Videonystagmography (VNG) is a non-invasive diagnostic procedure that evaluates the balance system, including the inner ear and the brain. It records eye movements to assess the vestibular system, which maintains balance, motion, and spatial orientation. This test helps identify potential issues contributing to balance problems.
Why a VNG Test is Performed
Healthcare providers recommend a VNG test for symptoms like unexplained dizziness, vertigo, or balance issues. Vertigo often presents as a sensation of spinning, either of oneself or the surroundings.
The VNG test helps determine if balance problems stem from the inner ear, known as a peripheral vestibular disorder, or from the brain and central nervous system. Identifying the origin of the problem is important for guiding further diagnostic steps and treatment plans.
Components of a VNG Test
A VNG test involves several components, each designed to assess different aspects of the balance system. Patients wear specialized goggles with infrared cameras that record eye movements. These recordings capture involuntary eye movements, known as nystagmus, which can indicate vestibular dysfunction.
Oculomotor testing evaluates how well the eyes track visual targets. This involves following moving lights or dots on a screen, assessing eye movements like saccades (rapid eye movements), smooth pursuit (tracking slow-moving objects), and optokinetic nystagmus. Positional testing moves the patient’s head and body into various positions. This helps identify if specific head or body positions provoke nystagmus, which can be associated with certain inner ear conditions.
The caloric test is the final part of the VNG, measuring ear-specific peripheral vestibular function. Warm and cool air or water are gently introduced into each ear canal, one at a time. This stimulation causes a temporary temperature change in the inner ear, provoking eye movements that are recorded and analyzed.
Understanding VNG Test Results
VNG test results reveal specific eye movement abnormalities that help pinpoint the nature and location of a balance disorder. Abnormalities detected during oculomotor testing, such as irregular saccades or impaired smooth pursuit, often suggest issues within the central nervous system or brain. For example, an inability to smoothly track a moving target could indicate a central neurological problem.
Findings from positional testing are useful for diagnosing conditions like benign paroxysmal positional vertigo (BPPV). In BPPV, specific head movements trigger brief episodes of vertigo and a characteristic nystagmus. The direction and duration of this nystagmus can help identify which inner ear canal is affected.
Caloric testing helps assess the function of each inner ear independently. A significant difference in eye responses between the two ears, typically more than 20-25%, can indicate a weakness or dysfunction in one inner ear. This unilateral weakness may be seen in conditions such as vestibular neuritis. The VNG test helps differentiate between problems originating in the inner ear (peripheral) and the brain (central).
Preparing for Your VNG Test
Proper preparation for a VNG test helps ensure accurate results. Patients are advised to avoid certain medications for 24 to 48 hours before the test. These can include anti-vertigo drugs, sedatives, tranquilizers, and some over-the-counter medications like antihistamines, as they can influence test responses. It is important to discuss all current medications with the healthcare provider before discontinuing any prescribed drugs.
Patients should refrain from consuming caffeine and alcohol for at least 24 to 48 hours prior to the test. Eating lightly is recommended, typically avoiding solid foods for 2 to 4 hours before the appointment. Wear comfortable clothing and avoid eye makeup, as it can interfere with the infrared cameras in the goggles. Some individuals may experience temporary dizziness after the test, so arranging for someone to drive them home is suggested.