Oculomotor abnormalities in diseases of the basal ganglia.

Disorders of eye movements have been described in diseases of the basal ganglia for over a century. Recent neurophysiological and clinical work has greatly clarified the oculomotor role of these structures: their major involvement appears to be in the generation of "voluntary" saccades, and in the suppression of "reflex" saccades. The observed abnormalities of saccadic eye movements in Huntington's (HD) and Parkinson's (PD) diseases conform very well to predictions based on a combination of known disease pathology and recent neurophysiological work. This is not quite the case for other types of eye movement, such as smooth pursuit, largely because the exact role of the basal ganglia in their generation has not been defined neurophysiologically. Several diseases other than HD and PD both involve the basal ganglia and have effects on eye movements; such diseases include progressive supranuclear palsy and Wilson's disease. Unfortunately, the pathological processes in these conditions are too widespread to allow comment on how well oculomotor abnormalities fit in with predictions.