BASIC AND CLINICAL ASPECTS OF VERTIGO AND DIZZINESS Head Impulse Testing Using Video-oculography Klaus Bartl, a Nadine Lehnen, a Stefan Kohlbecher, and Erich Schneider Department of Neurology, Ludwig-Maximilians-University, Munich, Germany Head impulses are a routine clinical test of semicircular canal function. At the bedside, they are used to detect malfunctioning of the horizontal semicircular canals. So far, 3- D-search-coil recording is required to reliably test anterior and posterior canal function and to determine the gain of the vestibulo-ocular reflex (VOR). Search-coil recording cannot be done at the bedside. Here we tested whether video-oculography (VOG) is suitable to assess VOR gain for individual canals at the bedside. We recorded head impulses in healthy subjects using a mobile high-frame-rate, head-mounted VOG-device and compared the results with those obtained with standard search-coil recording. Our preliminary results indicate that high-frame-rate VOG is a promising tool to measure and quantify individual semicircular canal function not only at the bedside. Key words: head thrust test; search-coil recording; high-frame-rate video-oculography (VOG); bedside test; vestibulo-ocular reflex (VOR); semicircular canal Head impulses are fast, small-amplitude passive head rotations in the plane of a pair of semi- circular canals. 1 In healthy subjects, they evoke a compensatory eye movement in the opposite direction, mediated by the vestibular-ocular re- flex (VOR), which stabilizes gaze. If the VOR is deficient, the eyes move with the head and the patient makes a catch-up saccade to refix- ate the target. Bedside head impulse tests assess these catch-up saccades as an indirect sign of impaired horizontal canal function. However, catch-up saccades are not always detectable. 2 To reliably assess horizontal as well as ante- rior and posterior canal function, and to de- termine the gain of the VOR, 3-D-search-coil recording is required. 3,4 Search-coil recordings cannot be done at the bedside. Here, we re- port preliminary results of our effort to estab- lish high-frame-rate video-oculography (VOG) for testing each individual semicircular canal Address for correspondence: Nadine Lehnen, Department of Neuro- logy, Marchioninistr. 23, 81377 Munich, Germany. Voice: +49 89 7095 4833; fax: +49 89 7095 4801. Nadine.Lehnen@med.uni-muenchen.de a Contributed equally to this work. and determining the gain of the VOR at the bedside. We measured eye and head movements during standard horizontal head impulses 4 in healthy subjects using search-coil and VOG recording (consecutive measurements on the same day). Search-coil recording at 1 kHz was performed as previously de- scribed. 5 VOG-recording consisted of a mobile, head-mounted VOG-device (“EyeSeeCam”) 6,7 which measured eye movements at a 300-Hz frame rate. The EyeSeeCam is based on swim- ming goggles with rubber bands minimizing slippage. Head movements were measured with a pair of six-degree-of-freedom inertial sensors mounted on the VOG goggles (assessing move- ment of the goggles) and by the same iner- tial sensors mounted on a bite bar (assessing head movement directly). To compensate for eye movement measurement errors due to gog- gle slippage relative to the subject’s head, the position of the bite bar relative to the goggles was recorded by a high-speed digital camera mounted on the goggles. This information and a geometrical model of the pupil projection Basic and Clinical Aspects of Vertigo and Dizziness: Ann. N.Y. Acad. Sci. 1164: 331–333 (2009). doi: 10.1111/j.1749-6632.2009.03850.x C  2009 New York Academy of Sciences. 331