Instability of gaze during locomotion in patients with deficient vestibular function.

We measured the stability of gaze in the horizontal and vertical planes, in 2 patients with bilaterally deficient vestibular function while they sat, stood still, walked in place, and made active horizontal and vertical head rotations. During sitting and standing, gaze was equally as stable as that in normal subjects. During walking in place, however, gaze velocity was double that of normal subjects. Thus, our patients' complaints of impaired vision and oscillopsia during walking could be ascribed to excessive motion of images on their retinas. Eye movements compensated for head rotations more effectively (higher gain) during active head rotations than during locomotion; this difference may be due to the predictable nature of active head movements. We conclude that testing of patients with vestibular symptoms should include stimuli corresponding to the rotational head perturbations that occur during locomotion; such head rotations have nonpredictable characteristics and a frequency range of 0.5 to 5.0 Hz.