Introduction
Vestibular function tests or vestibular testing are a series of tests used to evaluate hearing function. The primary goal of these tests is to determine any harm or damage to the vestibular portion of the inner ear. This portion of the ear controls the balance of the body. These tests are usually ordered when a patient experiences symptoms such as dizziness (feeling fainting or head spinning), vertigo (sensation of everything around is moving or spinning), or a feeling off balance. The tests will help in determining whether the symptoms experienced by the patient are due to an inner ear problem or a neurological problem.
What Is the Vestibular System?
The vestibular system is located in the inner ear. It is laterally bordered by the middle ear and medially to the temporal bone. There are three components of this system, which include:
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Peripheral apparatus.
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Central processors.
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Motor output.
The body requires three sensory systems to work together to feel the body balanced, which include - vision (sight), proprioception (touch), and vestibular (inner ear). The information from the vestibular system with other sensory inputs, such as vision and proprioception, helps coordinate the movements between the eyes and head and provides information to the brain about postural orientation.
The vestibular system in each ear consists of:
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Three semicircular canals (head rotation sensors).
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Two otolith organs (gravity sensors).
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Vestibular nerve.
The three sensory systems work together to assist the body in -
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Standing upright.
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Prevent falls.
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Walk gracefully.
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Let the eyes follow moving objects.
The vestibular system aims to keep a focused and stable vision while the head and body move. This is possible because of a response called vestibulo-ocular reflex (VOR). The vestibular test evaluates the function of vestibulo-ocular reflex response.
What Are the Causes of Dizziness, Vertigo, and Body Imbalance?
The symptoms of dizziness, vertigo, and imbalance have different causes, and the reason behind them can be associated with the following:
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Inner ear.
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Vision.
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Brain.
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Heart.
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Medications.
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Injury.
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Illness.
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Aging process.
The factors mentioned above can affect one or more of the components of the overall balance system.
What Are the Types of Vestibular Function Tests?
The ENT (ear-nose-throat) specialist, audiologists, and otolaryngologists perform vestibular function tests to determine the health of the vestibular portion of the inner ear. The various vestibular tests are described below -
Electronystagmography (ENG) or Videonystagmography (VNG) - The electronystagmography or videonystagmography test helps in the evaluation of the inner ear. In both these tests, the movement of both eyes is recorded in light and dark rooms. During the ENG test, small electrodes are placed on the skin near the eyes to record eye movements. In the VNG test, eye movements are recorded with the help of a video camera mounted inside the goggles worn during testing.
ENG and VNG tests evaluate the movement of eyes while following a visual target (tracking test) or during body and head position changes (positional test).
Caloric Test - The caloric test evaluates the movement of the eye in response to cold or warm air (or water) in the ear canal. If no response is noticed to warm or cold air, water or ice water may produce a response. This test helps determine the difference between the function of the left and right inner ear. The patient can also experience dizziness or nausea, and the doctor may ask some questions to distract the patient from getting adequate results.
Rotary Chair Test - This test is done along with the VNG to confirm the diagnosis and assess the functioning of the vestibular system. This test measures the response of head movements similar to daily activities. This test is not required in every case, and because of the expensive equipment, it is not easily accessible. During this test, the patient sits on a chair that moves left and right at various speeds, and eye movements are recorded to help determine the vestibular loss in both ears.
Computerized Dynamic Visual Acuity (DVA) - The DVA test helps determine how well a person can see when doing activities such as walking, riding a car over bumpy roads, or turning head from side to side. In addition, this test helps measure how well the vestibular ocular reflex (VOR) works. The vestibular ocular reflex allows for keeping objects focused while moving the head. People with problems with VOR have jumping vision (oscillopsia) and cannot keep objects in focus when moving the head.
During this test, the letter E will be displayed on the screen, and the patient must tell the direction it is pointing while keeping the head still. Then, the same test is done again while keeping the head moving. A similar test using an eye chart can be done, which begins with the head still and then repeats with head movement at a certain speed.
Computerized Dynamic Posturography (CDP) - The CDP test helps to evaluate how well a person can use visual, vestibular, and sensory systems during balance. In addition, this test measures the body sway under different conditions. In this test, a patient will be tested with eyes closed and open, with the platform static or moving.
Another modified low-tech test known as the modified clinical test for sensory integration of balance (mCTSIB) can be done in place of CDP in case the facility does not have a computerized machine.
Subjective Visual Vertical (SVV) - The SVV test evaluates the utricle, one of the inner ear organs responsible for sensing gravity. In this test, in a dark room, a projected image of a line on the wall is shown, and when it moves to the vertical position, a patient has to click on a mouse. Patients have to complete ten trials of this test. In case of damage in the inner ear or the brainstem, the lines may appear tilted.
Vestibular Evoked Myogenic Potential (VEMP) - The VEMP test evaluates whether the saccule (inner ear organs) and the vestibular nerve work normally. The saccule is sensitive to sound, and its response to the sound can be measured by recording electrical activity in a muscle located in the front of the neck. For this, small electrodes are placed on the neck, repetitive loud clicks or sounds are produced, and the electrical response of the muscle is recorded.
Video Head Impulse Test (vHIT) - This test uses a camera and sensors (mounted on the goggles) to observe the movement of the eyes during rapid head movements.
Risk of Falls Assessment - This test evaluates some factors to predict which people will likely experience future falls and injuries.
What Do the Results of Vestibular Function Tests Mean?
After conducting the required tests, the audiologists will review the test results. A normal test result means there is no sign of vestibular dysfunction as a cause for the reported symptoms.
An abnormal test result means signs of vestibular or neurologic problems contributing to the symptoms a patient is experiencing. In this case, the health care professional may advise for some additional tests and will formulate a treatment plan as required.
Conclusion:
Vestibular function tests are commonly advised in patients experiencing dizziness or off balance. Patients should carefully follow all the instructions before or during the test. These are very safe and common test which does not require any preparation before conducting the test. The significance of these tests extends beyond mere diagnosis, as their outcomes inform rehabilitation strategies, fostering improved patient outcomes and a better quality of life for individuals grappling with balance-related issues.
