Electronystagmography (ENG) is a diagnostic tool used to assess the vestibular system, the body’s balance mechanism located primarily in the inner ear. It measures the electrical activity generated by eye movements, which are connected to the inner ear and brain through the vestibulo-ocular reflex. This reflex automatically adjusts eye position to stabilize vision during head movement, and the ENG test evaluates how effectively this system is working. The test provides objective data that helps physicians pinpoint the source of symptoms, determining whether a balance problem originates in the inner ear or the brain.
The Purpose and Indicators
A doctor typically orders an ENG test when a patient reports persistent or unexplained symptoms such as vertigo, general dizziness, or chronic imbalance. Vertigo, the false sensation of spinning or motion, is a strong indicator for this evaluation. Sudden or unexplained hearing loss, especially when accompanied by balance disturbances, can also prompt a physician to recommend the test.
The main goal of the procedure is to determine the location of the dysfunction. The results help differentiate between a peripheral vestibular disorder, which involves the inner ear structures like the semicircular canals, and a central vestibular disorder, which relates to the brainstem or cerebellum. This distinction is important because treatment strategies for inner ear conditions like Meniere’s disease or labyrinthitis differ significantly from those for central nervous system issues. By analyzing the patterns of involuntary eye movements, the test offers a window into the health of the nerves connecting the ear and brain.
Understanding the Procedure
The ENG procedure records eye movements, or nystagmus, using small electrodes placed on the skin around the eyes. These electrodes detect the corneo-retinal potential, the electrical charge difference between the front and back of the eyeball, translating eye movements into measurable tracings.
The test begins with oculomotor evaluation, where the patient performs visual tasks, such as following a light that moves back and forth or tracking a light quickly across the field of vision. These tracking tests assess how well the eyes and the brain’s control centers work together to keep gaze steady.
A subsequent component is positional testing, which involves moving the head and body into specific positions, such as lying down quickly or turning the head while seated. This assesses the balance system’s response to changes in gravity and body orientation, looking for nystagmus that is only triggered by certain head positions.
The final and most definitive part is the caloric test, where warm and cool air or water is introduced into each ear canal separately. This temperature change stimulates the horizontal semicircular canal in the inner ear, inducing a temporary, measurable nystagmus by creating a convection current in the fluid within the inner ear.
The caloric test provides specific information about the function of each inner ear independently. A healthy inner ear produces a predictable eye movement response; the absence or significantly weaker response from one ear indicates weakness in that ear’s vestibular nerve function. This allows the physician to identify if one side of the peripheral balance system is under-performing.
Preparing for the Test and Expected Sensations
Proper preparation ensures accurate results, and patients are instructed to avoid certain substances for 24 to 48 hours before the test. This includes abstaining from alcohol and caffeine, as these can interfere with the body’s vestibular and eye responses. Patients are also usually asked to stop taking specific medications, such as sedatives, tranquilizers, and anti-vertigo drugs, but they must consult with their doctor before discontinuing any prescribed medicine.
Patients should arrive without eye makeup, as the electrodes need to adhere directly to the skin around the eyes. Because the test can intentionally trigger dizziness and nausea, doctors recommend eating only a light meal or fasting beforehand.
During the caloric phase, the patient will experience a brief, intense sensation of spinning or dizziness, which is a normal and expected reaction as the inner ear is stimulated. This sensation is temporary, and a technician monitors the patient closely throughout the procedure to manage any discomfort.
Interpreting the Outcomes
The data collected during the ENG test is recorded as a series of tracings representing the involuntary eye movements. A specialized healthcare professional, typically an audiologist, analyzes these tracings for abnormalities in the frequency, direction, and intensity of the nystagmus. A normal result demonstrates symmetrical eye responses to the stimuli, showing that the vestibular system is functioning correctly on both sides.
Abnormal results may indicate a problem with the inner ear or the central nervous system pathways. For example, a significant difference in the response between the two ears during the caloric test, known as canal paresis, strongly suggests a peripheral issue in the weaker inner ear. Conversely, abnormal eye movement patterns during the tracking or gaze tests, where the eyes fail to fixate or track smoothly, can point toward a central nervous system problem. By comparing the results from the oculomotor, positional, and caloric subtests, the physician can diagnose the underlying cause of the patient’s dizziness, such as Benign Paroxysmal Positional Vertigo (BPPV) or a more complex neurological disorder.