Comparison of vestibulo-ocular reflexes in earth-horizontal and earth-vertical axis rotations

Ten normal subjects and nine patients with peripheral labyrinthine lesions were subjected to sinusoidal rotation about an earth-horizontal (EHA) and earth-vertical axis (EVA) using a new device. In normal subjects the gain of the vestibulo-ocular reflex (VOR) in EHA rotation was significantly larger than that of the VOR in EVA rotation. This difference may be attributed to the interaction of the semicircular canals and otolithic organs. Unlike normal subjects, patients with unilateral lesions showed no differences in gain between EHA and EVA rotations toward either the intact or abnormal side. Patients with bilateral lesions also showed no differences in gain. These observations suggest that the interaction of the semicircular canals with the otolithic organs enhancing VOR gain does not occur if one of the otolithic organs is defective in either ear. This does not appear to recover once such a dysfunction develops.