GB2140935A

GB2140935A - Eye testing system

Info

Publication number: GB2140935A
Application number: GB08413418A
Authority: GB
Inventors: Daniel Kligler; Yair Mendels
Original assignee: Yissum Research Development Co of Hebrew University of Jerusalem
Current assignee: Yissum Research Development Co of Hebrew University of Jerusalem
Priority date: 1981-04-10
Filing date: 1984-05-25
Publication date: 1984-12-05
Also published as: GB8413418D0; GB2140935B; IL62627A0; GB2096791B; JPS5911833A; JPS6216086B2; IL62627A; DE3212853A1; GB2096791A

Abstract

A system for testing eyes includes an eye position monitoring means comprising means 19 for transmitting light waves to the patient's eyes, means 21 for detecting and determining the position of light reflected by the patient's eyes including photodiode means comprising a first array for detecting the horizontal position of the reflected light and a second array for detecting the vertical position of the reflected light. Optical means are provided for transmitting the reflected light to the first and second arrays. <IMAGE>

Description

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SPECIFICATION Eye testing system

5 Field of the invention

This invention is concerned with methods and equipment for testing the eyes and more particularly with automatic perimetry systems for use in visual field testing.

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Background of the invention

The testing of the patient's field of vision is an extremely important diagnostic tool used to identify and analyze diseases and defects of the retina and 15 visual pathways, such as glaucoma, optic neuropathy, multiple sclerosis and optic nerve compression. In the past such tests were run using manually operated field of vision test instruments known as perimeters. The maunally operated perimeters re-20 quire the services of a physician or a skilled technician. In the most widely used system (the Goldmann system), the patient must sit with his head clamped in place to eliminate the uncertainties of added head movements. The procedure presently widely used is 25 unduly tiring forthe patient and the clinician and because of the fatigue and of a heavy reliance on subjective human factors, the results of the tests have proved inconsistent or irreproducible or both. More recently, automatic perimeters have been 30 marketed and used. However, even these basically use the Goldmann system and incorporate the control of a microprocessor.

The Goldmann system requires the patient to sit facing a hemispherical screen with his head strap-35 ped to a head-rest. Thus he must maintain a constant sitting position forthe duration of the test. He fixes his eye continuously on a "fixation point" at the centre of the screen. The examination can last for somewhere between 20 minutes and an hour. A 40 small point of light of varied intensity, size and colour is projected onto the screen and its position is varied by the operator. The limits of the visual field are determined on the basis of patient's indications as to when the point of light comes into or goes out 45 of view as the light is moved radially between the periphery and the centre of his view. The examiner must continuously watch the patient to assure that the eye of the patient is fixated on the centre of the screen. The examination is worthless if the patient's 50 view is wandering and is not fixed on the fixation point. Thus the examination of the extent of the field of vision using the commonly available Goldmann system is basically subjective. It depends to a large extent on the skill of the examiner, the patient's 55 fatigue level and the effectiveness of the examiner in communication with the patient.

It is an object of the present invention to provide new and improved perimetry systems in which the above referred to disadvantages are substantially 60 reduced or overcome.

According to the present invention there is provided a system for testing eyes including eye position monitoring means, said eye position monitoring means comprising:

65 means for transmitting light waves to the patient's eyes, and means for detecting and determining the position of light reflected by the patient's eyes including photodiode means,

70 said photodiode means comprising a first array for detecting the horizontal position of the reflected light, a second array for detecting the vertical position of the reflected light, and optical means for transmitting said reflected light 75 to said first and second arrays.

Helmet means fitting the patient's head may be provided for supporting said eye position monitoring means whereby movement of the patient's head during the test does not affect the test results. 80 A further feature of the invention includes microprocessor means for automatically interpreting data from the eye position monitoring means during the tests.

The operation and utilization of the present inven-85 tion will be more fully apparent from the description of a preferred embodiment taken in conjunction with the accompanying drawings, in which:

Figure 1 is a pictorial drawing showing a test system including a helmet strapped onto a patient's 90 head connected to energizing and control equipment;

Figure 2 is a block diagram type drawing of the fixation means;

Figure 3 is a block diagram of the spot projecting 95 and scanning means; and

Figure 4 is a block diagram showing details of the control equipment shown originally in Figure 1.

General description 100 In Figure 1, the system 11 is shown as including a helmet 12 which is strapped to the patient's head 13 using strapping means shown generally as straps 14. The helmet 12 is shown as being of hemispherical construction and covering the face of the patient. 105 The view of the helmet 12 in Figure 1 is partially broken away to show its interior. Within the helmet there is a hemispherical screen indicated by line 16. The inner surface of the helmet can serve as the screen. Shown attached to the helmet is an electro-110 mechanical system 17 which includes means for moving a mirror scanner 18 according to a program designed to move the light spot to various positions on the screen. The spot is generated by the spot generating optics device 19 also attached to the 115 helmet.

Means are provided for determining that the patient's eye is affixed to the centre of the screen. More particularly electro-optical eye position monitoring or detection means are shown generally by 120 box 21 mounted to the outer periphery of the helmet device. Cables 22 act as an umbilical cord connecting the helmet to console equipment shown generally as 23.

The console equipment 23 includes means for 125 generating the light used by the optical equipment to the helmet. The light source equipment is shown generally as block 24. It should be noted that the cable directing the light from block 24, the helmet and its equipment includes fibre optic cabling 25. 130 The console also includes a microprocessor and

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interface circuitry in block 26 and a CRT screen with the appropriate controls shown generally as block 27. Shown connected to block 27 is keyboard arrangement 28 for putting information into the 5 system. A block 29 is shown to indicate hard copy output equipment. The hard copy output gives the doctors a permanent record of the test. With the use of the helmet the test can be conducted while the patient is sitting, standing or lying down. Also 10 because of the use of the helmet rather than the clamping of the head the test is conducted a lot faster because any movement of the head also moves the spot and therefore does not disrupt the test.

15 In Figure 2 details of the unique eye position detector 21 is shown. It operates by detecting and determining the position of light reflected from the patient's eye. The detector is shown as comprising a box 31. The box has a vertical side 32 and a 20 horizontal side 33. Mounted from the vertical and horizontal sides are means for detecting an infra-red image of the eye. More particularly photodiode arrays 34 and 36 are shown. These arrays are commerically available such as, for example, self-25 scanned photodiode arrays No. RL-64 P manufactured by Reticon Company of the United States. The array is a row of 64 light sensors. Each sensor is 50x50 microns in size. The arrays 34 and 36 are shown as having windows 37 and 38 respectively for 30 enabling light to enter and shine upon the light sensors. One array indicates the horizontal position of the eye while the other array indicates the vertical position of the eye.

When subjected to infra-red light, the reflected 35 image of the eye is bright at the pupil becuase of reflection from the retina. The iris reflection is distinctly darker. The system is thus capable of detecting pupil size within approximately 0.3 mm and eye orientation within one degree in each 40 dimension. Thus, the eye position detector also can be used to provide additional information invaluable to the diagnostician. The eye position detector 21 also includes a fibre optic light guide 39 which is brought to unit 21 as part of the umbilical cord 22. In 45 addition electrical cable 41 is brought to unit 21 to provide the electrical power for the photodiode arrays. The fibre optic light guide 39 transmits light which is reflected by a mirror 42 through a lens 43 to the eye 44 of the patient. The light reflected from the 50 eye is transmitted through a receiving lens 46 onto a beam splitter 47. The beam splitter directs the reflected light to windows 37 and 38 to enable the photo arrays to determine the position of the eye relative to horizontal and vertical axes. 55 The outputs of the arrays are transmitted through the cable 41 and back to the console where they are processed. They form the basis forthe microprocessor's determination of the position of the eye. When the signal indicates that the patient is no longer 60 fixating on the centre and the test results are therefore not valid, the equipment automatically stops the test and indicates this to the patient. When the patient fixes his gaze on the centre the test recommences. This means can equally monitor 65 fixation on a point otherthan centre screen or can record eye motion. During the test, the microprocessor also determines and records pupil size on the basis of the outputs of the arrays.

The screen 16 is shown in Figure 2 positioned relatively close to the eye. In a preferred embodiment the distance between the screen and the eye is 10cm,thus Figure2 is definitely notto scale.

Figure 3 shows details of the electro-mechanical unit 17 for scanning or moving the light spot and the optics 19 for controlling the size and focus of the light spot. The optical equipment 19 comprises a fibre optic light guide 48 mounted into a special fibre optic mounting bracket 49. The end 51 of the fibre optic cable is positioned to transmit the light coming through the conductor through spot sizing means such as aperture 50 to a focusing lens 52. The lens 52 is mounted in a lens holder assembly 53 which enables focusing the light spot.

The bracket 49 includes a screw arrangement 54 for clamping the end 51 of the fibre optic conductor 48. The bracket 49 is coupled to a base unit 56 that is mounted to the helmet 12 by means such as mounting fastener 57. The lens holder assembly is mounted in groove 62 in base unit 56.

Means are provided for controlling the size of the spot. More particularly disc unit 61 is rotatingly mounted to base unit 56 with screw 58. The disc unit 61 has a circular array of apertures therethrough such as aperture 50. The apertures have different diameters and control the size of the light spot. Thus the disc is rotated until the aperture giving the desired size of light spot is positoned under end 51 of optical fibre light guide 48.

An alternative light spot sizing device may be provided. For example a fibre optic bundle could be used, having the fibres at the output end arranged in concentric rings. At the input end, the fibre bundle would branch into smaller bundles, with each input bundle corresponding to a particular output ring. Thus, by selectively illuminating the desired input branches, an output spot of variable size would be obtained. This output spot of variable size would be imaged onto the screen to provide the variable test-spot size.

The disc position locking clamp arrangement 63 is provided. More particularly the clamp 64 is attached to an arcuate member 66 fixed to the periphery of the disc. The clamp 64 is clamped into position on base unit 56 by tightening threaded means such as threaded fastener 67. This holds the disc in the desired position with the selected spot size.

The lens holder assembly is positioned so that the light strikes the mirror 71 in tubular unit 69 of system 17 which is cut away at 68 to admit the light. Scanning means are provided to position the spot as required by moving the mirror 71 vertically and horizontally while the light strikes the mirror so that the reflected spot of light moves on the screen according to a definite program. The scanning means are light and efficient and therefore ideally suited for mounting to the helmet 12.

The elctro-mechanical scanning device 17 comprises a base 72. The base is attached to the light spot generating unit base 56 with fastener 73. The clamp means 49 is shown fastened to the base 72

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with a threaded fastener 74.

The cylindrical tube 69 houses the mirror assembly for mirror71,The mirror71 is equipped to rotate vertically and horizontally. It is rotated around a 5 horizontal axis 76 by stepping motor 77. The stepping motor 77 causes rotation of shaft 78 to which a gear 79 is attached by fastener 81. Gear 82 is fixed to axle 76 and causes the rotation of axle 76 and accordingly the rotation ofthe mirror71 about the 10 horizontal axis.

Bearing means 83 and 84 support the shaft 78 in its rotation. Bearing assembly clamping member 87 aids in fixing the position ofthe mirror relative to the cutaway 68. Thus there is a set screw 68 which goes 15 through the clamping member 87 ofthe bearing assembly 83.

The mirror is rotated around an axis coaxial with shaft 78 by stepping motor 91. The rotation of stepping motor 91 rotates belt driven wheel 92 20 through belt coupler 93. The rotation ofthe wheel 92 rotates the mirror holding unit 94. More particularly the wheel is fixed to a collar 96 which is in turn fixed to a hollow cylindrical shaft 97 that extends into the outer cylindrical tube 69 and is coupled to the mirror 25 carrying assembly by means such as set screw 99. Thus the entire mirror carrying assembly rotates with the belt motivated wheel 92 to horizontally move the point of light generated at unit 19. The light is moved according to the actuation ofthe stepping 30 motors 91 and 77. Each step of the motors moves the spot of light on the screen 16 according to the program position.

The unit 17 is also shown as being equipped with a bearing section 101 between the shaft 78 and the 35 outertubularcylinder69. It minimizes the wobble and assures that the spot travels in accordance with the program on fixed lines with minimal wobble and vibrational effects.

In Figure 4 pertinent details ofthe light source and 40 optical system are shown within block 24. More particularly a light source 111 is shown as comprising a quartz halogen lamp for example. The quartz halogen lamp is shown as being energized over alternating current conducting cable 112. A cooling 45 fan 113 is shown directly behind the halogen lamp. The fan 113 is energized over conductors 114.

The light from the lamp is twice transmitted. One transmission occurs to the eye position detector through optical fibre bundles 39 and the other 50 transmission occurs to the test spot scanner through fibre optical bundle 48. A third bundle (not shown) conveys light from the lamp to the screen to provide uniform background illumination.

Between the light source 111 and fibre optic 55 conductor 39 there is shown a long pass (IR) filter 116. After the filter there is a focusing lens 117.

Between the light source and the test spot scanning cable 48 there are a pair of focusing lenses 118 and 119 separated by a series of colour and intensity 60 filters generally shown as 121 used to control the colour and intensity ofthe light spot. The filters are removed or inserted under the control ofthe microprocessor, with commands coming over conductor 122. The removal and insertion of the filters is done 65 in a way known to those skilled in the art. This enables automatic control ofthe intensity and colour ofthe spot being scanned which provides another dimension to the test equipment.

Block 26 of Figure 4 is shown as having the microprocessor and electronic control equipment. Block 26 also contains some ordinary electrical supply equipment such as the transformer 126 which is used for powering the light source for example. The microprocessor 127 is an ordinary commercial available microprocessor unit such as an LSI-11. It is connected to the CRT 27, keyboard 28 and hard-copy unit 29 over conductors 128 ad 129 for example.

Means are provided for using the signals received from the eye position detector for generating positional signals which can be compared to the position ofthe light spot. More particularly analog-to-digital converters 131 and 132 are shown as being coupled to and receiving signals from arrays 34 and 36 respectively over conductors 133 and 134. The A to D converters 131 and 132 are commercially available units such as, for example, those supplied by Analog Devices ofthe United States under No. AD 7574.

The output of the A to D converters are coupled to signal processing circuit 136. The circuit 136 provides signals which are indicative ofthe position of the eye and the pupil diameter. These are vector quantities taking into consideration both the horizontal and vertical coordinates. In the microprocessor unit that signal is converted to coordinates of eye position, which are compared with programmed instructions. As long as the eye is at the proper orientation, the microprocessor continues to perform the test and operate the scanner.

The scanner control unit 137 is coupled to the microprocessor over conductors, generally shown as conductors 138. The scanning control unit 137 includes stepping motor pulse generators 149 and 151. The output ofthe stepping motor pulse generators goes to conductor 152 and 153 respectively for the horizontal and vertical control stepping motors 77 and 91 respectively.

The microprocessor controls the pulse generators as follows: from its program and memory the microprocessor determines the start- and end-points and the speed ofthe desired scan. It accordingly sends signals over conductors 138 to the pulse generators 149 and 151 starting their operation and peforming the scan at the desired speed until the end point is reached. By counting the pulses of generators 149 and 151, the microprocessor monitors the position of the test spot. When the patient signals manually that he has seen the spot, an electrical signal is received over conductor 154 by the microprocessor, which then records the position at which the point was seen.

Thus in the system shown the scanning is automatically accomplished underthe control ofthe microprocessor in accordance with a program entered through a keyboard and conducted by conductors such as conductor 128. The outputs of the test are also transferred through the microprocessor to the hard copy producter conductors such as conductor 129. The hard copy provides a record to the physician. The test can be run in a shorter period of time

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than normally taken with the ordinary Goldmann system because among other things the patient's head is not immobilized and accordingly he is much more relaxed forthe test. The test provides much 5 more accurate, reliable and repeatable measurements because the human factor is reduced to a minimum.

In operation the helmet 12 is placed on the patient's head and the patient is told to keep the eye 10 being tested on the centre of the screen. One eye is covered and the test is run on one eye at a time. The helmet 12 is put on the patient's head and the spot is projected onto the screen 16. The patient is told to indicate that he sees the spot and the test com-15 mences. The spot is then automatically programmed for movement and the patient indicates when he loses the spot in his peripheral vision and/or when the spot returns. The equipment automatically determines when the patient is not fixating, in which case 20 the test stops and repeats. The program varies the colour and intensity ofthe spot. The test with the described equipment is automatic and can be run by relatively unskilled personnel ratherthan requiring the time of either a doctor or a skilled technician. 25 While the principles ofthe invention have been described above in connection with specific apparatus and application, it is to be understood that this description is made byway of example only and not as a limitation on the scope ofthe invention.

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Claims

1. A system for testing eyes including eye position monitoring means, said eye position monitoring

35 means comprising:

means for transmitting light waves to the patient's eyes, and means for detecting and determining the position of light reflected by the patient's eyes including 40 photodiode means,

said photodiode means comprising a first array for detecting the horizontal position ofthe reflected light, a second array for detecting the vertical position ofthe reflected light, and 45 optical means fortransmitting said reflected light to said first and second arrays.

2. A system of Claim 1, wherein supporting means is provided for supporting said eye position monitoring means on the patient's head, whereby

50 the patient's head remains mobilethroughoutthe test.

3. The system of Claim 2, wherein said supporting means comprises helmet means.

4. The system of Claim 3 wherein means respon-55 sive to the position ofthe reflected light are provided for determining whether or not to continue the test.

5. A system substantially as hereinbefore de-cribed by way of example and with reference to the accompanying drawings.

Printed in the UK for HMSO, DS818935,10/84,7102.

Published by The Patent Office, 25 Southampton Buildings, London,

WC2A1 AY, from which copies may be obtained.