What Is Electronystagmography?
Electronystagmography (ENG) is a test that examines the movement of your eyes in order to assess how well two cranial nerves within your brain are functioning. These nerves are the acoustic (or vestibulocochlear) nerve (the nerve connecting the brain and the inner ear controlling hearing and balance) and the oculomotor nerve (the nerve connecting the brain to the muscles of the eyes).
Purpose of an ENG
The ENG is designed to detect disorders in the parts of your inner ear that are responsible for orientation and balance, as well as in the nerves that connect your brain to your eyes and ears.
Your doctor may recommend this test if you are suffering from any of the following symptoms:
- problems with balance
- hearing loss
Your doctor may also perform an ENG if you suffer from one of the following conditions:
- Usher syndrome: a disorder that causes total deafness
- acoustic neuroma: a slow-growing tumor in the nerve that connects the brain and the ear
- labyrinthitis: inflammation of the inner ear
- Ménière’s disease: an inner ear disorder that affects balance
- any known lesion in your inner ear
If you do have one of these conditions, your doctor will likely perform regularly scheduled ENG tests as a way to track treatment effectiveness and disease progression.
The Types of ENG Tests and How They Are Performed
There are a number of different types of ENG tests. Your doctor may administer one or several.
Water Caloric Test
For this test, electrode patches are placed above, below, and at each side of each of your eyes. Another electrode is attached to your forehead. While your head is held in position, your doctor will put cold water into one of your ears. The electrodes will record all the movements of your eye as the water stimulates your inner ear and the nerves nearby. As cold water enters the ear, your eyes should move rapidly from side to side. Your doctor will then repeat this procedure with the other ear.
For the next stage of the test, your doctor will put warm water into one of your ears. This should cause your eyes to move quickly in the direction of the warm water and then to move away slowly. This procedure will then be repeated with your other ear.
For this test, your doctor will ask you to track a light that is at a distance of around six feet with your eyes. This test will determine if you suffer from a condition in which the movements of your pupils go beyond their target.
Gaze Nystagmus Test
Nystagmus is an involuntary movement of the eye that reflects your brain’s detection of movement. It can vary from fast to slow. You wouldn’t be aware of nystagmus.
For this test, your doctor will ask you to sit or lie down and stare at a fixed light. The light may be placed directly in front of you or to the side. This test will assess how well you are able to fix your eyes on a target without any involuntary eye movement.
While the gaze nystagmus test involves staring at a fixed light, for this test your doctor will ask you to track a light as it moves from side to side like the pendulum of a clock. This test measures how well you can move your eyes.
During this test, your doctor will ask you to keep your head still while allowing your eyes to follow a light as it moves quickly across and beyond your field of vision, and then back again.
For this test, your doctor will ask you to turn your head quickly to one side or to lie down and then sit or stand very quickly. This test measures the amount of activity in your eyes while you are making these movements.
Understanding the Results of an ENG
If the results of your ENG tests are abnormal, it may indicate a problem with your inner ear or the area of your brain that is responsible for controlling the movement of your eyes.
Other diseases or injuries to the acoustic nerve can cause vertigo, including:
- blood vessel disorders that cause bleeding in the ear
- blood clots in the ear
- ear tumors
- hereditary disorders
- damage to the inner ear
- medications that are toxic to the ear nerves
- multiple sclerosis
- movement disorders
- some poisons
What Are the Risks of the Test?
There are a number of minimal risks linked to ENG, including dizziness or mild nausea.
You may also feel some slight discomfort during the water caloric test. Those who have been diagnosed with perforated eardrums should not undergo this part of the test.
Any existing problems you have with your back or neck may be aggravated by rapid movements or changes in position required by some of these tests.
Some conditions or medications may affect the functioning or accuracy of ENG, including:
- impaired vision
- frequent blinking
- sedatives, anti-vertigo medications, and tranquilizers
If you wear a pacemaker, you should not undergo ENG as the equipment may interfere with its function.
Preparation for the Test
Inform your doctor of any prescription medications, over-the-counter medications, or herbal supplements you are taking.
Your doctor may advise you to avoid eating for four hours before the test and to avoid drinking caffeine or alcohol for 24 to 48 hours before the test. He will also ask you to refrain from taking any sedatives, tranquilizers, or anti-vertigo medications before the test.
The morning of the test, clean your ears to remove excessive earwax.
If you wear a hearing aid or glasses, take them along with you to the test.
You may be asked to sign a consent form before taking the test.
Following Up After the Test
After your doctor has completed the test, he or she will remove the electrode patches and wash off the conductive paste.
If you are experiencing nausea, dizziness, or weakness, you will need to sit or lie down until those feelings have passed.
Your doctor will let you know when you can resume taking any medications you stopped taking in preparation for the procedure.