[Evaluating otolith function with subjective visual vertical discrimination].

Abstract

This report summarizes our experiences with the subjective visual vertical (SVV) as a clinical neuro-otological tool. In the SVV test, patients have to orient a dim light bar in an otherwise dark surrounding earth-vertical, using a remote-control. Normal subjects in an upright position did not deviate more than 2 degrees from true vertical. After vestibular neurectomy, the SVV was consistently tilted by some 12 degrees toward the affected ear. Smaller tilts (approximately 7 degrees) of the SVV occurred in patients with spontaneous peripheral vestibular diseases. This shift in SVV disappeared within weeks to months, similar to the spontaneous nystagmus. After stapes surgery slight deviations of the SVV towards the unoperated ear were seen in about 20% of the patients, indicating a slight irritation of the otolith organs. Assessed in an upright position, the SVV thus may be regarded as reflecting tonic otolithic input differences between the two ears. Asymmetries in the shifts of the SVV induced by roll tilts of the gravito-inertial vector by eccentric rotations of the subject have been proposed as a test for otolithic sensitivity. In our studies such asymmetries in the shifts of the SVV could not be induced by 26 degrees or 90 degrees roll tilts of subjects towards the affected or healthy ears. A simple clinical test to reveal unilateral otolithic sensitivity (comparable to an otolithic "caloric test") thus still has to be found.