Advances in Audiologic and Vestibular Testing

80 Advances in Audiologic and Vestibular Testing

Jill M. Anderson, Fawen Zhang, and Ravi N. Samy

Although the mainstays of the diagnosis of patients with audiologic or vestibular disorders are history and physical examination, the differential diagnosis may be narrowed with a battery of tests. Unfortunately, the varying pathologies often cause similar symptomatology. Advances in these tests have improved the understanding of the disease processes as well as improved the determination of the site-of-lesion. Newer testing modalities have allowed greater objectivity with less subjective variability. As the field of audiology continues to expand, it is prudent for the practicing otolaryngologist to dialogue with the audiologist to improve and further the understanding of otologic diseases and to stay at the forefront of diagnosis and management. Before proceeding to the newest advances in audiologic and vestibular testing, it is prudent to review the basic testing.

image Vestibular Testing

The sense of balance requires the integrity of the visual, somatosensory, and vestibular system. Balance disturbance can be present in the form of dizziness, vertigo, or disequilibrium. Clinical assessment of balance disorders includes observation of spontaneous eye movement, Romberg and Fukuda testing, gait and tandem gait testing, and head shake and thrust tests. During clinical testing, the observation of nystagmus is enhanced through the use of special glasses called Frenzel lenses to avoid central suppression caused by fixation. In addition to physical examination and clinical assessment, multiple established vestibular tests exist.

Vestibular tests include identification of gaze-evoked nystagmus, evaluation of dynamic positionally induced vertigo and nystagmus using the Dix-Hallpike and other positioning maneuvers, evaluation of static positionally induced nystagmus, and evaluation of the vestibular ocular reflex (VOR). Testing for the VOR includes saccade and smooth pursuit testing. Finally, horizontal semicircular canal function is measured by caloric stimulation using warm and cool air or water.


Electronystagmography (ENG) is a technique that objectively records nystagmus by measuring the corneoretinal potential resulting from the VOR when the balance system is stimulated. The resulting nystagmus is measured using the slow phase velocity (SPV, the angle of the slow phase of the nystagmus in degrees per second) to identify the existence of vestibular pathology.

ENG includes a series of test categories such as spontaneous nystagmus, ocular-motor tests, the Dix-Hallpike maneuver, positional tests, and caloric tests. The spontaneous nystagmus test is performed to identify pathological un-provoked nystagmus and to rule out the influence of spontaneous nystagmus on the response in other vestibular tests.

The ocular-motor test battery evaluates the function of VOR pathway with the saccade test, the gaze fixation test, the sinusoidal tracking test/smooth pursuit test, and the optokinetic test. Abnormalities of these tests are more suggestive of central disorders of the vestibular nuclei or cerebellum.

The Dix-Hallpike maneuver evaluates the function of the posterior semicircular canal by observing evoked nystagmus directly or via video-recording equipment. Usually, this test is used to provoke nystagmus and vertigo commonly associated with benign paroxysmal positional vertigo (BPPV).

The positional test assesses eye movements as the head is slowly positioned in different directions. Abnormalities may reflect peripheral or central abnormalities depending on the results of the test.

The caloric test evaluates the eye movements as warm (44°C) or cold (30°C) water (or air) is circulated in the ear canal. The function of the left and right horizontal semicircular canal can be evaluated separately and compared in the caloric test. Abnormalities of this test correlate with inner ear vestibular pathology.

Sinusoidal Harmonic Acceleration/Rotational Chair Tests

The sinusoidal harmonic acceleration (SHA) test battery assesses the eye movement induced by back-and-forth sinusoidal movement on a motorized chair rotated at several different speeds. SHA tests can be performed in addition to ENG testing to confirm a diagnosis. The SHA test battery includes a saccadic eye movement test, smooth pursuit, optokinetic nystagmus, gaze nystagmus, spontaneous nystagmus, and fixation of nystagmus during rotational testing. This motion stimulates the horizontal semicircular canals in both ears simultaneously and so cannot separate out unilateral vestibular pathology. The measurements of the results include gain (response amplitude divided by stimulus amplitude), phase (timing of the response relative to the stimulus), bias (average value of slow phase eye velocity over a complete cycle), and gain asymmetry (comparison of gain during rotation to the right versus rotation to the left).

Dynamic Platform Posturography/Computerized Dynamic Posturography

Dynamic platform posturography (DPP) and computerized dynamic posturography (CDP) constitute a test battery that assesses the ability to use sensory (eg, visual, vestibular, or somatosensory) input to coordinate the motor responses for balance maintenance. Changes in the sensory information (somatosensory or visual) such as tilting the platform or providing inaccurate visual reference result in the change of the patient’s center of gravity (COG). Sensors located under the feet measure voltage changes caused by the change of COG. The patients utilize the sensory input and adjust their position to avoid falling. In the case of vestibular disorders, the cues from other sensory systems become more important. Information gleaned from this test can identify malingering patients or may be used to craft treatment plans for vestibular rehabilitation.

The motor control test (MCT) assesses the patient’s responses to sudden movements of the platform. The adaptation test (ADT) evaluates a patient’s ability to minimize sway when exposed to a series of platform rotations in the toes-up or toes-down direction. In the posture-evoked response (PER) test, surface electrodes are placed on the medial gastrocnemius and tibialis anterior muscles to record compound muscle contraction activity of each muscle group when rapid rotations of the platform are used.

image Innovations in Vestibular Testing

Newer vestibular tests should have advantages over established testing. They should be more convenient to perform, and they should be able to assess the function of more components of the vestibular system because arguably the most important objective vestibular examination, caloric testing, measures only the function of the lateral semicircular canal. New vestibular tests should yield objective and quantitative data and are discussed following here.

Videonystagmography (VNG) is quite similar to ENG, but there are some important differences. For this test the subject wears goggles while video cameras are used to record eye movements in the horizontal and vertical axes. The greatest advantage of the video-oculographic system is its ability to record and analyze eye movement from each individual eye when the vestibular tests are executed. Video systems are typically more accurate than the standard ENG method because they are less sensitive to lid artifact and are not affected by electrical noise. Moreover, the calculation of measurements such as precision (gain or accuracy), latency, or peak velocity based on eye movements is more accurate. Computer-driven systems are used to better control variables and provide greater accuracy of stimulus presentation, data collection, and data analysis. These systems may use light-emitting diodes (LEDs) on a light bar anchored to the wall or in a self-contained oculomotor stimulator, promising a high level of control over stimulus presentation. More sophisticated measurements such as the short and long time constants of the SPV versus time function have been used to characterize the dynamic changes of the vestibular system response during stimulation. Results can be compared with normative data. The contemporary analysis techniques may integrate algorithms that can be used to separate the contributions of the peripheral and central vestibular system and the visual-oculomotor system.

More naturally occurring stimulating situations may be better models for physiological function. For example, the Vestibular Autorotation Test (VAT, Western Systems Research, Inc., Pasadena, CA) is a fast test lasting 18 seconds that evaluates the VOR function under more natural conditions. The patient is instructed to look at the visual target and perform horizontal and vertical head movement. The VAT may be more sensitive than other vestibular tests. It records responses of both the horizontal and two vertical canals, the superior and posterior canals. Due to these advantages, the VAT can be used as the first screening test for patients with balance problems as well as to monitor the effectiveness of vestibular rehabilitation.

Portability of a testing system is an important feature. For example, the IntelliNetx VNG I Video ENG System (Eye Dynamics, Inc., Torrance, CA) allows ENG tests to be performed anywhere. ICS Chartr 200 system (GN Otometrics, Taastrup, Denmark) combines VOG and ENG in a single convenient device and comes with features such as a remote control and built-in fixation light as well as software for automatic calculation and interpretation analysis.

Tests evaluating not only horizontal but also other semicircular canals and otolith organs have been developed. For example, VNG can evaluate the function of the vertical semicircular canal. Further, to test the function of semi-circular canals other than the posterior semicircular canal, a series of modified Dix-Hallpike maneuvers have been developed with head positioning in the plane of the vertical semicircular canals.

A high torque rotary chair test provides the ability to perform unilateral utricular assessment. The chair is fitted with a translation sled that can move the subject along an interaurally oriented axis, during which one utricle becomes aligned with the axis of rotation. Thus the utricle on the stimulated side is assessed. This stimulus induces ocular counterrolling (OCR) that can be measured with three-dimensional video-oculography (3D VOG). The OCR output is a measure of the utricular function of the stimulated side.

Off-vertical axis test evaluates the function of the otolith organ by assessing the eye movement during rotation about an axis that is tilted away from earth vertical.

The subjective visual vertical (SVV) test is a method to evaluate the perception of the head position relative to gravity. The subject is instructed to adjust a visible luminus line in complete darkness to what they consider to be gravitational vertical. This test is used to evaluate utricular function.

The galvanic vestibular test might be a test of otolith function. It consists of using a direct current of 1 to 5 mA on the mastoid process in an attempt to stimulate the vestibular while eye movement and postural sway are recorded.

Jun 5, 2016 | Posted by in OTOLARYNGOLOGY | Comments Off on Advances in Audiologic and Vestibular Testing
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