You are in: eMedicine Specialties > Otolaryngology and Facial Plastic Surgery > AUDIOLOGY ElectronystagmographyArticle Last Updated: Jan 14, 2008AUTHOR AND EDITOR INFORMATIONSection 1 of 10
  Author: Angela G Shoup, PhD, Director, Assistant Professor, Department of Otolaryngology, Division of Communicative and Vestibular Disorders, University of Texas Southwestern Medical Center Angela G Shoup is a member of the following medical societies: Association for Research in Otolaryngology Coauthor(s): April Liehr Townsley, MA, Faculty Associate/Assistant Director, Department of Otolaryngology-Head and Neck Surgery, Division of Communicative & Vestibular Disorders, University of Texas Southwestern Medical Center Editors: Michael E Hoffer, MD, Co-director of Defense Spatial Orientation Center, Department of Otolaryngology, Naval Medical Center of San Diego; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Gerard J Gianoli, MD, Clinical Associate Professor, Department of Otolaryngology-Head and Neck Surgery, Tulane University School of Medicine; Christopher L Slack, MD, Otolaryngology-Facial Plastic Surgery, Private Practice, Associated Coastal ENT; Medical Director, Treasure Coast Sleep Disorders; Arlen D Meyers, MD, MBA, Professor, Department of Otolaryngology-Head and Neck Surgery, University of Colorado School of Medicine Author and Editor Disclosure Synonyms and related keywords: electronystagmography, ENG, nystagmus, dizziness, vertigo, balance dysfunction, vestibular system, nystagmography, electrooculography, electro-oculography, oculomotor system, peripheral vestibular disorder, central vestibular disorder, videonystagmography, video nystagmography, VNG OVERVIEWSection 2 of 10
  Electronystagmography (ENG) is a study used to clinically evaluate patients with dizziness, vertigo, or balance dysfunction. ENG provides an objective assessment of the oculomotor and vestibular systems. 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 vestibuloocular reflex (VOR). Essentially, the standard ENG test battery consists of the following 3 parts:
Although ENG testing cannot be used to determine the specific site of lesion, the information acquired can be integrated with history, symptoms, and other test results to aid in diagnosis. Comparing results obtained from various subtests of an ENG evaluation 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. An ENG evaluation can also be useful in ruling out potential causes of dizziness. In a large study of patients tested with ENG in a wide range of clinical settings, Stockwell (2000) found abnormal test results in approximately 39% of patients tested, and only about 29% of test results revealed the site of lesion.1 Peripheral vestibular abnormalities were found in approximately 23%, whereas central abnormalities were found in only approximately 5% of patients tested. Although 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 who presents with dizziness or vertigo. EQUIPMENTSection 3 of 10
ENG equipment varies from basic to advanced. Traditional systems use a strip recorder for acquisition of responses. Although some traditional systems may still be in use, most systems currently provide computerized stimulus generation, response acquisition, and interpretation. Stimulus generation Oculomotor stimulus generation was initially accomplished with manually controlled objects. Gaze and saccadic testing used dots placed on the wall and/or ceiling at specified places (ie, 10°, 20°, and 30° in each direction), optokinetic testing was conducted with a rotating drum with stripes of contrasting colors, and smooth pursuit testing was conducted with a swinging pendulum or metronome. Whereas these systems could provide gross evaluation of the various oculomotor subsystems, fine analysis of latency and accuracy of eye movements in response to the stimulus was not possible. Systems with computer-generated stimuli locked to the acquisition of the responses allow for more sophisticated analysis (eg, latency, amplitude). Computerized systems may use light-emitting diodes (LED) on a light bar anchored to the wall or in a self-contained oculomotor stimulator or computer-generated stimuli projected on a screen or video monitor. Response acquisition For response acquisition, the clinician can choose to use only 1 channel to evaluate horizontal eye movements. However, a minimum of 2 channels is recommended; this facilitates evaluation of both horizontal and vertical eye movements. A 3-channel recording system further increases the power of analysis by allowing horizontal recording of each eye and vertical recording of one. Finally, some newer systems provide acquisition of both horizontal and vertical movements of each eye. Electrodes Traditional electronystagmography includes the use of electro-oculography to objectively measure eye movements. This recording is possible because of the corneal-retinal potential difference; the cornea is electropositive relative to the retina. With a fixed recording site, voltage differences can be recorded for eye movements. Electrodes are placed around the patient's eyes to record the corneal-retinal potential differences. By placing electrodes on both a horizontal and vertical axis around the eyes, tracings are produced for eye movements on both axes (see Image 1). Infrared video Increasingly, clinicians are using infrared technology to record eye movements for VNG offers many advantages that make it a preferred method over electrodes. Probably the most important of these advantages is that all eye movements are captured on video and can be viewed by the clinician during and after testing. In addition to capturing horizontal and vertical eye tracings, the clinician is able to visually assess for torsional eye movement by observing the striations of the iris. This is especially important for the diagnosis of benign paroxysmal positional vertigo (BPPV). PATIENT CONSIDERATIONSSection 4 of 10
Vision For the oculomotor portion of the evaluation, patients must have adequate vision to follow targets. Although the oculomotor portion cannot be completed without adequate vision, the rest of the electronystagmography (ENG) and videonystagmography (VNG) test battery can be conducted in patients with limited or absent vision. General physical status If the patient has back or neck injuries, consider positional testing (head hanging) and the Dix-Hallpike maneuver to avoid further complications. The clinician may want to screen for vertebrobasilar insufficiency prior to any positional or positioning test that may constrict the vertebrobasilar artery (ie, head-hanging or Dix-Hallpike maneuvers). This may include having the patient engage in mental tasking (eg, counting, reciting multiplication tables) while gradually tilting the head back and then holding. Change in cognitive status or reports of lightheadedness may be significant. This screening method is especially important for older patients. Status of the outer and middle ear Outer and middle ear status should be confirmed prior to caloric assessment. Presence of drainage in the outer ear canal may affect the results obtained with air caloric stimulation because moisture changes the calibrated temperature, thus limiting interpretation. Pressure equalization tubes or perforation of the tympanic membrane precludes the use of water irrigation. Furthermore, large unilateral perforations limit the interpretation of air caloric irrigations. Large perforations can increase stimulation with cool air above calibrated expectation and can exhibit a cooling effect for warm air as moisture of the middle ear mucosa is evaporated. Excessive cerumen must be removed prior to any caloric stimulation. Middle ear fluid limits the effective stimulation of the vestibular system with air and water. Medications Many medications can affect test results. With physician approval, patients should discontinue all medications, unless contraindicated, for 24-72 hours prior to testing. Any medications taken should be clearly noted on the test results. Alcohol ingestion can affect ENG test results for 72 hours postingestion; results are unpredictable because alcohol can be an agonist or antagonist. History of seizures Oculomotor stimulation with lights may cause seizures. Inform patients that ENG may cause dizziness, nausea, or both. Patients should be advised to limit food intake prior to examination and arrange for transportation after the examination, which usually takes 1-1.5 hours. For many parts of the test, mental tasking is necessary to prevent central suppression of responses. If the examiner does not speak the patient's language or the patient is hearing impaired, an interpreter may be necessary to assist in instructing, explaining, and mental tasking. Patient education ELECTRONYSTAGMOGRAPHY SUBTESTS - OCULOMOTOR EVALUATIONSection 5 of 10
The visual system provides information about whether the environment is stationary or mobile. Stabilization of visual information is accomplished by foveation. The visual system is subserved by the motor system, the premotor system, and the command (control) eye movement system, which controls saccadic eye movements, pursuit, and vergence. Saccades (calibration) The saccade test, also called the calibration test, evaluates the saccadic eye movement system. This system is responsible for rapid eye movements and refixation of the target on the fovea. For saccadic testing, one may place dots on the wall or ceiling at specified distances from each other (usually center and 10°, 20°, and 30° off center) and then instruct the patient to look back and forth between the dots, keeping the head fixed. More current technology allows the examiner to control (via computer) the presentation of pinpoints of light on a light bar, projection screen or in an oculomotor stimulator. This allows randomized presentation of the stimuli and more specific assessment of eye movements. With older technology, a clinician could only visually assess the tracings of eye movements to look for gross deviations from normal. With computer-generated stimuli and analysis, the clinician can assess latency and velocity of eye movements. Interpretation Saccadic test results are influenced by patient cooperation and visual acuity. Various drugs can also affect performance. Accuracy, latency, and velocity should all be taken into consideration when interpreting saccades.
GazeGaze testing is conducted to evaluate for the presence of nystagmus in the absence of vestibular stimulation. In the ENG test battery, essentially 3 types of information are obtained: presence or absence of spontaneous nystagmus (no task or center gaze); presence, absence, or exacerbation of nystagmus with addition of off-center gaze tasks to stress the system; and fixation suppression of spontaneous nystagmus. Administration For gaze testing, the patient is instructed to look straight ahead and then fixate on a target 30° to the right, left, up, and down. Fixation is maintained for approximately 30 seconds in center gaze and 10 seconds in eccentric gaze. The test can be conducted with the same targets placed on the wall or ceiling for calibration or with computer-generated stimuli as mentioned above. For evaluation of spontaneous nystagmus, eliminating any possibility of suppression is important. Fixation suppression can be eliminated by having the patient's eyes open in a dark room with Frenzel lenses or dark goggles used for infrared assessment. With electrode-based systems, spontaneous nystagmus may be evaluated with the patient’s eyes closed. In addition, the patient may be asked to participate in a number of mental tasks (eg, answering questions, counting by multiples of 2). Interpretation
Smooth Pursuit TrackingThe smooth pursuit system is responsible for following targets within the visual field. Tracking can be evaluated horizontally and vertically. As a rule, vertical tracking is not as smooth as horizontal, even in healthy subjects. Care should be taken in interpreting smooth pursuit test results in geriatric and pediatric patients. Tracking is also affected by attention and patient cooperation. Administration The patient is instructed to follow a sinusoidal moving target with his or her eyes only. The target can be a pendulum, metronome, or computer-generated stimulus. Interpretation Tracking test results should resemble a smooth sinusoid. Breakup of movement may indicate CNS pathology. Nystagmus may be seen in tracking test results when also observed in spontaneous (center gaze) recordings. Optokinetic TestingAdministration For optokinetic testing, the patient tracks multiple stimuli. These may take the form of stripes on a rotating drum or a stream of lighted dots across a light bar or the field of an oculomotor stimulator. Some recent devices allow more natural stimulation, such as a full-field array of moving stars or trees. Stimuli are moved at a rate of 300, 400, or 600 per second in each direction. Some clinics use both slow and fast speeds; others test at one intermediate speed only. Interpretation Eye movements that are generated by moving fields resemble nystagmus. The clinician primarily evaluates symmetry of the response. If responses are not symmetrical, CNS pathology may be suspected. Some patients are unable to appropriately complete this task in either direction. ELECTRONYSTAGMOGRAPHY SUBTESTS - POSITIONING AND POSITIONAL TESTINGSection 6 of 10
Dix-Hallpike ManeuverThe Dix-Hallpike maneuver is conducted specifically to assess the presence or absence of nystagmus associated with benign paroxysmal positional vertigo (BPPV). When test results are classically positive (see Interpretation), canalith repositioning and vestibular rehabilitation therapy may be indicated. Administration
Positional TestsAdministrationThe examiner places the patient in each position and evaluates him or her for a minimum of 20-30 seconds. Mental tasking is used to keep the patient from suppressing nystagmus. Visual suppression must also be avoided by the use of infrared goggles or with the patient’s eyes closed with electrodes. Some standard positions used include the following:
Many clinics do not assess in the lateral right and left positions unless nystagmus is observed in the supine position with the head to the right or left. The lateral right and left positions are used to rule out neck rotation as a cause for nystagmus. ELECTRONYSTAGMOGRAPHY SUBTESTS - CALORIC STIMULATIONSection 7 of 10
Caloric StimulationCaloric stimulation of the vestibular system offers an assessment of the lateral semicircular canal. This is a valuable tool because it allows for the objective measurement of function from each labyrinth individually. This test is considered nonphysiologic since isolating and stimulating one labyrinth at a time in nature is physiologically impossible. The equivalent speed of stimulation for this test is a very low frequency. Although this is a limiting factor in diagnosis, other tests of vestibular function at higher frequencies are currently not readily available in most clinical settings. Vestibular stimulators include water, air, and closed-loop cuff; water and air are commonly used. Water caloric irrigations provide a strong stimulus but cannot be used with patients with pressure equalization tubes or perforation of the tympanic membrane. Use of water as a stimulus should also be avoided in patients whose immune systems are compromised. Administration The patient is placed in a reclining position with his or her head at a 30° angle. This position orients the lateral semicircular canals in the most vertical plane. Before recording responses to caloric stimulation, spontaneous nystagmus is evaluated in this position. Caloric stimulation can be accomplished with an alternating binaural bithermal, simultaneous binaural bithermal, or monothermal protocol. Simultaneous binaural bithermal protocols are not traditionally used clinically; thus, alternating binaural bithermal and monothermal protocols are discussed here. In patients with responsive vestibular systems, caloric irrigation produces nystagmus in a predictable manner.
For a comparison of responses between ears, the test must be performed in exactly the same manner for each ear. Careful otoscopic examination allows the stimulus to be directed appropriately and at an equivalent depth in each ear canal. Furthermore, when using electrodes, recalibration is recommended prior to each irrigation to account for variations in corneal-retinal potential.2
Interpretation In the normal vestibular system, adequate, equivalent responses should be obtained from each ear. A normal caloric response does not rule out a vestibular pathology, however, since this test only measures a response from part of the labyrinth at a very low frequency of stimulation. Slow phase velocity is determined for each recording for use in the following calculations:
A negative number indicates a right unilateral weakness, and a positive number indicates a left unilateral weakness. Unilateral weakness is indicative of a peripheral vestibular lesion that involves the nerve or end-organ on the side of the weakness.
Fixation SuppressionAfter each caloric stimulus, the patient is instructed to fixate on a light or other stationary target. Fixation should normally eliminate or greatly reduce the induced nystagmus. If visual fixation does not inhibit nystagmus, central pathology at the level of the brain stem is indicated. The clinician must ensure that fixation suppression testing is completed as soon as the peak nystagmus response has been recorded. Fixation suppression testing is not accurate if the clinician waits to introduce the stimulus until the response has naturally decayed. Interpretation Compute the fixation index (FI): An FI of 0.60 or greater is considered significant. SPECIAL APPLICATIONSSection 8 of 10
Pressure Fistula TestSome patients have vertigo caused by a perilymph fistula. Fistula testing can be conducted with electronystagmography (ENG) to determine which patients are likely to benefit from perilymph fistula repair surgery.3 Administration The patient is placed in an upright position. While the patient is involved in mental tasks, recordings are conducted with his or her eyes open in the dark (wearing infrared goggles) or with eyes closed with electrodes. The presence or absence of spontaneous nystagmus is noted. Next, a probe from an immittance bridge is placed in the ear canal, and a seal is obtained. Pressure is then varied from 0-200 mm H2O and held for approximately 15 seconds. Pressure is then decreased to -400 mm H2O and held for 15 seconds. The patient is questioned for subjective symptoms. Interpretation The presence of a fistula is confirmed if the pressure causes nystagmus. Tullio PhenomenonThis is not as routinely used as pressure fistula testing, but the Tullio phenomenon is an option for patients on whom a hermetic seal cannot be obtained. Administration Follow the procedure for a pressure fistula test, but instead of varying the air pressure, present a 500-Hz tone at 95 dB for no longer than 3 seconds. Monitor eye movements and ask the patient about his or her subjective experience. Interpretation Results of Tullio phenomenon testing are positive if nystagmus is observed. Head-Shake Nystagmus TestThe head-shake nystagmus (HSN) test is most useful in the assessment of vestibular disorders that produce asymmetries in vestibular function. Administration The patient is placed in an upright sitting position with his or her head tilted forward 30°. The examiner rotates the head back and forth (45° to either side), completing 30 full cycles at a frequency of about 2 cycles per second. If nystagmus is observed following head rotation, eye movements should be recorded for at least one minute. Interpretation Nystagmus produced following the head rotation is considered significant if at least 5 consecutive beats of at least 2° per second are observed. HSN is described by the following classifications:
A positive finding of HSN is highly suggestive of an underlying vestibular pathology. A negative HSN test result does not rule out a vestibular pathology. HSN usually beats away from the side of a peripheral lesion; however, since this is not the rule, HSN should be used in conjunction with other vestibular tests in determining the side of the lesion. Cross-coupled HSN is suggestive of CNS pathology. Vibration-Induced NystagmusNystagmus may be induced in patients by stimulating the head and/or neck with vibrations. Vibration-induced nystagmus (VIN) may be useful in the diagnostic confirmation of unilateral lesions. Administration The patient is placed in an upright sitting position, and a vibrator is applied to the mastoid. Eye movements are recorded in the dark while a vibratory stimulus of 100 Hz is presented to the mastoid. Recordings should be obtained separately for the right and left mastoid. Vibratory stimulation may likewise be presented to the sternocleidomastoid muscles to induce VIN. The VIN test should be considered with caution if the patient has any history of a detached retina. Interpretation A positive finding of vibration-induced nystagmus occurs when nystagmus appears during vibratory stimulation and disappears when the stimulation terminates. The nystagmus may have several components but is predominantly horizontal. Healthy subjects have reportedly displayed up to 1.5°/second VIN with mastoid stimulation.4 In patients with a unilateral lesion, the VIN most often beats in the direction of the nonaffected side. The exception to this is Ménière Disease, in which the VIN may beat in either direction.5 MULTIMEDIASection 9 of 10
REFERENCESSection 10 of 10
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