GB2276467A - Device for measuring the vestibulo-ocular reflex function - Google Patents

Device for measuring the vestibulo-ocular reflex function Download PDF

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Publication number
GB2276467A
GB2276467A GB9306052A GB9306052A GB2276467A GB 2276467 A GB2276467 A GB 2276467A GB 9306052 A GB9306052 A GB 9306052A GB 9306052 A GB9306052 A GB 9306052A GB 2276467 A GB2276467 A GB 2276467A
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Prior art keywords
display
subject
device
head
head movements
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GB9306052A
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GB2276467B (en )
GB9306052D0 (en )
Inventor
Anthony Robert Gardner-Medwin
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London University College
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London University College
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    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/103Detecting, measuring or recording devices for testing the shape, pattern, colour, size or movement of the body or parts thereof, for diagnostic purposes
    • A61B5/11Measuring movement of the entire body or parts thereof, e.g. head or hand tremor, mobility of a limb
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B3/00Apparatus for testing the eyes; Instruments for examining the eyes
    • A61B3/10Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
    • A61B3/113Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for determining or recording eye movement
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2562/00Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
    • A61B2562/02Details of sensors specially adapted for in-vivo measurements
    • A61B2562/0219Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/68Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
    • A61B5/6801Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
    • A61B5/6802Sensor mounted on worn items
    • A61B5/6803Head-worn items, e.g. helmets, masks, headphones or goggles

Abstract

A device for measuring errors in compensatory eye movements during voluntary head movements by a subject while continuing to observe a visual display in the subject's field of view comprises an LED display 35 for producing a cyclically varying visual display, an Infrared sensor (14 Fig. 1) for measuring said voluntary head movements which are in phase with the cyclic variations in the visual display, and an adjustable calibrated plate indication means 37 operable by the subject to indicate the relationship between the true variations in the visual display and the apparent variations as observed by the subject during said voluntary head movements. The sensor (14) detects left and right flashing infra-red LEDs 18, 19 and 21, 22, head movements to the left or right being detected in the sensor output by a phase-sensitive detector (29). Embodiments for measuring other types of vestibule-ocular reflex function and alternative forms of display, sensor and indication means are also described. <IMAGE>

Description

DEVICE FOR MEASURING THE VESTIBUL0oOCULAR REFLEX FUNCTION The present invention relates to a device for measuring the vestibulo-ocular reflex function, that is to say a device for measuring the accuracy with which eye movements are made to compensate for voluntary head movements, for assessment of operator performance or clinical deficits in the relevant physiological mechanisms.

Assessment of vestibular function and vestibular reflexes are standard requirements for clinical and physiological assessment.

Most available techniques use expensive bulky equipment, for example rotating chairs. Portable monitoring equipment could be of value particularly in clinical monitoring, especially where patients are not mobile and are undergoing treatments (for example with aminoglycoside antibiotics: streptomycin, gentamicin, etc.) that carry a risk of damaging the vestibular system.

The vestibulo-ocular reflex serves to make the eyes move to compensate, so far as possible, for head rotations that are sensed by the vestibular organs (labyrinths, etc.). This is one of the most important vestibular reflexes, and is constantly used in subjects with normal visual and vestibular function. Assessment of the compensation is normally carried out by combined measurement of head and eye movements, using either imposed or voluntary patterns of motion. Since errors of a few percent in the compensation may be significant, each of the two measurements must be made to a high degree of accuracy for adequate assessment. Direct assessment of the errors in compensation (reflected in movement of the retinal image) are normally restricted to subjective reports by the subject of whether and when the world appears to move during head movements (oscillopsia) or performance of such tasks as reading or acuity assessment while carrying out head movements.

An object of the present invention is to provide a device which allows the movement of the retinal image during head movements to be assessed quantitatively and accurately in the course of just a few minutes (or a few seconds once the subject is familiar with the procedures).

According to the present invention, a device for measuring errors in compensatory eye movements during voluntary head movements, while the subject continuously views a visual display, comprises a sensor for measuring said head movements, display means for producing a varying visual display in phase with the head movements, and indication means operable by the subject or an assistant to indicate the relationship between the true variations in the display and the apparent variations seen by the subject during the voluntary head movements.

It will be appreciated that the true and apparent variations only differ when there are errors of compensation.

Conveniently, the visual display will vary throughout the assessment In directions which are perpendicular to the directions of the voluntary head movements and the indication means operates to indicate the relationship between the true directions of display variation and the apparent directions of display variation as observed by the subject.

Alternatively, the visual display may have an initial format in which it varies in directions which are perpendicular to the directions of the voluntary head movements and the indication means operates to alter the true directions of display variation until the apparent directions of display variation, as observed by the subject, assume said initial format (or some other predetermined format).

Conveniently, a vertically varying visual display would be used in conjunction with side-to-side horizontal head movements, a horizontally varying visual display would be used in conjunction with up-and-down vertical head movements, and a radially varying visual display would be used in conjunction with circumferential (torsional) head movements about an axis parallel to the subject's optic axis.

Conveniently, the display means may comprise a set of light emitting devices, an oscilloscope, or a computer screen e.g. with short persistence phosphor.

Conveniently, the sensor comprises either a coil for mounting on the subject's head and operative to generate an emf related to its orientation in an AC magnetic field, or a photosensor for mounting on the subject's head as the sensor and operative to detect infra-red or other radiation emitted from sources with intensity varying in opposite phase at sites separated in a plane perpendicular to the axis of roation to be measured, or an accelerometer, gyroscope or other mechanical sensor for mounting on the subject's head and detecting rotation.

Conveniently, the device is either arranged for measuring and displaying horizontal, vertical, or torsional head rotations.

Conveniently, the indication means is provided with parallel lines in front of the display or as part of the display whose orientation can be adjusted to match the tilt of the perceived movement of the stimulus.

Conveniently, in the case of tortional head rotations, the parallel lines have the same adjustable orientation relative to radii from a point on the display produced by mechanical means in front of the display or as part of the display on an oscilloscope or computer screen and capable of being adjusted to match the appearance of the moving elements of the display.

Conveniently, where the indication means operates to alter the true directions of display variation until the apparent directions of display variation, as observed by the subject, assume the initial format (or some other predetermined format), then displacement of elements of the visual stimulus occurs also perpendicular to the stated principal direction and in proportion to the head movements, with the relative amplitude of perpendicular movements being adjustable by the indication means to provide the subject with a standard appearance of the stimulus.

Conveniently, in this latter case, the movement perpendicular to the principle direction has also an adjustable phase relative to the head movements.

In one form of assessment, considered here by way of example, the subject is instructed to rotate the head from side-to-side by a few degrees in an approximately regular rhythm (typically at 1-5 Hz), while looking at a screen on which is displayed a visible dot that moves vertically in proportion to the horizontal head movements.

The frequency of head movement can be selected by the operator and Indicated to the subject using an auditory or visual cue (e.g.

an electronic metronome) and the orientation of the head can be measured continuously during these movements, using electromagnetic, optical, accelerometry or any other conventional system, with the orientation signal used to control the height of the dot.

What the subject is actually looking at in this assessment, is a dot moving up and down in a vertical line and if the head movements are slow enough (e.g. ca. 1 Hz even in vestibular disabled subjects), this is what is perceived. At faster speeds, however, if the eye movements do not exactly compensate for the horizontal head movements, the retinal image of the dot will move horizontally on the retina due to the error in compensation, as well as moving vertically due to its own actual movement. The result is generally that the perceived line becomes tilted with the angle of tilt, for small angles, proportional to the Z error in compensation and the direction of tilt dependent on whether over-compensation or undercompensation has occurred. What is seen is, in effect, similar to a graph of the error in compensation plotted against the head movements. This can be a loop rather than a single line (if the error Is not in phase with the head movements) although at moderate frequencies, a tilted straight line is generally seen.

To measure the amount of error, the subject can match the orientation of the line that is seen with the orientation of a set of faint lines seen as part of the display or ruled on a transparent moveable panel immediately in front of the dot display. The set orientation can be read and recorded manually or electronically and converted into a percentage error of compensation, using appropriate calibrations.

Alternatively, the tilt can be nulled by introducing an adjustable horizontal component to the movement of the dot, which is set to match and cancel the errors of vestibulo-ocular compensation with the relationship adjusted by the subject to achieve a perceived vertical (or other standard) appearance. This technique allows errors that are out of phase with the head movements (producing loops in the simple display) to be compensated and measured also.

In order to measure compensation for vertical head movements, the sensor system must be arranged to detect this orientation of head movement and the spot must be made to move horizontally rather than vertically. This may (depending on the sensor system) require no more than rotation of the instrument through 90 degrees.

Measurement of torsional errors can be carried out using a similar principle. Torsional movements are measured as the subject makes head movements rotating about a horizontal axis parallel to the optic axis. The display in this case consists of one fixed and one moving dot, or two or more dots that move radially away from and towards a fixed point on the screen in proportion to the measured head movements. When torsional compensation is correct, the dots are perceived as moving on radial lines. Errors of compensation makes the lines inclined to the radial, to an extent that can be measured or (most easily with a computer graphic display) nulled.

Errors of less than 5 percent in lateral eye movements are generally found in most normal subjects at 4 Hz. Systematic errors can be induced and measured with an accuracy of a few percent in normal subjects, for example by mounting a weak telescope in front of one eye to give a small magnification or diminution of visual angles.

Prototype embodiments of the invention employ for the display either (a) an oscilloscope with short persistence blue phosphor or (b) the red channel on a conventional colour computer graphic display (which has shorter persistence than the blue or green channels) or (c) a row of 40 light emitting diodes (LEDs) at 2.5 mm spacing. The LED display gives the most compact instrument. With the LED display, the details of mounting of the LEDs and the fact that the visible dots are produced by a row of emitters that can only in fact produce a vertical line are obscured from the subject by a dark coloured filter in front of the display that transmits the LED light but obscures incident and reflected light. A circular perspex plate with parallel scoring at 5 mm spacings is mounted in front of the filter and can be rotated to align the scoring with the apparent movement of the oscilloscope or LED dots.

Several alternative measurement systems may be used for sensing the orientation changes of the head.

The first of these systems, and the most accurate, employs a small electromagnetic pickup coil taped to the subject's forehead or mounted on a pair of goggles, generating an emf at 10 kHz proportional to the intersection that the coil makes with a uniform horizontal 10 kHz magnetic field generated in the region of the subject's head by sets of coils placed either side of the head. The emf is measured with a phase sensitive detector.

An alternative system of measuring head movement differs from the first system in having the magnetic field generated within the instrument box containing the display in front of the subject. This is more compact but gives a less uniform magnetic field.

In another alternative, using a photosensor secured on the subject's head, the photosensor picks up signals from infra-red LEDs. These are mounted on either side of the instrument box in front of the subject, and they flash out of phase with each other at 1 kHz. The 1 kllz photosensor signal (measured with a phase sensitive detector) is zero when the sensor is pointing symmetrically between the left and right diodes, and has an amplitude (positive or negative) proportional to angular displacements either way.

In a final alternative, an accelerometer is mounted on a bite plate held between the subject's teeth to measure rotations of the head about a vertical axis. This gives measurements of angular acceleration, which are integrated to give a signal proportional to changes of orientation. This has the advantage of compactness and complete independence of the position of the subject's head. High engineering standards are required, however, to give good signal quality at low frequencies (ca. 1 Hz).

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a block diagram of an instrument set up for assessing vestibulo-ocular function in normal subjects and in patients with established vestibular disorders as evidenced when the subject moves the head to and fro from side to side in a normal fashion (as when disagreeing with someone).

Figure 2 shows, on a larger scale, a detail of the instrument face in the equipment of Figure 1; and Figure 3 is a diagrammatic representation of how an instrument might be used to measure incorrect torsional compensation (in place of the side-to-side compensation being measured in Figures 1 and 2).

The electronic circuits shown in block outline in Figure 1 are housed in an instrument case (220 x 150 x 100 mm), which is positioned 50 cm in front of the seated subject 10, on a level with the eyes.

The movements of the subject's head about an axis 12 over the vertebral column, are detected by a compound infra-red sensor 14 mounted on a pair of ordinary safety goggles worn by the subject (over spectacles when appropriate).

The sensor 14 is turned towards the instrument box, on the face 16 of which there are four infra-red light-emitting diodes (LEDs) that flash at a frequency of 1 kHz. Flashes from the two diodes 18,19 on the left of the instrument face 16 occur in synchrony with one another but alternate with the flashes from the two diodes 21,22 on the right of the face 16. This is arranged by means of a 2 kHz oscillator 23 operating via frequency divider 24 and gating circuits 26,27 as shown.

If the sensor 14 points symmetrically between the emitter pairs 18,19 and 21,22, there is equal detection by the sensor of the alternate flashes and no signal component is generated (at 1 kHz).

However, head movements to the left or right bias the detection to the infra-red light from either diodes 18,19 or diodes 21,22 because of the sensor's directionality, producing a 1 kHz signal from sensor 14 that is measured by a phase sensitive detector 29 after suitable amplification in amplifier 31.

The signal from the detector 29 is fed to a standard module 33 for controlling an array 35 of forty visible red light LEDs mounted on the face 16 of the instrument box at 2.54 mm spacings. This signal from module 33 operates in a mode ("dot-mode") in which the position of a single lit LED varies linearly with the signal voltage. Thus, the position of the visible dot is (for movements less than about t5 degrees) an adequately linear measure of the head movements (ca. 4 mm/degree).

The compound sensor 14 consists of three photo-diodes oriented slightly differently in the vertical plane, and this, and the use of the two vertically displaced infra-red LEDs on either side of the visible wavelength array 35, makes the system relatively insensitive to up and down movements of the head.

The subject is not aware of the flashing infra-red LEDs 18,19 and 21,22.

In front of the LED visible wavelength array 35 is a dark red celluloid filter (not shown), so that the subject sees (even in bright illumination) only the LED that is lit. In front of this filter is a circular perspex plate 37, mounted on roller bearings 39 in the instrument face 16 so that it can be rotated in its own plane by the subject, using a handle 41. On this plate are scored several thin parallel lines 43. Away from the central zone of the display, the lines 43 are enhanced in visibility with thick white lines to improve ease of use for subjects with poor vision or in conditions in which the image is defocussed for experimental reasons.

The instrument is normally used in ordinary room light.

In use, the subject moves the head in time with a continuous audible tone that varies sinusoidally in pitch (e.g. at 1 Hz or 4 Hz, as set by the operator). This tone is generated by a circuit also included in the instrument box.

The subject describes the appearance of the moving red dot (which is normally a line or a narrow loop) and is instructed to set the orientation of the lines on the adjustable perspex plate to be parallel to the orientation of the perceived line or loop. The slant is read by the operator on a scale attached to the edge of the perspex plate.

In fact, the dot is actually always moving up and down vertically, but with errors of eye movement compensation it appears to move on a slant. Such errors are conspicuous to subjects with bilateral vestibular disorders when moving the head faster than ca. 2 Hz (producing apparent slants of 45 degrees or more, corresponding to less than 50% of correct compensation).

With normal subjects, slants greater than five degrees are rare (corresponding to errors of a few percent in compensation), though significant errors can be measured when the subject dons reading glasses (which alter the visual magnification) or views objects at different distances seen in the same line of sight.

Only head movements of a few degrees are required, with the subject instructed to keep the visible dot within the inner of two circles 45 inscribed on the plate. The outer circle 46 is used for calibration checks.

In a first modification of this instrument, the signal from the phase sensitive detector 29 is also fed to a peak detector and period timer, to measure the period of the head movements, since some subjects can easily make regular head movements but find it difficult to do this in time with a cue.

In a second modification, the movement of the perspex plate 37 can be arranged with a remote control so that the subject find it more convenient.

In a third modification, the 2 kHz component of the signal from the sensor 14 could be used to compensate automatically for errors in the distance of the subject from the display. Such errors affect the calibration, and though they are of little significance given the magnitude of the compensation errors seen with clear clinical conditions, they can be significant in research studies. For accurate studies, the same psychophysical principle can be used with a more bulky conventional laboratory system for measuring the head movements (e.g. using uniform oscillating magnetic fields).

Turning now to the table shown in Figure 3, this illustrates how an instrument in accordance with the present invention can be used for torsional studies where relative torsional movement between the head and the instrument occurs about an axis parallel to a line through the centre of the instrument display face and a point mid-way between the two eyes of the subject.

Thus in Figure 3, the left-hand column illustrates the actual sample displays which might appear on the instrument face, reference letter 'A' indicating a fixed LED and reference letters 'B' indicating moving LEDs. Three alternatives are shown, each of them colinear due to correct torsional compensation, but differing according to other types of movement that may be incorrectly compensated and according to a frame of reference the subject may interpret as stable.

The second column in the table illustrates the corresponding expected appearances of the LEDs to a subject with correct torsional compensation ("CTC") showing colinear appearance of dots.

The third column in the table illustrates the corresponding expected appearances of the LEDs to a subject with incorrect torsional compensation ("it") showing the angle to be measured to assess the error in torsional compensation.

In the second and third columns, only the fixed LEDs have been identified (by reference 'A'), all the other LEDs depicted in these two columns being moving LEDs.

It is to be noted that the apparent orientation of the displays and apparent movement of the fixed dots in the last two columns of the table are irrelevant, since these are also affected by non-torsional movements and their extent of compensation.

It is an advantage of the equipment as hereinbefore described that it is portable and can be used repeatedly for monitoring of patients confined to bed during treatment. The extent of subject cooperation required is minimal, and any distress is likely to be restricted only to patients who find any form of head movement intolerable.

Claims (18)

1. A device for measuring errors in compensatory eye movements during voluntary head head movements, while the subject continuously views a visual display, comprising a sensor for measuring said head movements, display means for producing a varying visual display in phase with the head movements and indication means operable by the subject or an assistant to indicate the relationship between the true variations in the display and the apparent variations seen by the subject during the voluntary head movements.
2. A device as claimed in Claim 1 in which the visual display will vary throughout the assessment in directions which are perpendicular to the directions of the voluntary head movements and the indication means operates to indicate the relationship between the true directions of display variation and the apparent directions of display variation as observed by the subject.
3. A device as claimed in Claim 1 in which the visual display has an initial format in which it varies in directions which are perpendicular to the directions of the voluntary head movements and the indication means operates to alter the true directions of display variation until the apparent directions of display variation, as observed by the subject, assume said initial format (or some other predetermined format).
4. A device as claimed in any of Claims 1 to 3 in which a vertically varying visual display is used in conjunction with side-to-side horizontal head movements.
5. A device as claimed in any of Claims 1 to 3 in which a horizontally varying visual display is used in conjunction with up-and-down vertical head movements.
6. A device as claimed in any of Claims 1 to 3 in which a radially varying visual display is used in conjunction with circumferential (torsional) head movements about an axis parallel to the subject's optic axis.
7. A device as claimed in any preceding claim in which the display means comprises a set of light emitting devices.
8. A device as claimed in any of Claims 1 to 6 in which the display means comprises an oscilloscope.
9. A device as claimed in any of Claims 1 to 6 in which the display means comprises a compute-r screen.
10. A device as claimed in any preceding claim in which the sensor comprises a coil for mounting on the subject's head and operative to generate an emf related to its orientation in an AC magnetic field.
11. A device as claimed in any of Claims 1 to 9 in which the sensor comprises a photosensor for mounting on the subject's head as the sensor and operative to detect infra-red or other radiation emitted from sources with intensity varying in opposite phase at sites separated in a plane perpendicular to the axis of rotation to be measured.
12. A device as claimed in any of Claims 1 to 9 in which the sensor comprises an accelerometer, gyroscope or other mechanical sensor for mounting on the subject's head and detecting rotation.
13. A device as claimed in any preceding claim arranged for measuring and displaying horizontal, vertical, or torsional head rotations.
14. A device as claimed in any preceding claim in which the indication means is provided with parallel lines in front of the display or as part of the display whose orientation can be adjusted to match the tilt of the perceived movement of the stimulus.
15. A device as claimed in Claim 14 for use with tortional head rotations in which the parallel lines have the same adjustable orientation relative to radii from a point on the display produced by mechanical means in front of the display or as part of the display on an oscilloscope or computer screen and capable of being adjusted to match the appearance of the moving elements of the display.
16. A device as claimed in any preceding claim when including the limitations of Claim 3 in which displacement of elements of the visual stimulus occurs also perpendicular to the stated principal direction and in proportion to the head movements, with the relative amplitude of perpendicular movements being adjustable by the indication means to provide the subject with a standard appearance of the stimulus.
17. A device as claimed in Claim 16 in which the movement perpendicular to the principle direction has also an adjustable phase relative to the head movements.
18. A device for measuring errors in compensatory eye movements during voluntary head movements substantially as hereinbefore described with reference to, and/or as illustrated in, Figures 1 and 2 or Figure 3 of the accompanying drawings.
GB9306052A 1993-03-24 1993-03-24 Device for measuring the vestibulo-ocular reflex action Expired - Fee Related GB2276467B (en)

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GB9306052A GB2276467B (en) 1993-03-24 1993-03-24 Device for measuring the vestibulo-ocular reflex action
PCT/GB1994/000524 WO1994021162A1 (en) 1993-03-24 1994-03-16 Device for measuring the vestibulo-ocular reflex function

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Cited By (3)

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EP0733338A1 (en) * 1995-03-24 1996-09-25 Commissariat A L'energie Atomique Device for measuring the position of the fixation point of an eye on a screen
WO1999009881A1 (en) * 1997-08-22 1999-03-04 Massachusetts Institute Of Technology Apparatus and method for measuring vestibular ocular reflex function
US9183756B2 (en) 2007-11-26 2015-11-10 Ultrathera Technologies, Inc. Vestibular stimulation systems and methods of use

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RU2480155C1 (en) * 2011-12-01 2013-04-27 Государственное Научное Учреждение "Научно-Практический Центр Профилактической И Клинической Медицины" Государственного Управления Делами Method of estimating state of vestibular-motor projection and system for its realisation
WO2018107108A1 (en) * 2016-12-08 2018-06-14 Oregon Health & Science University Method for visual field perimetry testing

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US4582403A (en) * 1984-03-05 1986-04-15 Weinblatt Lee S Head movement correction technique for eye-movement monitoring system

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EP0363521B1 (en) * 1988-10-14 1991-09-25 PANARES TECHNISCHE ENTWICKLUNGEN GMBH &amp; CO. BETRIEBS KG Function testing apparatus for otoliths

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Publication number Priority date Publication date Assignee Title
US4474186A (en) * 1979-07-17 1984-10-02 Georgetown University Computerized electro-oculographic (CEOG) system with feedback control of stimuli
US4582403A (en) * 1984-03-05 1986-04-15 Weinblatt Lee S Head movement correction technique for eye-movement monitoring system

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0733338A1 (en) * 1995-03-24 1996-09-25 Commissariat A L'energie Atomique Device for measuring the position of the fixation point of an eye on a screen
FR2731896A1 (en) * 1995-03-24 1996-09-27 Commissariat Energie Atomique Device for measuring the position of the attachment point of an eye on a target, METHOD eye lighting application and displaying images whose images change according to the eye movement
US5668622A (en) * 1995-03-24 1997-09-16 Commissariat A L'energie Atomique Device for measuring the position of the fixing point of an eye on a target, method for illuminating the eye and application for displaying images which change according to the movements of the eye
WO1999009881A1 (en) * 1997-08-22 1999-03-04 Massachusetts Institute Of Technology Apparatus and method for measuring vestibular ocular reflex function
US5942954A (en) * 1997-08-22 1999-08-24 Massachusetts Institute Of Technology Apparatus and method for measuring vestibular ocular reflex function
US9183756B2 (en) 2007-11-26 2015-11-10 Ultrathera Technologies, Inc. Vestibular stimulation systems and methods of use

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WO1994021162A1 (en) 1994-09-29 application
GB9306052D0 (en) 1993-05-12 application

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PCNP Patent ceased through non-payment of renewal fee

Effective date: 19970324