The vestibulo-ocular reflex (VOR) is tested by turning the head quickly and checking whether the eyes stay locked on a target. A normal VOR keeps your vision stable during head movement. When the reflex is impaired, the eyes drift with the head and then snap back with a corrective jump, a sign of inner ear or neurological dysfunction. There are several ways to test the VOR, from simple bedside exams to high-tech lab equipment, each revealing different aspects of the reflex.
What the VOR Actually Does
Every time you turn your head, your inner ear detects the motion and sends a signal through a three-step nerve pathway to your eye muscles. The signal travels from the balance organ through the vestibular nerve into a cluster of processing centers in the brainstem, then out to the six muscles that move each eye. This entire loop fires in under 15 milliseconds, making it one of the fastest reflexes in the human body. The result: your eyes rotate in the equal and opposite direction of your head, keeping whatever you’re looking at perfectly centered on your retina.
When this reflex breaks down on one side, the world appears to bounce or blur during head movements. You might notice it while walking, driving over bumps, or simply turning to look at someone. Testing the VOR pinpoints whether the problem is in the inner ear, the nerve, or the brain itself.
The Bedside Head Impulse Test
The simplest and most widely used VOR test requires no equipment at all. A clinician holds your head steady, asks you to stare at their nose, then delivers a small, fast, unpredictable head turn to one side, roughly 15 degrees at high speed. The key is that the turn must be quick and unpredictable. Slow, expected head movements can be compensated by other brain systems, masking a VOR deficit entirely.
In a healthy person, the eyes stay perfectly fixed on the target throughout the turn. If the VOR is impaired on one side, the eyes get dragged along with the head during a turn toward the affected ear, then snap back to the target with a visible corrective eye movement called a saccade. That catch-up saccade is the hallmark of a positive test. It tells the examiner which ear is damaged based on which direction of head turn produces the error.
A variation called the SHIMP test flips the logic. Instead of looking for saccades in patients, it looks for saccades in healthy people, which can make abnormalities easier to spot at the bedside. In SHIMP testing, it’s the absence of a corrective saccade that signals a problem.
Video Head Impulse Test (vHIT)
The vHIT is the instrumented version of the bedside test and has become the standard tool for objectively measuring VOR function. You wear lightweight goggles fitted with a high-speed camera that tracks your eye movements while a clinician performs the same quick head turns. The system calculates a VOR gain score: the ratio of how fast your eyes move compared to how fast your head moves.
A perfect VOR gain is 1.0, meaning the eyes match head speed exactly. Normal values sit close to that. A gain below 0.8 is a common threshold for suspecting vestibular loss, and a gain below 0.68 to 0.7 is widely used as a firm cutoff for diagnosing a deficit. For example, one study found average gain in healthy subjects was 0.99 for one direction and 0.92 for the other, showing that even normal results can vary slightly between sides.
Beyond the gain number, vHIT also records the timing and speed of any corrective saccades. Some saccades happen during the head turn itself (covert saccades) and are invisible to the naked eye. Others happen after the head stops (overt saccades) and are the ones a clinician can see at the bedside. Covert saccades can mask a deficit during a manual exam, which is one reason the instrumented version provides more complete information.
Among individual vestibular tests, vHIT has the highest specificity, around 90%, meaning it rarely flags someone as abnormal when they’re not. Its sensitivity is lower, near 48%, so a normal vHIT doesn’t always rule out a problem. That’s why it’s often combined with other tests.
Caloric Testing
Caloric testing evaluates each ear independently by stimulating the inner ear with temperature changes. With your head tilted back about 30 degrees, warm water (44°C) or cool water (30°C) is gently irrigated into the ear canal over 25 to 30 seconds. The temperature change creates a small convection current in the fluid of the inner ear, triggering the VOR and producing a characteristic eye movement pattern called nystagmus.
The expected response follows the mnemonic COWS: Cold Opposite, Warm Same. Cold water causes the fast-beating eye movement to point away from the irrigated ear, while warm water causes it to point toward the same ear. If one ear produces a significantly weaker response than the other (a difference of 26% or more between sides is a common cutoff), it points to a vestibular loss on the weaker side.
Caloric testing has the highest sensitivity of the common VOR tests, catching about 75% of vestibular problems. It’s particularly useful for conditions like Meniere’s disease, where the caloric response is often abnormal even when the vHIT gain remains normal. This dissociation happens because caloric irrigation stimulates a lower-frequency range of the vestibular system than the quick head turns used in vHIT.
Rotary Chair Testing
For rotary chair testing, you sit in a motorized chair in a dark room while it oscillates back and forth at different speeds, typically ranging from very slow (0.025 Hz) to moderate (1 Hz). Sensors track your eye movements throughout. The test measures three things: VOR gain (how well eye speed matches chair speed), phase (the timing relationship between eye and head movement), and symmetry (whether responses are equal for turns in both directions).
Rotary chair testing is the only method that can assess both ears simultaneously across a range of frequencies, making it especially valuable when both sides might be affected. Its sensitivity is similar to caloric testing (about 76%), with moderate specificity around 78%. One practical limitation is that the equipment is expensive and only available in specialized vestibular labs.
VOR Suppression Testing
This test checks whether your brain can turn the VOR off when it needs to. During normal activities like following a moving object with your eyes while your head also turns, the cerebellum actively suppresses the VOR so your eyes can track the target smoothly. To test this, you fixate on your outstretched thumbs while your whole upper body is rotated side to side. If suppression is working, your eyes stay locked on your thumbs with no jumping.
When the cerebellum is damaged, suppression fails. Instead of smooth tracking, the eyes drift opposite to the body rotation and then snap back with corrective jumps. In healthy people, this suppression reduces unwanted eye movement by about 93 to 95%. In patients with cerebellar disorders, suppression only reduces it by roughly 42%, leaving obvious jerky eye movements that a clinician can observe directly. A failure of VOR suppression points toward a central (brain-based) problem rather than an inner ear issue, making it a useful tool for sorting out the cause of dizziness.
Choosing the Right Test
No single VOR test catches everything. The vHIT excels at confirming a specific canal deficit and is quick, portable, and well-tolerated. Caloric testing is better at detecting subtle or low-frequency losses that vHIT can miss. Rotary chair testing fills in gaps when bilateral loss is suspected or when caloric results are unclear. VOR suppression testing adds a different dimension entirely, screening for cerebellar dysfunction rather than inner ear damage.
In practice, a thorough vestibular evaluation often combines two or three of these methods. The vHIT is typically performed first because it’s fast and gives immediate, objective canal-by-canal results. If results are normal but symptoms persist, caloric or rotary chair testing can probe frequency ranges that vHIT doesn’t cover. VOR suppression testing is added when there’s any suspicion the problem originates in the brain rather than the ear.