The Vertical Linear Vestibulo-ocular Reflex in Patients with a Hyperactive Response During Horizontal Angular Acceleration *

Abstract

Objective-In clinical routine, some patients show a bilateral hyperactive response of the angular vestibulo-ocular reflex (AVOR). The aim of this prospective study was to determine whether these patients also show hyperactivity of the linear VOR (LVOR). Material and Methods-In 10 patients with a hyperactive AVOR (total amplitude of post-rotatory nystagmus >400° per 30 s) and 10 healthy subjects the AVOR (stopped after 180 s of rotation at 90°/s) and vertical LVOR (amplitude 5 cm, frequency 1.2 Hz) were tested with eyes open in the dark. During vertical linear acceleration, each subject was instructed to look at an earth-fixed target and they performed vertical smooth pursuit as stationary observers.Results-The mean eye velocity of the AVOR was significantly higher in the patients than the healthy subjects (19 vs 5°/s; p=0.00016). During vertical linear acceleration in darkness (49 vs 23°/s; p=0.004) and combined maculo-visual stimulation (88 vs 52°/s; p=0.007) the patients showed a significantly higher mean vertical eye velocity. When vertical smooth pursuit was performed, no significant differences were registered. All 20 subjects showed a significant (p=0.01) positive Spearman correlation (r s =0.79) between the eye velocities of AVOR and LVOR. Conclusion-Patients with a hyperactive AVOR also showed hyperactivity of the LVOR. Because two different sensory end organs and neuronal pathways are involved in these responses, a central rather than a peripheral vestibular lesion must be held responsible.