Multiplanar Video Head Impulse Test

The horizontal vHIT and the vHIT in the Right-Anterior-Left-Posterior (RALP) and Left-Anterior-Right-Posterior (LARP) canal planes were performed using the Video-Head Impulse Test device from Otometrics at center 1 and 2 (Otometrics, Taastrup, Denmark). At center 3, horizontal vHIT was performed using the Eye-SeeCam (Interacoustics, Munich, Germany). The testing method was described previously (45 (link), 46 (link)). In brief, the technician stood behind the subject (who was sitting on a static chair) and held their head firmly without touching the goggles. The subject was instructed to maintain visual fixation on an earth-fixed target at a distance of 2 m at centers 1 and 2 and 1.8 m at center 3. Head impulses comprised fast unpredictable, low-amplitude (±20°) head movements in the horizontal plane (all three centers, peak head velocity > 150°/s) and in the RALP and LARP planes (center 1 and 2, peak head velocity > 100°/s). The Otometrics system defines the VOR gain as the ratio of the area under the eye velocity curve to the area under the head velocity curve from the impulse onset until the head velocity drops to zero again (47 (link)). The inter-acoustics system divides the eye and head velocity at a certain point in time (around 60 ms after impulse onset) (46 (link)).