v-HİT

Head Impulse (Thrust), known in Turkish as the head thrust test, was first described in 1988 by Ian Curthoys. It is a bedside evaluation test primarily used to detect peripheral vestibular pathologies. Because the names Halmagyi and Curthoys are credited with introducing this test into the medical literature, it is also known as the “Halmagyi test” or “Halmagyi-Curthoys test”.

Although the head impulse test is an indispensable method for skilled and experienced clinicians, it is difficult to quantify. In situations where recording is required—especially in research studies—special devices called “coils” were placed on the eye to record and analyze eye movements. However, this procedure was very uncomfortable and distressing for patients, making it not easy to perform. In 2009, Halmagyi and his team developed a version and device known as the Video Head Impulse Test (vHIT), which digitizes head impulse measurements and even allows for the measurement of vertical canals in addition to the horizontal ones.

v-HIT is an advanced diagnostic method that evaluates the function of the vestibular system by measuring the Vestibulo-ocular Reflex (VOR) generated during vestibular stimulation. During the test, the patient fixates on a target, and the clinician rotates the patient’s head with small, unexpected amplitude, precise timing, high speed, and high acceleration. The eye movements the patient makes to compensate for the head movement are recorded and analyzed.

This test plays a critical role in differentiating peripheral causes such as vestibular neuritis from disorders originating in the central nervous system. Its ability to examine all semicircular canals, detect functional loss during high-frequency movements, and identify both covert and overt saccades makes v-HIT a reliable tool in vestibular system evaluations. As a fast and effective method that prioritizes patient comfort, v-HIT provides important guidance to clinicians in achieving an accurate diagnosis.

What Is the Video Head Impulse Test (v-HIT)?

vHIT is a modern diagnostic tool used in the evaluation of dizziness and balance disorders. This test measures the vestibulo-ocular reflex by assessing how visual stability is maintained during rapid head movements. The VOR is responsible for producing eye movements in the opposite direction of the head movement to ensure clear vision. vHIT quantitatively records the eye responses that occur in response to sudden, passive head movements, providing a comprehensive analysis of the vestibular system’s functionality.

The origins of v-HIT are based on the Head Impulse Test (HIT) described by Halmagyi and Curthoys in 1988. The traditional HIT relied on observing corrective eye movements to detect peripheral vestibular dysfunction; however, it could only detect overt saccades and often missed covert saccades.

Advances in technology using high-speed video systems have enabled the development of v-HIT. These systems can detect both overt and covert saccades, allowing for a more precise evaluation of the VOR. The first v-HIT report published by the Bárány Society in 2004 marked an important milestone in vestibular evaluations.

Today, v-HIT is widely accepted due to its non-invasive nature, its ability to evaluate all six semicircular canals, and its clinical accuracy. Advanced devices have increased the reliability of measuring VOR gain, making v-HIT an indispensable tool in vestibular system evaluations.

How Is v-HIT Performed?

v-HIT is a test carefully performed to evaluate the functional status of the vestibular system. The procedure requires special equipment and specific application steps. The patient is seated comfortably and wears special goggles equipped with high-speed cameras and motion sensors to simultaneously measure head movements and eye responses. For accurate measurements, the goggles are fitted securely and calibrated. At this stage, the patient is asked to focus on a fixed target.

During the test, the examiner passively rotates the head with small amplitude movements (10°–20°) and sudden motions. These movements are performed unpredictably so that the patient’s voluntary eye movements do not affect the test. The direction and timing of the head movements are adjusted to evaluate different semicircular canals. Although there may be slight variations in test techniques depending on the equipment used, the eye movements in response to head movements are always recorded. The VOR gain is then calculated from the recorded data. A normal gain is approximately 1.0, meaning that the head movement is completely compensated by the eyes. In some cases, the gain may decrease and/or the presence of corrective saccades may indicate vestibular dysfunction. The test usually takes 5–10 minutes and, being non-invasive, is well tolerated by patients. The lightweight design of the equipment and the quick application of the test enhance patient comfort and provide reliable results.

Which Conditions Can v-HIT Diagnose?

Vestibular Neuritis: Vestibular neuritis is a condition that results from inflammation of the vestibular nerve, typically presenting with acute, severe vertigo. v-HIT plays a critical role in diagnosing this condition by detecting reduced VOR gain and corrective saccades in the affected semicircular canals. Its faster and more practical nature compared to caloric and rotational tests is a significant advantage, especially in early diagnosis.

Ménière’s Disease: Ménière’s disease is characterized by hearing loss, vertigo, tinnitus, and a feeling of fullness in the ear. v-HIT can detect functional abnormalities in the semicircular canals, especially in advanced stages of the disease. However, v-HIT findings in Ménière’s disease should be supported by other vestibular tests because its sensitivity may vary depending on the dynamic course of the disease.

Bilateral Vestibulopathy: Bilateral vestibulopathy is characterized by a loss of vestibular function in both ears, generally leading to imbalance and visual stability issues. Thanks to v-HIT’s ability to evaluate all six semicircular canals, it is very effective in diagnosing this condition by revealing reduced VOR gain and corrective saccades on both sides.

Peripheral and Central Differentiation: Peripheral vestibular disorders are generally accompanied by reduced VOR gain, while in central causes of vertigo, v-HIT findings are usually normal. This feature makes v-HIT an indispensable method for differentiating between central and peripheral sources of vertigo.

Why Is v-HIT Preferred Over Traditional Vestibular Tests?

Among the various tests used to evaluate the function of the vestibular system, v-HIT stands out due to the significant advantages it offers. Compared to traditional methods such as the caloric test and the rotational chair test, v-HIT offers remarkable superiority in both diagnostic accuracy and patient comfort.

• Evaluation of All Semicircular Canals:

While caloric and rotational chair tests only evaluate the horizontal semicircular canals, v-HIT provides the capability to comprehensively examine all semicircular canals in both ears. This feature is especially critical for detecting dysfunctions in the vertical canals, thereby enabling a more detailed vestibular evaluation.

• Analysis of High-Frequency Head Movements:

v-HIT is capable of measuring the VOR during high-frequency head movements that frequently occur in daily life. It provides valuable information about real-life conditions that the caloric test, which evaluates low-frequency responses, cannot offer.

• Detection of Saccades:

v-HIT can detect both overt and covert saccades to determine VOR deficiencies. This detail is crucial for understanding the side and severity of vestibular dysfunction and for planning the appropriate rehabilitation approach.

• Non-invasive, Comfortable, and Fast:

The non-invasive nature of v-HIT, its ability to be completed in just a few minutes, and the fact that it does not cause significant discomfort—especially for children and sensitive patients—are significant advantages. Side effects such as vertigo and nausea that may be caused by the caloric test are eliminated with v-HIT. These factors make v-HIT a practical, comfortable, and modern option.

What Do v-HIT Results Mean?

v-HIT is an extremely sensitive and specific method for evaluating the function of the vestibular system. The key findings of the test—namely, the VOR gain values and the presence of corrective saccades—provide important information about the degree and type of vestibular dysfunction.

Normal results indicate that the VOR gain is between 0.8 and 1.2 and that no corrective saccades are present. These results demonstrate that the vestibular system is functioning properly. However, values outside this range may indicate a range of vestibular disorders.

In abnormal results, a VOR gain below 0.8 is indicative of vestibular hypofunction. For example, a VOR gain of 0.78 is considered a critical threshold associated with vestibular loss. The presence of corrective saccades supports this finding. In particular, overt saccades can be observed after head movement, while covert saccades can only be detected with advanced equipment like v-HIT. These saccades indicate that the eyes are unable to maintain fixation on a target and that the vestibular system is insufficient.

The analysis of these findings assists clinicians in differentiating between peripheral vestibular dysfunction and central causes. Additionally, v-HIT results facilitate the development of patient-specific treatment plans. For instance, reduced gain and frequent saccades indicate the necessity for vestibular rehabilitation or other treatment methods.

Dr. Ody. Emel Uğur

Dr. Audiologist Emel Uğur was born in 1982 in Çanakkale. She worked for 15 years at Istanbul Training and Research Hospital, specializing in Pediatric Audiology, Otologic Diseases, and Vestibular System Disorders. In 2015, she joined the Acıbadem Healthcare Group. She currently works as a Dr. Audiologist at Acıbadem Altunizade Hospital and also serves as a faculty member and program director of the Audiometry Department at Acıbadem University Vocational School of Health Services.