Dizziness: Videonystagmography (part 2)
By Heather Meyer
At Midwest ENT Centre, we work with patients who may be experiencing dizziness, imbalance or vertigo episodes. Depending on the patient’s symptoms, the doctor may request further assessment of the inner ear balance system, called the Vestibular System. One of the tests routinely performed by our audiologists here is Videonystagmography (VNG). What a mouthful!
What exactly is VNG testing all about?
VNG is composed of a series of tests used to determine the cause of a patient's dizziness or balance problems, and whether or not it is due to inner ear disease. It is one of the only tests available today that can decipher between a unilateral (one ear) and bilateral (both ears) vestibular problem. If dizziness is not caused by the vestibular portion of the inner ear, it might be caused by the brain, by medical disorders such as low blood pressure, or by psychological problems such as anxiety.
The test records nystagmus (quick eye jerks) using video imaging technology. There are neural connections between the balance mechanism in the inner ear and the muscles of the eye. A disorder of the balance system results in small eye jerks that are detected by a camera attached to a pair of infrared goggles the patient wears during a series of tasks. So you could say that the eyes are not only a “window into your soul” but also a “window into your vestibular system”!
Videonystagmography: what should I expect?
VNG testing is non-invasive, and only minor discomfort is felt by the patient as a result of wearing the goggles. A patient may also experience weakness, dizziness, or nausea during a VNG test, but this generally passes after a few minutes. If medically possible, patients are advised to abstain from food for four hours prior to the test, as a full stomach is more likely to cause discomfort or nausea. Some may feel as though they are going to fall down during testing, but we take special care to ensure this does not happen. The effects of the test are temporary and the level of discomfort depends on the underlying cause of the symptoms. In the event of prolonged dizziness, we recommend that patients arrange to have someone else drive them home.
There are 4 main parts to a VNG test:
The saccade test evaluates rapid eye movements.
The tracking test evaluates movement of the eyes as they follow a visual target.
The positional test measures dizziness associated with changes in position of the head or body.
The caloric test measures responses to warm and cold air circulated in the ear canals.
Because the hearing and balance functions of your inner ear are closely related, a hearing test will likely be administered as well. Appointments usually last about 60-90 minutes.
What if my symptoms have improved: should I still go ahead and take the VNG test?
Yes! The VNG test is designed to determine the underlying cause of your dizziness and other symptoms. Although these may have gotten better, the doctor still needs to find what the cause of your initial symptoms were and how the balance system is recovering. Importantly, the VNG results may be able to tell how likely you are to experience another episode in the future.
Source: The National Dizziness and Balance Center
Vestibular Function: Evaluation and Treatment (2004) Alan Desmond, AuD