Impairment of contrast discrimination in amblyopic eyes

A successive two-alternative, forced-choice procedure incorporating a double-interleaved staircase was used to measure monocular contrast discrimination in strabismic and/or anisometropic amblyopes, strabismics without amblyopia, and normals. Standard contrast was 25%, with comparison contrasts starting at 10 and 40%. Spatial frequencies were 0.5, 2.0, and either 4.0 or 8.0 c deg-1. The amblyopic eye consistently required more contrast than the fellow dominant eye for the task. Results in each eye of the normals and strabismics without amblyopia were similar and normal. The findings clearly demonstrate impairment of contrast discrimination in amblyopic eyes, presumably due to early abnormal visual experience. Such impairment could contribute to the increased steady-state accommodative error found in amblyopic eyes.