A vestibular test is a noninvasive diagnostic tool used to investigate the root cause of balance problems, dizziness, and vertigo. These symptoms, which feel unpleasant and disruptive, are often signals that the body’s complex spatial orientation system is not working correctly. Healthcare providers use a battery of specialized tests to determine if the issue originates in the inner ear or the brain, which is the first step toward finding an effective treatment.
Understanding the Vestibular System
The vestibular system is a sensory apparatus located within the inner ear. It is composed of five organs: three fluid-filled semicircular canals and two otolith organs, the saccule and the utricle. The semicircular canals detect rotational movements, such as turning the head side-to-side.
The otolith organs detect linear acceleration and the pull of gravity, informing the brain about the head’s position relative to the ground. This system sends signals to the brainstem and cerebellum, which coordinate with the visual system and proprioception (the sense of where the body is in space). This coordination maintains balance and clear vision during movement, and a malfunction can lead to dizziness or vertigo.
Components of a Vestibular Evaluation
A complete vestibular evaluation is a collection of distinct tests designed to check different parts of the balance system. These tests objectively measure the vestibulo-ocular reflex (VOR), the automatic mechanism that stabilizes the eyes when the head moves. The most common component is Videonystagmography (VNG), which uses infrared video goggles to record and analyze involuntary eye movements, known as nystagmus.
The VNG test includes several parts. Oculomotor testing involves the patient following moving lights on a screen, while positional testing moves the head and body into specific positions to check for positional vertigo. Caloric testing involves introducing warm or cool air or water into the ear canal to stimulate the semicircular canals. This stimulation creates a temporary temperature difference between the two inner ears, causing a predictable eye movement response that allows doctors to compare the function of the left and right inner ears.
Another common procedure is Vestibular Evoked Myogenic Potential (VEMP) testing, which assesses the function of the saccule and utricle. Electrodes are placed on the neck and facial muscles to record a reflex response generated when a loud sound or vibration is delivered to the ear. The response measured in the neck is the cervical VEMP (cVEMP), which evaluates the saccule, while the response measured near the eye is the ocular VEMP (oVEMP), which evaluates the utricle.
Computerized Dynamic Posturography (CDP) is a functional test that measures the patient’s ability to maintain balance while standing on a specialized platform. The test manipulates the sensory information available—vision, proprioception, and vestibular input—to determine which system the patient is relying on or struggling with. The patient is secured in a safety harness while the platform surface and visual surroundings move, forcing the balance system to adapt to various conditions.
Preparation and Procedure Timeline
Certain substances can interfere with vestibular test results by suppressing the reflexes being measured. Patients must avoid the following before the evaluation:
- Alcohol, sedatives, and anti-dizziness medications for 24 to 48 hours.
- Caffeine and nicotine for several hours leading up to the appointment.
Patients should arrive with clean skin, avoiding facial or eye makeup, especially mascara, as it can interfere with the infrared camera used in the VNG goggles. It is recommended to have a light meal beforehand, as the caloric and positional portions of the test can cause brief nausea or temporary dizziness. The entire battery of vestibular tests takes between 90 minutes and two hours to complete.
Interpreting the Test Results
The results of the vestibular test battery help clinicians isolate the location and nature of the balance disorder. For instance, weakness in the caloric portion of the VNG test, which assesses the horizontal semicircular canal, suggests a problem in the peripheral vestibular system of that specific ear. This finding, especially when combined with a normal VEMP result, is seen in conditions like Vestibular Neuritis or Labyrinthitis.
Abnormalities in the VEMP test, which reflect otolith organ function, can point toward specific diagnoses like Ménière’s Disease or Superior Semicircular Canal Dehiscence. Ménière’s Disease, characterized by episodic vertigo and hearing changes, often shows a significant asymmetry in VEMP responses, indicating a difference in inner ear fluid pressure. A positive finding during the positional testing component of the VNG is a strong indicator of Benign Paroxysmal Positional Vertigo (BPPV), which is caused by dislodged crystals in the inner ear canals.