Main question for this research was if deficits in visual function are more frequent in children with developmental dyslexia (DD) than in typically developing (TD) readers. Analysis investigated which functions were most affected, the frequency and magnitude of abnormal findings and whether deficits were more evenly distributed across the developmental dyslexia group or clustered in a subgroup.
Vergence
Despite the fact that convergence insufficiency is thought to be a problem in children with reading problems, the frequency of children who met the criteria for a diagnosis of vergence deficit was unexpectedly similar in their DD and TD groups. Furthermore, the deficit in both groups was much more likely to be due to convergence excess rather than convergence insufficiency, which was uncommon in the sample.
Accommodation
In the DD group, more than half of the children (55%) met the criteria for an accommodation deficit diagnosis, compared to only three (9%) in the TD group. In the DD group, about two-thirds of the children had accommodative insufficiency, with the rest having generalized accommodative dysfunction. The amplitude of accommodation was lower in the DD group than in the TD group in individual tests, which is consistent with other studies. On the monocular and binocular accommodative facility tests, children in the DD group recorded fewer cycles, indicating that their accommodation dynamics were slower to react than those in the TD group.
Ocular Motor Tracking
More than half of the children in the DD group (62%) exhibited ocular motor tracking deficits when reading nonlinguistic stimuli (DEM). Even when reading text at their grade-equivalent level with adequate comprehension, they showed elevated deficits in rate, fixations, and regressions on the Visagraph.
Visual Function and Reading
Although this study shows that children with DD have a higher rate of impaired vision, the link to the reading process is unclear. Patients with accommodation deficits may experience blurry vision at close range, words that come in and out of focus, difficulty maintaining clear vision while reading, and difficulty switching focus from distance to close range. Despite the fact that the DD group’s accommodation amplitude was not within the range expected to cause near-vision work-related blur or asthenopic symptoms, the push-up method we used overestimates accommodation amplitude. As a result, if objective measures had been used, the decrease in accommodation observed in the DD group could have been even greater, within a range that could cause difficulty maintaining clear near vision.
Even if the accommodative facility has been linked to reading ability in first-graders and vergence facility has been linked to reading rate in children with learning disabilities, the direction of causation and functional significance remains unknown. Eye exercises improved near work-related symptoms in children with reduced accommodation and convergence, according to the Convergence Insufficiency Treatment Trials. Eye exercises improved vergence, accommodation, and tracking in children with learning disabilities who had nonstrabismic binocular vision anomalies, but their effect on reading was not studied.
Reading has also been linked to tracking. Children with dyslexia and poor readers have a link between their horizontal DEM scores and their reading rate. Beginning readers also have more fixations, longer fixation durations, shorter saccades, and more regressions than skilled readers, but these deficits persist in children with dyslexia and are only related to reading.
To conclude, In this cohort study, school-aged children with developmental dyslexia exhibited more deficits in visual function—vergence, accommodation, and/or ocular motor tracking—than did a nonrandomized control group of typically developing children.
Source: Raghuram, O. A. D., PhD. (2018, October 1). Frequency of Visual Deficits in Children With Developmental Dyslexia. Ophthalmology | JAMA Ophthalmology | JAMA Network. https://jamanetwork.com/journals/jamaophthalmology/article-abstract/2687496?utm_campaign=articlePDF&utm_medium=articlePDFlink&utm_source=articlePDF&utm_content=jamaophthalmol.2018.2797