Krista Kelly¹, Norah Nyangau², Mina Nouredanesh³; ¹School of Optometry and Vision Science, University of Waterloo, ²Retina Foundation of the Southwest, ³Max Rady College of Medicine, University of Manitoba

Introduction: Amblyopia (lazy eye) is characterized by reduced vision in one eye and impaired binocular vision (suppression, reduced stereoacuity), which can impact ocular motor control. Previous studies report abnormal saccades in amblyopia, but primarily under monocular viewing or in adults. Since amblyopia typically develops by age 7 years, understanding saccadic function in affected children during binocular viewing is critical. Methods: We examined saccade kinematics in 35 children (7-14 years) with amblyopia and 31 age-similar controls. Amblyopic children were classified by etiology (19 anisometropia, 16 strabismus) and stereoacuity status (18 present, 17 absent). Using an EyeLink 1000 binocular eye tracker, saccades were recorded during binocular viewing at 40 cm. Children fixated a central cross, then shifted gaze to dot appearing left or right at 5° or 10° (10 trials per location, 40 total). Outcomes included onset latency, peak velocity, primary and corrective saccade gain, gain error, and % trials with corrective saccades. Results: No between-eye differences were observed; fellow eye data only are reported. Compared to controls, amblyopic children exhibited delayed onset latency (control, 201±25 msec vs amblyopia, 219±33, p=0.02), reduced gain (0.95±0.06 vs 0.89±0.07, p<0.001), increased gain error (0.10±0.03 vs 0.14±0.04, p<0.001), and more corrective saccades (52±16% vs 63±16%, p=0.01). Strabismic amblyopia showed delayed latency (p=0.03), while anisometropic amblyopia showed increased corrective saccades (p<0.001). Amblyopic children with absent stereoacuity exhibited delayed latency, reduced gain, increased gain error, and increased corrective saccades (ps<0.04) compared to controls, whereas those with stereoacuity present were similar to controls (ps>0.10). No associations were found with amblyopic eye visual acuity (ps>0.17). Conclusions: During binocular viewing, amblyopic children demonstrate impaired saccade kinematics. These deficits are linked to binocular vision status, particularly absent stereoacuity, rather than visual acuity. These findings may have implications for understanding functional deficits, such as slow reading, in children with amblyopia.

Acknowledgements: NIH EY028224; NSERC RGPIN-2024-03992