Suppression rather than visual acuity loss limits threshold stereoacuity.

Abstract

Purpose : Stereoacuity is low or absent in patients with abnormal binocular vision, however, the relative contribution of inter-ocular differences in visual acuity and severity of suppression is not known. We hypothesize that threshold stereoacuity is limited by the depth of suppression, rather than the extent of visual acuity decrement. We further hypothesize that stereoacuity will improve when inter-ocular contrast balance is altered to neutralize suppression.

Methods : Visual acuity (EDTRS), stereoacuity (random dot kinematogram - Hess et al. IOVS 2016) and depth of suppression (inter-ocular contrast balance – Kwon et al., PLoS One 2014) were tested in adult participants with both normal (n=14; age 24 ± 2 years) and abnormal binocular vision (n=21; age 24 ± 2 years). Stereoacuity testing was retested in a subsample of participants following contrast reduction of the stimulus presented to dominant eye to neutralize of suppression. Correlation and multiple regression analyses were used to determine interactions between the depth of suppression, visual acuity decrement and stereoacuity threshold.

Results : Participants with abnormal vision had greater inter-ocular visual acuity difference, poorer stereoacuity thresholds and higher contrast balance ratios than participants with normal binocular vision (p<0.01). Stereoacuity significantly correlated with both inter-ocular acuity difference (rs=0.492; p<0.01) and contrast balance ratio (rs=0.737; p<0.01). Multiple regression modelling showed that poorer stereoacuity threshold was associated with depth of suppression (p=0.007), but not with visual acuity decrement (p=0.640). Stereoacuity improved after inter-ocular contrast balance was altered to neutralize suppression.

Conclusions : Severity of suppression, rather than visual acuity loss, limits stereoacuity. Stereoacuity can improve when suppression is eliminated.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.