Deficient binocular combination reveals mechanisms of anisometropic amblyopia: signal attenuation and interocular inhibition.

Amblyopia is a developmental disorder that results in deficits of monocular and binocular vision. It is presently unclear whether these deficits result from attenuation of signals in the amblyopic eye, inhibition by signals in the fellow eye, or both. In this study, we characterize mechanisms underlying anisometropic amblyopia using a binocular phase and contrast combination paradigm and a contrast gain control model. Subjects dichoptically viewed two slightly different images and reported the perceived contrast and phase of the resulting cyclopean percept. We found that the properties of binocular combination were abnormal in many aspects in amblyopic vision. The observed abnormalities can be explained by a combination of (1) attenuated monocular signal in the amblyopic eye, (2) stronger interocular contrast gain control from the fellow eye to the signal in the amblyopic eye (direct interocular inhibition), and (3) stronger interocular contrast gain control from the fellow eye to the contrast gain control signal from the amblyopic eye (indirect interocular inhibition). We conclude that anisometropic amblyopia led to both monocular and interocular deficits. A complete understanding of the mechanisms underlying amblyopia requires studies of both monocular deficits and binocular interactions.