The balance and dizziness examination consists of different tests. All of these tests need not be performed on all of the patients and on all of the occasions. The ability to evaluate the vestibular system (balance-sensing organ of the inner ear) in more detail has been a topic of focus by many researchers over centuries. Nobel Prize winner Dr Robert Bárány discovered that the vestibular system of the ear performed a different function from hearing. He described how a manually turned rotation chair resulted in eye movements generated from the vestibular system and that water irrigated into the ear canals (caloric test) also resulted in eye movements that can be used as a means of quantifying vestibular function. These discoveries earned Dr Bárány a Nobel Prize in 1914.
It needs to be stressed that these tests cannot stand alone and has to be interpreted in conjunction with a comprehensive patient history and meticulous clinical examination. The following tests are available:
Videonystagmography
Spontaneous and evoked nystagmus
Nystagmus is defined as involuntary repetitive eye movements. It may be indicative of a central(brain) or peripheral (inner ear and nerve) vestibular disorders. Nystagmus can usually be seen with the naked eye by an observer but when small or short lasting special equipment is needed. Videonystagmography(VNG) utilises infrared cameras fitted into goggles which resemble scuba diving or swimming goggles. It is able to observe, record and with certain software computer programs to analyse nystagmus. The type, characteristics and direction of the nystagmus can help to localise the problem. Even if the problem is in the inner ear the effect is most often see in the eye response. Some patients present with nystagmus and this is referred to as spontaneous nystagmus. In other patients nystagmus needs to be evoked or elicited or modified by certain maneuvers. VNG is not a painful test but may lead to dizziness. This is usually short lasting. Evoked nystagmus testing include hyperventilation, post head shake, body position influence, neck influence, pressure and positioning testing for BPPV.
Central and oculomotor tests
Gaze nystagmus
The test for gaze nystagmus is considered a central (brain function) test. Gaze nystagmus is seldom found with peripheral ear problems. Gaze nystagmus is nystagmus that is elicited by asking the patient to maintain eccentric gaze. Looking forward, straight ahead, does not require active input from the brain. However, in order to be able to maintain eccentric gaze there has to be a functional interaction between the eye muscles and the central neural integrator, which is located in the brain. A normal person is able to maintain steady eccentric eye gaze for at least 30 seconds. If the time is shortened it may indicate pathology. The test is influenced by certain eye problems, which should be excluded before the test. It is not a painful test and seldom causes dizziness, if at all! Gaze nystagmus is looked for in the horizontal and vertical plain. The presence of gaze nystagmus may indicate structural or degenerative brain lesions. The vestibulocerebellum is especially sensitive. It is often also seen with depressive central nervous system medication and alcohol.
Saccade testing
Saccades are fast reflexive eye movements intended to refocus on a new visual target. It is considered a central (brain function) test and is not abnormal with peripheral ear disease. Saccades are conjugate (symmetrical) movements between the eyes. Normally it has a rapid onset, is fast and accurate. Saccade testing is assessed in the horizontal and vertical plane. It is not a painful test and does not cause dizziness. Brain tumours, stroke, Parkinson’s disease, Myasthenia gravis and Huntington’s disease can lead to abnormal saccades. Patients with progressive supranuclear palsy (PSP) may have difficulty performing vertical saccades. Disconjugate horizontal saccades where the two eyes do not work together is often seen with intranuclear ophtalmoplegia (INO) and a sign of multiple sclerosis (MS)
The patient is asked to accurately look at a target in the form of a light that randomly appears at different places on a screen. Eye movements can also be evaluated in the vertical plane. The cameras on the video goggles worn by the patient record and display the eye responses of the patient. In a normal patient it should ideally follow on the target line. Abnormal responses can include slowing of initiation of eye movement (latency), slow or fast speed of eye movements (velocity) and accuracy of the eyes hitting the target. Accuracy can be abnormal either due to the eye stopping short or the eye overshooting.
Pursuit testing
This test of oculomotor function is considered a central (brain function) test. Pursuit/pendulum or smooth pursuit testing assesses a patient’s ability to follow or tract a moving target. Any person with a normal pursuit system is able to accurately follow a moving target across the visual field in the horizontal and vertical plane. This is usely only possible for slow moving targets of up to 100 degrees per second. The test is influenced by vision, brightness of the target, age and attention. It is not a painful test and seldom causes dizziness. An abnormality in smooth pursuit system is a senstive indicator of central pathology. Alcohol, sleeping pills and anti- epileptic drugs cause abnormal pursuit. Furthermore abnormal pursuit can also be found in Parkinson’s disease, brain tumours, cerebellar disorders and Alzeimer’s disease.
The patient is asked to accurately follow a target in the form of a light that moves to and fro horizontaly or verticaly across the screen. The cameras on the video goggles worn by the patient record and display the eye responses of the patient. In a normal patient the eyes should ideally follow accurately on the target line. Abnormal responses can include asymmetry between eye movements in different directions, slower or faster eye movements (phase abnormalities) , smaller or larger responses (gain abnormalities) and jerking eye movements (saccadic).
Optokinetic testing
Optokinetic testing assesses the optokinetic reflex that is normally present in humans from the age of six months. It consists of a slow tracking movement of the eyes (smooth pursuit) combined with a corrective movement (saccade) at the end. An example of this reflex is when someone is sitting in a bus without moving the head and follows the telephone poles going by. As the pole being followed moves out of view the eyes quickly jump back to the next pole. This reflex can be abnormal or absent with central (brain) pathology.
Caloric Testing
Caloric testing with air or water utilises a temperature gradient to evaluate each inner ear seperately. The warm irrigation stimulates and the cold irrigation suppresses the horizontal semicircular canal function. The function is recorded in terms of the nystagmus induced. Although temperature is a non physiological stimulus of the inner ear it does give some indication of the low frequency range of the system between 0.002Hz – 0.004Hz.
VORTEQ™
VORTEQ™ is a fast, quantitative assessment of the vestibulo-ocular reflex (VOR) in individuals with vestibular and balance disorders. VORTEQ™ tests include video head impulse testing (vHIT), dynamic visual acuity (DVA) and active head rotation (also referred to as vestibular autorotation testing). Active head rotation tests can be used in conjunction to rotation chair tests; it can provide information about the high frequencies, and determines the contribution of the inner ear, cognitive input and neck inputs to nystagmus rather than the contribution of the inner ear alone.
Video head impulse test (vHIT)
The video head impulse test (vHIT) is used to identify unilateral and bilateral vestibular deficits. It is a highly specific test for the semicircular canal function. The vestibulo ocular reflex (VOR) of the six semicircular canals can be assessed individually. The VOR is the reflex when the vestibular system of the inner stabilizes the eye and gaze in space during head movements in order to maintain clear vision. It does this by generating equal and opposite compensatory eye movemnets. If the VOR were defective the visual world would blur if a fast head movement were performed in the plain of the defective semicircular canal. The influence by the visual pursuit system in eye stabilization during head motion is eliminated by these very fast movements, making it highly specific. The examiner applies small amplitude fast head thrusts whilst the eye responses to the semicircular canal stimulation are measured. VOR gain, asymmetry and covert and overt corrective saccades are displayed. It is not a painful test and only seldom may lead to temporary dizziness. Not only can this test help to diagnose vestibular disorders but it can also help to monitor the progress in a patient undergoing a course of vestibular rehabilitation.
Dynamic visual acuity (DVA)
The dynamic visual acuity (DVA) test analysis the ability of a patient to maintain stable vision during head movements. Without this ability the visual surroundings would blur during head movements and the patient would feel dizzy. DVA depends on the interaction of the vestibular ocular reflex (VOR), the central (brain) eye pursuit and optokinetic systems and the cervico ocular reflex (COR) from the neck. The test can be performed at different speeds and is performed as a standard in the vertical and horizontal planes. It is not a painful test but may lead to temporary dizziness. Firstly, vision is measured without any head movement (static visual acuity). The head is then shaken and the vision measured again (dynamic visual acuity). There are specific normal values for different head velocity. Age can impact the results. The DVA test helps to determine the functional ability in high performing individuals such as pilots and athletes. It is also used to determine poorly compensated single sided vestibular loss or vestibular loss on both sides, often seen with ototoxic medication.
Vestibular autorotation testing
The vestibulo ocular reflex (VOR) normally serves to stabilize gaze in space during head movements by generating equal and opposite compensatory eye movements. The vestibular autorotation test is performed at slower rates than the VHIT test. With the passive vestibular autorotation test the examiner moves the head of the patient and with the active vestibular autorotation test the patients moves his own head in rhythm with a metronome. It can be performed at different head speeds. A sensor compares the head speed with the video recording of the eye responses. The software then analyses the response. During testing, vertical and horizontal VOR are tested to record gain, phase and symmetry. It is not a painful test and may lead to temporary dizziness. It is also helpful in vestibular rehabilitation. Vestibular autorotation testing analyses vestibular function and are of value in patients with bilateral vestibular loss and in those where compensation of the vestibular system after surgery or damage wants to be determined. It can also help to monitor the progress in a patient undergoing a course of vestibular rehabilitation.
Subjective visual vertical (SVV)
The subjective visual vertical (SVV) test is designed to evaluate a person’s perception of verticality. In normal people the perception of up is straight up and the perception of down is straight down. Vestibular disorders may affect this so that the perception of vertical is tilted, being perceived as normal by the patient. In fact if this wrong perception of verticality is corrected the patient may then feel as if tilted! A tilt of the SVV is the most sensitive sign of vestibular tone imbalance in the roll plane. The bucket test for SVV is a clinical test and is not painful. It does not cause vertigo. It is of value in patients with acute vertigo, acute brainstem strokes and some eye movement disorders. It can also be incorporated as part of rotation chair testing where it helps to evaluate the function of the utricle of the inner ear.
Vestibular evoked myogenic potentials (VEMP)
The vestibular evoked myogenic potential (VEMP) test is a test of vestibular function that evaluates the otolithic organs and related neural pathways of the inner ear vestibular system. The otolithic organs consist of the saccule and urtricle and are responsible for the measurement of linear acceleration and tilt. They contain calcium carbonate crystals. The VEMP test utilises sound or vibration to elicit a response in muscle activity of the neck muscles (cervical or cVEMP) or eye muscles (ocular or oVEMP). These muscles respond to stimulation of the otolithic organs. It is not painful and performed with the patient seated or lying. Electrodes are placed around the patient’s eyes (oVEMP) and on the neck (cVEMP). These responses are recorded as waves and then interpreted. It may supply information on different conditions of the vestibular system for instance superior canal dehiscence (SCD), acoustic neuroma and Meniere’s disease (MD).
Electrocochleography (ECOG)
The electrocochleography (ECOG) test is a test of the potentials generated in the cochlea and part of the auditory nerve. It looks at the cochlear microphonic (CM), summating and peripheral auditory nerve action potentials. It is very reliable. A sound stimulus is introduced into the ear and the electrical responses measured by means of surface electrodes placed on the head. These responses are recorded as waves and then interpreted. It is not painful and performed with the patient lying. It may supply information on different conditions of the cochlea most commonly Meniere’s disease (MD), perilymph fistula (PLF) and acoustic neuroma.
Rotational Chair
The development of electronically driven rotation chairs resulted in improvement of Bárány’s test (as explained above), allowing for objective quantification of eye movement responses. Modern rotation testing involves the patient seated in a dark room in a chair mounted atop a computer-controlled torque motor with the head coupled securely to the chair. This allows a precise and repeatable stimulus to be presented to the head by rotating the whole body. The eye movement of the patients are measured and used to determine whether or not dizziness may be due to a disorder of inner ear (a vestibular disorder) or brain. Both inner ear vestibular organs are tested simultaneously. Testing is conducted over the frequency range between 0.01 Hz- 1.0 Hz. Rotational chair testing shows how the central nervous system (CNS) processes vestibular information and how the CNS integrates visual and vestibular information. Rotation chair tests are the “gold standard” for diagnosis of bilateral vestibular loss. Although rotation chair testing is not necessary in all patients it is a valuable adjunct to video nystagmography (VNG) testing, vestibular evoked myogenic potential (VEMP) testing and video head impulse testing (vHIT) by confirming an abnormality.
Computerised dynamic posturography (CDP)
Computerized dynamic posturography (CDP) is a quantitive non-invasive test of balance function. It analysis the central nervous systems adaptive mechanisms in the control of posture and balance in terms of the sensory, motor and brain function. The patient is placed on a platform (forceplate) that can move in the horizontal plane or rotate. The patient is strapped in to prevent injury. Sensitive sensors in the forceplate detect tiny movements or oscillations, made by the patient. This vertical forces exerted through the patient’s feet measure the center of gravity (COG) position and postural control. A moving visual surround measures the patient’s use of visual information to maintain balance. It provides assessment capabilities on either a stable or unstable support surface and in a stable or dynamic visual environment. This information is then interpreted by a computer, matched with height and weight norms and the results displayed in a graphical way. It is not a painful test.
The different protocols of CDP testing include:
- Sensory Organization Test (SOT)
- Motor Control Test (MCT)
- Adaptation Test (ADT)
- Weight Bearing Squat (WBS)
- Unilateral Stance (US)
CDP is of value in the assessment of patients with vertigo, dizziness and balance problems. It may help to determine the risk of falling in elderly patients. In normal persons it can be used in sports training and physical education. Patients with balance disorders may be helped in a structural way in terms of physical therapy and postural re-training.
