Normal square wave jerks.

Fixation stability of the saccadic system was investigated by infrared reflection oculography in 29 normal subjects, young and elderly. Square wave jerks consisting of spontaneous horizontal saccadic excursions of 0.5 degree and over, followed some 200 msec later by corrective saccades, were recorded in 24% of subjects. The frequency of square wave jerks in the elderly was significantly higher than in young subjects. The results suggest that square wave jerks more frequent than 9/min in young patients can be considered abnormal.