What Is the Video Head Impulse Test?
The video head impulse test (VHIT) is a diagnostic procedure used to assess the function of the peripheral vestibular system, specifically the semicircular canals. By measuring the vestibulo-ocular reflex (VOR), the test helps clinicians determine whether brief, rapid head movements are being compensated for by accurate eye movements. VHIT has become an essential component of modern vestibular assessment, complementing other tests such as caloric testing and vestibular evoked myogenic potentials.
How VHIT Works
During a VHIT examination, the patient wears lightweight video goggles equipped with a high-speed infrared camera. The camera records eye movement while the examiner delivers small, unpredictable, high-acceleration head impulses, typically in the horizontal plane. The test may also target the vertical canals by rotating the head in specific diagonal directions.
The key measurement is the gain of the vestibulo-ocular reflex, calculated as the ratio of eye velocity to head velocity. In a healthy individual, the eyes move in the opposite direction to the head with nearly equal speed, producing a gain close to 1.0. If the VOR is deficient, the eyes do not keep pace with the head movement, resulting in corrective saccades that appear after the head impulse. These catch-up saccades are a hallmark of peripheral vestibular hypofunction.
Key Advantages of VHIT
One major advantage of VHIT over older test methods is its speed and patient tolerability. The procedure is well tolerated by most patients, including the elderly, because it avoids the unpleasant vertigo commonly induced by caloric testing. In addition, VHIT evaluates the VOR at high frequencies that resemble natural head movements during daily activities, whereas caloric testing primarily stimulates the low-frequency horizontal canal. This makes VHIT particularly useful for identifying semicircular canal dysfunction that may not appear on other tests.
Another strength of VHIT is the ability to assess each semicircular canal individually. This provides a topographic view of vestibular function and can help distinguish between superior vestibular nerve involvement, inferior vestibular nerve involvement, and central causes of imbalance.
Clinical Applications of the Head Impulse Test
VHIT is widely used in the evaluation of acute vestibular syndrome, where it assists in differentiating a peripheral cause such as vestibular neuritis from a central cause such as a stroke. The presence of a normal head impulse test result in a patient with acute vertigo raises suspicion for a central lesion and prompts further neuroimaging. Conversely, an abnormal VHIT result supports a peripheral origin.
The test is also valuable in monitoring patients undergoing treatment for vestibular schwannoma, in assessing the extent of vestibular damage before and after ototoxic drug therapy, and in documenting the natural recovery of vestibular function after neuritis. In addition, VHIT contributes to the assessment of bilateral vestibulopathy, a condition marked by reduced VOR gain on both sides and associated with oscillopsia and gait instability.
Limitations and Considerations
While VHIT is a powerful tool, it does have limitations. The test requires patient cooperation and the ability to maintain gaze on a fixed target. Poor blink suppression or excessive head movement by the patient may affect data quality. Vertical canal testing can be technically more challenging than horizontal testing, and subtle deficiencies may require careful interpretation. The results should always be considered alongside the clinical history, clinical head impulse testing, and other vestibular assessments such as posturography and audiometry.
Understanding the VHIT Results
In a normal VHIT report, the gain of the VOR is within the expected range and no overt corrective saccades are observed. In abnormal results, the gain may be low, and covert or overt saccades may appear. Covert saccades occur during the head movement itself and are often missed by clinicians who perform the bedside head impulse test without video goggles. VHIT captures both types of saccades automatically, providing objective data for diagnosis and rehabilitation planning.
Vestibular rehabilitation programmes can use VHIT findings to design personalised exercises that promote central compensation and improve gaze stability. Follow-up VHIT testing helps measure progress and guide therapeutic decisions over time.
Key Topics in This Article
- Video head impulse test
- Vestibulo-ocular reflex gain
- Semicircular canal evaluation
- Corrective saccades
- Acute vestibular syndrome
- Vestibular neuritis
- Bilateral vestibulopathy
- Vestibular rehabilitation
- Balance assessment
- Dizziness diagnostics