Videonystagmography (VNG) is a diagnostic tool used to evaluate the function of the vestibular system, the balance-sensing apparatus located in the inner ear and brain. This non-invasive test measures nystagmus, which is an involuntary eye movement that occurs when the inner ear and central nervous system are not communicating effectively. The VNG uses specialized goggles equipped with infrared cameras to record these eye movements while the patient performs various activities. Documenting how the eyes react to different stimuli provides an objective assessment of the sensory signals that maintain spatial orientation and equilibrium.
Symptoms and Conditions Diagnosed by VNG
Patients are referred for a VNG evaluation when they experience persistent symptoms related to a balance disturbance, signaling an issue with the vestibular system. Common symptoms prompting this test include chronic dizziness, vertigo (the sensation of spinning or whirling), and unsteadiness. These symptoms significantly impact daily life and increase the risk of falls.
The VNG helps clinicians differentiate between peripheral vestibular disorders, which originate in the inner ear, and central disorders, which stem from issues in the brainstem or cerebellum. Peripheral conditions VNG helps diagnose include Benign Paroxysmal Positional Vertigo (BPPV), Meniere’s disease, and inflammatory conditions like labyrinthitis or vestibular neuritis.
The results can also point toward central neurological disorders that disrupt balance processing. Conditions like multiple sclerosis, certain types of stroke, or tumors that affect the brain’s balance centers may be suggested by specific patterns of nystagmus observed during testing. Identifying the source of the imbalance is the first step toward developing a targeted treatment plan.
The Three Stages of the VNG Procedure
The VNG procedure is divided into three sections, testing different aspects of the vestibulo-ocular reflex (VOR), the mechanism that stabilizes vision during head movement. The entire test typically lasts 60 to 90 minutes, during which the patient wears infrared goggles that track and record eye movements. The first segment is Ocular Mobility Testing, which assesses the brain’s ability to control and coordinate eye movements using visual targets.
Ocular Mobility Testing
During this test, the patient follows lights or dots projected onto a screen, evaluating three specific eye movements: saccades, smooth pursuit, and optokinetic nystagmus. Saccades are the rapid jumps the eyes make when shifting focus between stationary targets. Smooth pursuit measures the eyes’ ability to track a slow-moving target. The optokinetic test involves viewing a full-field moving pattern to assess how the visual system integrates with the balance system. Abnormalities here suggest a problem with the central nervous system’s control over eye movements.
Positional Testing
The second stage is Positional Testing, which involves moving the patient’s head and body into various positions to see if gravity changes provoke nystagmus. The provider guides the patient from sitting to lying down, often turning the head right and left. This maneuvering is sensitive in identifying positional vertigo, which is caused by displaced otoconia (calcium carbonate crystals) within the inner ear’s semicircular canals. Observing the direction, intensity, and duration of the resulting nystagmus helps localize the affected canal.
Caloric Testing
The final component is Caloric Testing, the only part of the VNG that tests each inner ear independently. This involves introducing small amounts of warm and then cool air or water into the ear canal, one ear at a time. The temperature change creates a convection current within the fluid of the horizontal semicircular canal, temporarily simulating head movement and stimulating the vestibular nerve. This stimulation induces a brief period of nystagmus and potentially mild dizziness, which is recorded. Comparing the eye response between the warm and cool stimuli, and between the left and right ears, identifies a unilateral weakness or loss of function in one inner ear.
Preparing for the Test and Understanding the Results
Proper preparation ensures VNG results accurately reflect balance system function without interference. Patients must avoid sedatives, tranquilizers, and anti-vertigo medications, such as meclizine, for at least 48 hours before the test. These drugs suppress the eye movements the test measures. Caffeine and alcohol should also be avoided for 24 to 48 hours prior, as they can affect the central nervous system and alter findings.
Patients should refrain from eating solid foods for approximately four hours before the procedure, though a light, bland meal is permitted. This precaution is necessary because caloric stimulation and positional changes can induce temporary nausea or dizziness. Furthermore, no eye makeup, including mascara and eyeliner, should be worn, and false eyelashes must be removed. The infrared camera relies on clear visualization of the pupil to track movements.
Interpreting VNG results centers on analyzing the recorded nystagmus for its direction, intensity, and suppression by visual fixation. If abnormal eye movements are present only under specific positional changes and are suppressed by visual fixation, this suggests a peripheral lesion localized to the inner ear. Conversely, if the nystagmus is vertical or persists even with visual fixation, this points toward a central balance disorder originating in the brain. The final report provides an objective assessment of vestibular function, guiding the healthcare provider toward a definitive diagnosis and appropriate therapeutic intervention.