Dizziness and Balance
The VNG balance test is a 90 minute procedure. ENT Physicians delegate this test to Audiologists or other highly trained persons. Besides the inner ear as the source of dizziness, other pathologies that cause dizziness, to name a few, might be high blood pressure, anemia, central or brain abnormalities / injuries, a viral infection or possibly a side effect of a prescribed medication. Because the auditory nerve and the vestibular nerve, the VIIIth cranial nerve, is a combined nerve a full hearing assessment is usually part of the vestibular evaluation. For example, patients with an illness like Meniere’s syndrome often show a low frequency hearing loss and a vestibular weakness on the VNG assessment. Today’s VNG is very similar to the ENG of forty years ago but we’ve gone digital. No longer are the test results printed on expensive paper. Today, we now call the test VNG which stands for Videonystagmography because rather than using electrodes to measure eye movements, we now use small infra-red cameras to video eye movements. These eye movements are all digitized and stored on the hard-drive for analysis. Further, I no longer have to hand measure the nystagmus, the computer does it for me.
Briefly, the VNG consists of 3 segments.
The first segment is testing of the ocular motor system that gives us the eye movements.
The second part of the test consists of positional changes such as rapidly lying down from a sitting position to a head hanging position followed by a supine and head right, head left and lateral positions. Often physicians will try to do some of these positioning tests in their office but unless the eye movements are very strong, they might not see them. VNG recordings are much more sensitive and pick up nystagmus missed during clinic visits, mainly due to something called fixation suppression. This is where the eyes fixate on an object and the nystagmus is suppressed.
The third and final portion of the test involves water or air stimulation of the ears with different temperatures which produces fluid movement in the inner ear semi-circular canals which in turn causes nystagmus. Water caloric testing has been done for nearly 100 years. In 1914, Doctor Robert Barany was awarded a Nobel Prize in Physiology / Medicine for his amazing research on the inner ear. Basically, if the same temperature stimulates the right ear and then the left ear, the corresponding eye movement or nystagmus should be the same. If one side is weaker than the other, the weaker side or the inner ear with the reduced vestibular response most likely is the source of a patient’s dizziness.
Results of all three segments of the VNG along with a full Audiologic assessment gives Doctor Robertson information to base his diagnosis. With that information, along with other information, Doctor Robertson will provide a treatment plan.