The physiologic basis of conjugate eye movements.

We review the physiologic basis for conjugate eye movements and the role of the cerebellum in their regulation. Specifically, the characteristics of the vestibulo-ocular reflex, the optokinetic reflex, pursuit eye movements, and saccadic eye movements are discussed, emphasizing that the ocular motor system operates to minimize the slip of an image on the retina under various behavioral conditions. Such conditions include changes in the position of the head in space and various combinations of eye and head movements that occur while pursuing a target in visual space. The importance of the cerebellum in regulating smooth pursuit movements is emphasized, and the general categories of deficits resulting from abnormalities in this function are reviewed briefly. The abnormalities in conjugate eye movements observed after cerebellar lesions are related to the abnormalities in movements of the extremities observed in the same patients.