How To Test Vor Bedside Vhit And Caloric Tests?

Testing your vestibular system can feel like a medical mystery, but doctors use a few specific bedside tools to check how your inner ear and brain work together. The vestibulo-ocular reflex (VOR) keeps your eyes stable when your head moves. If it fails, your vision blurs during simple actions like walking or turning your head. The two most common bedside tests are the head impulse test (vHIT) and caloric testing. The head impulse test checks the VOR at high speeds, while caloric testing checks it at low speeds. Both are essential for diagnosing dizziness and balance disorders, and here is how doctors actually perform them.

What Is the Vestibulo-Ocular Reflex (VOR)?

The VOR is a reflex that stabilizes your gaze. When you turn your head to the right, your eyes automatically move to the left at the same speed. This keeps the world from blurring. The reflex works through a three-neuron arc: the inner ear senses head rotation, the brainstem processes that signal, and the eye muscles respond within milliseconds.

This reflex has two main parts. The angular VOR responds to head rotation and is tested by the head impulse test. The otolith organs respond to gravity and linear movement, but they are not the focus of these bedside tests. When the VOR fails, patients often report that the world “bounces” or “slides” when they move their head, especially while walking or driving.

Damage can occur on one side or both sides. One-sided damage is common after vestibular neuritis or labyrinthitis. Both-sided damage can happen from certain medications, head trauma, or autoimmune conditions. The bedside tests help doctors tell which side is affected and how severe the problem is.

How To Test VOR Bedside: The Head Impulse Test (vHIT)

The head impulse test, also called the head thrust test, is the most reliable bedside test for the VOR. It was described by Dr. G.M. Halmagyi and Dr. I.S. Curthoys in 1988. The test works by moving the patient’s head quickly and watching whether the eyes can stay fixed on a target.

Here is how the test is performed. The patient sits facing the examiner and focuses on the examiner’s nose. The examiner holds the patient’s head firmly and turns it about 10 to 20 degrees to one side. Then the examiner quickly thrusts the head back to the center with a small, fast, unpredictable movement. The movement must be brief and high-velocity, roughly 100 to 200 degrees per second. The examiner repeats this several times on each side, with unpredictable timing and direction.

In a patient with a normal VOR, the eyes stay locked on the examiner’s nose during the entire movement. In a patient with a weak VOR on the tested side, the eyes drift off the target during the head movement, and the patient makes a quick corrective saccade — a small jump of the eyes — to catch up. This corrective saccade is the key sign of a positive test.

Video head impulse testing (vHIT) adds a camera and computer to this process. The patient wears lightweight goggles with a camera that tracks eye movement and sensors that measure head velocity. The software calculates the VOR gain, which is the ratio of eye velocity to head velocity. A normal gain is roughly 0.8 or higher. A gain below 0.7 on one side suggests a deficit. The video version also detects covert saccades, which are so fast that the naked eye cannot see them.

The head impulse test is most useful in the acute phase of dizziness. In patients with vestibular neuritis, the test is usually positive on the affected side. In patients with central causes of dizziness, such as a stroke in the brainstem or cerebellum, the test is usually normal. This distinction is critical in the emergency department setting.

How To Test VOR Bedside: Caloric Testing

Caloric testing is a different approach. Instead of moving the head, the test uses warm or cool water or air in the ear canal to stimulate the inner ear. The temperature change creates a convection current in the fluid of the horizontal semicircular canal, which mimics head rotation. This stimulates the VOR at a low frequency, around 0.003 Hz, which is much slower than the head impulse test.

Here is how the test is performed. The patient lies with the head elevated about 30 degrees so the horizontal semicircular canal is vertical. One ear is irrigated with water at 30°C (cool) or 44°C (warm) for about 30 to 40 seconds. The patient’s eye movements are observed or recorded. In a normal response, cool water causes the eyes to drift slowly toward the irrigated ear, followed by a fast corrective beat away from it. Warm water causes the opposite pattern.

Each ear is tested with both cool and warm water, with a rest period of at least 5 minutes between tests to allow the inner ear to return to body temperature. The doctor compares the response from the right ear to the left ear. In a healthy person, the responses are roughly equal. A difference of more than 25 percent between the two ears is considered a significant unilateral weakness.

Caloric testing is more sensitive than the head impulse test for detecting one-sided inner ear loss. However, it is less comfortable and takes more time. It can also be less accurate in patients with a narrow or blocked ear canal, a perforated eardrum, or a thick wax buildup. In those cases, air caloric testing may be used instead of water.

Which Test Should Be Used First?

In most clinical settings, the head impulse test is performed first. It is quick, painless, and can be done at the bedside in under a minute. It is also highly specific for peripheral vestibular loss when a corrective saccade is observed. If the head impulse test is positive, the diagnosis of a peripheral vestibular disorder is likely, and caloric testing may not be needed immediately.

Caloric testing is usually reserved for cases where the head impulse test is normal but the patient still has significant dizziness, or when the diagnosis is unclear. It is also part of a full vestibular assessment in a neuro-otology clinic, alongside tests like the rotary chair and vestibular evoked myogenic potentials.

Both tests have limitations. The head impulse test only evaluates the high-frequency VOR, and it can miss low-frequency deficits. Caloric testing only evaluates the low-frequency VOR, and it can miss high-frequency deficits. A patient can have a normal head impulse test and an abnormal caloric test, or the reverse. This is why both tests are often performed together for a complete picture.

What Do the Results Mean?

A positive head impulse test with a corrective saccade indicates a peripheral vestibular deficit on the side opposite the head movement. For example, if the head is thrust to the left and a corrective saccade occurs, the left ear is likely the problem. This finding is common in vestibular neuritis, labyrinthitis, and Meniere’s disease.

A normal head impulse test in a patient with acute dizziness raises concern for a central cause, such as a stroke. This is why the test is so valuable in the emergency setting. The HINTS exam, which stands for Head Impulse, Nystagmus, and Test of Skew, combines the head impulse test with two other bedside tests to distinguish central from peripheral causes of acute vertigo. When the head impulse test is normal but nystagmus is present, the risk of stroke is higher.

Caloric testing results are reported as a percentage of unilateral weakness. A unilateral weakness of 25 percent or more is considered abnormal. This finding localizes the problem to one inner ear or one vestibular nerve. Bilateral weakness, where both ears respond poorly, suggests a condition affecting both ears, such as ototoxicity from certain antibiotics or autoimmune inner ear disease.

It is important to understand that these tests measure function, not the underlying cause. An abnormal test tells you that the VOR is weak on one side, but it does not tell you why. Additional testing, such as MRI or blood work, may be needed to determine the cause of the weakness.

Common Mistakes and Pitfalls in Bedside Testing

Several mistakes can make these tests unreliable. The most common error in the head impulse test is moving the head too slowly. The test only works if the head movement is fast and unpredictable. If the head moves slowly, the patient can use smooth pursuit eye movements to track the target, and the test will appear normal even in a patient with a weak VOR.

Another mistake is allowing the patient to blink or close their eyes during the test. The examiner must watch the eyes closely and repeat the test if a blink occurs. The test also requires the patient to be alert and focused on the target. Fatigue or distraction can produce false results.

In caloric testing, the most common error is not positioning the head correctly. If the head is not elevated 30 degrees, the horizontal canal is not in the optimal position, and the response may be reduced or absent. The water temperature and duration must also be consistent. Too little water or too short a duration produces a weak response that can be mistaken for a deficit.

Patients who are taking vestibular suppressants, such as benzodiazepines or antihistamines, may have reduced responses on both tests. These medications should be stopped, with a doctor’s approval, before testing when possible. Alcohol can also suppress the VOR and should be avoided before testing.