Sunwoo Kwon^1,2,4, (), Julien Belen¹, Jessica Lien¹, Artashes Yeritsyan¹, Nam Do¹, Dennis Levi^1,2,3; ¹Herbert Wertheim School of Optometry and Vision Science, UC Berkeley, ²Center for Innovation in Vision and Optics, UC Berkeley, ³Helen Wills Neuroscience Institute, UC Berkeley, ⁴Exponent

Amblyopia is associated with impaired visual acuity, abnormal processes in primary visual cortex (V1), and reduced coordination of activity in binocular neurons. Recent studies have demonstrated that these abnormalities extend beyond V1 with potential impacts on higher order processing and in oculomotor areas that affect visually-guided behaviors. While large fixational instabilities found in amblyopic eyes are highly correlated with worsening acuity in these patients, no such correlation was found in a neurotypical population (Raveendran et al., 2019). It is unclear whether the poor acuity causes fixational instability or vice versa or if the two are correlated as a byproduct of abnormal processes in V1. Therefore, we investigated whether visual acuity is truly a limiting factor in oculomotor and visually-guided behavior. We simulated reduced visual acuity observed in the amblyopic eye in the non-dominant eyes (NDEs) of corrected-to-normal neurotypical observers by applying convex lenses to induce retinal-defocus while the observers viewed naturalistic stimuli – a filtered version of “Where’s Waldo” – while performing a visual search task. We tested a set of logMAR acuity differences (0.2, 0.4, 0.6, and 0.8) as observed in amblyopic patients and compared the oculomotor behavior of the normal eye with lens-induced acuity loss in the following conditions: monocular NDE and binocular viewing. We observed lens induced acuity loss had a significant impact on the observer’s drift magnitude and fixational instabilities compared to the no-blur condition in the NDE; however, further reductions in visual acuity did not have any significant impact. Binocular viewing significantly improved fixational instability and reduced reaction time when compared with monocular viewing in both amblyopes and neurotypicals; this effect persisted as a function of retinal-defocus induced reduction in visual acuity. Our results demonstrate that the reduced visual acuity of patients with amblyopia cannot be fully accounted for by abnormal fixational eye movements.

Acknowledgements: Center for Innovation in Vision and Optics (CIVO) Fellowship, NEI R21