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

Abstract

HYPOTHESIS: Unilateral vestibulo-ocular reflex (VOR) adaptation training causes some increase towards the non-adapting 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 non-adapting side. BACKGROUND: Unilateral vestibular 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 towards the non-adapting (normal) side, which is undesirable because the VOR will be over-compensatory (causing non-stable vision) during head rotations towards 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 stabilisation that could be set differently for leftward and rightward head rotations. We tested 10 subjects (6 controls and 4 patients with vestibular hypofunction). We measured the active and passive VOR gain before and after unilateral VOR adaptation training. RESULTS: In control subjects, for rotations towards the adapting side (target gain = 1.5) the VOR gain increased due to training by 26.1 ± 23.4% during active head impulses and by 14.6 ± 13.0% during passive head impulses. In contrast, for rotations towards the non-adapting side there were no statistically significant increases. CONCLUSION: A visual stimulus driving the VOR gain to unity towards the non-adapting side aids unilateral adaptation more so than no visual stimulus.