Binocular performance in patients with unilateral cataract using the Regan test: binocular summation and inhibition with low-contrast charts.

Recent reports have shown that binocular contrast sensitivity is an important indicator for assessing the visual function of a unilateral cataract. Binocular sensitivity, assessed in terms of binocular summation and inhibition, is dependent on the difference between the two eyes. Maximum binocular summation, obtained when the sensitivities of two eyes are equal, decreases if they are made unequal. Further increases in the monocular difference produce binocular inhibition, defined as a binocular sensitivity which is lower than the monocular. The aim of this study was to investigate whether the binocular effects in unilateral cataract that have been shown using laboratory-based equipment can be demonstrated using commercially available Regan charts. Binocular scores were compared with monocular scores in 16 unilateral cataract patients and 16 aged-matched normals using a high-contrast chart (96%) and a low-contrast (11%) chart. Normal subjects showed binocular summation with both charts. The cataractous patients showed no summation at high contrast and binocular inhibition with low-contrast charts. The implications of binocular inhibition at low contrast are discussed.