An electronystagmography, commonly referred to as an ENG test, is a diagnostic procedure used to evaluate patients experiencing dizziness, vertigo, or issues with balance. It is a standard tool in audiology and neuro-otology, providing objective data about the functionality of the vestibular system. By measuring and recording eye movements, the ENG test helps doctors determine if symptoms are related to a problem in the inner ear or the neurological pathways that control balance. The information gathered is used alongside other clinical findings to pinpoint the source of the patient’s balance disorder.
What Electronystagmography Measures
The ENG test assesses the integrity of the vestibular system, the balance-sensing organ located within the inner ear, and the neural connections that link it to the eyes. This intricate connection, known as the vestibulo-ocular reflex (VOR), is a natural mechanism that stabilizes vision during head movement. The inner ear constantly monitors the head’s position and motion, sending signals to the brainstem to coordinate reflexive eye movements that keep images steady on the retina.
The primary goal of electronystagmography is to detect and record nystagmus, which is an involuntary, rapid, and rhythmic movement of the eyes. The presence of abnormal nystagmus, or a lack of expected nystagmus, suggests a dysfunction. By stimulating the inner ear and measuring the resulting eye movements, the test offers a precise assessment of how well the balance system is operating. This data is crucial for determining if the balance issue originates in the peripheral system (the inner ear) or the central nervous system.
Pre-Test Instructions and Preparation
Preparatory steps are required before an ENG test to ensure the recordings are accurate. It is important to avoid any substances that could suppress or alter your natural eye movements and inner ear responses. Patients are generally instructed to stop taking certain medications, such as sedatives, tranquilizers, and anti-dizziness drugs, for a period of 24 to 48 hours before the appointment. You should always consult with the prescribing physician before discontinuing any medication.
You must fast for a few hours before the test or avoid solid food for at least four hours, as the test can sometimes induce nausea or vomiting. You must also refrain from consuming alcohol and caffeinated products for 24 hours prior to the test. On the day of the test, avoid wearing any face or eye makeup, lotions, or creams, since electrodes need to adhere directly to the skin around the eyes. Comfortable clothing is recommended, and you should arrange for someone to drive you home afterward, as you may feel temporarily dizzy.
How the ENG Test is Performed
The ENG test is a collection of smaller sub-tests that takes approximately 60 to 90 minutes to complete. The procedure begins with the placement of small electrodes, which are metal discs or sticky patches, around the eyes and sometimes on the forehead. These electrodes detect the electrical activity generated by eye movement, allowing the equipment to record the direction, speed, and intensity of the eye movements.
Ocular Motility and Tracking Tests
The first part involves ocular motility or tracking tests, which assess how well the eyes follow visual targets. You will be asked to keep your head still while following a light that moves in different patterns, such as a pendulum swing or a light that jumps between points. This evaluates the function of the nerves and muscles that control voluntary eye movement.
Positional Testing
The next phase is positional testing, where the technician quickly moves your head and body into various positions, such as moving from sitting to lying down with the head turned. This maneuver is designed to provoke nystagmus by stimulating the inner ear’s sensitivity to gravity and head position.
Caloric Test
The final and most distinct component is the caloric test, which stimulates the vestibular system directly using temperature changes. Warm and cool air or water is gently introduced into each ear canal sequentially. The temperature difference creates a convection current within the fluid of the inner ear’s horizontal semicircular canal, artificially generating a temporary feeling of spinning and inducing a measurable nystagmus. This stimulation is the only way to test the function of each inner ear separately and is often the part of the test that causes the brief, expected dizziness.
Understanding Your Test Results
The recorded data from the ENG test is analyzed to identify patterns of eye movement that indicate a problem in the balance system. A typical result shows symmetrical and appropriate responses from both the left and right ears, along with precise eye tracking during the visual tests. The caloric test, in particular, should produce an equal and expected amount of nystagmus when each ear is stimulated with warm and cool temperatures.
An abnormal result often involves asymmetry, meaning one ear responds significantly less than the other during the caloric test, which points to a peripheral vestibular disorder, or inner ear damage, on the weaker side. Other abnormal findings include nystagmus that changes direction or is not suppressed when the patient fixates on a visual target, suggesting a central nervous system issue. The physician reviews these specific patterns of eye movement to gain topographical information, helping to localize the source of the dizziness. The final diagnosis is then made by integrating the ENG findings with the patient’s full medical history and other physical examination results.