Some studies suggest that children with developmental dyslexia may also exhibit visual deficits that could contribute to their reading difficulties. In this blog post, we included the research whose main question was whether deficits in visual function are more frequent in children with developmental dyslexia (DD) than in typically developing (TD) readers.
The analysis investigated which functions were most affected, assessing the frequency and magnitude of abnormal findings, and determining whether deficits were evenly distributed across the developmental dyslexia group or clustered within a subgroup.
Table of contents
- What is Developmental Dyslexia?
- Comparing Visual Deficits in Children with Developmental Dyslexia and Typically Developing Readers
- Visual Function and Reading: Discussing Results of the Study
- Vision Therapy for Dyslexia: Behavioral Vision Therapy or Orthoptics
- Implications for Interventions and Support
What is Developmental Dyslexia?
Developmental dyslexia is a specific learning disability. It affects the reading skills of children and adults who otherwise have intelligence, motivation, and schooling required for correct and fluent reading. It is a common learning disorder that affects children’s ability to read, write, and spell.
While it is primarily characterized as a phonological processing deficit, there has been an ongoing debate about the potential involvement of visual processing difficulties in dyslexia. Individuals with this condition struggle with word identification, relationship between letters and sounds, and spelling.
It is a neurobiological condition with a strong genetic component, and it occurs in individuals across different languages and cultures. The disorder affects 25% to 65% of the children of parents who have the disorder, as well as around 40% of siblings of children with developmental dyslexia. Interestingly, children with higher IQs have a higher heritability for developing dyslexia.
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Dyslexia primarily affects phonological processing, which involves recognizing and manipulating the sounds in spoken words.
It is estimated that developmental dyslexia affects around 10% of the population.
Comparing Visual Deficits in Children with Developmental Dyslexia and Typically Developing Readers
The eyes move in opposite left-right directions during vergence movements; these are disjunctive motions.
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.
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: Discussing Results of the Study
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.
What About Eye Exercises?
Eye exercises improved near work-related symptoms in children with reduced accommodation and convergence, according to the Convergence Insufficiency Treatment Trials. Additionally, 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.
Developmental Dyslexia and Eye Tracking
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.
Vision Therapy for Dyslexia: Behavioral Vision Therapy or Orthoptics
All dyslexics should have complete ophthalmological tests, including cycloplegia, to detect masked hyperopia and to do a detailed analysis of ocular motility and accommodative capacity. Furthermore, all refractive abnormalities must be addressed since they may worsen the reading problems.
When there are saccade or pursuit abnormalities, orthoptic rehabilitation inspired by “behavioural vision therapy” is occasionally suggested.
Implications for Interventions and Support
The presence of visual deficits in some children with dyslexia highlights the importance of a comprehensive assessment when diagnosing and supporting individuals with reading difficulties. Understanding a child’s unique cognitive profile, including both phonological and visual processing skills, can inform targeted interventions.
Determining the exact frequency of visual deficits in children with dyslexia is complex, as research findings vary. Some studies have reported that a significant proportion of children with dyslexia also exhibit visual processing difficulties, while others have found no conclusive evidence of such associations.
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.
Developmental dyslexia is a specific learning disability that affects the reading skills of children and adults who otherwise have intelligence, motivation, and schooling required for correct and fluent reading.
Problems with vergence eye movement, accommodation, ocular-motor tracking, and other binocular vision disorders.
Vision therapy can help with dyslexia symptoms if there are deficits in visual function, such as convergence insufficiency.
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