Cerebellar control of fixation eye movements.

Human subjects normally have miniature eye movements during tasks that require steady visual fixation. These eye movements were compared in 12 control subjects and 4 patients with degenerative cerebellar disorders. Slow drifts, small fixation saccades, square waves, saccadic oscillations, flutter, and vertical nystagmus occurred in both control subjects and patients. In the patients, however, fixation eye movements were enlarged and square waves and saccadic oscillations were more frequent. It appears that some forms of pathologic fixation instability are due to defective cerebellar control of fixation eye movements, and that precise measurements of these eye movements may quantitate disorders of cerebellar function.