Deficient Binocular Combination Reveals Mechanisms of Anisometropic Amblyopia

Abstract

Amblyopia is a developmental visual disorder that results in poor spatial vision. Why the amblyopic eye has poor vision remains unclear: some suggested that signals in the amblyopic eye are attenuated; others suggested that they are inhibited by signals in the fellow eye. Huang et al. (2009) measured the perceived phase of the cyclopean image as a function of the contrast ratio between two monocular sinewave gratings of the same spatial frequency but different phases (Ding & Sperling, 2006). Although the study provided empirical measures of the relative strength of the amblyopic eye in binocular phase combination, we could not distinguish attenuation and inhibition models of amblyopia -- they make mathematically equivalent predictions on phase perception. Additional constrains are required. Here, we elaborated the Ding-Sperling paradigm, measuring both the perceived contrast and phase of the cyclopean images. We found that the effective contrast of the amblyopic eye is different in phase and contrast perception, and the perceived contrast of cyclopean images was independent of the relative phase of the monocular sinewave gratings. We developed a new binocular combination model in which each eye exerts gain control on the other eye's signal and over the other eye's gain control, followed by separate phase and contrast computations. The empirical data and computational model enabled us to identify the mechanism of amblyopia: signals in the amblyopic eye are attenuated; And, the amblyopic eye exerts weaker inhibition on the gain control from the fellow eye.

Footnotes

  Supported by NEI, Natural Science Foundation of China.