that the intention of the trial was to compare efficacy of real-world practices and concluded that current prescribed office-based therapy is superior to home-based therapy which, in reality, lacks equivalent treatment duration and intensive therapist contact (18).
A reduction of CI symptoms in all treatment groups (including the placebo group) correlated with improvement in academic behavior as assessed by a survey of the subjects' parents (19). The improvement in academic behavior did not correlate with signs of CI such as near point of convergence or fusional amplitudes. A study on attention and reading effects is underway (16,19,20).
The CITT study group has demonstrated that intensive office-based therapy is more efficacious than less intensive home-based therapies. However, interpretation of the CITT results needs to consider the following additional findings.
- All 3 studies showed a reduction of symptoms in the placebo group (placebo group 31%–35% compared with treatment group 42%–73%) (9–11).
- Most patients who were asymptomatic 12 weeks after placebo therapy remained asymptomatic after one year (16).
- Patients who responded to placebo therapy had an improvement in their academic survey scores similar to patients who responded to other modes of therapy (19).
- The CITT showed that among patients with symptomatic CI, there was no association between the severity of the clinical signs (i.e., near point of convergence and fusional amplitudes) and the level of symptoms (21). Thus, it is questionable whether the Convergence Insufficiency Symptom Survey reflects objective measures of CI.
- CI symptom reduction (even in the placebo group) correlated with improved academic survey scores. However, there was no correlation of clinical signs of CI and academic survey scores (19).
- The cost of office-based treatment is substantial—approximately $1,125/patient in addition to inconvenience such as transportation and time away from work and school (5).
In conclusion, convergence therapy has been shown to be effective for the treatment of CI. However, the role of office-based therapy is still controversial. It remains to be determined if more intensive home-based treatment will be feasible and as effective as office-based treatment. In addition, it might be more cost effective to practice a stepwise approach in which home-based therapy is first-line treatment and intensive office-based therapy is reserved only for patients who do not respond to home-based treatment. As treatment of CI addresses ocular alignment, it is consistent with the philosophy of traditional efferent therapy. CI therapy is endorsed by ophthalmologists, orthoptists, and optometrists.
Reading Speed and Comprehension and Learning Disability
The issues of poor reading ability, learning disability, and dyslexia and their relationship to eye movements are often confused in the literature; however, attention in this section will be given to evidence regarding vision therapy in the context of reading ability, in general. Eye movement behavior during normal reading in the English language includes a staircase of saccades from left to right with each saccade advancing 8–10 letters, backward saccades for verification and comprehension, large oblique right to left saccades at the end of each line to move to the next line, and periods of visual fixation in between saccades (22–24). When reading at near, the convergence system also is involved.
There is no scientific basis for the concept of treating poor reading ability with most ocular motor exercises. Smooth pursuit, so-called “ocular tracking,” is not used for reading; thus there is no biological plausibility for visual therapy interventions directed at “ocular tracking” to improve reading. Similarly, vestibular and optokinetic nystagmus movements are not used during reading, so there is no basis for reading treatment directed at these types of eye movements. Specific ocular motor abnormalities have not been documented to occur more frequently in poor readers compared with control subjects (24). Eye movement recordings from 40 learning disabled children showed no abnormality of eye movements compared with age-matched controls (25). In addition, many patients with ocular motor deficits are able to read normally (26).
The primary ocular motility abnormalities documented in poor readers are prolonged fixation duration and an increased number of backup saccades during reading (24). Similar ocular motility findings occur in normal children early in development when learning to read and in normal adults while reading more difficult text. The increased number of backup saccades and prolonged fixation duration result from poor reading comprehension and are not a cause of it (23,24,27).
Many studies addressing issues of visual processing and efficiency during reading are hampered by variable inclusion criteria and therapy methods and lack of proper age-matched control groups and placebo-interventions (13). The immature ocular motor system of the child does not behave identically to that of an adult, and any study on ocular motor abnormalities in children should include an age-matched control group (24). One controlled study of 36 children with reading deficits and “visual and/or perceptual difficulties” randomized subjects to treatment and placebo-control groups (28). The assessment of visual/perceptual difficulties included tasks such as alternate hopping on each foot, alternate ball bouncing, and right-left differentiation. The treatment group had statistically significant improvement in several measures of reading performance (28). However, the specific treatment was not described or standardized. The visual training consisted of an individualized program of “perceptual therapy” based on a “developmental hierarchy beginning with gross-motor control (28).” “The final stage was the development of conceptualization (28).” Therefore, it is not possible to assess the validity of this study due to the absence of details and variability of the treatment regimens applied (13,28). Two recent reviews concluded that there is no scientific evidence to support the use of eye exercises for the treatment of learning and reading disabilities (1,13).
As reading involves convergence, it is biologically plausible that vergence therapy could potentially improve reading speed, but there is no evidence that this translates into better school performance. A study of 134 children with reading difficulties who underwent either base-in prism therapy or computerized home-based vision therapy for CI demonstrated improvement in reading times and reduction in reading errors after treatment (29). This study was limited by lack of a placebo-control group. As discussed, the CITT correlated a reduction of CI symptoms with improvement in academic behavior as assessed by a survey of the subjects' parents (19). The improvement in academic behavior did not correlate with signs of CI such as near point of convergence or fusional amplitudes. Although the relationship of CI to reading remains to be clarified, there is no disagreement that clinically significant CI should be treated.
As reading also involves saccades, there may be biological plausibility in the concept of saccade ocular motor training to improve reading ability. Two studies (30,31) have assessed treatment intervention with King–Devick (K-D) remediation software, which presents numerical stimuli in a left to right orientation on a computer screen, with variable speed of presentation increasing as subject accuracy improves. This program simulates reading and induces the saccades and fixations that are integral to reading. A prospective, single-blinded, randomized trial of 76 grade-school children randomized subjects into a treatment group (using the K-D software simulating reading, 6-week course of treatment, 6 hours total treatment) or a control group (using the K-D software but presenting numbers centrally only without simulating reading, same course duration and dose) (30). Higher reading fluency scores were found posttreatment in the treated group. A study applying the same paradigm with a 5-week duration to a cohort of 327 high school students was reported to show greater improvements in reading fluency and comprehension in the treated group (31). Furthermore, in this study, a “high-needs” student group with poor reading performance was shown to achieve the greatest benefit from treatment.
In conclusion, vergence training may improve symptoms of CI that occur while reading, such as asthenopia, visual blur, and diplopia. However, it is unknown if this translates to improved performance at school or work. CI treatment addresses ocular alignment and is, therefore, consistent with the philosophy of traditional efferent therapy. More recently, randomized controlled evidence is emerging that intervention with a training methodology simulating saccades during reading may improve reading ability. However, the role of saccadic training to improve reading ability remains to be determined. There is no evidence that other therapies improve reading ability.
Dyslexia is defined as a primary reading disorder, distinct from secondary forms caused by “…visual or hearing disorders, intellectual disability, experiential and/or instructional deficits, and other problems” (26). According to a Joint Technical Report endorsed by the American Academy of Pediatrics (AAP), dyslexia is a “…receptive language-based learning disability that is characterized by difficulties with decoding, fluent word recognition, and/or reading comprehension skills…, (resulting)…from a deficit in the phonologic component of language that makes it difficult to use the alphabetic code to decode the written word” (26). The most accepted model is the phonological model, which consists of the awareness that speech can be segmented in sounds and phonics and the understanding that sounds can be represented by printed forms (26).
Although the predominant theory of causality for dyslexia relates, as above, to impaired auditory-phonological processing, Gori et al provide evidence that deficits in the visual magnocellular-dorsal (MD) pathway may contribute as well (32,33). The MD pathway originates in retinal ganglion cells, projects to the M-layer of the lateral geniculate nucleus, and ultimately to the occipital and parietal lobes. The MD pathway responds to motion, luminance contrast, and low spatial frequencies. Patients with dyslexia have deficient motion processing and postmortem studies have shown that lateral geniculate nucleus magnocellular neurons are smaller than normal in dyslexic individuals (32–34); however, there has been a long-standing debate as to whether these deficits are the cause or result of dyslexia (35). Gori et al (33) showed that deficient motion processing in 72 5-year-old children (preformal reading training, those able to read at this age were excluded) was predictive of poor reading development during the following year (the year of initiation of formal reading training). This finding suggests that deficient motion processing is causal and not merely associated with poor reading ability. If MD pathway dysfunction contributes to the development of dyslexia, then it would be biologically plausible that therapies directed at improving MD pathway function could potentially improve reading ability. In support of this, Gori et al showed that children (n = 11) and adults (n = 18) with dyslexia who performed targeted MD training (through a video game in children and perceptual learning task requiring discernment of whether motion was present in a stimulus or not in adults) had improved reading ability (33). Thus, in addition to therapies directed at phonological processing, training the MD pathway may ultimately be an important component of the treatment of dyslexia.
Many studies report abnormal ocular motor behavior during reading in subjects with dyslexia (36–38). However, other studies with age-matched control groups have not documented specific ocular motor deficits in dyslexics and concluded that dyslexia does not occur from ocular motor impairment (25,39–43). Patients with acquired ocular motility deficits do not develop dyslexia (26). Ocular motor behavioral changes in dyslexic subjects are considered to be secondary to poor reading comprehension and there is inadequate scientific evidence to support the view that ocular motor dysfunction causes or increases its severity (26). Thus, it follows that dyslexia would not be directly amenable to vision therapy.
The official policy of the American Academy of Optometry and the American Optometric Association is that vision therapy is not a treatment for learning disabilities, but that it does improve visual processing and efficiency (44). However, the definition and assessment of “visual processing and efficiency” varies between studies, most of which are nonrandomized, unmasked, and lack a control group (1). The American Academy of Ophthalmology, the American Association of Pediatric Ophthalmology and Strabismus, and the AAP published official statements emphasizing a lack of scientific evidence to support the use of optometric behavioral vision therapy for the purpose of improving visual processing or perception (45,46). These organizations specify that “No scientific evidence exists for the efficacy of eye exercises or special tinted lenses in the remediation” of learning disabilities or dyslexia (45). In addition, it is stated that behavioral vision therapy, eye exercises, and special tinted filters or lenses are not endorsed and should not be recommended. In summary, there is no evidence that any therapy directed at eye movements effectively treats dyslexia.
Attention-Deficit Hyperactivity Disorder
ADHD is a chronic condition characterized by inattention, hyperactivity, and, in some instances, impulsivity. Children with this disorder may have poor school performance and difficulty maintaining attention while reading. There is no scientifically rigorous evidence that vision therapy improves ADHD (1,13).
Given that the symptoms of CI (i.e., ability to concentrate for extended reading) may overlap with those of ADHD, a retrospective review of 266 patients with CI who also underwent evaluation for ADHD, and vice versa, addressed this issue (47). A 3-fold greater incidence of ADHD was identified in subjects with CI compared with the incidence of ADHD in the general US population. Furthermore, there was a 3-fold greater incidence of CI in the ADHD population. The authors emphasized that although they demonstrated an association between CI and ADHD, this does not imply that CI is a cause of ADHD. They recommend that patients with ADHD be evaluated for CI, and that CI, if present, should be treated. However, treatment of CI will not cure the ADHD.
In summary, although there may be an association between ADHD and CI, there is no evidence that ocular motility deficits cause ADHD or that therapy directed at eye movements is an effective treatment for ADHD.
- Convergence exercises improve the symptoms and signs of CI.
- The optimal convergence exercises and the optimal dose of the exercises (duration and frequency) are unknown.
- The CITT showed that patients treated with in-office convergence exercises had better outcomes than patients treated exclusively with home-based exercises. However, the office-based treatment groups had a greater dose of convergence exercises.
- Office-based convergence exercises are significantly expensive, estimated at $1,125/patient, according to the CITT study group. It may be cost-effective to practice a stepwise treatment approach starting with home-based therapy and reserving office-based treatment for patients who do not respond to home-based therapy.
- The treatment of CI can reduce symptoms while reading. However, there is no evidence that treating CI is beneficial for learning disabilities, poor reading ability, dyslexia, or ADHD.
- Patients with learning disabilities, dyslexia, or ADHD do not have specific ocular motor deficits.
- Patients with ocular motor deficits do not develop learning disabilities, dyslexia, or ADHD and are often able to read normally.
- There is no current rigorous evidence that ocular motor exercises effectively treat learning disabilities, poor reading ability, dyslexia, or ADHD. The literature is currently mixed. Randomized controlled studies would be beneficial to clarify the role of these methods.
STATEMENT OF AUTHORSHIP
Category 1: a. Conception and design: J. C. Rucker, Paul Phillips; b. Acquisition of data: J. C. Rucker, P. H. Phillips; c. Analysis and interpretation of data: J. C. Rucker, P. H. Phillips. Category 2: a. Drafting the manuscript: J. C. Rucker, P. H. Phillips; b. Revising it for intellectual content: J. C. Rucker, P. H. Phillips. Category 3: a. Final approval of the completed manuscript: J. C. Rucker, P. H. Phillips.
1. Barrett BT. A critical evaluation of the evidence supporting the practice of behavioural vision therapy. Ophthalmic Physiol Opt. 2009;29:4–25.
3. Shainberg MJ. Vision therapy and orthoptics. Am Orthopt J. 2010;60:28–32.
4. Scheiman M, Rouse M, Kulp MT, Cotter S, Hertle R, Mitchell GL. Treatment of convergence insufficiency in childhood: a current perspective. Optom Vis Sci. 2009;86:420–428.
5. Kushner BJ. The treatment of convergence insufficiency. Arch Ophthalmol. 2005;123:100–101.
6. Ciuffreda KJ. The scientific basis for and efficacy of optometric vision therapy in nonstrabismic accommodative and binocular vision disorders. Optometry. 2002;73:735–762.
7. Seithi HS, Saxena R, Sharma P, Sinha A. Home exercise for convergence insufficiency in children. Arch Ophthalmol. 2006;124:287.
8. Birnbaum MH, Soden R, Cohen AH. Efficacy of vision therapy for convergence insufficiency in an adult male population. J Am Optom Assoc. 1999;70:225–232.
9. Scheiman M, Mitchell GL, Cotter S, Cooper J, Kulp M, Rouse M, Borsting E, London R, Wensveen J; Convergence Insufficiency Treatment Trial Group. A randomized clinical trial of treatments for convergence insufficiency in children. Arch Ophthalmol. 2005;123:14–24.
10. Scheiman M, Mitchell GL, Cotter S, Kulp MT, Cooper J, Rouse M, Borsting E, London R, Wensveen J. A randomized clinical trial of vision therapy/orthoptics versus pencil pushups for the treatment of convergence insufficiency in young adults. Optom Vis Sci. 2005;82:583–595.
11. Convergence Insufficiency Treatment Trial Study G. Randomized clinical trial of treatments for symptomatic convergence insufficiency in children. Arch Ophthalmol. 2008;126:1336–1349.
12. Scheiman M, Gwiazda J, Li T. Non-surgical interventions for convergence insufficiency. Cochrane Database Syst Rev. 2011;3:CD006768.
13. Rawstron JA, Burley CD, Elder MJ. A systematic review of the applicability and efficacy of eye exercises. J Pediatr Ophthalmol Strabismus. 2005;42:82–88.
14. Jethani J. Convergence insufficiency: randomized clinical trial. Arch Ophthalmol. 2005;123:1760; author reply-1761.
15. Convergence Insufficiency Treatment Trial Study G. The convergence insufficiency treatment trial: design, methods, and baseline data. Ophthalmic Epidemiol. 2008;15:24–36.
16. Convergence Insufficiency Treatment Trial Study G. Long-term effectiveness of treatments for symptomatic convergence insufficiency in children. Optom Vis Sci. 2009;86:1096–1103.
17. Wallace DK. Treatment options for symptomatic convergence insufficiency. Arch Ophthalmol. 2008;126:1455–1456.
18. Cotter S, Kulp M, Scheiman M, Hertle R, Mitchell GL, Rouse M; Convergence Insufficiency Treatment Trial Executive Committee. Response to editorial about the convergence insufficiency treatment trial. Arch Ophthalmol. 2009;127:1229–1230; author reply 30–31.
19. Borsting E, Mitchell GL, Kulp MT, Scheiman M, Amster DM, Cotter S, Coulter RA, Fecho G, Gallaway MF, Granet D, Hertle R, Rodena J, Yamada T; CITT Study Group. Improvement in academic behaviors after successful treatment of convergence insufficiency. Optom Vis Sci. 2012;89:12–18.
20. Group C-AI, Scheiman M, Mitchell GL, Cotter SA, Kulp M, Chase C, Borsting E, Arnold E, Denton C, Hertle R. Convergence Insufficiency Treatment Trial—Attention and Reading Trial (CITT-ART): design and methods. Vis Dev Rehabil. 2015;1:214–228.
21. Bade A, Boas M, Gallaway M, Mitchell GL, Scheiman M, Kulp MT, Cotter SA; Rouse M for the CITT Study Group. Relationship between clinical signs and symptoms of convergence insufficiency. Optom Vis Sci. 2013;90:988–995.
22. Abrams SG, Zuber BL. Some temporal characteristics of information processing during reading. Reading Res Q. 1972;8:40–51.
23. Rayner K. Eye movements in reading and information processing. Psychol Bull. 1978;85:618–660.
24. Hoyt C. Visual training and reading. Am Orthopic J. 1999;49:23–25.
25. Polatajko HJ. Visual-ocular control of normal and learning disabled children. Dev Med Child Neurol. 1987;29:477–485.
26. Handler SM, Fierson WM; Section on Ophthalmology, Council on Children with Disabilities, American Academy of Ophthalmology, American Association for Pediatric Ophthalmology and Strabismus, American Association of Certified Orthoptists. Learning disabilities, dyslexia, and vision. Pediatrics. 2011;127:e856.
27. Rayner K. Eye movements in reading and information processing: 20 years of research. Psychol Bull. 1998;124:372–422.
28. Seiderman AS. Optometric vision therapy—results of a demonstration project with a learning disabled population. J Am Optom Assoc. 1980;51:489–493.
29. Dusek WA, Pierscionek BK, McClelland JF. An evaluation of clinical treatment of convergence insufficiency for children with reading difficulties. BMC Ophthalmol. 2011;11:21.
30. Leong DF, Master CL, Messner LV, Pang Y, Smith C, Starling AJ. The effect of saccadic training on early reading fluency. Clin Pediatr (Phila). 2014;53:858–864.
31. Dodick D, Starling AJ, Wethe J, Pang Y, Messner LV, Smith C, Master CL, Halker-Singh RB, Vargas BB, Bogle JM, Mandrekar J, Talaber A, Leong D. The effect of in-school saccadic training on reading fluency and comprehension in first and second grade students: a randomized controlled trial. J Child Neurol. [published ahead of print October 10, 2016] doi: 10.1177/0883073816668704.
32. Gori S, Facoetti A. Perceptual learning as a possible new approach for remediation and prevention of developmental dyslexia. Vis Res. 2014;99:78–87.
33. Gori S, Seitz A, Ronconi L, Franceschini S, Facoetti A. Multiple causal links between magnocellular-dorsal pathway deficit and developmental dyslexia. Cereb Cortex. [published online ahead of print September 22, 2015] doi: 10.1093/cercor/bhv206.
34. Livingstone MS, Rosen GD, Drislane FW, Galaburda AM. Physiological and anatomical evidence for a magnocellular defect in developmental dyslexia. Proc Natl Acad Sci U S A. 1991;88:7943–7947.
35. Goswami U. Sensory theories of developmental dyslexia: three challenges for research. Nat Rev Neurosci. 2015;16:43–54.
36. Pavlidis GT. Do eye movements hold the key to dyslexia? Neuropsychologia. 1981;19:57–64.
37. Jainta S, Kapoula Z. Dyslexic children are confronted with unstable binocular fixation while reading. PLoS One. 2011;6:e18694.
38. Bucci MP, Nassibi N, Gerard CL, Bui-Quoc E, Seassau M. Immaturity of the oculomotor saccade and vergence interaction in dyslexic children: evidence from a reading and visual search study. PLoS One. 2012;7:.
39. Brown B, Haegerstrom-Portnoy G, Yingling CD, Herron J, Galin D, Marcus M. Tracking eye movements are normal in dyslexic children. Am J Optom Phys Opt. 1983;60:376–383.
40. Black JL, Collins DW, De Roach JN, Zubrick S. A detailed study of sequential saccadic eye movements for normal- and poor-reading children. Percept Mot Skills. 1984;59:423–434.
41. Helveston EM, Weber JC, Miller K, Robertson K, Hohberger G, Estes R, Ellis FD, Pick N, Helveston BH. Visual function and academic performance. Am J Ophthalmol. 1985;99:346–355.
42. Lennerstrand G, Ygge J, Jacobsson C. Control of binocular eye movements in normals and dyslexics. Ann N Y Acad Sci. 1993;682:231–239.
43. Wahlberg-Ramsay M, Nordstrom M, Salkic J, Brautaset R. Evaluation of aspects of binocular vision in children with dyslexia. Strabismus. 2012;20:139–144.
44. Vision, learning and dyslexia. A joint organizational policy statement. American Academy of Optometry, American Optometric Association. J Am Optom Assoc. 1997;68:284–286.
45. American Academy of Pediatrics Committee on Children with Disabilities. American Academy of Pediatrics (AAP) and American Academy of Ophthalmology (AAO), American Association for Pediatric Ophthalmology and Strabismus (AAPOS). Learning disabilities, dyslexia and vision: a subject review. Pediatrics. 1998;102:1217–1219.
46. American Academy of Pediatrics. Section on Ophthalmology, Council on Children with Disabilities; American Academy of Ophthalmology; American Association for Pediatric Ophthalmology and Strabismus; American Association of Certified Orthoptists. Joint statement—learning disabilities, dyslexia and vision. Pediatrics. 2009;124:837–844.
47. Granet DB, Gomi CF, Ventura R, Miller-Scholte A. The relationship between convergence insufficiency and ADHD. Strabismus. 2005;13:163–168.