Electronystagmography

Definition

Electronystagmography (ENG) is a diagnostic test measures eye movements and isused for individuals who exhibit symptoms of dizziness, balance problems, or vertigo.

Purpose

The ENG test performs balance measurements on the muscles that control eye movements.(Balance to the body is provided by the inner ear, brain, brainstem, eyes, and sensory nerves.) The ENG, which has been performed since the 1940s, provides an assessment of the vestibular and oculomotor systems. The vestibular system monitors the head's movements and positions while stabilizing visual images. The oculomotor system controls the fixation of the eye along with its horizontal, rotational, and vertical movements.

The ENG test is used to determine whether or not structural nerve damage within the inner ears is the cause of dizziness or vertigo. Assessment of the eyes is performed because damage to the vestibular portion of the acoustic nerve is a frequent cause of vertigo. The ENG may be recommended when a person is experiencing dizziness or vertigo but may also be suggested when the patient complains of diminished hearing and, in other cases, when the doctor suspects an adverse antibiotic reaction or determines a psychological underpinning. The test provides precise measurements of eye movements when the eyelids are closed or open, and in combination with the head and body in various positions.

Precautions

Although ENG is a widely used clinical laboratory test to assess vestibular function, a negative (normal) reading does not always indicate that a patient has normal function. Therefore, in addition to the ENG, a complete clinical history and otologic examination of the patient should be performed (including a hearing test) in order to establish a diagnosis and treatment plan. The patient should be aware that minor discomfort such as dizziness might be felt during the test. Some patients taking the caloric test find that cool or warm water in their ears to be uncomfortable. Patients with back or neck problems need to be identified before application of some components of this test.

Description

The ENG procedure consists of seven tests in three parts: (1) oculomotor evaluation, (2) positional testing, and (3) caloric stimulation of the vestibular system. The complete battery takes from 1.0 to 1.5 hours. For the first two parts, small recording electrodes are placed (generally with tape, paste, or headband) to the side, above, and below each eye. A ground electrode is attached on the forehead. These electrodes are able to record eye movements due to the voltage differences between retina and cornea, so that as the eyes move, the voltage change is picked up by the electrodes.

Eye movements are recorded during the following seven tests.

• Gaze: Patient looks straight ahead, to the left and right, up and down, and with eyes open and closed (physician searches for the presence of nystagmus under each condition);
• Saccades: Patient looks back and forth between two horizontal points (physician searches for defects of saccadic eye movement);
• Pendular Tracking: Patient follows a slowly moving target (physician looks for defects of smooth pursuit eye movement);
• Optokinetic: Patient watches vertical stripes or a light moving horizontally at several different speeds (physician determines whether nystagmus has different intensities as the stimulus speed and direction chances);
• Positional: Patient with eyes both open and, then, both closed, is placed in various positions while eyes move (physician looks for presence of nystagmus in any position);
• Dix-Hallpike: Patient is moved by the clinician rapidly from sitting to the head hanging position (physician looks for nystagmus following each movement); and
• Caloric: Patient s ears are irrigated twice, once with air or water that is above body temperature and once below body temperature (physician determines whether the sensitivities of the right and left vestibular mechanisms are equal).

Preparation

There are no preparations necessary for the ENG test. The patient should provide information about any medications that are being taken. Any medicines for anti-depression or anti-dizziness should be temporarily stopped, along with any antihistamines, for a period of 72 hours before the test. Alcohol should not be consumed prior to the test. Women should not wear facial makeup so that electrodes can be applied. The patient should not eat heavily before the test. The caloric test should not be taken if the eardrum has been perforated because risk from ear infection is possible.

Aftercare

There is no aftercare necessary for the ENG test.

Complications

There is little risk associated with the caloric test. Excessive water pressure can injure, but only rarely, an already damaged eardrum. The caloric test may produce unreliable or difficult to interpret results because pouring warm or cold water into the ear can cause the patient to react unexpectedly.

Results

The results of the ENG helps in determining whether a disorder is central (of the brain) or peripheral (of the inner ear).

If a negative (normal) result is received, then eye movements are smooth and precise while tracking a moving object. If a positive (abnormal) result is received, then indistinct (not smooth and precise) involuntary eye movements have occurred.

In the caloric test, a negative result shows normal direction and intensity. Vertigo may be detected. With a positive result, there is a lack of response or a diminished response. No vertigo is detected, or less than expected.

With abnormal conclusions, damage to the nerves of the inner ear may have earlier resulted. Diseases or injuries such as atherosclerosis of the ear's blood supply, clots, congenital disorders, toxic medications, poisons, rubella, trauma, or tumors, may have caused the damage.

Health care team roles

An audiologist performs the ENG test and the test results are interpreted by an ENG specialist.

KEY TERMS

Acoustic nerve— Nerve within the inner ear that supplies hearing and assists with balance.

Otologic— Study and treatment of the ears.

Saccadic— Rapid, irregular eye movements as it changes focus from one point to another point.

Vestibular— Relating to the middle cavity of the inner ear.

Resources

BOOKS

Malarkey, Louise M., and Mary Ellen McMorrow. Saunders Nurse's Guide to Laboratory and Diagnostic Tests. Philadelphia, PA: W.B. Saunders Co.

Shtasel, Philip. Medical Tests and Diagnostic Procedures: A Patient's Guide to Just What the Doctor Ordered. New York, NY: HarperPerennial.

OTHER

"Electronystagmography." AllRefer.com, A.D.A.M., Inc., American Accreditation HealthCare Commission. 〈http://health.allrefer.com/health/electronystagmography-info.html〉 (accessed November 16, 2005).

"Electronystagmography." eMedicine. 〈http://www.emedicine.com/aboutus.shtml〉 (accessed November 16, 2005).

"Electronystagmography." University of Maryland Medical Center. 〈http://www.umm.edu/ency/article/003448.htm〉 (accessed November 16, 2005).

"Electronystagmography: Clinical Application and Determination." Craig W. Johnson, Au.D., Audiology Associates, Ltd. 〈http://www.aaiaudiology.com/engcj.ppt〉 (accessed November 16, 2005).

"Vestibular Testing." American Hearing Research Foundation. 〈http://www.american-hearing.org/name/vestibular_testing.html〉 (accessed November 16, 2005).