What is vHIT and what does it measure?

• A. Video Head Impulse Test; low-frequency VOR gain
• B. Visual Head Impulse Test; high-frequency VOR gain
• C. Vestibular Head Impulse Test; high-frequency VOR gain to each canal
• D. Video Head Impulse Test; high-frequency VOR gain to each semicircular canal

Answer: (D)

Video Head Impulse Test evaluates the vestibulo-ocular reflex during rapid, unpredictable head movements. It uses a high-speed camera to track eye movements and a head-motion sensor to record the head impulse, delivered in the plane of each semicircular canal. The main measurement is the VOR gain, the ratio of eye velocity to head velocity during the impulse. In a healthy system the gain is about 1, meaning the eyes move to keep gaze stable despite the brisk head turn. If a canal is deficient, the gain drops and the eyes may make corrective catch-up saccades after the impulse. This test is canal-specific because each impulse is aligned with a particular canal, so it measures high-frequency VOR gain to each semicircular canal.