Pilot study of a new rehabilitation tool: Improved unilateral short-term adaptation of the human angular vestibulo-ocular reflex

Hypothesis: Unilateral vestibulo-ocular reflex (VOR) shortterm adaptation training causes some increase toward the nonadapting side (∼30% of increase on adapting side). We conducted a pilot study to determine if the increase could be reduced by providing a visual stimulus during rotations to the nonadapting side.

Background: Unilateral vestibular short-term adaptation is a technique that could increase the ipsilesional VOR response of vestibular patients with unilateral hypofunction. However, this technique results in the VOR response increasing for rotations toward the nonadapting (normal) side, which is undesirable because the VOR will be over-compensatory (causing nonstable vision) during head rotations toward the normal side.

Methods: We built a portable helmet device that sensed horizontal angular head velocity to generate a visual target that required a preset VOR gain (eye velocity/head velocity) for optimal image stabilization that could be set differently for leftward and rightward head rotations. We tested 10 subjects (six controls and four patients with vestibular hypofunction). We measured the active and passive VOR gain during high peak- acceleration, unilateral, transient head rotations (head impulses) before and after unilateral VOR adaptation training.

Results: In control subjects, for rotations toward the adapting side (target gain = 1.5), the VOR gain increased because of training by 26.1% ± 23.4% during active head impulses and by 14.6% ± 13.0% during passive head impulses. In contrast, for rotations toward the nonadapting side, there were no statistically significant increases.

Conclusion: A visual stimulus driving the VOR gain to unity toward the nonadapting side aids unilateral adaptation more so than no visual stimulus.