Head-shake vestibulo-ocular reflex testing: comparison of results with rotational chair testing.

The currently accepted "gold standard" for rotational testing of the vestibulo-ocular reflex uses a servo-controlled chair for sinusoidal whole-body rotation. Previous work in our laboratory has shown good concordance between conventional rotational chair testing and head-on-body (or "head-shake") testing for gain and phase values of the vestibulo-ocular reflex as recorded and analyzed on our rotational chair system's software. In this article we describe results obtained from 10 normal subjects and 20 patients with reduced caloric responses using a portable system being developed in our laboratory that allows an examiner to generate both whole-body and head-on-body rotational stimuli. Test frequencies within the range 0.25 to 1.0 Hz were chosen for comparison with results obtained by conventional rotational chair testing. Visual conditions for all tests included both visually enhanced vestibulo-ocular reflex (real earth-fixed target) and mentally enhanced vestibulo-ocular reflex (imagined earth-fixed target, in darkness or with vision obscured) paradigms. Our results show general agreement between head-shake and rotational chair testing and both manual whole-body rotation and head-shake testing on our portable system for vestibulo-ocular reflex gain and phase testing, with the largest differences noted at 1.0 Hz. Portable rotational testing was well tolerated by young and elderly subjects alike. We expect manual whole-body rotation and head-shake testing will be useful adjuncts for examining vestibulo-ocular reflex function when more formal rotational chair testing is not possible.