Effects of cerebellectomy on eye movements in man.

A patient with a right hemicerebellectomy and recurrence of a tumor on the left cerebellar hemisphere was examined regarding oculomotor and vestibuloocular functions. The findings were as follows: inability to maintain eccentric gaze; defective smooth pursuit system; failure to suppress by visual fixation the nystagmus induced by sinusoidal horizontal rotations; moderate increase of the vestibulo-ocular reflex gain when rotated in the dark; relative preservation of the slow phases of the optokinetic nystagmus, as compared to the slow phases induced by tracking a pendulum; decreased gain of the vestibulo-ocular reflex when rotated with the lights on fixating the environment; square wave jerks; and no saccadic dysmetria.