Oculomotor Dysfunctions in Non-Reading Tasks in Children with Developmental Dyslexia: Saccadic and Optokinetic Findings

Specific learning disorder (SLD) is a neurodevelopmental disorder characterized by difficulties in reading, writing and math skills. Saccadic eye movements play a critical role in fluent reading and visual scanning. 40 children with dyslexia and 40 healthy controls were included in this study according to DSM-5 criteria, since children with dyslexia have reading fluency disorders and saccadic eye movements are necessary for fluent reading. Psychiatric evaluations and structured clinical interviews were conducted by an experienced child and adolescent psychiatrist. Saccadic eye movements (saccadic velocity, accuracy and latency) were recorded using a videonystagmography (VNG) system and compared between the two groups. Results showed that children with dyslexia exhibited significantly lower saccadic velocity (307.5°/s vs. 453.5°/s, p < 0.001) and saccadic accuracy (71.5% vs. 98.5%, p < 0.001) and significantly longer saccadic latency (260.0 ms vs. 131.5 ms, p < 0.001). Optokinetic responses in the right eye were significantly less in the SLD group (p = 0.028), whereas no significant difference was observed in the left eye responses (p = 0.067). These findings suggest that children with dyslexia have significant oculomotor dysfunction independent of the act of reading. This may contribute to reading difficulties and impaired visual information processing, and oculomotor assessment in dyslexia may be a useful tool in the development of etiologic diagnosis and interventions.