vHIT

Viral head impulse test? No, vHIT stands for video head impulse test. It is a clinical assessment of the angular vestibulo-ocular reflex (VOR) at high frequencies. The test uses lightweight goggles that contain an infrared camera and inertial sensors to record eye movements while the examiner delivers rapid, unpredictable head impulses in the plane of each semicircular canal. Eye and head velocity traces are analyzed to calculate the VOR gain, defined as eye velocity divided by head velocity, and to identify compensatory saccades that correct for a deficient reflex.

Procedure and data: after calibration, the patient fixates on a visual target at a comfortable distance. The clinician performs multiple quick head impulses in each canal plane (horizontal, and the two vertical canals via appropriate head tilts). The device provides gain values for each canal and displays whether covert (during head movement) or overt (after) saccades accompany the response.

Interpretation: in healthy individuals, VOR gain is near 1. Abnormal gain on one side with corrective saccades indicates unilateral vestibular hypofunction. Bilateral reduced gains suggest bilateral dysfunction. The presence and timing of covert versus overt saccades help characterize the dysfunction and compensatory status. vHIT primarily assesses high-frequency VOR (roughly 5–7 Hz), reflecting more natural head movements, and complements other tests such as caloric testing, which assesses low-frequency VOR.

Advantages and limitations: vHIT is rapid, bedside, and canal-specific, requiring minimal patient setup. Limitations include dependence on proper calibration and fixation, potential artifacts from goggle slippage, blinks, or movements outside canal planes, and device- and norm data variability. It does not replace caloric testing but provides valuable, frequency-diverse information about vestibular function.