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Inventis - June 2023

What are the principles and mechanics of the Video Head Impulse Test (vHIT)?

Vishal Pawar

July 14, 2025

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Question

What are the principles and mechanics of the Video Head Impulse Test (vHIT), and how is the remote camera vHIT system advancing modern vestibular diagnostics?

Answer

The Video Head Impulse Test (vHIT) is a cornerstone in the objective evaluation of semicircular canal function and the integrity of the vestibulo-ocular reflex (VOR). Developed to address the limitations of the traditional clinical Head Impulse Test (cHIT)—which detects only overt saccades and misses covert refixations—vHIT enables high-frequency, quantifiable assessment of VOR performance.

Among the most recent innovations, the remote camera Synapsys vHIT system by Inventis stands out for its ability to enhance patient comfort, minimize motion artifacts, and deliver exceptional diagnostic accuracy, thereby advancing the standard of care in modern vestibular testing.

1. Foundational Principles

From a physiological perspective, the vestibular system’s response is influenced by the mass, elasticity, and viscosity within the cupulo-endolymphatic system. The function of the vestibulo-ocular reflex (VOR) varies across different frequency domains: low-frequency stimuli are more reliant on visual feedback, whereas high-frequency stimuli depend predominantly on vestibular input.

The Video Head Impulse Test (vHIT) is uniquely designed to evaluate high-frequency head movements, making it especially effective in identifying unilateral vestibular deficits and covert saccades that may go undetected by other means.

2. Why vHIT over cHIT?

The traditional clinical Head Impulse Test (cHIT), also known as the Halmagyi test, offers a binary result (positive/negative) and is limited to the detection of visible overt saccades. It cannot capture covert saccades, which occur during head motion and are imperceptible to the naked eye.

According to the literature, up to 14% of patients with vestibular pathology may exhibit covert saccades only, making instrumented evaluation essential. This diagnostic gap is precisely what vHIT was developed to fill.

3. The Mechanics of vHIT

The vHIT assesses the vestibulo-ocular reflex (VOR) by calculating gain, the ratio of eye velocity to head velocity, and by identifying the presence of refixation saccades. To achieve accurate results, the test requires:

  • Precise measurement of head and eye velocities
  • High-speed infrared video recording
  • Reliable calibration and real-time graphical analysis

4. Remote Camera vHIT: A Technological Leap

Unlike traditional goggle-based systems that rely on head-mounted accelerometers, the remote camera Synapsys vHIT system by Inventis utilizes advanced image-processing algorithms for both eye tracking and head pose estimation.

This innovation offers several key advantages:

  • Elimination of slippage artifacts: Head-mounted systems are prone to motion between the goggles and the skull, often resulting in inaccurate readings. Remote camera systems avoid this issue entirely.
  • Enhanced patient comfort: Particularly beneficial for pediatric patients, post-operative cases, or individuals with facial asymmetry.
  • Greater examiner flexibility: The clinician can move the patient’s head freely without interfering with the device.
  • Improved repeatability: Fewer head impulses are required—typically 5, compared to 15–20 with goggle-based systems—for reliable results.
  • High-resolution accuracy: The Synapsys system offers exceptional tracking precision, with eye/head tracking accuracy of ±0.1°, gaze direction accuracy of ±0.4°, and VOR gain accuracy of ±0.08.

5. Illustrative Screen Outputs

To support clinical interpretation, remote camera vHIT systems provide comprehensive visual outputs, including:

  • Canalograms displaying VOR gain across all six semicircular canals (Figure 1).

Figure 1 29359

Figure 1

  • Velocity graphs defining eye and head movements (Figure 2).

Figure 2 29359

Figure 2

  • Position traces and alignment graphs for identifying potential artifacts (Figure 3).

Figure 3 29359

Figure 3

6. Case Illustration: When Remote Camera vHIT Made the Difference

Case Scenario:
A 31-year-old male presented with a 3-day history of severe spinning vertigo, characterized by spontaneous onset and worsened by head movements. The vertigo was continuous and accompanied by vomiting.

Examination Findings:

  • Head Impulse Test: Abnormal on the left side
  • Nystagmus: Unidirectional to the right, suppressed with visual fixation
  • Skew Deviation: Absent
  • Hearing Loss: None
  • Unterberger’s Test: Rotation toward the left side

The patient underwent a video head impulse test, which revealed reduced gain in the left anterior and left lateral canals. Overt saccades were observed in the left lateral canal tracings (Figure 4).

Figure 4 29359

Figure 4

Final Diagnosis:

Left acute unilateral vestibulopathy involving the left superior branch of vestibular nerve.

Management:

The patient was started on targeted vestibular rehabilitation therapy, focusing on the left anterior and lateral canals, along with appropriate medical management.

Significance of vHIT:

The video head impulse test (vHIT) plays a critical role in cases like this by providing objective identification of canal-specific vestibular deficits. It enables precise localization of the lesion to the affected nerve and supports the development of individualized, targeted rehabilitation strategies.

7. Additional Clinical Applications of vHIT

  • Subtyping Vestibular Neuritis: vHIT enables classification of superior, inferior, or ampullary involvement by analyzing canal-specific gain.
  • Monitoring Ototoxicity or Surgical Outcomes: Useful in tracking vestibular function following gentamicin therapy, labyrinthectomy, or vestibular schwannoma resection.
  • Acute Vertigo Triage: As part of the HINTS+ protocol, vHIT assists in differentiating peripheral from central causes of acute vestibular syndrome.
  • Tracking Rehabilitation Progress: The presence of covert saccades may indicate compensation and help tailor the intensity and focus of vestibular rehabilitation.
  • Vertical Canal Testing: vHIT effectively assesses the RALP and LARP planes, offering superior multidimensional analysis compared to traditional caloric testing.

8. Comparative Advantages Over Head-Mounted Systems

Feature

Head-Mounted Systems

Remote Camera vHIT

Patient Comfort

Less comfortable (tight-fitting goggles)

Highly comfortable (no contact)

Artifact from Slippage

Frequent

Absent

Pediatric Use

Challenging

Feasible even in infants

Required Maneuvers

15–20 head impulses

5 head impulses

Examiner Maneuverability

Limited

Unrestricted

Eye Tracking Technology

Accelerometer + camera

Pure image-based analysis

Calibration Requirements

Laser-dependent

None

Visual Field Obstruction

Present

None

 

9. Conclusion: Shaping the Future of Vestibular Diagnostics

Remote camera vHIT systems represent a true paradigm shift in modern vestibular testing. Their contact-free design eliminates common sources of artifact, improves patient tolerance, and enables fast, objective, and reproducible measurements. By incorporating advanced gaze tracking, head pose estimation algorithms, and artifact-free performance, these systems provide a level of precision that not only enhances diagnostic accuracy but also supports targeted rehabilitation and the monitoring of recovery over time.

As the field of vestibular diagnostics continues to evolve, remote camera vHIT is emerging not merely as a diagnostic tool but as a transformative technology redefining how clinicians approach vertigo evaluation and neurotologic care.

Resources for More Information 


vishal pawar

Vishal Pawar

Dr. Vishal Pawar - Specialist Neurologist MBBS, DNB Medicine, DNB Neurology, SCE Neuro (RCP UK), VAM (American institute of Balance), International Vestibular diploma, Fellow of European board of Neurology. Dr. Pawar is a licensed neurology specialist with several years of experience in the field. His area of expertise focuses on the treatment of patients suffering from headaches, vertigo, strokes, and back pain. He is speaker at national and international congresses, seminars, and webinars and author of publications in national and international scientific journals.


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