This video by Jack Bennett - International Clinical Trainer at the Interacoustics Academy - describes the clinical process, interpretation and clinical utility of the VOR Suppression on the Rotary Chair.
You can read the full transcript below.
VOR suppression testing is also known as the visual vestibular fixation, VOR fixation, or VOR cancellation. We will be comparing the gain measured during sinusoidal harmonic acceleration with the gain measured during VOR suppression. The only difference being that when performing the VOR suppression test, the patient will be able to see a fixation light inside their goggle. As they have something to look at, they should be able to suppress the eye movements that are generated by the chair movements - this is a centrally regulated process.
Just like SHA testing, the patient will be in darkness with the goggles on and they will be given a mental alerting task throughout. It is said that the VOR supression is much like measuring the fixation index when doing caloric testing. Caloric testing stimulates nystagmus as if a low frequency stimulus of 0.003 hertz is being used.
The rotational assessment however, has a stimulus of a much higher frequency. As such, VOR supression testing is sensitive to central conditions that are much more mild, as the higher frequency in VOR testing taxes the central system to a higher degree. Here we can see the much reduced eye velocity while the chair is rotating.
The results are very simple to read. The circle is the gain recorded during the sinusoidal harmonic acceleration. The triangle is the gain recorded during VOR suppression. And now we can see the reduction in gain is plotted and indicated by the triangle here. The grey area is the abnormal range. This is dependent on many factors, not least including age.
VOR suppression testing is very useful for all patients that are undergoing rotational chair testing. But it is especially indicated for those for whom a central lesion is suspected. It is also important to test anybody with a peripheral condition where there appears to be a lack of central compensation. Any patients who have abnormalities when doing optokinetic testing or smooth pursuit testing are also recommended to undergo VOR suppression testing.
In 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.