Module 1 · Introduction

Introduction

What vHIT is and where it fits
Where you'll see it
A 56-year-old woman is referred for "dizziness." She describes brief spinning when she turns her head, with no hearing change. Her examiner did a bedside head impulse test and thought it looked normal — but wants quantitative confirmation. You sit her down at the vHIT goggles. Ten minutes later, you have a six-canal trace, gain values to two decimal places, and a clear answer about her semicircular canal function. That is the test you're about to learn.
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What vHIT is

The video head impulse test — vHIT — measures how well your eyes stay locked on a visual target when someone gives your head a small, fast, unpredictable thrust. If the vestibulo-ocular reflex (VOR) is working, your eyes counter-roll instantly and gaze stays on target. If it's not, your eyes drift with the head and then snap back with a corrective saccade. The goggles measure both head velocity and eye velocity at high speed, and the ratio of the two is the VOR gain.

The bedside head impulse test was described by Halmagyi and Curthoys in 1988 as a way to diagnose unilateral canal paresis without a caloric irrigation[Halmagyi GM 1988]. For two decades it remained a clinical sign — useful but unmeasurable. In 2009, MacDougall and colleagues published the first validation of the video version against scleral search coils — the gold standard of eye-movement recording — and the modern vHIT was born[MacDougall HG 2009].

Where vHIT fits in the vestibular workup

vHIT is a high-frequency, high-acceleration test of all six semicircular canals. It complements rather than replaces caloric testing — calorics probe the lateral canal at very low frequency (~0.003 Hz), while vHIT probes head movements at 2–5 Hz. The two tests can dissociate in characteristic ways. Reduced caloric response with a preserved vHIT is highly specific for Meniere disease[Cordero-Yanza JA 2019]. Reduced vHIT with normal calorics is unusual and usually points to a high-frequency-selective lesion or, more commonly, to a technique issue.

vHIT also adds something calorics cannot: it tests all six canals in their natural planes, in minutes, at the bedside or in any quiet room. The vertical canals (anterior and posterior) are not testable with calorics — the validation paper for vertical-canal vHIT came in 2013[MacDougall HG 2013]and unlocked the diagnosis of inferior vestibular neuritis and other vertical-canal-specific patterns.

What you'll learn in this atlas

The atlas is built in three layers, and each chapter has all three present:

  • Foundation — what the concept is, why it matters, the bedside picture.
  • Trainee — the underlying mechanism, the relevant numbers, the studies that define current practice.
  • Clinician — the edge cases, the controversies, and the things you only learn from doing thousands of tests.

You can switch between levels using the selector at the top of each chapter. The simulators are meant to be used while you read — pattern recognition is built by handling many traces, not by reading about them.

Key teaching points

  • vHIT measures VOR gain (eye velocity divided by head velocity) and detects corrective saccades.
  • Validated against scleral search coils — it is a quantitative, not a qualitative, test[MacDougall HG 2009].
  • Tests all six canals at high frequency, complementing low-frequency caloric testing.
  • Technique matters: head must be aligned with canal planes, thrusts must be small and unpredictable, goggles must not slip.

References

  1. Halmagyi GM, Curthoys IS. A clinical sign of canal paresis. Archives of Neurology 1988;45:737–9. doi:10.1001/archneur.1988.00520310043015
  2. MacDougall HG, Weber KP, McGarvie LA, Halmagyi GM, Curthoys IS. The video head impulse test: diagnostic accuracy in peripheral vestibulopathy. Neurology 2009;73:1134–41. doi:10.1212/WNL.0b013e3181bacf85
  3. Curthoys IS, Halmagyi GM, Manzari L, McGarvie LA, MacDougall HG. A review of the geometrical basis and the principles underlying the use and interpretation of the vHIT in clinical vestibular testing. Frontiers in Neurology 2023;14:1147253. doi:10.3389/fneur.2023.1147253
  4. Halmagyi GM, Chen L, MacDougall HG, Weber KP, McGarvie LA, Curthoys IS. The video head impulse test. Frontiers in Neurology 2017;8:258. doi:10.3389/fneur.2017.00258
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