WO2009076554A2 - Device for comparing rapid head and compensatory eye movements - Google Patents

Abstract

This invention provides a device and methods of using a device for evaluating the vestibular function in a subject. The device comprises a head movement measuring device, an eye rotation measuring device to measure rotation of the eye relative to movement of the head and a comparing device for comparing subject head measurements and eye rotations to reference data. Such a comparison can aid or generate the formation of a diagnosis of a disorder, especially disorders of vestibular function.

Description

PRIORITY CLAIM AND GOVERNMENT INTEREST STATEMENT

This application claims the benefit of under U.S. provisional patent application Ser. No. 60/996,909 filed 12/11/2007.

The invention arose from research conducted under grant K08 DC006869 from the National Institutes of Health, National Institute for Deafness and Other Communication Disorders. The Government may have certain rights in the invention.

FIELD OF THE INVENTION

This invention relates to the quantitative assessment of vestibular function, in particular to methods and apparatus for evaluation of patients with complaints of dizziness, oscillopsia, imbalance, or disequilibrium.

BACKGROUND OF THE INVENTION

Dizziness has been reported to be the most common complaint of elderly patients presenting to a doctor. Patients with symptoms of imbalance, dizziness, oscillopsia (movement of the visual world with head movement) or disequilibrium may have loss of function of the peripheral vestibular apparatus located in the inner ear. The peripheral vestibular apparatus consists of five end-organs: the horizontal (or lateral) semicircular canal; the superior (or anterior) semicircular canal; the posterior semicircular canal, the utricle, and the saccule. The first three organs, which are oriented orthogonal to one another, measure rotational motion and the last two measure linear accelerations. Together, all three organs define the orientation and motion of the head in space. The organs are paired bilaterally so that the axes of the left and right horizontal semicircular canals are parallel, those of the left posterior and right anterior canals are parallel, and those of the right posterior and left anterior canals are parallel. Each of the semicircular canals is connected by the eighth cranial nerve to the brain. At rest, each fiber from the canal has a baseline firing rate of several dozen spikes per second. When the head is rotated to the right, the firing rate of afferents innervating the right horizontal canal increases and those from the left horizontal canal decrease. A similar "push-pull" system exists for the other two pairs of canals. With very rapid head motions, one canal is silenced. For example, a rapid head motion to the right would increase the firing rate of afferents innervating the right horizontal semicircular canal to well above 100 spikes/second and would decrease the firing rate on the left side to zero. An analogous effect is believed to occur in afferents related to the otolith organs during rapid linear head motions.

Quantitative assessment of vestibular function relies primarily on measurements of reflexive eye movements (i.e. the vestibulo-ocular reflex, or VOR) evoked by either natural or artificial stimulation of the vestibular receptors of the inner ear. Visual acuity is maintained during head movement by the generation of compensatory eye movements that maintain the direction of gaze fixed in space. A comprehensive clinical evaluation of a patient with possible peripheral vestibular dysfunction relies on determining if 1 ) both ears or just one is dysfunctional; 2) only one ear is affected, which one; 3) how severe the dysfunction is. Serial clinical evaluations allow determination if the dysfunction is intermittent or constant; and if overall function is improving, remaining stable, or worsening with time. Unfortunately, current tests of balance dysfunction may be costly, non-portable, complex, and/or produce only qualitative information.

Two types of clinical tests are in general use to determine the function of the VOR: caloric and rotation. The caloric test artificially stimulates the inner ear vestibular receptors using either warm- water or cold-water irrigations of the external ear canals. This evokes eye movements, which are measured and compared across ears to determine vestibular asymmetry. Patients are placed in a supine position with the head elevated about 30° in a darkened room. This head position places one set of vestibular receptors, the horizontal semicircular canals, into an earth-vertical orientation. Irrigation of the external auditory canal on one side creates a thermal gradient across the inner ear that stimulates the horizontal canal, primarily by inducing a convective fluid movement within the distal loop of the canal, and secondarily, by direct thermal effects. This fluid movement stimulates receptor hair cells, which in turn modulate the activity of afferent fibers within the eighth cranial nerve that innervate the horizontal canal. A warm water irrigation results in an increased afferent discharge rate, and a cold water irrigation causes a decreased discharge rate. The increased discharge rate caused by warm irrigations evokes a sensation of sustained head rotation toward the irrigated ear and evokes a compensatory VOR eye rotation away from the irrigated ear. Cold water irrigations evoke oppositely directed sensations and compensatory eye movements. The peak velocity is taken as a measure of the responsiveness of the ear to a particular irrigation.

A complete caloric test typically consists of measuring the peak velocity response to four separate irrigations (both warm and cold irrigations in each of the two ears). These four peak velocity measures are scored by the calculation of percentage measures of "reduced vestibular response" (RVR), sometimes referred to as canal paresis. If responses are significantly different in the two ears (typically RVR greater than 25% difference), the ear with the lower response is considered to be abnormal. If all four irrigations produce below normal or absent responses, this implies that the patient may have bilaterally reduced or absent vestibular function. The chief advantage of the caloric test is that each ear is stimulated individually. This allows for the identification of reduced vestibular function in an ear even though the patient might be well compensated for the lesion and may not express any other overt signs of an acute vestibular lesion. In addition, the RVR measures are quantitative in nature and can be used to grade the severity of the vestibular asymmetry.

Caloric testing has several significant limitations. The thermal stimulus that reaches the inner ear depends upon many anatomical factors (i.e., temporal bone thickness, dimensions of middle ear space, fluid in the middle ear space, variation in blood flow) and procedural factors such as the technician's skill. As a result, there is high variability across subjects in delivery of the thermal stimulus to the inner ear, due to differences in temporal bone thickness dimensions of middle ear space, fluid in the middle ear space, and variations in blood flow. These factors make it difficult to detect small differences in responses between both ears. The end result is that test-retest reliability is poor, making the test a poor choice (unsuitable) for tracking changes in vestibular function over time. Response variability limits the detection of small differences in responses between the two ears. The identification of bilateral vestibular loss is also uncertain due to the wide variations in response amplitudes in a normal population. The unusual nature of the stimulus (evoking sensations of a long duration rotational motion in a supine position that conflicts with gravity cues from the otolith organs of the inner ear) often provokes nausea in subjects (poor tolerance by subjects) susceptible to motion sickness. Finally, the caloric test simulates a head motion at a very low frequency well below the normal operating range and therefore does not give good information about the VOR at frequencies encountered in daily head movements (1-4 Hz).

The second major vestibular testing paradigm is the rotation test. Rotation testing differs from caloric testing in that a natural rotational stimulus, which stimulates both ears simultaneously, is used to evoke compensatory VOR eye movements. Patients are tested in a completely dark room to eliminate visually generated eye movements. During testing, they are seated upright in a chair mounted on a servo-controlled motor. The motor delivers accurately controlled rotational motions of the chair about an earth-vertical axis. This motion stimulates primarily the horizontal semicircular canals in both ears. In a subject with normal vestibular function, a rotation towards the right causes an increased neural discharge rate in afferent fibers of the eighth cranial nerve innervating the right side horizontal canal, and a decreased discharge rate in afferents innervating the left horizontal canal. The opposite occurs for rotations to the left. The central nervous system (CNS) uses this "push-pull" neural activity in the two ears to generate VOR eye movements in a direction opposite to the head rotation.

The motion profiles used in rotational testing typically are sinusoidal with frequencies ranging from 0.01 to 1.0 Hz with a typical peak velocity of 100 deg/sec (Leigh and Zee 2006). Rotational velocity step stimuli (Baloh et al. 1979; Honrubia et al. 1985), and sometimes pseudorandom or sum- of-sines stimuli are also utilized (Peterka et al. 1990). Rotation-evoked eye movements are analyzed in a manner similar to caloric-evoked eye movements. With sinusoidal head stimulation, a slow phase eye velocity component is generated and modulated at the stimulus frequency. A sinusoidal curve fit to the eye velocity gives quantitative measures of the VOR response that include: VOR gain

(response amplitude divided by stimulus amplitude), VOR phase (timing of the response relative to the stimulus), VOR bias (average value of slow phase eye velocity over a complete stimulus cycle), and VOR gain asymmetry (comparison of VOR gain during rotation to the right versus rotation to the left). These response parameters vary as a function of the stimulus frequency, and deviations from the normal pattern can suggest different types of vestibular dysfunction.

The natural stimulus used by rotation testing, and the precise means available for delivering the rotational stimulus, provide several advantages over caloric testing. First, the test-retest reliability of rotation testing is good, making rotation testing amenable to tracking function over time. For sinusoidal rotation tests, the repetitive nature of the stimulus affords great opportunity to use averaging to improve test reliability and the possibility to obtain useful results from partially corrupted data records. Finally, rotation testing is well tolerated by nearly all patients and only rarely evokes nausea. The chief disadvantage of rotation testing is that it often does not provide reliable information about which ear is abnormal in a patient with unilateral vestibular dysfunction. This is because, at the low stimulus amplitudes attainable on a conventional rotatory chair, the central nervous system is often able to compensate for weak or absent input from dysfunctional peripheral vestibular receptors by altering its central circuitry with input from the intact side (Baloh et al. 1984; Hess et al. 1985; Jenkins et al. 1982).

Two methods exist for measuring eye motion (ie measuring the VOR) in a clinical setting. The older is ENG, or electronystagmography. This is performed by measuring the voltages across surface electrodes placed at the lateral and medial canthi of the eye and the upper and lower lid. The comeoretinal potential, which is normally generated by the eye, causes a change in the voltage across the surface electrodes as the eye's position in the orbit changes. A calibration process is used to determine the relationship between the voltages and the eye position. ENG can only measure eye movements in the vertical and horizontal directions. Activation of the horizontal semicircular canal moves the eyes principally in a horizontal direction, meaning that ENG is able to measure movements of the eye driven by the horizontal canal. However, vertical movement of the eye depends on activation of the superior or posterior semicircular canals, which move the eye in a more complex trajectory including torsional rotations about the axis of the eye (Cohen et al. 1964; Cremer et al. 2000a; Cremer et al. 2000b). This means that comprehensive evaluation of each of the semicircular canals in a standard clinical setting cannot be accomplished with ENG alone. A newer clinical method for measuring eye movement is videooculography (VOG). VOG systems are generally more expensive than ENG systems but offer several important advantages. They are much easier to calibrate and less likely to fall out of calibration during testing. They are less sensitive to surrounding electromagnetic interference. A critical advantage of VOG over ENG is that video recording devices are able to measure eye movements in three dimensions (vertically, horizontally, and torsionally about the axis of the eye from the retina to the cornea) allowing better evaluation of the superior and posterior canals. A chief disadvantage of video recording has been relatively slow frame-rates, typically on the order of 30 to 60 frames/second. This has prevented rapid eye movements from being measured accurately.

The recently described "head impulse test" is a bedside vestibular test that offers significant advantages over other tests such as caloric or rotational testing (Halmagyi et al. 1990). In this test, the patient's head is rapidly accelerated by the examiner though an angle of about 20-30° about the axis of one pair of semicircular canals while the patient attempts to maintain gaze on a distant target. In a patient with only one functioning labyrinth, a rotation in the plane of the horizontal semicircular canal toward the functioning side will generate a normal or near-normal VOR. However, when rotating in the direction of the dysfunctional labyrinth, the firing rate of afferents leading from the functioning labyrinth drops to zero, leaving the VOR without any input from either labyrinth. This leads to an inadequate compensatory VOR. This inadequate VOR allows the eyes to move off target, with the result being that a visually guided corrective saccade is generated to reacquire the target at the conclusion of the head rotation. The presence of this corrective saccade is a qualitative clinical sign indicating abnormal canal function. A similar technique can be used for examining the otolith organs, providing a rapid linear impulse instead of a rapid rotational impulse (Crane et al. 2003).

A significant advantage of the head impulse test is that it can be performed on individual canals. Conventional rotational testing sums the input from both horizontal canals responding to the same rotation, but the rapid motion of the head in the plane of each of the pairs of the semicircular canals during the head impulse test silences the canal away from the rotation and tests only the canal in the direction of rotation (an analogous situation exists for the other semicircular canals and for the otolith organs). A second advantage of head impulse testing is that the central nervous system is relatively poor at compensating for high-amplitude head motions compared to low-amplitude motions. Thus head impulse testing may detect partially compensated peripheral vestibular losses that would be missed using other techniques. Another advantage of head impulse testing is that it can be performed by a semi-skilled practitioner with no equipment. Another advantage of the head impulse test is that, unlike many other vestibular tests, it does not have to be done in darkness. This is because visual feedback mechanisms that may override signs of vestibular loss during caloric and rotational testing are too slow to provide feedback in response to head motions as fast as those employed in the head impulse test. Another major advantage of the head impulse test is that it moves the head rapidly enough to be within the normal range of VOR function, which is believed to be well above those frequencies typically studied in rotational chair testing (Leigh and Zee 2006). Another advantage of the head impulse test is that it can be performed about an appropriate axis to test either of the posterior or superior canals, whereas the caloric and conventional rotational exam test only the horizontal canal.

Unfortunately, in a standard clinical setting the head impulse test can currently only be used in a qualitative way. Quantitative testing has generally relied on scleral search coil technology to measure eye movements, but this requires expensive and sensitive equipment, placement of a special contact lens on the anesthetized surface of the cornea, and extensive calibration procedures. To achieve a quantitative result, the head is moved multiple times by an examiner, typically by hand, and the resulting multiple eye and head movements are averaged and compared to each other. Quantitative testing has been shown to represent a substantial improvement over qualitative testing (Weber et al. 2008).

Several efforts have been made to bring quantitative head thrust testing into the clinical setting. One technique has used an external motor to rotate the head on the neck and ENG techniques to measure eye movements in the horizontal plane (Hirvonen et al. 2007). Again, multiple repetitions are averaged and a resulting gain calculated. This device relied on mechanical delivery of the test stimulus, which prevented it from measuring function of any but the horizontal semicircular canals. This device relied only on ENG technology to measure eye movements. US Patent 6796947 describes a device to measure the responses of the VOR to an impulse of rotation of the entire body. Like the technique described above, this device measured eye movements using ENG technology, limiting its utility in measuring all but function of the horizontal semicircular canals, and relied on a large apparatus to hold and move the patient. US Patent 7285099 describes a novel "bias-probe" stimulus distinct from a head-impulse stimulus designed to achieve a similar goal of silencing vestibular input from one side. This patent does not describe the use of video recording technology, requires the use of a specialized motor and software to deliver the rotational stimulus, and does not describe delivering a linear stimulus to the patient in order to measure function of the otolith organs.

What is needed in the art is a device that can be performed in the clinic or at the bedside by those with only technical (e.g. non-medical) training, can measure function of both the semicircular canals and otolith organs, and I provides quantitative data.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a device of the present invention. Figure 2 shows data collected from the device from an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments, aspects, advantages, and features of the present invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art by reference to the following description of the invention and referenced drawings or by practice of the invention. The aspects, advantages, and features of the invention are realized and attained by means of the instrumentalities, procedures, and combinations particularly pointed out in these embodiments and their equivalents. In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that the embodiments may be combined, or that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense.

In various embodiments, the invention described here would overcome many of the limitations of conventional clinical tests of vestibular function described above by providing a set of clinical tests to aid in the diagnosis of patients complaining of symptoms of dizziness and balance instability, oscillopsia, or patients who are at risk for balance disorders. The invention comprises of a testing device and some combination of a test stimulus, data collection and recording methods, and associated analysis methods that can be used to characterize dysfunction of inner ear (vestibular) balance function. Various embodiments are based on an underlying principle that vestibular responses in one ear can be turned off during rapid head motions to allow responses in the other ear to be evaluated. In an embodiment, this is accomplished using a novel combination of a rotational stimulus, an eye and head motion recording system fixed to the subject's head, and data collection and analysis methods to compare the velocity of the head rotation to the velocity of the eye movement. In an embodiment, the invention allows the latency, gain, or latency and gain of the vestibulo-ocular reflex in a subject to be calculated and compared to normative values to determine the level of functioning of the peripheral vestibular system (including the semicircular canals and/or the otolith organs) of the subject. MODE FOR CARRYING OUT THE INVENTION

In one aspect, the present invention involves rapidly moving a subject's head. The head can be moved rotationally about any axis or linearly along any vector. In one embodiment, the stimulus (i.e. the head movement) is provided by manually moving the head by the examiner. In another embodiment, the head movement is provided by mechanical means to move the head such as a device held against the head manually. In another embodiment, the head movement is provided by an external device held against the head from an external framework. In another embodiment, the head movement is provided by an external device fixed to the head.

Optionally, the invention further comprises a means for recording the rotation of the eye; e.g. by a recording device. By way of example, the rotation can be recorded by videography, photography, computer, or any other means known to the ordinary skilled artisan. The movement of one eye or optionally 2 eyes can be recorded. Where the movement of both eyes is desired, one or two recording devices can be used (e.g. one device for both eyes or one device per eye). The frame rate of the videographic embodiment is rapid enough (in a non-limiting example, 250-500 Hz) to allow accurate recording of eye movements during a head-impulse maneuver. In another possible embodiment, the recording apparatus consists of an ENG recording device. In one embodiment, the ENG device is able to measure in one dimension. In another embodiment, the ENG device is able to measure in two dimensions. In the ENG embodiment, comeoretinal potentials can be recorded using surface electrodes or using needle electrodes. The mechanism by which eye position is measured is termed the "eye movement monitoring system".

In the video embodiment, the eye movement (i.e. rotation) eye movement monitoring system must be held stable with respect to the head. This is accomplished in one or a combination of several methods. The eye movement monitoring system may be attached to the head by a strap. The system can be attached to the head by a bite-block grasped between the teeth. In one embodiment, this bite- block consists of firm rubber or similar material able to be gripped safely and securely between the teeth. In another, the bite-block consists of moldable material, such as dental impression material, that may be used to make individualized bite-blocks for each subject. In one embodiment, this bite- block is disposable and is replaced between each subject. In another embodiment, the bite-block is not disposable. In one embodiment, the eye movement monitoring system may be attached to the head by a stereotaxic apparatus temporarily fixed to the head at one or several points including, for example, the nasal bridge, orbit, external auditory canal, and occiput. In another embodiment, the eye movement monitoring system may be attached to the head by foam molded to the shape of the subject's head. Embodiments of the invention may take advantage of one or more of the methods described above to stabilize the eye movement monitoring system.

In one version of the video embodiment, the eye is illuminated by infrared light from a distant source. In another version of the video embodiment, the eye is illuminated by visible light from a distant source. In another version, the eye is illuminated by infrared light from a light source held steady with respect to the patient's head. In another version, the eye is illuminated by visible light from a light source held steady with respect to the patient's head. Stabilization of the light source with respect to the patient's head may be accomplished in one or a combination of several methods. The light source may be attached to the head by a strap. The light source may be attached to the head by a bite-block grasped between the teeth. In one embodiment, this bite-block consists of firm rubber or similar material able to be gripped safely and securely between the teeth. In another, the bite-block consists of moldable material, such as dental impression material, that may be used to make individualized bite-blocks for each subject. In one embodiment, this bite-block is disposable and is replaced between each subject evaluated using the apparatus. In one embodiment, the light source may be attached to the head by a stereotaxic apparatus temporarily fixed to the head at one or several points including, for example, the nose, orbit, external auditory canal, and occiput. In another embodiment, the light source may be attached to the head by foam molded to the shape of the subject's head. The light source may be attached directly to the camera. Embodiments of the invention may take advantage of one or more of the methods described above to stabilize the light source.

As taught here, a means for measuring the movement of the subject's head can be a ratemeter or ratemeters oriented to measure rotations about one, two, or three axes. In another embodiment, rotational movement of the head is measured using an array of multiple linear accelerometers oriented to measure rotations. In one embodiment, a means for measuring the movement of the subject's head can be a a linear accelerometer or accelerometers oriented suitably to measure linear accelerations of the head in one, two, or three dimensions.

It can be desirable that the means for measuring the movement of the subject's head is stable with respect to the head. For example, the head movement means may be attached to the head by a strap. The head movement means may be attached to the head by a bite-block grasped between the teeth. The head movement means may be attached to the head by a stereotaxic apparatus temporarily fixed to the head at one or several points including, for example, the nose, orbit, external auditory canal, or occiput. The head movement means may be attached to the head by foam molded to the shape of the subject's head. Embodiments of the invention may take advantage of one or more of the methods described above to stabilize the head movement monitoring component.

In one embodiment, the means for measuring the rotation of the eye and head movement means are coupled into one unit. In another embodiment, they are two separate units each stabilized independently with respect to the head.

In one embodiment, the eye rotation and head movement is determined and recorded, In one embodiment, the eye rotation and head movement data are carried directly by wire to a computer (e.g. a desktop or laptop computer). In another embodiment, the data are transmitted by an infrared connection to a computer . In another embodiment, the data are transmitted by a radio frequency connection to a computer . In one embodiment, processing of data will be performed by filtering and/or amplifying the signal from the eye and/or head movement monitoring components before and/or after transmission to the computerized device.

The head rotation is intended to be of adequate velocity and acceleration to silence input from the labyrinth of one ear (for rotational testing, typically rotational velocity greater than 250 deg/sec and rotational acceleration greater than 2000 deg/sec/sec; for linear testing, typically 0.1-1.6 g (Halmagyi et al. 1990; Kessler et al. 2007)). In one embodiment, the motion profile of the head is immediately assessed by software to determine whether it represents an adequate stimulus. The result of this determination is reported to the examiner immediately by a mechanism such as a digital readout of velocity or acceleration, LED indicator, or audible signal indicating that an appropriate motion profile had been delivered.

In the embodiment of the invention using a video camera or cameras, video signal from the camera or cameras is analyzed by a computer system to determine the motion of the eye in the orbit over time. In one embodiment of the device, the video camera system is able to measure eye motion in one dimension. In another embodiment, the video camera system is able to measure eye movements in two dimensions. In a third embodiment, the video camera system is able to measure eye movements in three dimensions. In the embodiment of the invention using an ENG system, signal from the electrodes is ampllified and filtered before being analyzed by a computer system to determine the motion of the eye in the orbit over time.

The resulting data can be combined together and the resulting head movements combined together (each combined through averaging, for example) so that the combined stimuli from the head (i.e. the head movement) and eye may be compared. Values such as gain (peak velocity of eye divided by peak velocity of eye at a particular point in time after the stimulus has begun) or latency (length of time between the onset of head motion and the onset of eye motion) could be calculated. In one embodiment, this combination will be performed immediately by software. In another embodiment, data tracings are saved and analyzed offline. In one embodiment, an individual head and eye movement from each individual repetition are compared individually before combining (by averaging, for example). In another embodiment the head movement tracings are combined (by averaging, for example), the eye movement tracings are combined (by averaging, for example), and the results of these combinations are compared with each other. When testing the semicircular canals, for example, one comparison that may be made is that of gain, defined as eye velocity/head velocity, at any particular point in time following onset of the stimulus. This ratio is typically approximately 1.0, but ratios calculated from eye responses generated by stimulating a dysfunctional semicircular canal may be substantially less. Another is that of latency, or the time delay between the onset of head motion and the onset of eye motion. This value is normally approximately 10 ms, but becomes significantly longer in patients with vestibular loss (Tabak et al. 1997). These or other measures may be determined in normal subjects to form a set of normative data against which responses of test subjects is compared. Subjects whose gain and/or latency or values for other measures fall beyond the limits of normal function may be identified as having vestibular dysfunction. In one embodiment, the invention further comprises a means for comparing the measured movement of the head to the measured eye rotation in response to head displacement to a reference population.. A reference population can be normal individuals to provide a basis of comparison (e.g. age and gender matched subjects). The reference population can be data accumulated from a population of subjects with defects in vestibular function..

The means for comparing can be a computer, chart, or other electronic logic processor.

Example 1.

An embodiment of the invention described here was constructed. Figure 1 shows a bite-block that was used to hold the camera and ratemeter fixed in place relative to the head. The ratemeter and video camera were coupled together. Labels indicate the bite block, the video camera, and the rate meter.

Example 2.

The device of Example 1 was used to collect data shown in Figure 2. Data were collected from a normal subject; nine repetitions of the stimulus are shown. Gray lines show head velocity. Black lines show eye velocity. The latency of the response is measured as the delay between the onset of the head motion and the onset of the eye response. The gain of the response is measured as the ratio of the eye velocity (in degrees per second) to the head velocity (in degrees per second) at a specified time following the onset of the rotation. Pathologic patients may be identified by an increase in latency and/or a decrease in gain. Latency and gain are typically measured using techniques described previously (Halmagyi et al. 2008; Tabak et al. 1997) The unexpected results generated by the device of Example 1 are shown in Figure 2 are equivalent to those previously reported for normal subjects undergoing the head impulse test whose eye movements were recorded using scleral search coil techniques in a controlled laboratory setting (Delia Santina et al. 2002).

Although this invention has been described with respect to specific embodiments, the details of these embodiments are not to be construed as limitations.

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18. Weber KP, Aw ST, Todd MJ, McGarvie LA, Curthoys IS and Halmagyi GM. Head impulse test in unilateral vestibular loss: vestibulo-ocular reflex and catch-up saccades. Neurology 70: 454-463, 2008. INDUSTRIAL APPLICABILITY

The invention can be useful for determining the progression of loss of function of the peripheral vestibular system during therapy with drugs currently described or in the future developed, including chemotherapeutic drugs, antibiotics, diuretics, or others, known to be or in the future found to be ototoxic. The invention can be useful in determining the presence of malingering in a patient complaining of imbalance. The invention can be useful for determining improvement of function with treatment for benign intracranial hypertension, also known as idiopathic intracranial hypertension or pseudotumor cerebri. The invention can be useful for measuring the improvement in function with therapy, including current therapies such as physical therapy or future therapies such as sensory substitution devices, vestibular prostheses, or cellular or molecular therapies to restore vestibular function. The invention can be useful for determining whether the vestibular system is deficient in one ear or both, and whether the loss of function is partial or total. The invention can be useful in tracking the degree to which a patient compensates to a vestibular lesion over time. The invention can be useful for use in children, who are otherwise very hard to test for vestibular function.

Devices according to the present unexpectedly now improve the prior art by being well tolerated by most test subjects, can be performed at the bedside by those with only a technical training, can measure function of both the semicircular canals and otolith organs, does not require active participation by the test subject, is quantitative, and is less expensive than other tests.

Claims

CLAIMSWe claim:

1. A device for evaluating the vestibular function in a subject comprising: a means for measuring the movement of the subject's head, a means for measuring the rotation of the eye of the subject relative with respect to the subject's head, and a means for comparing the measured movement of the head to the measured eye rotation in response to displacement of the head to reference population, wherein the head movement measuring means or the eye rotation measuring means or both measuring means are affixed to the subject's head.

2. The device of Claim 1 further comprising a means for displacing the subject's head.

3. The device of Claim 1 wherein the means for measuring the eye rotation is a videooculography means or an electrooculography means or both.

4. The device of Claim 1 wherein the means for measuring the rotation of the eye of the subject relative to the head is fixed to the head.

5. The device of Claim 1 wherein the means for comparing the measured movement of the head to the measured eye rotation is a computer.

6. The device of Claim 1 wherein the head movement measuring means is a videocamera.

6.1. The device of Claim 1 wherein the head movement measuring means or the eye rotation measuring means or both measuring means are affixed to the subject's head by a bite block. 6.11 The device of Claim 1 wherein the head movement measuring means or the eye rotation measuring means or both measuring means attached to the head using a strap.

6.12 The device of Claim 1 wherein the head movement measuring means or the eye rotation measuring means or both measuring means are attached to the head using a stereotaxic device.

6.13 The device of Claim 1 wherein the head movement measuring means or the eye rotation measuring means or both measuring means are attached to the head using contoured foam. 6.2 The device of Claim 1 wherein the head movement measuring means is a linear accelerometer.

6.3 The device of Claim 1 wherein the head movement measuring means is a rotational ratemeter.

6.4 The device of Claim 6.1 wherein the head movement measuring means or the eye rotation measuring means or both measuring means are a videocamera.

6.5 The device of Claim 6.4 wherein the device further comprises a source of external lighting such that the videocamera resolution and the source of external lighting provide for clinically relevant measurements of head movement and eye rotation.

6.6 The device of Claim 6.5 wherein the source of external lighting is attached to the head using a bite-block.

6.7 The device of Calim 6.5 wherein the source of external lighting is attached to the video camera. 6.8 The device of Claim 6.5 wherein the source of external lighting is attached to the head using a strap.

6.9 The device of Claim 6.5 wherein the source of external lighting is attached to the head using a stereotaxic device.

6.10 The device of Claim 6.6 wherein the source of external lighting is attached to the head using contoured foam.

7. A method of evaluating the vestibular function in a subject, comprising: a step of displacing the head of the subject , a step of measuring the movement of the subject's head, a step of measuring eye rotation of the subject with respect to the subject's head, and a step of comparing the measured head movement and eye rotation in response to displacement of the head to reference data wherein the head movement measuring step or the eye rotation measuring step or both measuring steps are performed by a device affixed to the subject's head.

8. The method of Claim 7 wherein the reference data is derived from further comprising measurements of data collected from a plurality of individuals with one or more defects in vestibular function.

9. The method of Claim 7 wherein the head displacement is angular rotation or linear displacement or both.

10. The method of Claim 7, wherein the subject's head is moved by hand and wherein the head displacement and head movement and eye rotation measurement are optionally repeated one or more times.

11. The method of Claim 7, wherein the subject's head is moved by a mechanical device and wherein the mechanical device is optionally affixed to the subject's head.

12. The method of Claim 7 wherein the subject's head is displaced by angular rotation about an axis of rotation parallel to the axes of a pair of the semicircular canals and wherein the head displacement and head and eye rotation measurements are optionally repeated one or more times.

13. The method of Claim 7, wherein the subject's head is displaced by movement in a linear direction and wherein the head displacement and head movement and eye rotation measurements are optionally repeated one or more times.

14. The method of Claim 7, wherein the eye rotation of the subject is measured by videooculography or electrooculography or both.

15. The method of Claim 7, wherein the step to measure eye rotation is accomplished by a video camera and wherein the video camera is optionally attached to the head.

16. The method of Claim 7, wherein the eye is illuminated by an infrared light source attached to the head.

17. The method of Claim 7, wherein the eye is illuminated by a visible-spectrum light source attached to the head.

18. The method of Claim 7, wherein the eye is illuminated by a light source attached to the head using a bite-block.

18.1 The method of Claim 7, wherein the eye is illuminated by a light source attached to the video camera.

18.2 The method of Claim 7 wherein the source of external lighting is attached to the head using a strap.

18.3 The method of Claim 7 wherein the source of external lighting is attached to the head using a stereotaxic device.

18.4 The method of Claim 7 wherein the source of external lighting is secured to the head using contoured foam.

19. The method of Claim 7, wherein the eye is illuminated by a source distant from the subject.

20. The method of Claim 7, wherein the subject's head displacement is angular rotation and the head movement is measured by a plurality of rotational ratemeters oriented to measure head rotations in one, or optionally two, or optionally three dimensions and wherein the ratemeter are attached to the subject's head.

21. The method of Claim 7, wherein the subject's head displacement is linear displacement and where the displacement is measured by a plurality of linear accelerometers oriented to measure linear accelerations in one, or optionally two, or optionally three dimensions and wherein the linear accelerometers are attached to the head.

22. The method of Claim 1 wherein at least one of the one or more image recorders are attached to the subject's head by a head strap.

23. The method of Claim 1 wherein at least one of the one or more image recorders are attached to the subject's head by a bite-block held between the subject's teeth.

24. The method of Claim 1 wherein the mechanical device that moves the head is attached securely to the head, in which fixation is accomplished using a stereotaxic apparatus mechanically engaging various parts of the skull.

25. The method of Claim 7, wherein the eye movement is measured in two or optionally three dimensions.

26. The method of Claim 7, wherein the head movement is measured in two or optionally three dimensions.

27. The method of Claim 7, further comprising a step for recording the head and eye movements.

28. The method of Claim 7 wherein the device for performing the head movement measuring step and the device for performing the eye rotation measuring step or both are affixed to the subject's head by a bite block.

29. The method of Claim 28 wherein the device for performing the head movement measuring step and the device for performing the eye rotation measuring step or both are a videocamera.

30. The method of Claim 29 wherein the method further comprises the step of providing external illumination.