Vestibulo-Ocular Reflex (VOR) Suppression
What is the vestibulo-ocular reflex (VOR) suppression test?
The VOR cancellation test, also referred to as the vestibulo-ocular reflex (VOR) suppression test, is a diagnostic procedure used to assess the patient's ability to suppress the VOR during rotational movements. During the test, the patient is rotated in a pendular pattern at different frequencies, typically ranging from 0.04 Hz to 0.32 Hz. While wearing enclosed goggles, the patient focuses on a fixation light. By comparing the patient's vision-denied SHA (sinusoidal harmonic acceleration) results with the VOR suppression results at the same rotational frequency, it becomes possible to calculate the percentage of gain reduction.
Patient instructions
“You will feel yourself rocking back and forth slowly in the chair. During the rotation, you will see a small green light appear within the mask (sometimes you may see more than one light, that is ok, just choose one light and focus on it). Please keep your eyes open and focused on the green light during the entire test. Try to prevent the light from ‘bouncing’ around in your view.”
Normal VOR suppression results
A patient with normal VOR suppression results will produce a tracing that shows significantly reduced nystagmus as the patient is rotated sinusoidally from left to right in the chair. The data points for each frequency tested will appear as triangles in the Gain (%) and Reduction (%) graphs above the eye position (°) and eye velocity (°/s) graphs on the summary screen. The circular data points represent the previously recorded SHA results at the same frequency of rotation.
The green data point denotes which frequency tracing is currently being displayed. Triangles that appear in the white region in the Reduction (%) graph represent a normal response. Triangles that appear in the shaded region indicate that the data falls outside of threshold limits. The first half-cycle of each frequency tested is excluded from analysis for improved reliability.
VOR Suppression test showing a normal response.
Abnormal VOR suppression results
A failure to sufficiently suppress the VOR can be an indicator of possible central pathology.
VOR Suppression test showing an abnormal reduction percentage at 0.32 Hz.
Conclusion
VOR suppression testing can be used to test the central vestibular pathways and allows the clinician to see the patient’s VOR suppression performance across multiple sinusoidal harmonic acceleration frequencies, typically above 0.04 Hz.
References
Jacobson, GP, and Shepard, NT. Balance Functional Assessment and Management, 2nd Ed. San Diego; Plural Publishing, 2015
Disclaimer
*NOTE: This is intended only as a guide, official diagnosis should be deferred to the patient’s physician.
