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 upon 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:
The ear is the organ of hearing. The parts of the ear include:
external or outer ear - consisting 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) - consisting 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 - consisting 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 - 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 - 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 - 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 - 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 - 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.
Reasons for the Procedure
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 Meniere's disease. If a known lesion exists this test can identify the actual site.
There may be other reasons for your physician to recommend an ENG.
Risks of the Procedure
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.