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Background: 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 vestibulo-ocular reflex (VOR). The majority of bedside and laboratory tests of vestibular function involve the observation or measurement of horizontal eye movements (i.e., horizontal VOR) produced by stimuli that activate the horizontal semicircular canals (SCCs) and the superior vestibular nerve. The video head impulse test (vHIT) is a new clinical test of dynamic SCO function that uses a high-speed digital video camera to record head and eye movement during and immediately after passive head rotations. The SYNAPSYS Inc. vHIT device measures the “canal deficit” (deviation in gaze) during passive head impulses in the horizontal and diagonal (vertical) planes. There is, however, a paucity of data that has been reported using this device. Purpose: The purpose of this study was to obtain normative data and assess the test-retest reliability of the SYNAPSYS vHIT (version 2.0). Research Design: A prospective repeated measures design was utilized. Study Sample: Thirty young adults with normal hearing, normal caloric test results, and a negative history of vestibular disorder, neurological disease, open or closed head injury, or cervical spine injury participated in the study. Data Collection and Analysis: A single examiner manually rotated each participant’s head in the horizontal and diagonal planes in two directions (left and right in the horizontal plane; downward and upward in each diagonal plane) resulting in the stimulation of each of the six SCCs. Each participant returned for repeat testing to assess test-retest reliability. The effects of ear, session, and semicircular canal (horizontal, anterior, posterior) on the magnitude of canal deficit during the vHIT were assessed using repeated measures analysis of variance. Results: The mean canal deficit of the horizontal canals (8.3%) was significantly lower than the mean canal deficit of the anterior canals (16.5%) and the posterior canals (15.2%); there was no significant difference between the mean canal deficits of the anterior and posterior canals. The main effects of session and ear on canal deficit were not significant, and there were no significant interaction effects. There was no significant difference between the mean canal deficit for session 1 and session 2 for the horizontal, anterior, and posterior canals. The 95th percentiles for canal deficit were 19, 26, and 22% for the horizontal, anterior, and posterior SCCs, respectively. Conclusions: Testing of all six SCCs was completed in most participants in ~10 min and was well-tolerated. The vHIT has some important advantages relative to more established laboratory tests of horizontal SCC function including the ability to assess the vertical SCCs, lower cost, shorter test time, greater portability, minimal space requirements, and increased patient comfort. Additional data, however, should be obtained from older participants with normal vestibular function and from patients with vestibular disorders. Within-subject comparisons between the results of the vHIT and the caloric and rotary chair tests will be important in determining the role of the vHIT in the vestibular test battery. [ABSTRACT FROM AUTHOR]