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Electronystagmography
Definition
Electronystagmography is a test to look at voluntary and involuntary eye movements. It evaluates the acoustic nerve, which runs from the brain to the ears (and control hearing and balance) and the occulomotor nerve, which runs from the brain to the eyes.
Alternative Names
ENG
How the test is performed
Patches called electrodes (similar to those used with ECG, but smaller) are placed above, below, and to the side of each eye. They may be attached by adhesive or by a band around the head. Another electrode is attached to the forehead.
The electrodes record eye movements that occur when the inner ear and nearby nerves are stimulated by delivering cold and warm water to the ear canal at different times. Sometimes, the test is done using air instead of water. Each ear is tested separately.
When cold water enters the ear, it should cause rapid, side-to-side eye movements called nystagmus. The eyes should move rapidly away from the cold water and slowly back. Next, warm water is placed into the ear. The eyes should now move rapidly toward the warm water then slowly away.
Patients may also be asked to use their eyes to track objects, such as flashing lights.
The electrodes detect the length and speed of eye movements, and a computer records the results.
The test takes about 90 minutes.
Electronystagmography provides exact measurements of eye movements detected by the electrical changes the movements produce. It is more objective than simply watching the eyes after flushing warm or cold water into the ears. It can record behind closed eyelids or with the head in a variety of positions.
How to prepare for the test
No preparation is necessary. Check with your health care provider if you are taking any medications.
How the test will feel
There is minimal discomfort. You may find cold water in the ear uncomfortable. Brief dizziness (vertigo) may occur during the test.
Why the test is performed
The test is used to determine whether a balance or nerve disorder is the cause of dizziness or vertigo.
Your doctor may order this test if you have dizziness or vertigo, impaired hearing, or suspected damage to the inner ear from certain medications.
Normal Values
Distinct involuntary eye movements should occur after instillation of warm or cold water into the ear canal.
Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
What abnormal results mean
Abnormal results may be a sign of damage to the nerve of the inner ear or other parts of the brain that control eye movements.
Any disease or injury that damages the acoustic nerve can cause vertigo. This may include:
- Blood vessel disorders with bleeding (hemorrhage), clots, or atherosclerosis of the blood supply of the ear
- Cholesteatoma and other ear tumors
- Congenital disorders
- Injury
- Medications that are toxic to the ear nerves, including aminoglycoside antibiotics, some antimalarial drugs, loop diuretics, and salicylates
- Multiple sclerosis
- Movement disorders such as progressive supranuclear palsy
- Rubella
- Some poisons
Additional conditions under which the test may be performed:
What the risks are
There is a small risk associated with the caloric stimulation part of the test. Excessive water pressure can injure a previously damaged eardrum, but this rarely occurs. Caloric stimulation should not be performed if your eardrum has been perforated recently because of the risk of causing ear infection.
References
Griggs RC, Jozefowicz RF, Aminoff MJ. Approach to the patient with neurologic disease. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier. 2007: chap 418.
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; Daniel B. Hoch, PhD, MD, Assistant Professor of Neurology, Harvard Medical School, Department of Neurology, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
