Galvanic stimulation in bilateral vestibular failure: 3-D ocular motor effects

BILATERAL galvanic vestibular stimulation (GVS) with current intensity of 3 mA was applied at mastoid level in 11 patients with chronic bilateral vest ibular-failure, in order to determine ocular motor responses by 3-D video-o culography. The following abnormal features were found: (1) a predominantly torsional or mixed torsional-horizontal nystamus at the onset of stimulati on with lower current intensities (1.0-3.0 mA)in nine patients; (2) a reduc ed amplitude of tonic ocular torsion by about 50% in nine patients (1.3 +/- 0.6 degrees at 3 mA); (3) a nystagmus in the opposite direction at stimula tion offset in five patients (rebound); (4) no eye movements at all in a pa tient with bilateral nerve failure. GVS stimulates the vestibular nerve, th us allowing differentiation of nerve failure from labyrinthine failure. The low thresholds for initiating nystagmus and the rebound, which appear to b e the most typical features of bilateral labyrinthine failure, can be expla ined by central compensation mechanisms. NeuroReport 10:3283-3287 (C) 1999 Lippincott Williams & Wilkins.