Journal of Vision - Binocular combination in anisometropic amblyopia, by Huang, Zhou, Lu, Feng, & Zhou

Chang-Bing Huang	Laboratory of Brain Processes (LOBES), Department of Psychology, USC, Los Angeles, CA, USA
Jiawei Zhou	Vision Research Lab, School of Life Sciences, USTC, Hefei, Anhui, China
Zhong-Lin Lu	Laboratory of Brain Processes (LOBES), Departments of Psychology and BME, USC, Los Angeles, CA, USA
Lixia Feng	Department of Ophthalmology, First Affiliated Hospital, Anhui Medical University, Hefei, Anhui, China
Yifeng Zhou	Vision Research Lab, School of Life Sciences, USTC, Hefei, Anhui, China, & State Key Lab of Brain and Cognitive Science, Institute of Biophysics, CAS, Beijing, China

Using a suprathreshold binocular summation paradigm developed by J. Ding and G. Sperling (2006, 2007) for normal observers, we investigated suprathreshold cyclopean perception in anisometropic amblyopia. In this paradigm, two suprathreshold sinewave gratings of the same spatial frequency but different spatial phases are presented to the left and right eyes of the observer. The perceived phase of the binocularly combined cyclopean image is measured as a function of the contrast ratio between the images in the two eyes. We found that both eyes contributed equally in normal subjects. However, stimulus of equal contrast was weighted much less in the amblyopic eye relative to the fellow eye in binocular combination. For the five amblyopes, the effective contrast of the amblyopic eye in binocular combination is equal to about 11%–28% of the same contrast presented to the fellow eye, much less than the ratio of contrast sensitivity between the two eyes (0.73–1.42). The results from the current study have many important implications in amblyopia research and treatment.