This test is also referred to as the visually enhanced VOR (VVOR).
See detailed section on VOR Suppression (in Section 1.4 Smooth Pursuit, Chapter: Eye Movements & Nystagmus)
To assess head rotations, the induced slow phases are measured when the patient’s head is oscillated back-and-forth in yaw (horizontal), in pitch (vertical) and in roll (torsion).
See section: VOR
The patient should be instructed to fix their gaze on the examiner's nose.
In a healthy subject, the eyes remain still, without significant refixation saccades. However, at extreme lateral head positions, some gaze-evoked nystagmus may make interpretation difficult.
- In cases of a hypoactive VOR, the eyes move away from the target in the direction of head rotation, leading to corrective “catch up” saccades back to the target.
- In cases of an abnormally high VOR gain, backup saccades will move the eye in the direction of head rotation.
The response not only depends on the severity of the vestibular deficit but is also frequency-specific.
Bedside testing has offered insights for the evaluation of mixed damage, as seen in cerebellar ataxia, neuropathy, and vestibular areflexia syndrome (CANVAS). In this case, the abnormal VVOR, when performed by an experienced examiner, reflects a deficit of the VOR, OKN, and SP.
(vv)VOR.mp4(tt)
For yaw and pitch rotations, the patient’s head is oscillated at a frequency of about 0.5 Hz with an amplitude that produces a slow phase which nearly crosses the entire oculomotor range. The examiner should look for corrective saccades (usually catch-up) as a sign of an abnormal VOR.
See: Head Impulse Test (HIT)
At the next stage, brief, high-acceleration head thrusts are applied, with the eyes beginning about 15° away from the primary position in the orbit, and with the amplitude of the head movement so that the eyes will end near the primary position of gaze. Again, the patient should be instructed to fix on the examiner's nose. A corrective saccade (usually catch-up) should be looked for as a sign of an inappropriate compensatory slow phase.