Symptoms elicited in persons with vestibular dysfunction while performing gaze movements in optic flow environments.

INTRODUCTION: People with vestibular disorders often experience space and motion discomfort when exposed to moving or highly textured visual scenes. The purpose of this study was to measure the type and severity of symptoms in people with vestibular dysfunction during coordinated head and eye movements in optic flow environments.
METHODS: Seven subjects with vestibular disorders and 25 controls viewed four different full-field optic flow environments on six different visits. The optic flow environments consisted of textures with various contrasts and spatial frequencies. Subjects performed 8 gaze movement tasks, including eye saccades, gaze saccades, and gaze stabilization tasks. Subjects reported symptoms using Subjective Units of Discomfort (SUD) and the Simulator Sickness Questionnaire (SSQ). Self-reported dizziness handicap and space and motion discomfort were also measured. RESULTS/
CONCLUSION: Subjects with vestibular disorders had significantly greater discomfort, oculomotor and disorientation symptoms, with some amount of symptoms in 55-60% of the trials, compared with control subjects, who had symptoms in less than 20% of the trials. The magnitude of the symptoms increased during each visit, but did not depend on the optic flow condition. Subjects who reported greater dizziness handicap and space and motion discomfort had greater severity of symptoms during the experiment (Spearman rho > 0.78). Compared with controls, subjects with vestibular disorders had about 10 deg less head excursion during the gaze saccade tasks. Overall, performance of gaze pursuit and gaze stabilization tasks in moving visual environments elicited greater symptoms in subjects with vestibular disorders compared with healthy subjects.