VNG & ENG
Electronystagmography (ENG)/Infrared Videonystagmography (VNG)
This is usually the first test your doctor will order for dizziness or loss of balance because it evaluates both the central and peripheral aspects of your overall balance system.
Electronystagmography (ENG) literally means electrical recording of nystagmus - a specific type of eye movement. Videonystagmography (VNG) is a similar test with the added enhancement of video recordings. Testing is performed using electrodes that are placed around your eyes (ENG) or through the use of video goggles placed over your eyes (VNG). Both the ENG and VNG record eye movements that will provide your physician with information about your brain's ability to coordinate balance signals, react to changes in position, and to determine the function of your inner ears.
Our eyes and ears depend on each other for good balance and clear vision. Head movement and other stimulation of the inner ear sends signals to the muscles of the eyes via the nervous system, called the VOR (vestibulo-ocular reflex). The VOR ensures the eye movements necessary to maintain clear vision as the head moves. Throughout a series of tests, the examiner stimulates the inner ears in controlled ways and measures the involuntary eye movements that result
The vestibular evoked myogenic potentials (VEMP) test is used to determine if certain
inner ear structures (the saccule, inferior vestibular nerve, and their central brain
connections) are working normally. The saccule, which is the lower of the two otolithic
motion sensors of the inner ear, has slight sound sensitivity which can be measured and
recorded when sounds are presented to the ear.
The wrist, neck, and sternum will be scrubbed clean and small electrodes will be taped to
the skin. An earphone will be placed in each ear canal. You will lie down with your head
lifted and turned to the side to elicit the VEMP response.
A computer will record several responses from the ear. The audiologist will find the
softest level that produces a VEMP response and determine the amplitude and latencies
of the response. This test takes approximately one hour.
Electrocochleography is a test that evaluates the cochlea, which is the organ of hearing in the inner ear. ECOG measures electric potentials or signals generated in the inner ear in response to sound. The responses are picked up by electrodes in the ear canals and displayed on a computer screen. The results can be used to further evaluate balance problems.
Auditory Brainstem Response Testing
Auditory brainstem response (ABR) testing may be ordered following a basic hearing test to further evaluate the status of the hearing nerve and brainstem pathways that conduct sound from the inner ear to the brain. In rare cases, the neural pathways may not conduct sound normally. Changes in the function of the neural pathways may occur for many reasons including growths along the nerve, demyelinating disease, stroke, viral infections and many others.
ABR testing is not uncomfortable. During the test, the patient is placed in a comfortable reclining chair and is asked to close their eyes and relax. It is important to relax the muscles in order to obtain accurate recordings. It is preferable to avoid caffeine the day of the test and arrive for testing somewhat tired, if possible. No response is required from the patient. In fact, the patient can sleep during the test session.