The electronystagmogram (ENG) is a test that is taken to identify the voluntary and involuntary movements of the eye. This test specifically evaluates the efficiency of the acoustic nerve. This is the nerve that connects the eyes to the brain.
For this test, electrodes which are very similar to the ECG leads, though smaller, are placed on the sides of the eyes. A band is placed around the head and the electrodes are attached to this band. An additional electrode is then attached to the forehead.
The procedure of the test is extremely sensitive to outside disturbances, and therefore, a lot of care has to be taken while performing the test. Cold and warm water are delivered to the ear canal at different times. Water with different temperatures is delivered in order to stimulate the nerves near the ear canal. As the nerves are stimulated, the electrodes placed on the sides of the eyes record movements.
The cold and hot water create different responses in the eyes. Normally, as the cold water enters the ear canal, there is rapid movement of the eyes. The eyes move from side to side at a high speed. This movement is technically known as nystagmus. As a reflex action, the eyes rapidly move away from the cold water and then come back to their normal position slowly. Warm water produces a different set of sensations, and therefore, the end result is also different.
In some cases, doctors may ask their patients to track movements of objects. Flashing lights may be used for this test. While the patient is following the objects, the electrodes quickly capture the speed of the movements of the eyes and the length of the darting of the eyes. The results are recorded by the computer. The entire procedure of the test takes about ninety minutes.
Nothing is required from the patient in terms of preparation for the test. If you are under any medication, you should discuss it with your doctor. Since the test is not intrusive, there is no specific discomfort. You may feel a little dizzy during the test because the varying temperature of water may upset the balance of the Eustachian tube in the inner ear. Some people may find the delivery of cold water slightly uncomfortable.
The results of the test are useful in determining the cause of vertigo. The test is specifically ordered when the patient complains of vertigo, dizziness, impaired hearing or damage and infection in the inner ear.