Abstract
Introduction: Stereoanomalous (SA) subjects have normal visual acuity but reduced stereopsis, and may have a prevalence of up to 30%. It has been suggested that in SA subjects an imbalance in interocular inhibition might underlie an asymmetry in sensory eye dominance (SED). Our study expands upon previous findings by examining binocular rivalry (BR) mean dominations durations, dichoptic masking (DM) thresholds and sensory eye dominance (SED) for a group of SA subjects compared to naïve controls. Method: We examined BR dominance durations and DM thresholds for 15 stereonormal (SN) subjects and 10 SA subjects with normal or corrected-to-normal visual acuity. Individuals who scored >6/9 on the Randot stereo test and < 100 arcmin on the PacMan Stereo Acuity test were considered SN. The criterion for SN was visual acuity of 20/40 or better, and less than two-lines difference between eyes. We compared near-vertical and near-horizontal oriented sine-wave gratings for BR and DM, in order to dissociate stereo-related mechanisms that rely on horizontal disparities from other eye-based integration mechanisms. Results: Randot scores for SN subjects were 8.53/9 with a PacMan stereoacuity of 32.5 arcmin, while SA subjects scored 2.5/9 and 3380 arcmin respectively. The difference in SED was 0.19 for SN and 0.48 for SA when measured with a neutral density filter bar. The SA group showed an interocular difference in BR durations that was significantly greater than normal (p = 0.004). Moreover, the interocular difference for DM was similarly greater for SA subjects (p = 0.04). We also found that both SN and SA subjects presented higher DM thresholds for vertical than horizontal orientations. Conclusions: SA subjects show a bias towards their dominant eye for both BR and DM, while SN subjects do not. These data may ultimately provide a practical link to better understand the heterogeneity of stereopsis in the population.