Electronystagmography
Encyclopedia
Electronystagmography is a diagnostic test to record involuntary movements of the eye caused by a condition known as nystagmus. It can also be used to diagnose the cause of vertigo
, dizziness
or balance
dysfunction by testing the vestibular system
.
(VOR). ENG provides an objective assessment of the oculomotor and vestibular systems. A newer standard for the recording is the use of infrared video systems which allow for a more detailed observation and analysis of these eye movements, called Video Nystagmography. A similar test is performed for testing vertigo by using the caloric reflex test
, which can be induced by air or water of specific temperatures, typically +/- 7 degrees Celsius from body temperature.
The standard ENG test battery consists of 3 parts:
The comparison of results obtained from various subtests of ENG assists in determining whether a disorder is central or peripheral. In peripheral vestibular disorders, the side of lesion can be inferred from the results of caloric stimulation and, to some degree, from positional findings.
ENG or VNG can be used to record nystagmus during oculomotor tests such as saccades
, pursuit and gaze testing, optokinetics and also calorics (bithermal or monothermal). Abnormal oculomotor test results may indicate either systemic or central
pathology as opposed to peripheral
(vestibular) pathology.
Optokinetics generally are used as a cross check on abnormal responses to oculomotor tests. Both of these tests use a "light bar" involving a moving light (usually red) which the patient will track with their eyes.
The caloric irrigation is the only vestibular test which allow the clinician to test the vestibular organs individually, however, it only tests one of the three semi circular canals - the horizontal canal.
While ENG is the most widely used clinical laboratory test to assess vestibular function, normal ENG test results do not necessarily mean that a patient has typical vestibular function. ENG abnormalities can be useful in the diagnosis and localization of site of lesion; however, many abnormalities are nonlocalizing; therefore, the clinical history and otologic examination of the patient are vital in formulating a diagnosis and treatment plan for a patient presenting with dizziness or vertigo.
Vertigo (medical)
Vertigo is a type of dizziness, where there is a feeling of motion when one is stationary. The symptoms are due to a dysfunction of the vestibular system in the inner ear...
, dizziness
Dizziness
Dizziness refers to an impairment in spatial perception and stability. The term is somewhat imprecise. It can be used to mean vertigo, presyncope, disequilibrium, or a non-specific feeling such as giddiness or foolishness....
or balance
Balance disorder
A balance disorder is a disturbance that causes an individual to feel unsteady, for example when standing or walking. It may be accompanied by feelings of giddiness or wooziness, or having a sensation of movement, spinning, or floating...
dysfunction by testing the vestibular system
Vestibular system
The vestibular system, which contributes to balance in most mammals and to the sense of spatial orientation, is the sensory system that provides the leading contribution about movement and sense of balance. Together with the cochlea, a part of the auditory system, it constitutes the labyrinth of...
.
Technique and Results
The test is performed by attaching electrodes around the nose and measuring the movements of the eye in relation to the ground electrode. The vestibular system monitors the position and movements of the head to stabilize retinal images. This information is integrated with the visual system and spinal afferents in the brain stem to produce the vestibulo-ocular reflexVestibulo-ocular reflex
The vestibulo-ocular reflex is a reflex eye movement that stabilizes images on the retina during head movement by producing an eye movement in the direction opposite to head movement, thus preserving the image on the center of the visual field. For example, when the head moves to the right, the...
(VOR). ENG provides an objective assessment of the oculomotor and vestibular systems. A newer standard for the recording is the use of infrared video systems which allow for a more detailed observation and analysis of these eye movements, called Video Nystagmography. A similar test is performed for testing vertigo by using the caloric reflex test
Caloric reflex test
In medicine, the caloric reflex test is a test of the vestibulo-ocular reflex that involves irrigating cold or warm water or air into the external auditory canal.-Utility:...
, which can be induced by air or water of specific temperatures, typically +/- 7 degrees Celsius from body temperature.
The standard ENG test battery consists of 3 parts:
- oculomotor evaluation
- positioning/positional testing
- caloric stimulation of the vestibular system
The comparison of results obtained from various subtests of ENG assists in determining whether a disorder is central or peripheral. In peripheral vestibular disorders, the side of lesion can be inferred from the results of caloric stimulation and, to some degree, from positional findings.
ENG or VNG can be used to record nystagmus during oculomotor tests such as saccades
Saccade
A saccade is a fast movement of an eye, head or other part of an animal's body or device. It can also be a fast shift in frequency of an emitted signal or other quick change. Saccades are quick, simultaneous movements of both eyes in the same direction...
, pursuit and gaze testing, optokinetics and also calorics (bithermal or monothermal). Abnormal oculomotor test results may indicate either systemic or central
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
pathology as opposed to peripheral
Peripheral nervous system
The peripheral nervous system consists of the nerves and ganglia outside of the brain and spinal cord. The main function of the PNS is to connect the central nervous system to the limbs and organs. Unlike the CNS, the PNS is not protected by the bone of spine and skull, or by the blood–brain...
(vestibular) pathology.
Optokinetics generally are used as a cross check on abnormal responses to oculomotor tests. Both of these tests use a "light bar" involving a moving light (usually red) which the patient will track with their eyes.
The caloric irrigation is the only vestibular test which allow the clinician to test the vestibular organs individually, however, it only tests one of the three semi circular canals - the horizontal canal.
While ENG is the most widely used clinical laboratory test to assess vestibular function, normal ENG test results do not necessarily mean that a patient has typical vestibular function. ENG abnormalities can be useful in the diagnosis and localization of site of lesion; however, many abnormalities are nonlocalizing; therefore, the clinical history and otologic examination of the patient are vital in formulating a diagnosis and treatment plan for a patient presenting with dizziness or vertigo.