What is electronystagmography?
Electronystagmography (ENG) is used to evaluate people with vertigo (a false sense of spinning or motion that can cause dizziness) and certain other disorders that affect hearing and vision. Electrodes are placed at locations above and below the eye to record electrical activity. By measuring the changes in the electrical field within the eye, ENG can detect nystagmus (involuntary rapid eye movement) in response to various stimuli. 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. This test may also be used to distinguish between lesions in various parts of the brain and nervous system.
Anatomy of the ear
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The ear is the organ of hearing. The parts of the ear include:
- External or outer ear - This consists of the pinna or auricle (the outside part of the ear) and the external auditory canal or tube (the tube that connects the outer ear to the inside or middle ear).
- Tympanic membrane (also called the eardrum). The tympanic membrane divides the external ear from the middle ear.
- Middle ear (tympanic cavity). This consists of ossicles (three small connected bones) that transmit sound waves to the inner ear, and the eustachian tube (a canal that links the middle ear with the throat area).
- Inner ear. This consists of the cochlea (contains the nerves for hearing), the vestibule (contains receptors for balance), and the semicircular canals (contain receptors for balance).
Different types of ENG tests
The ENG is actually a battery of tests that may include one or more of the following measurements:
- Calibration test. This involves following a light about 6 to 10 feet away with your eyes. This test measures ocular dysmetria (a condition in which movements of the pupil of the eye overshoot their target).
- Gaze nystagmus test. This involves staring 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 upon an object without your eyes moving involuntarily.
- Pendulum-tracking test. As its name suggests, measures how well you can follow a light with your eyes as it moves like the pendulum of 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. This involves moving 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 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.
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 performed if an individual is experiencing unexplained dizziness, vertigo, or hearing loss. Additional conditions in which ENG may be performed are acoustic neuroma, labyrinthitis, Usher syndrome, and Ménière’s disease. If a known lesion exists this test can identify the actual site.
There may be other reasons for your doctor to recommend an ENG.
ENG is associated with minimal risks. Some people may experience dizziness or nausea during the test.
ENG should not be used in individuals with pacemakers 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. Patients who have previously been diagnosed with a perforated tympanic membrane 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 doctor prior to the procedure.
Certain factors or conditions may interfere with ENG. These include, but are not limited to, the following:
- Impaired vision
- Frequent blinking
- Certain medications, such as sedatives, tranquilizers, and antivertigo medications
- Your doctor 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 doctor 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 doctor before the test.
- 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 doctor may request other specific preparation.
An ENG may be performed on an outpatient basis or as part of your stay in a hospital. 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 performed, 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 doctor can interpret the results.
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 observed for any signs of weakness, dizziness, and nausea, and may need to lie down or sit for a few minutes to recover.
Your doctor will inform you as to when to resume any medications you stopped taking before the test.
Your doctor may give you additional or alternate instructions after the procedure, depending on your particular situation.