What is electronystagmography?
Electronystagmography (ENG) is a test used to evaluate people with vertigo and certain other hearing and vision disorders. Vertigo is a false sense of spinning or motion that can cause dizziness.
For this test, electrodes are placed above and below the eye to record electrical activity. By measuring the changes in the electrical field within the eye, ENG can detect nystagmus in response to various stimuli. Nystagmus is an involuntary rapid eye movement. If nystagmus does not occur on stimulation, a problem may exist within the ear, nerves that supply the ear, or certain parts of the brain.
The ENG is actually a series of tests that may include one or more of the following measurements:
- Calibration test. For this test, you will follow a light with your eyes. This test measures ocular dysmetria, which is a condition in which movements of the pupil of the eye overshoot their target.
- Gaze nystagmus test. For this test, you will stare at a fixed light placed either to the center or side as you are seated or lying down. This test measures how well you can fix your gaze at an object without your eyes moving involuntarily.
- Pendulum-tracking test. For this test, you will follow a light with your eyes as it moves like a pendulum of a clock.
- Optokinetics test. This measures your ability to follow a light as it moves quickly across and out of your field of vision and back again while you keep your head still.
- Positional test. For this test, you will move your head and perhaps your whole body as opposed to just your eyes. For example, you may be instructed to turn your head quickly to one side, or you may be asked to sit up quickly after you have been lying down. The amount of eye motion that results from this activity is recorded.
- Water caloric test. This test involves introducing warm or cool water into the ear canal with a syringe so that it touches the tympanic membrane. If no problem exists, your eyes will move involuntarily to this stimulus. Air instead of water may be used as the stimulus for this test, especially in those who have a damaged tympanic membrane.
Why might I need an ENG test?
The ENG is used to detect disorders of the peripheral vestibular system, the parts of the inner ear that interpret balance and spatial orientation, or the nerves that connect the vestibular system to the brain and the muscles of the eye.
The test may be one if you are experiencing unexplained dizziness, vertigo, or hearing loss. These are symptoms, not a diagnosis. The ENG may help determine the exact cause of your symptoms. Possible causes include:
- Acoustic neuroma (a tumor of the nerve responsible for sound and balance)
- Labyrinthitis (inflammation of the inner ear, often caused by a virus)
- Usher syndrome (a congenital disorder that causes hearing loss)
- Meniere's disease (excess fluid in the inner ear that can affect hearing and balance)
If a known lesion exists this test can identify the actual site. There may be other reasons for your healthcare provider to recommend an ENG.
What are the risks of ENG tests?
There are very few risks with ENG. Some people may experience dizziness or nausea during the test.
ENG should not be used if you have a pacemaker because the equipment may interfere with pacemaker function.
Back or neck problems may be aggravated by rapid changes in position required for the test.
The water caloric test may produce mild discomfort. If you have been previously diagnosed with a perforated tympanic membrane, you should not undergo the water caloric portion of the ENG test.
There may be other risks depending on your specific medical condition. Be sure to discuss any concerns with your healthcare provider prior to the procedure.
Certain factors or conditions may interfere with ENG. These include:
- Impaired vision
- Frequent blinking
- Certain medications, such as sedatives, tranquilizers, and anti-vertigo medications
How do I get ready for an ENG test?
- Your healthcare provider will explain the procedure to you and offer you the opportunity to ask any questions that you might have about the procedure.
- You may be asked to sign a consent form that gives your permission to do the procedure. Read the form carefully and ask questions if something is not clear.
- You may be asked to avoid eating for at least four hours before the test.
- Avoid consuming caffeine and alcohol for 24 to 48 hours before the test.
- Notify your healthcare provider of all medications (prescribed and over-the-counter) and herbal supplements that you are taking.
- Discontinue taking sedatives, tranquilizers, and any other medications as instructed by your healthcare provider before the test.
- Carefully clean your ears of excessive earwax. Before the ENG, your ears will be examined for the presence of wax, inflammation, or other problems that may interfere with the test.
- If you wear eyeglasses and/or a hearing aid, bring them with you to the test.
- Based on your medical condition, your healthcare provider may request other specific preparation.
What happens during an ENG test?
An ENG may be done on an outpatient basis or as part of a hospital stay. Procedures may vary depending on your condition and your doctor's practices.
Generally, the ENG follows this process:
- If there is wax in the ear, it will be removed.
- Before positioning the electrodes, areas of the skin on your face will be cleaned with an alcohol-saturated cotton pad and allowed to air-dry.
- A paste will be used to attach the electrodes. One electrode will be positioned in the center of your forehead, and the other electrodes will be positioned above the eyebrow and below the eye in a way that allows you to close your eyes. Electrodes may also be placed to the side of each eye.
- Depending on the type of test being done, you may be asked to look up, down, or to the side or move your head and/or entire body. You may also be asked to close your eyes, which does not hinder the recording of eye movement.
- For caloric testing, either air or water will be introduced to the ear while eye movements are recorded.
- The electrical activity detected by the electrodes will be fed into a recorder, which amplifies the signal and charts it so that your healthcare provider can interpret the results.
What happens after the ENG test?
Once the test is complete, the electrodes will be removed and the electrode paste washed off. You may be instructed to avoid rubbing your eyes to avoid spreading the electrode paste.
You will be watched for any signs of weakness, dizziness, and nausea, and may need to lie down or sit for a few minutes to recover.
Your healthcare provider will inform you as to when to resume any medications you stopped taking before the test.
Your healthcare provider may give you additional or alternate instructions after the procedure, depending on your particular situation.
Before you agree to the test or the procedure make sure you know:
- The name of the test or procedure
- The reason you are having the test or procedure
- The risks and benefits of the test or procedure
- When and where you are to have the test or procedure and who will do it
- When and how will you get the results
- How much will you have to pay for the test or procedure