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Balance made possible

A solution for every step in your process of identifying and assessing balance disorders.

by Interacoustics


Videonystagmography provides ideal conditions for the observation, measurement and analysis of eye movements.
VNG Software and Goggle solutions:
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Rotary Chairs

The gold standard for a bilateral weakness is rotational chair testing and is often better tolerated with difficult-to-test populations compared to caloric stimulation.
Our Rotary Chair solutions:

Did you know?

Vertigo and dizziness are common and are linked to balance disorders, which have a number of causes.

Dizziness becomes more common in adults as they age, particularly after the age of 40.

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Air Fx & Aqua Stim

Our caloric irrigators can be used as a stand-alone device, or together with our VNG software. Choose between air or water stimuli:

Discover the power of vestibular testing

Are you keen to learn more about the benefits of vestibular testing? We have gathered some content that will enhance your knowledge about vestibular testing using the videonystagmography technology and vHIT testing.
Balance Quest
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TRV Chair

Thanks to its perfect balance, the TRV chair allows the examiner to easily rotate the patient 360 degrees along the plane of each semicircular canal (scc) and to hold the patient in any position for detailed examination of the semicircular canals.
Balance Quest
by Interacoustics

Bertec® CDP/IVR™ & Prime™ IVR

Advanced balance rehabilitation with immersive virtual reality. The CDP system is a clinical balance assessment tool that collects and analyzes force and moment data from a balance plate. IVR is a proven method of enhancing the rehabilitation of dizzy patients.

Excel at all steps

Prepare your balance clinic to excel at all steps of the path from identification of balance disorders to a complete and accurate assessment. Then deliver the full rehabilitation potential to your patients.

Good balance is a combination of interactions and signals flowing effectively from our eyes, head and body to our brain, which then integrates these inputs and allows us to move freely and safely.


On first arrival of the patient it is good to check that their outer and middle ear is in good health. Information from the tests ensures that you are confident to proceed with further balance testing.
A photo of a female patient that is undergoing an audiological evaluation with the Interacoustics video otoscope Viot.

Video Otoscopy

Otoscopy is a fundamental part of your practice prior to any audiological evaluation.
A photo of a boy having his left middle ear analyzed by a woman with an Interacoustics Titan instrument.


Analyzing the middle ear is an essential part of the pre-examination.
This photo illustrates a senior citizen getting a hearing test with the Interacoustics Callisto.


A hearing loss may be a good indication if something is wrong in the outer or inner ear.

Frequently Asked Questions

Vestibular rehabilitation

What are symptoms of benign paroxysmal positional vertigo (BPPV)?

Benign paroxysmal positional vertigo (BPPV) may induce inner ear dizziness, called vertigo, when lying on your back, while turning your head, when standing up out of bed, when looking upwards and downwards and with rotation in the horizontal plane. BPPV may also affect postural efficiency while walking or cause visual disturbances or nausea.

How can you treat benign paroxysmal positional vertigo (BPPV)?

Benign paroxysmal positional vertigo (BPPV) is a common pathology that can come from illness, aging or post head trauma. It can be identified with the Dix-Hallpike and Head Roll tests and can be treated with the Epley and Semont maneuvers and many other maneuvers. In addition, the TRV chair has emerged as an ideal solution to diagnose and treat BPPV, as it uses kinetic energy to improve the efficiency of the therapeutic maneuvers mentioned above. Residual lateral Canalithiasis linked to small and lightweight otoliths in the semicircular canal (SCC) can also be treated with the TRV chair.

What is the vestibular-ocular reflex (VOR)?

The vestibular-ocular reflex (VOR) allows us to maintain stable vision while our head is in motion. VOR impairments may result in movement-related dizziness, blurry vision, nausea or difficult focusing with activity. Measuring the VOR status quantifies changes in visual acuity with head movement. Measuring the functional VOR status provides information on an individual’s ability to maintain stable vision during daily life activities that involve head movement.

What role does caloric irrigation play in vestibular rehabilitation?

Caloric irrigation tests the lateral semicircular canals by examining the low-frequency responses of the peripheral vestibular system. An advantage of the caloric test is that it can test each inner ear labyrinth separately and can identify unilateral or bilateral vestibular weaknesses. Caloric irrigation therefore has clinical utility in the diagnostic assessment prior to vestibular rehabilitation. It can also be used as a baseline measure for vestibular function in progressive diseases or degenerative conditions.

What role does the video head impulse test (vHIT) play in vestibular rehabilitation?

As with caloric irrigation, the video head impulse test (vHIT) can create a baseline measure for vestibular function in progressive disease or degenerative conditions. The vHIT can also be used as a triaging tool and can measure vestibular compensation. This can be done by measuring the change in the latency and position of the refixation saccades over time. In general, the overt saccades will become covert and the saccades may disappear altogether over time. The suppression head impulse (SHIMP) test is a complementary test that can provide information about residual vestibular function, which can be useful when assessing patients with suspected bilateral vestibular weakness.

What are vestibular-evoked myogenic potentials (VEMPs)?

There are two types of vestibular-evoked myogenic potentials (VEMPs): ocular vestibular evoked myogenic potentials (oVEMPs) and cervical vestibular-evoked myogenic potentials (cVEMPs). oVEMP testing records the function of the utricle and the superior branch of the vestibular nerve. cVEMP testing records the function of the saccule and the inferior branch of the vestibular nerve. VEMP testing can identify several impairments, such as vestibular neuritis and superior semicircular canal dehiscence (SSCD).

What is balance?

Balance is broadly regarded as the successful integration of three sensory systems: vision, vestibular and somatosensory. The successful integration of these systems will enhance our postural stability and mobility. Postural stability is our ability to maintain our body’s center of gravity within our base of support. Postural mobility is our ability to accelerate our body’s center of gravity in the appropriate direction at the initiation of movement.

What are the primary goals of our vestibular system?

Our vestibular system has several primary goals. Firstly, it controls our eye movements to maintain clear vision while we or our environment are in motion. Secondly, it provides accurate perceptions of body position along with direction and speed of movement. Thirdly, it provides rapid displacement of our center of gravity, either from initiated movement or unexpected perturbations. Finally, it enables us to maintain our center of gravity within our base of support.

How does the ankle strategy help maintain or restore balance?

There are two main strategies to maintain or restore balance: the ankle and hip strategies. The ankle strategy is used when perturbations are slow or of low amplitude. The contact surface must be firm, wide and longer than the foot. In this strategy, our muscles are recruited distal-to-proximal and our head movements are in phase with our hips.

How does the hip strategy help maintain or restore balance?

The hip strategy is used when perturbations are fast or of large amplitude. This strategy is often applied when the surface is unstable or shorter than the foot. In the hip strategy, our muscles are recruited proximal-to-distal and our head movements are out of phase with our hips.

What characterizes a vestibular impairment?

A vestibular impairment can disrupt the brain’s ability to integrate the three sensory systems to maintain and moderate successful balance. The following provides some examples of vestibular impairments. If somatosensory input is compromised, then vestibular and visual inputs become more important. Subjects with poor vestibular function may be able to walk on uneven surfaces in daylight but may fall in the dark. Individuals with severe peripheral neuropathy in lower limbs will utilize vision and vestibular sensory information but are likely to fall if these are not available.

What is computerized dynamic visual acuity (DVA)?

Computerized dynamic visual acuity (DVA) is an objective measure of visual acuity during head movements, which allows for data-driven treatment decisions. DVA testing isolates impairments of gaze control related to the vestibular-ocular reflex (VOR). The goal of DVA testing is to identify the smallest target a patient can see with their head moving at a fixed velocity of 100 degrees per second. With the data that the computerized method offers, one can quantify the loss of acuity during active head movement and differentiate between directional loss of acuity. DVA testing is not a diagnostic assessment, thus any impairment identified is a functional impairment.

What is computerized gaze stability testing (GST)?

Computerized gaze stability testing (GST) documents how fast a patient can move their head and still maintain clear vision. Computerized GST can thus quantify the point just before retinal slip, i.e. the velocity at which vestibular-ocular reflex (VOR) exercises should be performed. VOR exercises can be performed and computerized GST velocities can give you direct feedback on the speed of head movement for home exercises.

What is posturography?

Posturography refers to any test that quantifies postural control. Static posturography is an assessment of balance while standing upright in the absence of any disturbance. In static posturography, sensory inputs can be manipulated by eye closure or by standing on a non-compliant surface. Dynamic posturography is an assessment of balance while the support surface or the visual surround is perturbed.

What is computerized dynamic posturography (CDP)?

Computerized dynamic posturography (CDP) is a scientific framework for understanding the control of balance and postural stability. It utilizes a force plate to measure the center of pressure in the anterior posterior and lateral directions. The center of gravity and the patient sway are estimated from the center of pressure. CDP can objectively quantify functional impairments and is ideal for physical therapy and rehabilitation exercises.

What is the sensory organization test (SOT)?

The sensory organization test (SOT) is a gold-standard assessment of postural control under six different visual and somatosensory conditions. It evaluates the contribution of the three sensory systems and their interactions are examined in different conditions by manipulating the visual scene or the support surface.

What is the motor control test (MCT)?

The motor control test (MCT) assesses postural control in response to translation of the support surface. Body movements are analyzed as the platform moves forward or backward. The test examines the patient’s automatic motor responses to support surface perturbations. A common test protocol would be three small, medium and large backward translations followed by three small, medium and large forward translations.

What is the adaptation test (ADT)?

The adaptation test (ADT) assesses postural control in response to repeated rotations of the support surface. The ADT is part of the motor coordination test battery of computerized dynamic posturography (CDP). It is designed to assess a patient’s ability to adapt to unexpected changes in orientation of the support surface over repeated exposures.

How can identifying functional impairments inform treatment?

Identifying sensory or motor impairments helps target and customize treatment. It provides objective information to aid functional impairment, which can be used to track improvements over time. Identifying sensory or motor impairments can also determine the strategy of an individualized treatment program. Treatment can be based on daily activities and use of sensory inputs, and modifications can be made to maximize compliance and outcomes.

What are the benefits of functional assessment?

Functional assessment is very important for clinicians, physical therapists and other professionals who are establishing appropriate baseline function prior to devising treatment strategies for the patient. Objective measures of dynamic visual acuity (DVA), gaze stabilization (GST) and postural control determine the interaction with balance control, allowing for data-driven treatment decisions and for functional outcome measurements.

How can immersive virtual reality (VR) be used for vestibular rehabilitation?

Immersive virtual reality (VR) can be used in vestibular therapy, as it can improve a patient’s ability to use different sensory inputs for postural control. Using life-like scenarios such as grocery markets, immersive VR can seem more engaging for the patient, and ultimately improve functional outcomes.

Rotary chair testing

What is rotary chair testing?

Rotary chair testing is a mid-frequency test of vestibular function, testing a range of different frequencies from 0.01 Hz to 0.64 Hz. Patients are tested with their eyes open without fixation, wearing videonystagmography (VNG) goggles with the cover on or in a dark enclosure. Mental alerting tasks are performed, and nystagmus is recorded and monitored. Rotary chair (head) speed is compared to eye movement speed to assess the vestibular-ocular reflex (VOR).

Seven benefits of rotary chair testing
  1. As the vestibular-ocular reflex (VOR) corrects from a vestibular insult, the phase abnormality and asymmetry begin to recover. Rotary chair testing is, therefore, a well-tolerated assessment to monitor the function of the peripheral vestibular system over time.
  2. The rotation is very accurately controlled and is generally well-tolerated by patients.
  3. The computer-controlled movements with rotary chairs eliminate any concerns regarding technique that are present in head impulse testing.
  4. Contraindications such as neck trauma do not apply nor is goggle slippage an issue.
  5. Rotary chair testing is well established in the literature and has a large base of normative data.
  6. Ototoxic drug affects can be monitored over time.
  7. Children are compliant to testing in rotary chairs when compared to the caloric test.
What is the sinusoidal harmonic acceleration (SHA) test?

In sinusoidal harmonic acceleration (SHA) testing, the patient is rotated several cycles in alternating directions and at multiple frequencies. This is carried out without fixation using the cover on videonystagmography (VNG) goggles. At the slow frequencies, it is a lengthy procedure to complete a cycle. Therefore, most clinicians start at a mid-frequency, such as 0.08 Hz, and work up and down the frequency range from that point, completing as many frequencies as time permits. The data is filtered and signal-averaged to calculate gain, phase and gain (a)symmetry.

Sinusoidal harmonic acceleration (SHA) testing: Gain

Gain is calculated by dividing peak eye velocity by peak head velocity. The assessment records a ratio of eye movement in comparison with head movement. A perfect vestibular-ocular reflex (VOR) would produce a ratio of 1.0. However, the VOR does not function physiologically at perfect gains of 1.0 for all frequencies of motion that are assessed during SHA testing. For slower speeds at the lower frequencies, the VOR response generated is generally at a ratio of less than 1.0. The software supports the clinician by providing the published normative thresholds for the VOR ratio for the chair frequencies tested.

Sinusoidal harmonic acceleration (SHA) testing: Phase

Phase is a measure of the timing relationship of eye movements relative to head movements. At frequencies larger than 0.16 Hz, a perfect timing would be 180 degrees out of phase, indicating eye movement that is equal and opposite to head movement. At frequencies lower than 0.16 Hz, eye movements lead head movement (phase lead). Vestibular weakness, such as following an impairment, is known to cause an increase in phase lead.

Sinusoidal harmonic acceleration (SHA) testing: Gain (a)symmetry

Gain (a)symmetry compares peak slow phase velocity (SPV) when the patient is turned clockwise versus counterclockwise. If an asymmetry is found, this reflects a bias in the system, such as spontaneous nystagmus, in acute conditions or injury. Mathematically, gain (a)symmetry is a ratio of the difference between clockwise and counterclockwise peak SPVs relative to the combined peak SPVs.

What is the vestibular-ocular reflex (VOR) suppression test?

The vestibular-ocular reflex (VOR) suppression test is a brief test of the central neurological mechanism’s ability to suppress induced nystagmus. The setup is like the sinusoidal harmonic acceleration (SHA) test, with the difference being that the patient is provided with a light on which to fixate their gaze position. Under normal circumstances, the VOR will suppress nystagmus. This is calculated by comparing the gain value in the VOR suppression test with the gain value in the SHA test. The gain should diminish by 80 % or better. If the value diminishes by less than 80 %, this could indicate a central abnormality.

What is the velocity step test?

The velocity step test, also commonly referred to as the step rotation test, consists of a rotation at constant velocity both clockwise and counterclockwise. The acceleration will cause a burst of nystagmus, which will diminish as constant chair velocity is sustained. When the rotary chair motion stops, the deceleration will cause another burst of nystagmus. The test is routinely performed once in each direction at two different speeds.

What does the velocity step test measure?

The rate of decay of the nystagmus is referred to as the time constant (Tc). The Tc is calculated during rotation and after rotation and is defined as the amount of time it takes for the slow component velocity of the nystagmus to decay to 37 % of its initial value. An average Tc should be 10-15 seconds. The test also measures gain, which should be at a ratio of 0.67 or higher to be considered normal.

Which pathologies can the velocity step test indicate?

Abnormally low time constants (Tcs) indicate a loss of central velocity storage and can identify both unilateral and bilateral lesions. An unusually long Tc (larger than 60 seconds) could indicate migraine, motion intolerance or a central pathology.


What is videonystagmography (VNG)?

Videonystagmography (VNG) is a vestibular assessment of peripheral vestibular systems located in the inner ear and of the central motor functions of eye movement. VNG testing uses goggles with infrared cameras to track eye movements with fixation removed during visual stimulation and positional tests. VNG tests for nystagmus, which can be present with dizziness, and can detect whether dizziness is related to peripheral vestibular impairments. The ocular motor tests, which examine the brain’s ability to move the eyes when tracking targets, are sensitive to central vestibular lesions and central nervous system impairments. Caloric testing stimulates each peripheral vestibular system independently and can be used to differentiate left from right vestibular impairments.

What are the benefits of videonystagmography (VNG)?

Videonystagmography (VNG) has emerged as the new standard over electronystagmography (ENG). Using video goggles to track and monitor eye movement in high resolution allows clinicians to visualize very small eye movements and quantify any changes in these measurements. VNG testing can help to determine if the patient is experiencing an abnormality from the peripheral or central vestibular system, or from an impairment in the centrally generated eye movements.

Why perform ocular motor testing?

Ocular motor testing is performed to determine if centrally generated eye movements indicate abnormalities that are the reason for the dizziness and imbalance that a patient may experience. Identification of ocular motor abnormalities allows more accurate interpretation of other eye movement recordings in the videonystagmography (VNG) test battery. Ocular motor testing can often indicate the location in the brain of the central lesion. Also, with binocular cameras, each eye can be measured individually and disconjugate and minute eye movements can be identified. This is important, not only for the diagnosis, but also prompts the clinician to test both eyes throughout the test for more accurate results.

What is gaze stability testing?

Gaze stability testing determines if there are any changes in the patient’s ability to maintain gaze in different conditions with and without fixation. The most common manifestation of gaze instability is nystagmus. If nystagmus is present with fixation, this will affect smooth pursuit, saccade and optokinetic testing. If nystagmus is present without fixation, this could be present in positional testing with a VNG goggle and within a caloric assessment without fixation. Gaze stability testing can suggest if the lesion is peripheral (the nystagmus always beats to the same direction) or central (the nystagmus changes directions).

What is the smooth pursuit system?

Smooth pursuit eye movements allow the eyes to follow moving targets in the visual fields. If the smooth pursuit system is damaged by a central lesion, the eyes will follow behind the moving target requiring catch-up saccades to get back to the target. This may contribute to any symptoms or sensations of dizziness that a patient may report.

What is smooth pursuit testing?

In smooth pursuit testing, a target moves across the screen in a sinusoidal pattern and the patient is instructed to follow the target movement with their eyes only, not moving their head. The targets can be moved at a constant speed, which is better for older subjects, or with a gradually increasing velocity. The objective measure is gain, which quantifies the eye movement relative to the target movement. A perfect gain ratio between target and eye movement is 1.0.

Which impairments can smooth pursuit testing identify?

Bilateral or symmetric change may be indicative of diffuse cortical dysplasia, basal ganglia lesions or cerebellar disease, or may be influenced by medication or age. Unilateral or asymmetric change may be due to focal lesions involving the ipsilateral cerebellar hemisphere, brainstem or parieto-occipital lobes. However, it is important to be sure that the patient was properly tasked and alert during the test to make a qualified diagnosis. The findings in the smooth pursuit test can be compared to other ocular motor tests, such as saccade testing.

What is saccade testing?

The saccade system allows us to perform fast and voluntary eye movements that bring images of a new object onto the fovea, which is the part of the retina that is responsible for successful visual acuity. Saccade testing generates quick and random horizontal and vertical eye movements (saccades) and tracks each of these eye movements. Saccade testing can be done with the targets in the horizontal, vertical or mixed planes. The targets should be randomized in jump distance so that the patient cannot predict the movement of the target.

How do you quantify saccade testing?

Saccade testing quantifies the latency, velocity and accuracy of eye movements.

  1. Latency corresponds to the time between initiation of target movement and initiation of eye movement. A prolonged latency is significant and can indicate basal ganglia disorders.
  2. The velocity is how fast the eyes arrive at the new target position. Slow velocity could be associated with supranuclear palsy and brainstem or basal ganglia lesions.
  3. Accuracy measures if the eyes arrived at the target or if there were undershoots or overshoots. Undershoots or overshoots are signs of a problem in the cerebellar vermis that controls the accuracy of eye movements.
What is optokinetic testing?

The optokinetic system allows us to keep our visual field in focus while we or our environment are in motion. Optokinetic stimulation requires a full-field stimulation that uses a checkerboard or a striped pattern (landscape or firetrucks for pediatrics), which induces nystagmus. The slow phases of the nystagmus are in the direction of the moving scene. Clinicians can measure the induced nystagmus to assess whether the patient is able to initiate these eye movements appropriately and symmetrically. If the eye movements are asymmetrical, one may suspect a central nervous system pathology to be present.

What is nystagmus?

Nystagmus is a common manifestation of gaze instability and dizziness. It consists of repetitive and involuntary jerk-type movements of the eyes. Nystagmus has physiological, pathological and congenital origins. Physiological nystagmus can be induced by rotational or caloric stimulation, by moving full-field visual images and by extreme eccentric gaze positions. Pathological nystagmus may be spontaneous, gaze evoked or positionally evoked.

How do you interpret nystagmus?

To interpret and explain the significance of nystagmus, you should determine the following characteristics for each gaze or head position: shape, direction of movement, intensity and effect of fixation. Normal and healthy individuals can display some low-amplitude nystagmus. If the nystagmus is greater than four degrees per second, it is considered pathological.

What characterizes nystagmus?

Nystagmus is characterized by the direction of its fast phases, but the abnormality is related to the slow phases. Nystagmus can be horizontal, vertical, torsional or a combination. For interpretation, break the nystagmus down to its primary components. Purely vertical or purely torsional nystagmus is almost always a central finding, but vestibular lesions can produce a combination of horizontal, vertical and/or torsional nystagmus.

What is spontaneous nystagmus?

The most common type of nystagmus found without fixation is spontaneous nystagmus, also known as vestibular nystagmus. It is defined as nystagmus that is present in the absence of visual-vestibular stimuli. In most cases, positional nystagmus in the static position test is a manifestation of spontaneous nystagmus. Note that if nystagmus direction changes in a single gaze or head position, it is not spontaneous nystagmus.

What is the spontaneous nystagmus test?

The spontaneous nystagmus test looks for nystagmus in the absence of visual, vestibular or cognitive stimuli. This is done by recording eye movements without fixation and with appropriate mental alerting when required. If nystagmus is present, you should record for at least 15 seconds. Afterwards, turn on the fixation light in the goggle and continue to record to determine if the response is suppressed with visual fixation or not. If the nystagmus does not reduce in velocity with visual fixation, this usually gives an indication of a possible central lesion.

What is the Dix-Hallpike test?

The Dix-Hallpike test is a proven method of diagnosing the pathological condition of benign paroxysmal positional vertigo (BPPV). The test can be performed by a single clinician, who repeatedly guides the patient from a seated position to a supine position. In the supine position, the patient’s face and torso faces upwards while the patient’s neck is extended 30 degrees below horizontal by the clinician. A positive test result may be indicated by the patient reporting vertigo or if the clinician observes nystagmus. The Dix Hallpike may be contraindicated by neck injuries or discomfort in the supine position. Thus, the patient’s cervical history and range of head and neck movement need to be assessed prior to carrying out the test.

What is the static position test?

The static position test looks for nystagmus in different head and body positions. This is done by recording eye movements without fixation as the patient holds different head and body positions. If nystagmus is present, record for at least 30 seconds in each position. You can also turn on the fixation light to see if the nystagmus suppresses.

Video head impulse test

What is the video head impulse test (vHIT)?

The video head impulse test (vHIT) is a high-frequency test of the vestibular-ocular reflex (VOR). It tests the function of all six semicircular canals in the peripheral vestibular system and offers a supplementary assessment to rotary chair and caloric testing. Compared to the traditional clinical head impulse test (cHIT) that is conducted with direct observation of the eye, the vHIT can objectively detect and record overt and covert refixation saccades. These measurements can be documented and used to identify any impairment or abnormality in the generated VOR.

How do you perform the video head impulse test (vHIT)?

To perform the video head impulse test (vHIT), you secure a goggle containing a high-speed video camera over the patient’s eye, and provide quick impulses to the left and right while asking your patient to maintain focus on a target in front of them. Head impulses can also be generated for up and down head movements. The vHIT measures eye movement versus head movement. A perfect vestibular ocular reflex (VOR) would result in eye movements that are equal and opposite to the head movements. The value is reported as a gain, so a perfect VOR would be a gain of 1.0.

What are the benefits of the video head impulse (vHIT)?

The video head impulse test (vHIT) is a very fast test with very little discomfort for the patient. The equipment used for the vHIT is portable and does not require much space or peripheral accessories. The vHIT is also user-friendly. It can be used by beginners after a brief training period on normal subjects, using feedback from the system to confirm the appropriate speed and direction of head impulses to measure the vestibular-ocular reflex (VOR) from the desired semicircular canal. From a diagnostic perspective, the vHIT can reliably identify unilateral or bilateral vestibular impairments, as it calculates the responses from the paired semicircular canals from the right and left peripheral vestibular organs, identifying any asymmetries between the sides.

How do you perform correct head impulses?

Head impulses should be rapid and unpredictable in both direction and timing. They should be of a small amplitude, approximately 10-15 degrees in the desired direction. The peak head velocity should be 150 degrees per second or more to specifically assess the vestibular contribution to the vestibular ocular reflex (VOR). To gather sufficient data, you should obtain seven to ten appropriate and artifact-free responses in each direction. The patient should clench their jaw and try to relax their neck and shoulders. The goggles should fit snuggly on the face to reduce any excessive goggle slippage.

What are refixation saccades?

Refixation saccades are corrective eye movements generated as a result of an impaired vestibular-ocular reflex (VOR). An overt saccade is a corrective eye movement post head movement, which usually occurs after 200 milliseconds. A covert saccade is a corrective eye movement initiated during the head movement, which usually occurs before 200 milliseconds. Thus, the majority of overt saccades may be visible to the naked eye, whereas a covert saccade requires video head impulse test (vHIT) software and a set of goggles with high-speed cameras to be detected. Without vHIT software and goggles with cameras, we may think a person with covert saccades is responding normally to the testing, as the naked eye cannot see the very fast saccade correction.

How do you interpret the quality of your vHIT data?

To assess the quality of your video head impulse test (vHIT) data, you need to be sure you have collected enough data. At a minimum, you need to complete seven to ten successful impulses in each direction. You need to confirm that you have performed the impulses at the appropriate velocity and in the correct directions that correspond to the orientation of the paired semicircular canals. You should also check to see if the left and right head impulses are comparable. In addition, check your data for artifacts. Artifacts can be caused by pupils moving outside of the image, eye blinks, makeup, long eye lashes, droopy eye lids, poor frame rates and goggle slippage.

How do you interpret the slow phases in your vHIT data?

When interpreting the slow phases in your vHIT data, it is important to look at both the instantaneous gain and regression gain values. To clarify whether these values are within a normal range, you should compare them with suggested thresholds that are either published or conducted in your clinical setting. You can also obtain your own normative data, as these values can vary based on the clinical setup and individual technique. In addition, if the gain asymmetry between the right and left sides is larger than 7%, this is considered abnormal.

How do you interpret the fast phases in your vHIT data?

Firstly, you must identify if any corrective eye movements are present. Identify their amplitude and whether they are overt, covert or mixed. Secondly, you need to look at their direction. For vestibular deficits, one would expect to see corrective eye movements in the same direction as the vestibular-ocular reflex (VOR) eye movements. Sometimes, spontaneous nystagmus may be seen and even anti saccades in the opposite direction of the VOR direction. These findings are not as common, and you can use other test results or the case history to support these findings.

How should you measure instantaneous gain?

Vestibular-ocular reflex (VOR) gain can vary over different points in time. The gold standard is to display and plot instantaneous gain values at 40, 60 and 80 milliseconds. This is a standardized method to accommodate for decreasing gain over time, which may be present with certain pathologies that affect the production of the VOR beyond the peripheral vestibular system.

Four tips to improve your vHIT data

If you are experiencing artifacts in your video head impulse (vHIT) results, there are several things you can do.

  1. Make sure you have performed an accurate calibration for the eye and head movements.
  2. Repeat any trials with noise present. Noise includes blinks and poor pupil tracking.
  3. Tighten the head strap on the patient’s head if you experience goggle slippage.
  4. Improve your technique by testing on a normal subject until you can produce a nice and repeatable gain plot.

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