Ocular fixation, vestibular dysfunction, and visual motion hypersensitivity

A subgroup of individuals with vestibular dysfunction and visual motion hypersensitivity (VMH) become dizzy and imbalanced in response to movement of the visual environment. The purpose of this study was to investigate ocular fixational stability during gaze on a target, with and without visual background movement. Binocular vision functions were also examined as possible contributory factors to the dizziness and imbalance.

Twenty-four individuals with VMH, 20 with vestibular disorders without VMH and 20 healthy subjects were tested. Assignment to the experimental group was by symptoms of VMH. Outcome measures included electro-oculogram recordings of horizontal fixation and blink. Four clinical binocular vision functions were also tested. The Dizziness Handicap Inventory was used to assess the level of dizziness.

Subjects with VMH made significantly more refixational eye movements and had higher levels of dizziness than those in the other 2 diagnostic groups. There were abnormalities of binocular function in both the VMH and vestibular dysfunction groups compared with the control group. Individuals with VMH were unable to maintain stable gaze and inhibit eye movements to background motion. The large number of subjects with diagnosis of fluctuating vestibular function in the VMH group compared with the vestibular dysfunction group may indicate that VMH is a maladaptation of the system.