Stereo-discrimination between diplopic images in clinically normal observers.

When retinal disparity exceeds the limits for fusion, the resulting images are perceived as diplopic. In a stereo test that allowed comparison of crossed and uncrossed disparity sensitivities, 74% of the subjects perceived convergent disparities more readily than divergent disparities. This asymmetric sensitivity to disparity did not appear to be related to measurements of phoria, vergence amplitudes, or clinical measurements of stereo acuity.