Electronystagmography (ENG) is a diagnostic test used to investigate dizziness, vertigo, and balance problems. The test works by recording nystagmus, the involuntary, rhythmic movements of the eyes. This is possible because the inner ear’s balance system is intricately connected to the eye muscles via the vestibular nerve pathway. By measuring the electrical activity generated by eye movements, the ENG provides objective data about the function of the inner ear’s vestibular system. This assessment helps localize whether a balance problem originates in the peripheral system (the inner ear) or the central system (the brain).
Conditions Diagnosed by ENG
Doctors often request an ENG when a patient reports persistent symptoms like vertigo, unexplained lightheadedness, or chronic unsteadiness. The test assesses the functionality of the vestibular apparatus, the sensory organ in the inner ear. The findings help confirm or rule out several inner ear disorders that disrupt balance.
The ENG is frequently used to diagnose Meniere’s disease (fluid buildup in the inner ear) and labyrinthitis (inner ear inflammation). It also evaluates individuals suspected of having Benign Paroxysmal Positional Vertigo (BPPV), which causes intense spinning sensations triggered by specific head movements. Because the vestibular system links to the brain, the test can also help distinguish inner ear issues from certain neurological conditions affecting balance control.
Necessary Preparation Before the Test
Patients must adhere to specific preparation guidelines to ensure accurate ENG results. The most important step involves discontinuing certain medications that can suppress the vestibular system’s natural response. Patients are typically instructed to stop taking vestibular suppressants, tranquilizers, sedatives, and some antihistamines 24 to 72 hours beforehand. Life-sustaining medications, such as those for blood pressure or seizures, should be continued.
Patients must also avoid central nervous system stimulants and depressants, including alcohol and caffeine, for at least 24 to 48 hours before the test, as these interfere with eye movement recordings. To facilitate electrode adherence, patients should not wear facial makeup, creams, or lotions on the day of the procedure. Fasting from solid foods for three to four hours before the test is often recommended to minimize potential nausea, a common side effect of inner ear stimulation.
Steps of the ENG Procedure
The ENG procedure is a battery of tests that objectively measures eye movements in response to controlled stimuli. The process begins with placing small, adhesive electrodes on the skin around the eyes and on the forehead. These electrodes detect and record the electrical changes that occur as the eyes move, tracking and quantifying involuntary eye movements.
Ocular Motor Testing
The first phase involves ocular motor testing, where the patient follows visual targets, such as a moving light or dot, on a screen. These tasks assess the brain’s ability to smoothly track objects and quickly shift gaze, providing baseline information about eye and brain coordination. Specific tests include the saccade test, which measures rapid eye movements, and the smooth pursuit test, which evaluates the ability to track slow-moving targets.
Positional and Positioning Tests
The next components are the positional and positioning tests, designed to provoke nystagmus by changing the patient’s head and body position. The clinician quickly moves the patient from sitting to lying, or turns the head to different sides while observing eye movements. This test is effective for identifying BPPV, where debris in the inner ear causes fleeting vertigo when the head is moved.
Caloric Test
The caloric test directly stimulates the vestibular system of each ear independently. This is performed by gently introducing warm and then cool air or water into the external ear canal. The temperature change creates a convection current in the inner ear fluid, temporarily mimicking a head movement and causing a controlled nystagmus. The resulting eye movements are recorded, and the strength of the response from each ear is compared to identify any imbalance or weakness in the peripheral vestibular system.
Interpreting the Diagnostic Findings
Analysis of the recorded eye movement patterns determines the diagnostic findings. A normal result shows symmetrical responses from both ears during caloric testing and predictable eye movements during visual and positional tests. Abnormal findings are categorized to help determine the location of the problem within the balance system.
For example, unilateral caloric weakness indicates one ear responds significantly less than the other to thermal stimulation, suggesting a peripheral vestibular disorder. Nystagmus patterns help distinguish between inner ear and brain problems. Nystagmus caused by a peripheral issue, like an inner ear lesion, often decreases when the patient focuses their vision. Conversely, nystagmus resulting from a central nervous system disorder is generally not suppressed by visual fixation, sometimes changes direction, and can be vertical. The ENG provides precise evidence that guides the doctor toward an accurate diagnosis and appropriate treatment plan.