Fig. (1) *(A). Typical eye-movement responses of a child with normal binocular vision to the introduction of 3 prism diopter base-out prisms to each eye. (B,C): Examples of typical eye movement responses of patients with history of congenital esotropia to fusional disparity vergence stimuli. Horizontal eye-movements of the left and right eyes are shown in plate (L) column. A positive change in eye position represents movement to the right. Vergence eye-movements (M): Vergence response, (right eye - left eye). Positive changes in vergence amplitude represent convergence. Version eye-movements (R): Conjugate response, (right eye + left eye)/2. In each image, the switch signal represents the introduction of the prisms into the subjects’ field of view.*In the figure movement of the eye to the right is displayed downward, and movement to the left is displayed upward in the graph.