Fig. 3. Every retinal point has a corresponding retinal area in the opposite eye, on which the similar image must project to be fused. The more peripheral retinal points have larger corresponding retinal areas. (Parks MM: Sensory adaptations in strabismus. Symposium on Strabismus, Transactions of the New Orleans Academy of Ophthalmology, p 101. St. Louis, CV Mosby, 1971)