Preeti Verghese¹ (), Ângela Gomes-Tomaz², Noelia Alcalde¹, Jian Ding², Adrien Chopin¹, Dennis Levi²; ¹Smith Kettlewell Eye Research Institue, ²University of California, Berkeley

An imbalance in contrast sensitivity between the eyes is thought to contribute to poor stereoacuity in amblyopia (Vedamurthy et al., 2015; Webber et al., 2020). However the precise locus (foveal or peripheral) that mediates stereoacuity was not determined. To investigate this, we made local measurements at the fovea and at multiple locations across the central 20° of the visual field, in controls and in persons with amblyopia. We used random-dot stimuli that scaled with eccentricity to measure both stereoacuity and contrast imbalance. Observers (14 controls; 5 with amblyopia: 3 strabismic, 1 anisometropic and 1 mixed) adjusted the contrast of the dominant-eye stimulus to match the perceived contrast of the non-dominant eye stimulus, at the fovea and at the locus of best stereopsis. Results showed no systematic relationship between stereoacuity and the contrast ratio at perceptual balance for controls at the fovea (r =-0.40, p = .16), or at the locus of best stereopsis (r = -0.15, p = .62), or for the amblyopic group at their best locus (r = 0.20, p =.78). Individuals with amblyopia had no measurable stereopsis at the fovea. We also used the Ding et al. (2013) model to estimate each eye’s contribution to binocular combination after contrast normalization, but this asymmetry ratio also showed no systematic relationship to stereoacuity at the fovea (control: r = 0.40, p = .16), or at the best locus (control: r = 0.15, p = .62, amblyopia: r =-0.20, p = .78). However, in the stereoblind fovea of individuals with amblyopia, asymmetry ratios were significantly larger (GLM p = 0.01, Cohen’s d=1.13, large effect size). Our results together with previous findings suggest that while contrast imbalance may contribute to impaired stereopsis in the central retina in amblyopia, this is not necessarily true at the (peripheral) locus of best stereopsis.

Acknowledgements: NIH R01 EY034370