A vestibular test is a comprehensive, non-invasive assessment used to evaluate the function of the balance system, which is centered within the inner ear and its associated neural pathways to the brain. It objectively measures how well the body maintains spatial orientation and stability. The goal is to pinpoint the source of balance-related symptoms, determining whether the issue originates in the peripheral structures of the inner ear or the central processing areas of the brain. The evaluation provides specific data that helps formulate an accurate diagnosis and an effective treatment plan.
The Role of the Vestibular System
The vestibular system is a sensory apparatus housed within the bony labyrinth of the inner ear, working closely with visual input and proprioception. This integrated system allows for spatial awareness and helps maintain postural equilibrium. Within the inner ear are two main types of organs: the semicircular canals and the otolith organs.
The three semicircular canals, oriented at right angles, detect rotational movements of the head, such as nodding or tilting, by monitoring the flow of fluid within them. The otolith organs (the utricle and the saccule) detect linear motion and the pull of gravity. The utricle senses horizontal movements, while the saccule monitors vertical movements.
Signals from these organs travel along the vestibular nerve to the brainstem, where they are integrated with information from the eyes and muscles. One immediate function of this pathway is the vestibulo-ocular reflex, which automatically adjusts eye position to stabilize vision during head movement. A disruption anywhere in this complex network can result in a loss of balance control.
Symptoms That Require Testing
A doctor typically orders vestibular testing when a patient experiences persistent symptoms related to balance and motion perception. The most common complaint is vertigo, a sensation of spinning or whirling even when the person is still. This differs from general dizziness, which is a broader term encompassing lightheadedness or faintness.
Patients may also report chronic imbalance or unsteadiness, increasing the risk of unexplained falls. Another specific symptom is oscillopsia, the sensation that stationary objects are bouncing or moving during head motion. These symptoms indicate a breakdown in the system’s ability to correctly sense and process movement.
Overview of Common Diagnostic Procedures
The evaluation of the vestibular system involves a battery of tests, each targeting a different part of the balance mechanism. This approach ensures that both inner ear structures and central neural pathways are thoroughly assessed. Most common tests focus on recording eye movements due to the direct connection between the inner ear and eye muscles via the vestibulo-ocular reflex.
Videonystagmography (VNG)
Videonystagmography (VNG) is a primary diagnostic tool that measures involuntary eye movements, known as nystagmus, using infrared video goggles. The test includes several sections that assess different aspects of the balance system. Ocular-motor testing evaluates how accurately the eyes track moving lights or targets, primarily checking the central nervous system’s control of eye movement.
Positional testing involves moving the patient’s head and body into various positions to see if these maneuvers provoke nystagmus, which can indicate inner ear issues. Caloric testing is the final part, where warm and cool air or water is gently introduced into the ear canal. This temperature change stimulates each horizontal semicircular canal separately, allowing comparison of the function of the left and right inner ears.
Rotary Chair Testing
The rotary chair test places the patient in a motorized chair within a dark enclosure, with eye movements still monitored by infrared goggles. The chair rotates at controlled speeds and frequencies, stimulating the semicircular canals of both inner ears simultaneously. This procedure is especially valuable for assessing the function of the vestibulo-ocular reflex across a range of motion.
The test measures how the eyes respond to the chair’s rotation, providing data on the gain, phase, and symmetry of the response. The results are important for diagnosing conditions that affect both inner ears equally, which may not be evident from caloric testing alone. The precise, computer-controlled movement makes it a reliable measure of the overall system response.
Vestibular Evoked Myogenic Potentials (VEMPs)
Vestibular Evoked Myogenic Potentials are electrophysiological tests that specifically assess the function of the otolith organs—the saccule and utricle. The test uses loud clicking sounds delivered to the ear through headphones to stimulate these gravity-sensing organs. The resulting muscle responses are recorded by electrodes placed on the neck or below the eyes.
Cervical VEMPs (c-VEMPs) record a response from the sternocleidomastoid muscle in the neck, primarily reflecting saccule function. Ocular VEMPs (o-VEMPs) record a response from muscles beneath the eyes, primarily reflecting utricle function. These specialized tests provide unique, ear-specific information about the parts of the inner ear that detect linear acceleration.
Computerized Dynamic Posturography
Computerized Dynamic Posturography (CDP) is a functional test that measures a person’s ability to maintain balance while standing on a specialized platform. The platform records the small movements of the body’s center of pressure, known as sway. The most common procedure, the Sensory Organization Test, systematically alters the reliability of the three sensory inputs for balance: vision, vestibular input, and somatosensory input (touch and pressure from the feet).
The test platform and a surrounding visual screen may move independently, forcing the patient to rely on different senses to stay upright. CDP does not localize a specific lesion but quantifies how effectively the patient uses and integrates sensory information to control posture. This helps identify which sensory channel the patient is over-relying on or is unable to use effectively.
Patient Preparation and Expectations
Proper preparation is important for ensuring accurate vestibular test results. Patients are usually instructed to discontinue certain medications for 24 to 48 hours before the appointment. These typically include anti-vertigo drugs, sedatives, tranquilizers, and some antihistamines, as these substances can suppress the natural reflexes the tests are designed to measure.
It is recommended to fast from solid foods for a few hours before the test and to avoid stimulants like caffeine and alcohol. Since eye tracking is important, patients are asked to arrive without eye makeup, especially mascara. Because some procedures can temporarily induce mild dizziness or nausea, patients are advised to arrange for transportation home following the assessment.
Interpreting Test Findings
Interpreting the findings involves a pattern analysis, combining data from all procedures to determine the location and nature of the dysfunction. The results help differentiate between a peripheral vestibular disorder and a central vestibular disorder. Peripheral issues, involving the inner ear and vestibular nerve, often result in nystagmus that beats in a single direction and is suppressed by visual fixation.
Conversely, central disorders, which affect the brainstem or cerebellum, may be indicated by nystagmus that changes direction with the direction of gaze, or is purely vertical. For instance, a unilateral weakness revealed by caloric testing points toward a peripheral problem in a single ear. Abnormal VNG results combined with abnormal pursuit or saccade tests often suggest a central processing issue. The findings guide appropriate management, which may involve vestibular physical therapy, medication, or further neurological evaluation.