Postural sway of patients with vestibular disorders during optic flow.

Patients with vestibular orders often complain of sensitivity to moving visual environments, leading to dizziness and imbalance. This study investigated standing postural sway of healthy adults and patients with vestibular disorders in response to optic flow in the central field. Visual conditions of varying properties were presented monocularly with a 60 degrees viewing field. The conditions included: eye open-no flow, eye closed, sinusoidal expansions/contractions at 0.3 Hz, a constant flow giving the appearance of tunnel, and a vertically translating checkerboard. Postural sway, defined in this study as movement of the center of pressure, was recorded using a force platform during presentation of the visual stimuli. Patients with vestibular disorders were found to have a significantly higher magnitude of postural sway than control subjects while viewing central optic flow stimuli. Sinusoidally expanding and contracting optic flow induced postural sway at the stimulus frequency in both the patients and controls; patients, however, had a much larger increase in sway at frequencies near the stimulus frequency. These results suggest that postural control in patients with vestibular disorders is particularly affected by optic flow stimuli to the central region of the visual field.