Electronystagmography (ENG)

The eyes are closely linked to the inner ear; these organs depend on each other for good balance and clear vision. Head movement or other stimulation of the inner ear sends signals to the muscles of the eyes via the nervous system; this is called the vestibulo-ocular reflex, or VOR.

The VOR normally generates eye movements that maintain clear vision with head movement. Electronystagmography is a battery (group) of eye-movement tests that look for signs of vestibular dysfunction or neurological problems by measuring nystagmus (a kind of involuntary eye movement) and record other eye movements in order to evaluate certain brain functions. ENG tests are probably the most common ones administered to people with dizziness, vertigo, and/or balance disorders, although the test battery and some testing methods vary widely.

During ENG, eye movements are recorded and analyzed via small electrodes placed on the skin around the eyes. The electrodes attach to the skin with an adhesive, much like a small bandage. Alternatively, eye movements may be recorded by infrared video camera while the person being tested wears goggles instead of sticky-patch electrodes.

While the eye movements are recorded, the person being tested will be asked a series of simple questions that are meant to keep the mind busy and alert during the tests.

One ENG test evaluates the movement of the eyes as they follow a moving target. Another observes eye movements as the head is positioned in different directions. During the caloric test (sometimes called bi-thermal caloric or mono-thermal caloric), warm or cold water or air is circulated in the ear canal. The temperature change stimulates the inner ear in order to test the nystagmus response.  

From VEDA publication F-6, Diagnostic Tests for Vestibular Problems.

For further information, see also VEDA publication E-8,
Common Misconceptions about ENG (Electronystagmography).