Effects of visual input on galvanic body sway test of unilateral vestibular deficiency in patients with unilateral vestibular schwannoma.

OBJECTIVE

Galvanic body sway tests (GBSTs) are performed with eyes fixed and closed. However, quantitative effect of fixation on GBST has been unknown. The purpose of this study is to address this question.

METHODS

We evaluated GBSTs of patients with unilateral vestibular schwannomas and normal controls, while their eyes were open and closed. We evaluated three GBST parameters: maximum amplitude of the response, velocity and latency of the onset of response.

RESULTS

Closing the eyes diminished stability, resulting in increased amplitude and velocity of the responses. However, apparent contribution to the latency of response could not be found. Contribution of visual fixation seems to be greater in apparatus with vestibular hypo-function than without it. Unilateral weakness (UW) was calculated for each parameter, and significant correlation, between with eyes fixed and closed, was found only for velocity parameter.

CONCLUSION

Fixation would stabilize the body of subjects, and diminish GBST responses. GBST with and without fixation can be evaluated together, using certain coefficient. On the other hand, fixation would not have any contribution to the latency of the GBST response. When we evaluate vestibular dysfunction of patients with unilateral vestibular schwannomas, velocity parameter should be employed.