The linear vestibulo-ocular reflex in normal subjects and patients with vestibular and cerebellar lesions

We measured the horizontal linear vestibulo-ocular reflex (LVOR) in normal human subjects and patients with abnormal angular vestibulo-ocular reflexes (AVOR) and abnormal smooth pursuit. Eye movements were induced by sinusoidal linear acceleration along the interaural axis (0.8 Hz, 0.5 g peak acceleration) on a parallel swing. Horizontal movement of each eye was recorded with an infrared limbus tracking device. Normal subjects increased LVOR sensitivity as real or imagined targets moved closer. Perceived target distance was more important than the vergence angle since changing the vergence angle alone with prisms resulted in only a slight change in LVOR sensitivity. Subjects suppressed the LVOR with real or imagined head-fixed targets. Patients with decreased horizontal AVOR responses had decreased horizontal LVOR responses with imagined earth-fixed targets in the dark. They were able to generate normal velocity LVOR responses with real earth-fixed targets. Patients with increased AVOR responses and poor smooth pursuit due to cerebellar atrophy had low LVOR responses that were minimally affected by real or imagined earth-fixed or head-fixed targets. We conclude that the smooth pursuit system and the cerebellum are critical for generating the eye movements required as subjects fixate a near target during translational head movements.