Revealing the benefit of eye motion for acuity under emulated cone loss

Retinal degenerative diseases progressively erode the cone photoreceptor mosaic, reducing the retina's spatial sampling power, yet visual acuity is remarkably resilient to cone loss. Prior work has shown that clinically normal visual acuity (20/25 or better) can persist despite up to 50% of cone cells being lost (Ratnam et al., 2013; Foote et al., 2018). However, studies on individuals with retinal degeneration cannot control for patients' stage of disease progression, creating the need for an experimental paradigm that can mimic these diseases in healthy subjects. The Oz Vision system creates visual percepts through programmable, per-cell stimulation of thousands of cone cells. We reprogram this system to emulate cone loss in healthy eyes by withholding stimulation from a subset of randomly selected cones, rendering them inactive, in a method we term 'cone dropout'. Using this approach, we characterize the visual system's robustness to cone loss, showing that visual acuity declines nonlinearly with increasing cone dropout. Importantly, we uncover the compensatory benefit that eye motion provides under cone-deprived conditions, finding that at the highest level of dropout, a visual system with eye motion has an equivalent acuity to a static dropout condition with nearly twice as many sampling elements. Through analysis of eye motion and stimulation data, we find that this benefit arises from the additional information accumulated by 'surviving' cones as they sample more of the letter through fixational eye motion.