Intra- and Inter-Examiner Reliability of the Binocular Video Head Impulse Test

The angular vestibulo-ocular reflex (VOR) ensures gaze stability during head rotations by generating eye movements that are equal and opposite to head rotation. The gain of the VOR (eye velocity/head velocity) for natural head movements, therefore, approaches unity in healthy individuals. The VOR has four main anatomic components: the semicircular canals (SCCs) and vestibular nerve in the peripheral vestibular system, the vestibular and ocular motor nuclei in the brainstem, and the extraocular muscles. The SCCs are positioned in three nearly orthogonal planes within the head thereby allowing for the detection of head rotation about any axis in space. The SCCs function as angular accelerometers in a push-pull fashion with two coplanar canals on each side of the head working together, i.e., left and right horizontal SCCs, the right anterior and left posterior SCCs or RALP, and the left anterior and right posterior SCCs or LARP. The observation or measurement of eye movement can aid in the detection and localization of vestibular pathology due to the relationship between the function of the vestibular sensory receptors in the inner ear and the eye movements produced by the VOR. The video head impulse test (vHIT) is a relatively new clinical test of dynamic SCC function that uses a high-speed digital video camera embedded in light-weight goggles to record head and eye movement during passive head rotations in the horizontal and vertical planes. An important precursor to the clinical use of a new diagnostic test is the evaluation of test reproducibility. If test reproducibility is poor, then the test is unlikely to be clinically useful. There are no published data concerning both inter- and intra-examiner reliability of the vHIT. The purpose of this study was to establish normal reference intervals and assess the test-retest reliability of the vHIT in young healthy adult participants using the Micromedical vHIT device, two examiners, and a prospective repeated measures design. Each examiner underwent five hours of training on the vHIT device prior to the initiation of the study. The vHIT was administered to each participant (n = 35) by each examiner on two different days. Inter-session interval ranged from 1 to 30 days and examiner order was alternated for successive subjects; canal-plane order was randomized. At each session, participants underwent head impulse testing in each plane resulting in the stimulation of each of the six SCCs. The dependent variable was VOR gain (eye velocity/head velocity) and the effects of examiner, session, eye, and SCC on the magnitude of VOR gain were assessed using repeated measures analysis of variance. The intra-class correlation (ICC) coefficient was used to assess intra- and inter-examiner reliability. The cut-offs (5th percentiles) for normal VOR gain were 0.76 (right and left horizontal SCCs), 0.68 (right anterior SCC), 0.70 (left anterior SCC), 0.69 (right posterior SCC), and 0.75 (left posterior SCC). There was no significant effect of examiner on VOR gain and the ICCs indicated fair-to-good inter- and intra-examiner reliability with better reliability for the horizontal SCCs than for the posterior and anterior SCC