What is electronystagmography?
Electronystagmography (ENG) is a test that shows the movement of your eyes in order to determine how well two cranial nerves within your brain are functioning. The two nerves are the acoustic (or vestibulocochlear) nerve and the oculomotor nerve. The acoustic nerve connects the brain and the inner ear and controls hearing and balance. The oculomotor nerve connects the brain to the muscles of your eyes.
Purpose of an ENG
The ENG detects disorders in the parts of your inner ear that are responsible for orientation, position sense, 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:
- severe or persistent dizziness
- vertigo (sense that the room is spinning)
- problems with balance
- unexplained hearing loss
Your doctor may also perform an ENG if you have any of the following conditions:
- Usher syndrome: an inherited disorder that affects vision, balance, and hearing
- acoustic neuroma: a benign tumor on the acoustic (vestibulocochlear) nerve
- labyrinthitis: inflammation of the inner ear
- Meniere’s disease: an inner ear disorder that affects balance and hearing
- any suspected lesion in your inner ear
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. The standard test typically consists of three parts.
For the caloric test, electrode patches are placed above, below, and on each side of each of your eyes. Another electrode is attached to your forehead. While your head is held in position, your doctor will stimulate your balance system using warm and cool air. Sometimes water is used as well. The electrodes will record all the movements of your eyes as your inner ear and the nerves nearby react to temperature changes.
For the oculomotor 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. This allows your doctor to understand how your eyes track and move when following a target.
For a positional 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 how your eyes respond to movement.
Videonystagmography: An additional option
Another option for inner ear function testing is videonystagmography (VNG). While similar to ENG, VNG testing involves goggles and special infrared cameras to measure eye movements. This is a departure from traditional ENG technology. It measures the movements of the muscles around the eyes.
Instead of wearing electrode patches, the VNG test involves wearing special goggles that measure eye movements. Once the data is collected, a computer analyzes the person’s eye movements. An audiologist will also examine the results to determine accuracy and help make a diagnosis.
Ideally, the accuracy of directly measuring eye movements while wearing the goggles is greater than indirectly measuring movements via eye muscle motion. Studies have generally supported the use of VNG over ENG. However, some professionals believe there is not enough evidence to recommend one method of testing over another.
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
- ear tumors
- hereditary disorders
- damage to the inner ear
- medications that are toxic to the ear nerves
- multiple sclerosis
- viral infections like chicken pox, measles, and the flu
- movement disorders
- chemical poisoning
What are the risks of the test?
There are a number of minimal risks linked to undergoing an ENG test, including dizziness or mild nausea. Those undergoing the VNG test can experience similar effects as well as minor discomfort from wearing the goggles, for an average of 1.5 hours of testing.
You may also feel some slight discomfort during the caloric 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. Oftentimes, a motorized chair is used to minimize movements the person needs to make.
Some conditions or medications may affect the functioning or accuracy of ENG, including:
- impaired vision
- frequent blinking
- caffeine, alcohol, sedatives, antivertigo medications, and tranquilizers
It is not recommended to have an ENG if you have a cardiac pacemaker. The electrical equipment may interfere with its function. VNG testing would be a safer alternative.
Preparation for the test
Inform your doctor of any prescription medications, over-the-counter medications, or herbal supplements that you are taking.
Your doctor may advise you to avoid eating for several hours before the test and to avoid drinking caffeine or alcohol for 24 to 48 hours before the test. They will likely also ask you to refrain from taking any sedatives, tranquilizers, or antivertigo medications.
Follow all instructions provided by your doctor for test preparation.
Following up after the test
After your doctor has completed the test, they will remove the electrode patches and wash off the conductive paste. Those undergoing the VNG test will simply remove the goggles.
Your doctor will let you know when you can resume taking any medications you stopped taking in preparation for the procedure.