Gaze Stability and the VOR: What Clinic Testing Measures

Updated 2026-10-22

Written by the Optics Trainer team from published research, with every source linked below.

Keeping vision clear while the head moves depends on the vestibulo-ocular reflex (VOR) working with visual fixation. Some eye care clinics look at gaze stability during head movement, while vestibular specialists use dedicated tests such as the video head impulse test. This guide explains what the VOR does, what the main tests measure and how reliable they are, the artifacts that affect video recording, and where eye-care testing fits alongside vestibular assessment.

What the VOR does

The VOR rotates the eyes opposite to head rotation to keep the line of sight stable, using input from the semicircular canals for rotation and the otoliths for linear movement. Its gain is the ratio of eye response to head movement. In healthy people tested with the video head impulse test (vHIT), gain is close to 1.0; in a sample of 91 healthy people aged 10 to 89, it fell at high head velocities but was largely unaffected by age into the 80s.

Looking at a target that moves with the head requires suppressing or cancelling the VOR, which, one laboratory study suggests, may share a smooth eye-movement mechanism with pursuit.

The video head impulse test (vHIT)

The head impulse test uses small, fast, passive and unpredictable head turns of about 15 degrees; vHIT records head and eye velocity with tightly fitted goggles. A variant with a head-fixed target (SHIMPs) tests the VOR under a suppression instruction.

vHIT gain showed good test-retest reliability in 40 people (20 healthy, 20 with vestibular pathology; intraclass correlations of at least 0.76) and in 28 typically developing children and adolescents. Corrective-saccade findings in the vertical canals were less repeatable than gain.

Artifacts in video recording

Video recordings of head movement are prone to artifacts:

In one study of patients with acute vertigo, 42% of 1,358 head impulse recordings could not be interpreted.
Goggle slippage can create apparent eye movement even when the eye is not moving, and strap tightness changes measured gain.
Children often cannot be given head impulses fast enough for full testing, especially in the vertical planes.

Dynamic visual acuity and the gaze stabilization test

Dynamic visual acuity (DVA) compares acuity with the head still and moving. One specialist-centre study reported intraclass correlations of 0.83 to 0.87 for computerised DVA, but another, in 46 healthy adults on a commercial system, found poor-to-fair reliability for DVA loss scores (raw scores were more reliable).

The gaze stabilization test (GST) measures the fastest head velocity at which a briefly flashed optotype can still be read. Reliability was 0.91 (a reliability index) in 14 patients and 14 controls, but intraclass correlations were only 0.41 to 0.63 in 50 high school and college football players, so it varies with the population and protocol.

The VOR item in concussion screening

The VOR item of the Vestibular/Ocular Motor Screening (VOMS) tool is scored by whether it provokes symptoms, not by measuring eye movement. In 108 healthy military personnel retested after six months, item intraclass correlations were 0.60 to 0.81. It is a symptom screen, not a measure of VOR gain and not a diagnosis.

VR and eye-tracking measurement

Measuring gaze stability in a headset is still at an early stage. In one study of 12 healthy adults, head impulses recorded in a VR headset with an add-on 250 Hz eye tracker gave gain within about 0.03 of vHIT after recalibration (0.07 before), but the headset's own head tracking produced artifacts above 200 degrees per second and external motion capture was needed. Eye-tracker sampling rate, head-tracking accuracy and calibration all limit measurement in headsets.

Where eye-care testing fits

Describing how steady fixation stays during head movement is a functional observation that can sit within an eye-care assessment. Diagnosing vestibular disorders requires vestibular, ENT or neurology assessment. Gaze stabilisation exercises with head movement are a guideline-supported part of vestibular rehabilitation for peripheral vestibular hypofunction, led by vestibular clinicians and physical therapists.

How Optics Tracker fits

Optics Tracker includes a Fixation and VOR test covering static fixation and dynamic visual-vestibular stability. It is not a video head impulse test, it is not presented as equivalent to vHIT, and vHIT gain cut-offs do not apply to it. None of the studies above evaluated Optics Tracker.

Optics Tracker is clinical decision-support software. Its results support, and do not replace, vestibular assessment, professional diagnosis and clinical judgement.

Frequently asked questions

What is a normal VOR gain?

In healthy people tested with the video head impulse test, VOR gain is close to 1.0 and changes little with age. That applies to vHIT protocols, not to other ways of measuring gaze stability.

What is VOR suppression?

Holding gaze on a target that moves with the head, which requires cancelling the VOR. One laboratory study suggests it may share a smooth eye-movement mechanism with pursuit.

Is the video head impulse test reliable?

Gain has shown good test-retest reliability in adults and children, but recordings are prone to artifacts such as goggle slippage, and in one acute-vertigo study 42% of recordings could not be interpreted.

Can an eye care clinic diagnose vestibular problems?

Describing gaze stability during head movement can be part of an eye-care assessment, but diagnosing vestibular disorders requires vestibular, ENT or neurology assessment.