What is the VOR test?
Vestibular-Ocular Reflex (VOR) test is used to diagnose the cause of recurrent vertigo (giddiness).
VOR is a reflex eye movement that stabilizes images on the retina during head movement. VOR testing should be considered an important part of a group of tests that evaluate vertigo. If a patient is diagnosed with a VOR deficit of one or both vestibular end organs, vestibular rehabilitation may be recommended, depending on the patient’s diagnosis. VOR does not depend on visual input and works even in total darkness or when the eyes are closed.
How is VOR reflex tested?
VOR can be tested using the following three methods:
1. Head impulse testing (HIT):
- Head impulse can be safely and quickly completed at the bedside with the patient. It is used primarily for identifying VOR deficits.
- To complete the test, the patient is asked to fixate on a target while the examiner rotates the head.
- The starting position should be such that the patient’s head is turned slightly past the midline (15-20°), and then the head should be thrust to the opposite side using abrupt movements.
- The normal response is that the eyes remain on the target. In the abnormal response, the eyes are dragged off the target when the head turns (in one direction), followed by eye movements back to the target. This response indicates a VOR deficit on the side of the head turn.
- The head impulse test has a higher specificity to differentiate peripheral vestibular lesion (inner ear or vestibular nerve) on that side.
- An abnormal head impulse test is reported to be a useful test to distinguish between central and peripheral vertigo.
- Movements should remain small (the patient’s head should not move very far either to the left or right), and the movement direction should be unpredictable.
- An abnormal result is indicated when the patient is unable to maintain a steady gaze on the target during a head thrust.
- If the patient has a unilateral loss, the abnormal HIT result will occur with a thrust toward the side of the lesion.
- In the bilateral loss, the abnormal result will occur with head thrusts in both directions.
2. Rotational chair testing:
- Another method of testing VOR is the computerized rotational chair test. This test causes stimulation of both the canals at once, which provides information about the function of the vestibular system as a whole during head rotation. Several rotational chair tests are used clinically to assess VOR function:
- Sinusoidal harmonic acceleration testing chair
- Constant angular acceleration chair
- Impulse angular acceleration chair
- Velocity step test chair
3. VOR testing in pediatric patients:
- VOR is generally tested by turning the patient's head on their long axis and observing for the doll's eyes response (DOLL). The eyes deviate opposite to the direction of head rotation.
- A possibly related maneuver has been used in infants as a neurologic test.
- The examiner turns 90-180° in 1-2 seconds, on their own long axis, while holding the upright infant at arm's length, face-to-face. The normal response to this test is usually described as the deviation of the eyes opposite to the direction of rotation.
- While using this maneuver (both as a neurologic test and to elicit eye-opening), it has been observed that deviation of the eyes in the direction of the rotation, rather than opposite to it, is an abnormal response.
References
Vestibulo-ocular Reflex Testing: https://emedicine.medscape.com/article/1836134-overview)
https://www.uptodate.com/contents/evaluation-of-the-patient-with-vertigo?search=vestibulo%20ocular%20reflex&source=search_result&selectedTitle=2~21&usage_type=default&display_rank=2
https://www.uptodate.com/contents/evaluation-of-the-patient-with-vertigo?search=vestibulo%20ocular%20reflex&source=search_result&selectedTitle=2~21&usage_type=default&display_rank=2
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