Cerebral square wave jerks.

Abnormal saccadic intrusions consisting of frequent sporadic horizontal saccades followed, after an interval, by corrective saccades occurred in 70% of 17 patients with acute or chronic focal cerebral lesions. These square wave jerks were significantly lower in amplitude than those in cerebellar system disease. The metrics of these jerks were uniform regardless of the site of cerebral damage. Mean durations approximated the reaction time for saccadic refixations triggered by visual feedback. Very short-latency corrective saccades in some patients are attributed to internal (nonretinal) feedback of eye position errors. Low-amplitude cerebral square wave jerks can be detected clinically by funduscopy.