Heterophoria and monocular occlusion.

Prism adaptation responses in orthophoric, exophoric and esophoric subjects are compared and found to be significantly different. Following a prolonged period of monocular occlusion the prism adaptation responses were compared, after occlusion the differences are no longer significant. This supports the theory that vergence (prism) adaptation is responsible for the existence of heterophoria. This paper shows that changes in heterophoria with monocular occlusion are caused by desaturation of prism adaptation.