Effect of Spatial Orientation of the Horizontal Semicircular Canal on the Vestibulo-ocular Reflex.

Objective: To determine if an alignment of the horizontal semi-circular canal (hSCC) with the plane of rotation would enhance the vestibular-ocular reflex (VOR) gain result as it has been previously suggested. Study Design: Comparative study of a physiological vestibular function test in healthy subjects. Setting: Tertiary referral center for otology and neurotology. Patients: Twenty two healthy volunteers were recruited for this study. Their mean age was 25.6 years and the sex distribution was 14:8 (M:F). None of the subjects had a history of audiovestibular disorders. Intervention: The video Head Impulse Test (v-HIT) was performed with the hSCC in the conventional position (head upright, horizontal gaze) and also with the hSCC in-line with the earth horizontal. Main Outcome Measures: 1. the VOR gain at 60 ms, 2. the regression slope VOR gain, depending on the alignment of the hSCC with the plane of head rotation. Results: There was no significant difference between the results, either for the VOR gain at 60 ms, or the regression slope gain, when the two alternative head positions were compared. Conclusions: The data acquired in this study show that the VOR as measured by the v-HIT is not enhanced by aligning the plane of the hSCC with the plane of rotation during the testing procedure. Hence, we recommend that the positioning of the patient, with the head upright and a horizontal gaze direction should be routinely used in the clinical evaluation of the angular VOR by v-HIT. Copyright (C) 2016 by Otology & Neurotology, Inc. Image copyright (C) 2010 Wolters Kluwer Health/Anatomical Chart Company

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