Eye movements in patients with absent voluntary horizontal gaze.

Despite the complete absence of horizontal saccades, two patients with pontine gliomas had horizontal reflex eye movements within a range of +/- 20 degrees. The gain (peak eye velocity/peak stimulus velocity) and phase of the vestibulo-ocular reflex were normal, but the optokinetic gain was decreased. The latency, accuracy, and peak velocity of vertical saccades were normal. Apparently the voluntary gaze centers in the pontine reticular formation are not crucial for generating horizontal vestibular or vertical saccadic eye movements.