Video Head Impulse Test (vHIT)

What Is the Video Head Impulse Test (vHIT)?

The video head impulse test, or vHIT, is a way to check how well your inner ear and eyes work together to keep your vision steady. This system is called the vestibulo-ocular reflex (VOR). The VOR acts like a stabilizer for your vision—it keeps things clear even when you’re moving your head quickly, like turning to look at someone or walking.

During the vHIT test, you wear special goggles equipped with infrared cameras that allow the machine to track your eye movements. The professional performing the test (doctor, audiologist or technician) moves your head gently but quickly in different directions while you focus on a target. The goggles record how your eyes move in response to these head movements. If the inner ear isn’t working properly, your eyes might make small corrective movements called saccades, which the goggles can detect.

What Does vHIT Actually Test?

The vHIT test checks all six balance sensors in your inner ear, called semicircular canals. There are 3 pairs of semi-circular canals (hence the total of six). These sensors tell your brain about head movement (rotational acceleration) in different directions:

• Horizontal canals: Detect side-to-side (horizontal) turns.

• Anterior canals: Detect up-and-down and diagonal turns.

• Posterior canals: Detect up-and-down and diagonal turns (works in tandem with the anterior canal)

The test measures how well each of these semicircular canals work by looking at how your eyes respond to quick head turns in each of those directions . 

How to Interpret vHIT Results?

In a normal test, when you fixate on a target and the examiner quickly moves your head, your eyes will move in the opposite direction of the head movement to keep your vision locked on the target. This movement should be instantaneous and match the speed of the head movement.

If there is an issue with the semicircular canals, the inner ear will detect the head movement with a slight delay, which is abnormal. This delay will manifest in two ways:

1. A saccade: Your eyes will make a corrective jump to catch up with the head movement. This movement will be recorded by the vHIT goggles.

2. A lower gain: Gain is a calculation that represents the relationship between head movement and eye movement. Since the ear detects the head movement late, there will be a mismatch between eye and head movement, resulting in a lower gain.

Why and How Do Doctors Use vHIT?

Doctors use vHIT for several reasons:

1. Diagnosing Dizziness and Vertigo: It helps figure out if dizziness is caused by an issue in the inner ear (like vestibular neuritis or a malfunctioning semicircular canal) or something in the brain. It's one of the essential tests used to evaluate the function of the vestibular system (along with the VNG and the VEMP).

2. Tracking Recovery: Doctors can use vHIT to see if treatments for balance problems are working. The vHIT is probably one of the most effective vestibular test for monitoring the recovery of a vestibular injury.

3. Emergency Use: In cases of sudden dizziness, vHIT can help rule out serious conditions like a stroke.

4. Testing Kids: Because it’s quick and doesn’t require much equipment, vHIT works well for children who might not sit still for other tests.

Advantages of vHIT Over Other Balance Tests

vHIT has some big advantages compared to other tests like the VNG:

• Tests Real-Life Movements: vHIT checks how well you handle fast head movements, which are more like what happens in daily life (as opposed to VNG that checks for very slow head movements). 

• Quick and Easy: The test takes just a few minutes and doesn’t require special rooms or equipment.

• Portable: It can be done anywhere, even at a patient’s bedside.

• Finds Hidden Problems: vHIT can detect subtle eye movements that other tests might miss.

Limitations of vHIT

Although vHIT is very useful, it does have some limits:

1. Misses Slow Problems: It’s not as good at finding issues with slow head movements, which are better tested with other methods like caloric testing (VNG).

2. Needs Training: Doctors and other professionals need practice to perform the test correctly and interpret results accurately.

3. Not Perfect for All Conditions: Some balance problems, like vestibular migraines, might not show up on vHIT.

4. Special Equipment Required: The goggles used for the test are expensive and may not be available everywhere.

Real-Life Example of How vHIT Helps

Imagine this scenario:

A 45-year-old woman comes to the doctor complaining of chronic dizziness that started 9 months ago. The dizziness originally began after a sudden vertigo spell that lasted two days, but resolved on its own. She now feels unsteady when walking and says her symptoms get worse when she moves her head quickly. She doesn’t have hearing loss or ringing in her ears. She saw a first doctor who evaluated her as having normal exam, and ordered a VNG which was also considered normal. She was referred to see a neuro-otologist.

To get a clearer picture, the neuro-otologist does a vHIT test. The goggles show that her right inner ear isn’t working properly—it’s not keeping her vision steady during head turns. Her eyes make small corrective jumps (saccades), confirming an issue with her vestibular system.

Diagnosis:  Unilateral vestibular weakness after an episode of vestibular neuritis (a problem with the inner ear).

Treatment includes exercises to help her balance system recover (vestibular physiotherapy). A follow-up test months later shows improvement, meaning she’s on the road to recovery.

The video head impulse test is an amazing tool that helps doctors understand balance problems quickly and easily. It’s simple for patients, provides clear results, and plays a key role in diagnosing and treating dizziness effectively!