Control of the saccadic and smooth pursuit systems after cerebral hemidecortication.

Saccadic and smooth pursuit eye movements were analysed in 5 patients eight to twelve years after cerebral hemidecortication. Saccadic peak velocities were mildly reduced and saccadic durations were prolonged in both horizontal directions. Slowing of saccades may signify a loss of cerebral modulation of the discharge frequency and duration of brain-stem burst units or a less specific susceptibility of the hemidecorticate brain to fatigue. Symmetrical latencies of saccades to 20- and 40-degree target steps into the hemianopic and intact visual fields provided evidence for brain-stem processing of retinal signals from the hemianopic field. Latencies of saccades to 5-degree target steps into the blind hemifield were significantly longer than to 5-degree steps into the intact field. Disparity between saccadic latencies to parafoveal (5 degrees) and peripheral (20- and 40-degrees) targets indicated that such visual capacity in the hemianopic field is dependent upon target eccentricity.