DEFICITS OF GAZE STABILITY IN MULTIPLE AXES FOLLOWING UNILATERAL VESTIBULAR LESIONS

Abnormalities in the vestibule-ocular reflex (VOR) after unilateral ve stibular injury may cause symptomatic gaze instability. We compared fi ve subjects who had unilateral vestibular lesions with normal control subjects. Gaze stability and VOR gain were measured in three axes usin g scleral magnetic search coils, in light and darkness, testing differ ent planes of rotation (yaw and pitch), types of stimulus (sinusoids f rom 0.8 to 2.4 Hz, and transient accelerations) and methods of rotatio n (active and passive). Eye velocity during horizontal tests reached s aturation during high-velocity/acceleration ipsilesional rotation. Rap id vertical head movements triggered anomalous torsional rotation of t he eyes. Gaze instability was present even during active rotation in t he light, resulting in oscillopsia. These abnormal VOR responses are a consequence of saturating nonlinearities, which limit the usefulness of frequency-domain analysis of rotational test data in describing the se lesions.