Importance: Developmental dyslexia (DD) is a specific learning disability of neurobiological origin whose core cognitive deficit is widely believed to involve language (phonological) processing. Although reading is also a visual task, the potential role of vision in DD has been controversial, and little is known about the integrity of visual function in individuals with DD.
Objective: To assess the frequency of visual deficits (specifically vergence, accommodation, and ocular motor tracking) in children with DD compared with a control group of typically developing readers.
Design, setting, and participants: A prospective, uncontrolled observational study was conducted from May 28 to October 17, 2016, in an outpatient ophthalmology ambulatory clinic among 29 children with DD and 33 typically developing (TD) children.
Main outcomes and measures: Primary outcomes were frequencies of deficits in vergence (amplitude, fusional ranges, and facility), accommodation (amplitude, facility, and accuracy), and ocular motor tracking (Developmental Eye Movement test and Visagraph eye tracker).
Results: Among the children with DD (10 girls and 19 boys; mean [SD] age, 10.3 [1.2] years) and the TD group (21 girls and 12 boys; mean [SD] age, 9.4 [1.4] years), accommodation deficits were more frequent in the DD group than the TD group (16 [55%] vs 3 [9%]; difference = 46%; 95% CI, 25%-67%; P < .001). For ocular motor tracking, 18 children in the DD group (62%) had scores in the impaired range (in the Developmental Eye Movement test, Visagraph, or both) vs 5 children in the TD group (15%) (difference, 47%; 95% CI, 25%-69%; P < .001). Vergence deficits occurred in 10 children in the DD group (34%) and 5 children in the TD group (15%) (difference, 19%; 95% CI, -2.2% to 41%; P = .08). In all, 23 children in the DD group (79%) and 11 children in the TD group (33%) had deficits in 1 or more domain of visual function (difference, 46%; 95% CI, 23%-69%; P < .001).
Conclusions and relevance: These findings suggest that deficits in visual function are far more prevalent in school-aged children with DD than in TD readers, but the possible cause and clinical relevance of these deficits are uncertain. Further study is needed to determine the extent to which treating these deficits can improve visual symptoms and/or reading parameters.