Decreased vestibulo-ocular reflex gain of vestibular schwannoma patients.

Objective: The vestibulo-ocular reflex (VOR) stabilizes gaze during head movements by producing compensatory eye movements. Gain of the VOR can be defined as the difference between the eye and corresponding head movement amplitudes. The objective of the study was to compare the gain of postoperative vestibular schwannoma (VS) patients with that of healthy controls.
Methods: The gain of 19 vestibular schwannoma (VS) patients and 100 healthy controls was measured with a head autorotation test (HART) in the five frequency bands of 1-5 Hz. It was computed as the ratio of the amplitude of the eye position signal to the amplitude of the head position signal. The mean gain was compared between the VS patients and healthy subjects in each frequency band by using an analysis of variance with statistical significance pre-defined as P < 0.05.
Results: The HART was abnormal in 58% of the VS patients, whose mean gains in the five frequency bands of 1-5 Hz were 0.85, 0.79, 0.72, 0.64 and 0.60, respectively. The mean gains of the VS patients were significantly (P < 0.05) smaller than those of the controls in all the frequency bands.
Conclusions: The deficit of the VOR gain seems to prevail in more than a half of postoperative VS patients, although this inaccuracy of compensatory eye movements may not lead to the occurrence of any symptoms. However, in these patients a potential threat to gaze stability exists.