Disorders of the balance system are not an uncommon complaint, particularly in the older population. When a subject presents with dizziness, or vertigo, useful information can be obtained from monitoring their eye movement.
Information gathering of eye movement may be as a result of intentional stimuli or tasking or as a result of spontaneous or involuntary events.
An Electronystagmogram (ENG) is the most common audiological test ordered for individuals complaining of dizziness or vertigo. This test records and measures voluntary and involuntary eye movements (the vestibular ocular reflex), specifically nystagmus. Nystagmus is an involuntary back and forth jerking movement of the eyes that occurs when the entire balance system is stimulated. When the vestibular and ocular systems are functioning normally, nystagmus is only rarely seen. For the purpose of testing, nystagmus can be elicited through certain movements or stimulation of the vestibular system (the balance organs of the inner ear). This helps to determine the cause or origin of your dizziness. An ENG evaluates the oculomotor system and the vestibular system. The test takes approximately an hour and a half to complete.
The ENG is Comprised of a Series of Subtests or Tasks. There are Three Main Parts:
- Oculomotor Analysis -- patients perform various visual tasks that require eye movement
- Positional Testing -- patients are placed in various body positions to determine if dizziness develops and to see if nystagmus occurs
- Caloric Stimulation -- small amounts of both warm and cool water are introduced into each ear canal to independently stimulate the inner ear vestibular system
Throughout each part of the test, patterns of normal and abnormal eye movements are analyzed. The main purpose is to look for the presence of nystagmus in both the absence and presence of vestibular stimulation, as well as look for symmetry of responses. Analysis allows for determining if the disorder is central, peripheral or systemic.
- Central problems are caused by disturbances in the brain or central nervous system
- Peripheral problems arise from disturbances in the labyrinth (inner ear balance organ)
- Systemic problems are the result of disturbances in the organs and peripheral nerves (nerves outside of the brain or spinal column)