Introduction
The study evaluates oculomotor function as a sensitive endophenotype to understand the etiology of autism spectrum disorder (ASD), attention deficit/hyperactivity disorder (ADHD) and the coexistence of both (ASD + ADHD). The detailed analysis of oculomotor characteristics, such as accuracy, sensory-motor processing and inhibitory control, aims to identify useful neurobiological markers to diagnose and differentiate these disorders.
Methods
Participants were 405 Australian children and adolescents (64 with ADHD, 66 with ASD, 146 with ASD+ADHD, and 129 neurotypical), aged 4–18 years (Mean = 9.64 years, SD = 3.20). Additional data were obtained from independent cohorts in the UK (n = 101) and the USA (n = 70). Four oculomotor tasks were used: visual guided saccade (VGS), anti-saccade (AS), sinusoidal pursuit, and step-ramp pursuit. Measurements, performed with the EyeLink 1000 system (500 Hz), were analyzed using linear mixed models controlling for age, sex, and family effects.
Results
Individuals with ASD + ADHD showed greater variability in final eye position (FEP) during the VGS task compared to neurotypicals (p = 0.025, d = 0.316), suggesting dysfunctions in sensorimotor circuitry and cerebellar feedback. Adolescents with ASD demonstrated greater number of corrective saccades during the step-ramp task (p = 0.015), indicating deficits in corrective and sensorimotor control. Although there were no significant differences in the AS task in the main cohort, confirmatory findings revealed greater number of directional errors in individuals with ASD compared to neurotypicals (Kansas Cohort, p = 0.019, d = 0.452).
Discussion
The identified oculomotor differences reflect alterations in both bottom-up (sensory-motor) and top-down (corrective and predictive) control networks. The motor control inefficiencies in individuals with ASD + ADHD and the unique corrective difficulties of individuals with ASD point to overlap and distinction in the underlying mechanisms of these disorders. Methodological and sampling differences limited the full replication of findings in confirmatory cohorts, highlighting the need for longitudinal studies.
Conclusion
Oculomotor characteristics offer promising insights to understand neurodevelopmental differences and contribute to more accurate diagnoses of ASD, ADHD and their coexistence. Future studies should investigate the neurobiology underlying the identified differences and explore the clinical applicability of these markers.
Reference :
Forbes, E.J., Tiego, J., Langmead, J., Unruh, K.E., Mosconi, M.W., Finlay, A., Kallady, K., Maclachlan, L., Moses, M., Cappel, K., Knott, R., Chau, T., Mohanakumar Sindhu, VP, Bellato, A., Groom, M.J., Kerestes, R., Bellgrove, M.A., & Johnson, B.P. (2025). Oculomotor function in children and adolescents with autism, ADHD, or co-occurring autism and ADHD. Journal of Autism and Developmental Disorders. https://doi.org/10.1007/s10803-024-06718-3
