AUTHOR=McGarvie Leigh A. , Martinez-Lopez Marta , Burgess Ann M. , MacDougall Hamish G. , Curthoys Ian S. 

TITLE=Horizontal Eye Position Affects Measured Vertical VOR Gain on the Video Head Impulse Test

JOURNAL=Frontiers in Neurology

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/neurology/articles/10.3389/fneur.2015.00058

DOI=10.3389/fneur.2015.00058

ISSN=1664-2295

ABSTRACT=<p><bold>Background/hypothesis:</bold> With the video head impulse test (vHIT), the vertical VOR gain is defined as (vertical eye velocity/vertical head velocity), but compensatory eye movements to vertical canal stimulation usually have a torsional component. To minimize the contribution of torsion to the eye movement measurement, the horizontal gaze direction should be directed 40° from straight ahead so it is in the plane of the stimulated canal plane pair. <italic>Hypothesis</italic>: as gaze is systematically moved horizontally away from canal plane alignment, the measured vertical VOR gain should decrease.</p><p><bold>Study design:</bold> Ten healthy subjects, with vHIT measuring vertical eye movement to head impulses in the plane of the left anterior-right posterior (LARP) canal plane, with gaze at one of five horizontal gaze positions [40°(aligned with the LARP plane), 20°, 0°, −20°, −40°].</p><p><bold>Methods:</bold> Every head impulse was in the LARP plane. The compensatory eye movement was measured by the vHIT prototype system. The one operator delivered every impulse.</p><p><bold>Results:</bold> The canal stimulus remained identical across trials, but the measured vertical VOR gain decreased as horizontal gaze angle was shifted away from alignment with the LARP canal plane.</p><p><bold>Conclusion:</bold> In measuring vertical VOR gain with vHIT the horizontal gaze angle should be aligned with the canal plane under test.</p>