GB2332271A

GB2332271A - Automated assessment of strabismus patients

Info

Publication number: GB2332271A
Application number: GB9812154A
Authority: GB
Inventors: Ahmed Abdel-Rahman Assaf
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-12-09
Filing date: 1998-06-08
Publication date: 1999-06-16
Anticipated expiration: 2018-06-08
Also published as: HK1035473A1; GB9812154D0; GB9725974D0; GB2332271B

Abstract

An automated device uses digital positional image analysis of the eye for the measurement of the angle of strabismus and the assessment of ocular motility disorders eg in strabismus (squint) patients. This device consists of a computer with a colour monitor and mouse or trackball, a secondary display for displaying targets, a digital camera D positioned at the centre of the secondary display, and a chin rest with eyepiece assembly G. The display may be a hemispherical screen A with a projector B, or a large TV screen. The camera takes images of the eye during cover test and ocular movement assessment and monitors fixation during testing. Programs in the computer create targets for fixation at eccentric positions of gaze and analyse the image of the eye for measuring angle of strabismus and degree of eye movement, for visual field testing, and for plotting under- or over-action of extra-ocular muscles using Hess test.

Description

2332271 AUTOMATIC ASSESSMENT OF STRABIMSUS PATIENTS

TECHNICAL FIELD This invention relates to motor assessment of strabimsus (squint) patients.

BACKGROUND RELATING TO ASSESSMENT OF STRABIMSUS

Two important clinical tests are routinely performed on strabismus patients: cover test (figure 1) and ocular motility assessment (figure 2). Neutralising eye movement during the cover test (prism cover test) allows the measurement of the size of the strabimsus. At present, such measurement is performed manually and largely dependent on the experience of the examiner. The amount of surgery performed on strabimsus patients is largely dependent of the size of the deviation as measured by prism cover test. Additionally, the assessment of the eye movements depends on a rough clinical estimate of the degree of under-action or over-action of the eye muscles in a particular direction of gaze. Such estimates vary from person to person and perhaps by the same person at different visits. Computerisation of these two important clinical activities in strabimsus patients is very beneficial.

Image analysis is becoming popular and easily implemented as a reflection of the significant increase in the computer speed at an affordable price. The other important development is the vast improvement in the digital cameras available. By combining Z these together it becomes possible to obtain (black and white or colour) photographs of the eyes in various positions. Image recognition and analysis of the positions of the eye during cover test and during eye movement to various positions of gaze will allow accurate assessment of the size of deviation and the degree of eye movements. Such a system can be easily calibrated to clinical situations. This process will significantly.

1 increase the speed and the accuracy testing, and allows storage and retrieval of the patients' data files.

BACKGROUND FOR HESS TEST

Hess proposed his test in 1916. It is particularly useful in diagnosing paretic or paralytic extra-ocular muscles (external eye muscles) situations. It is useful in the diagnosis of under-action and over-action of the extra-ocular muscles in paralytic, paretic, or restrictive strabimsus.

The principle of Hess test involves viewing red dots on a 3 feet blackclothe. The red dots subtend 5 degrees at the 4 sides of the visual field up to 30 degrees from the centre of fixation (figure 3). The patient wears red/green goggles and sees the red dots with the eye with red filter only. The examiner carries a green streak and with the head stationary, the patient superimposes the green streak (seen by the eye with the green filter) on the red dots. The goggles are reversed and the test is repeated. The result is charted as per the enclosed chart. A modification of this is Lee screen test using mirrors this time but with the same testing cardinal points (figure 4)

The above process is manual. Automation of this process will make the testing process less laborious, speed up the process of testing, and allow the storage of the results, therefore manipulating them, electronically. This will improve the process of retrieval and the range of the usefulness of such data. It is possible to teach the program to give a diagnosis after enough data is available in different pathological conditions.

2 LITERATURE SEARCH Literature search revealed numerous patented inventions dealing with computation of the eye position. The use of a camera to record the eye position has been recommended by most of the inventions. None of these uses digital camera and employs present computer technology to the full.

1 have access to the following documents: 1. International patent publication number WO 93/15650: Photo-deviometer 2. US patent publication number 509452 1: Apparatus for Evaluating Eye Alignment 1. International patent publication number WO 93/19661: Method and Apparatus for Ocular Motillts; Testing 4. European patent publication number EP 0547931: Measuring eye movement in vertical or horizontal directions using device with miniature video camera and light source.

US patent publication number WO 93/15650 is very different ftom the described apparatus. This project uses a camera (non-digital) and deviometer disk on which there are fixation images. It also uses mirrors but does not mention any thing about electronic image analysis or the use of any computer.

US 509452 1: This device uses lamps as targets for eccentric fixation rather than computer screen. It also uses ordinary camera with ftame grabber as opposed to digital camera.

3 WO 93/19661 uses ordinary screen/projector arrangement rather than the computer screen itself without indicating a set the position for the test points. It uses complicated multiple device apparatus which calculate different values. It does not employ the ordinary computer for analysis and storing of generated images. It analyses shifts in the visual axis relative to primary position rather than analysis of the eye images itself.

EP 0547931 calculates the position of an eye behind a video camera with light sources. No fixation targets or display screen were used. It does not employ cover test or shits in eye position at set positions in the field of gaze.

All the above inventions deal with measurement of strabimsus for near. None address the process of measurement of deviation for distant fixation or children who are unable to use a chin-rest.

4 PREFERABLE TECHENICAL FEATURES This invention consists of both hardware and software components:

1) Computer with colour monitor, keyboard, printer, and a mouse, trackball. joystick or a similar device.

2) A 50-cm diameter hemispheric dome is used as a display screen with a testing distance of around 350cm from the centre of the dome (figures 5 and 6). Attached to the inside of the dome are the followings: a) One mini-projector for projecting targets generated by the computer on the inside of the perimeter at locations controlled by the computer. Alternatively, the projector may have filters caps allowing it to display images of various colours, shapes, and sizes. This projector is mobile so as to project objects anywhere at 360 degrees around and up to 60 degrees away from the centre of the dome (figure 7). This mini-projector is controlled by the computer program. b) A second mini-projector for projecting targets on the inside of the perimeter as above. This miniprojector is also mobile as above. This mini-projector is controlled by a mouse, trackball or a lever (or another control device), via the computer that can be moved by the patient. c) A light source to give a uniform background illumination within the hernidome. d) Attached to one side of the dome on the examiner side is a LCD screen to monitor the patient fixation during testing. This screen can replace the computer colour monitor and used as a computer display as well.

Variation on test display screen:

Instead of the hemispheric dome used for testing a LCD screen with a minimum screen display size of 50cm x 50cm can be used. The screen is mounted on a height-adjustable holder that is attached to a table. The screen-eye distance should be ')Ocm or more and depends on the size of the screen (figure 8). Large screen is an essential part of this invention because:

a) The screen is required for the display of fixation targets at eccentric positions of gaze of 30-45 degrees.

b) To obtain a reasonable eye-screen testing distance of 30cm. while allowing the above under (a), This is the usual distance employed for near assessment of strabimsus patients. If the screen is smaller then the eye would have to be very close to the screen in order to allow for eye rotation to around 350 degrees away from the centre. For example if the screen size display is reduced to 40x40cm then the testing distance would have to be 24cm to allow for testing up to 30 degrees outside the central point. This will be still have to be closer for smaller size screens for example it will 13) cm for a standard 1Y' computer screen. Other means of obtaining a large display may include the use of data-show that projects the computer screen directly on a screen. Alternatively, the use of a large TV-screen with a TV-computer adapter. In these two instances a large LCD screen is not required.

3 3) Adjustable chin-rest both vertically and horizontally with a headrest and a headband. The central position of the chin-rest is where the root of the nose (i.e., half wa...7 between the two eyes) is directly in front of the camera lens, which is 1 6 located at the centre of the display device, and at the level of the two eyes. The chin-rest can be moved slightly to the right or left so as the left eye or right eye faces directly the camera respectively. Such movements to either side would equal half the inter-pupillary distance (approximately 3cms).

4) Eye pieces for dialling occluder, red filter, green filter, and plus lenses in front of each eye.

5) Digital camera zoom lens at the centre of the dome or the screen that is connected a digital camera that is connected to the computer.

6) Testing software: This allows ocular motility assessment of strabismus patients. using image positional analysis of images taken by the digital camera during cover test and lateral ocular rotations. The device can also be used for Hess ocular motility test. Visual field testing can also be performed depending on the software installed. The software can be trained to suggest diagnosis and recommend management based on the findings. The program also permits saving, retrieval and printing of test and patient data.

7 TESTING METHODS I) Strabismus angle measurement The patient and test data are entered first. If the patient has been tested previously his file is loaded and a new test data is entered.

A. Measurement Qf the deviation _for near in older children and adults:

The patient is seated with the chin on the chin rest at its central positions and head resting on the headband that can be held in position by a strap (if acceptable to the patient).

To test the right eye the chin-rest is moved to the left from its central position (by 3cm) so as the right eye now faces directly in front of the camera lens and the chinrest is adjusted vertically if required. The patient first looks directly at the camera that is attached to the centre of the display. A flash photo is taken for the right eye with both eyes open while the patient is looking centrally (directly at the camera or at a computer generated fixation target immediately above the camera). Next the left eye is covered with the occluder controlled by the operator (or computer) and another photo is taken for the open right eye while looking exactly at the same position as above. The operator verifies the eye fixation before the photos are taken.

Next the patient is asked to look at the flashing target (an image generated by the computer such as an animal or an object... etc) as it appears on the screen. First a target appears at 30 degrees to the right. A photo is taken for the right eye while both are open and another after covering the left eye while the patient is continuing to look 8 at the object displayed as above. The operator monitors the eye fixation all the time. Such process is repeated for the following positions: 30 degrees to the left, 30 degrees up. 30 degrees below, 30 degrees up and right, 30 degrees up and left, 350 dearees down and right. and 330 degrees down and left. Thus a total number of 18 photos is C_ 1 taken for the right eye, 2 for each of the 9 position of gaze. A further 2 photos are taken for the right eye as described for the primary (central) position this time with plus 3.00 diopter lens in front of each eye, making a total of 20 photos.

To test the left eye the chin-rest is moved back to the central position and a further hm to the right so as the left eye now faces directly in front the camera lens. Similarly, another 20 photos are taken for the left eye, as above, while both eyes were open and after covering the right eye.

The position of the each eye is then computed ftom each pair of photos taken for that eye while both eyes are open and while it's fellow eye is covered in the 9 positions of gaze and in the central positions with +3. 00 lenses in front of each eye. Normally, there should be no shifi or change in the position of either eye (in any of the above 10 positions) while both eyes are open compared to that when its fellow eye is covered. If there is any change in the position of an eye during these two instances in any position of gaze, this would indicate strabismus. The net change in position of an eye between the photos taken with both eyes open and the fellow eye closed would indicate the size of deviation in the primary position and at various positions of gaze. This different is calibrated to give the size of strabismus in degrees or prism dioptres.

9 For eyes with eccentric fixation there is no fixation in the squinting eye. In this instance a photo is taken in each position of gaze with both eyes open (without the need to cover either eye). The position of the fixing normal eye is taken as a reference in this instance. The difference between the position of 2 eyes at each location is considered to be equal to the angle of the squint in the primary position & various directions of gaze.

B. Measurement Qf the dei,iation_for near in i?lfants and_wunie children.

Used in uncooperative children or those too young or unable to use the chin-rest. Flash photos are taken by a digital camera while performing the standard cover test for near in the primary position and at the eccentric positions of gaze described above. The images obtained are analysed in a similar fashion.

C. Measurement Rf the deviation_for distance in all s-uiects:

Cover test is performed in the standard way for distance in the primary position only. Two digital photos are taken for either eye as above while performing this test as above. Image analysis will give the size of the deviation for distance in the primary position.

11) Ocular motility assessment A) Assessmeni Qf eye movements in all patients: The degree of eve movement can be derived from the analyses of photos taken for near as above for each eye while both eyes were open. This is achieved by comparing C- the change in eve position relative to the tion. If required assessment of primary posi i movements of the eye muscles can be performed at 451 rather that at 350' from the primary position as described above.

Normally, both eyes should move equal amounts and in the same direction. If there is a difference in the movement between the 2 eyes then this is abnormal. Under-actions and over-actions are elicited by comparing the data for the two eyes and those matched for the patient age. Matching for the age will also allow detecting bilateral limitations of eye movements compared what would be expected for the patient age.

The result of the data obtained for strabismus measurement and eye movements' analysis will be saved for each visit and compared with subsequent visits and following surgery. A histogram could be drawn for such data. The program later can be upgraded to suggest diagnosis and surgical options depending on these measurements.

111) Automated Hess Test A) Hemispheric dome display: The patient and test data are entered first. If the patient has been tested previously his file is loaded and a new test data is entered.

The patient puts his chin on the chin-rest at its central position and the head strap is applied, when appropriate. The eyepieces are placed in front of both eyes. The red filter is dialed before the right eye and green in front of the left eye. A plus 3.00 dioptre sphere lenses are dialed in front of each eye if the patient is presbyopic and not wearing his reading glasses. The computer then projects a green-target (for example a circle or a spot of certain size) at the first test point. This is achieved b 11 moving the mini-projector controlled by the computer program to the required degree of eccentricity.

The patient moves a mouse or track ball (or similar device) which control the second mini-pr Jector. This second mini-projector projects a red target complementary with 01 that of the first projector. The patient moves the pointing device (thus moving the second mini-projector) until the targets appear to superimpose. Once this is achieved he clicks the mouse or button and a sound is emitted indicating this action. The computer records the position of the second mini-projector display relative to that of the first mini-projector when the button or the mouse is clicked. The computer then moves the first mini-projector so as to display the green target at the second testing point. The patient moves the second mini-projector again (using the mouse or trackball) to superimpose the red target on the green of the target at its new location and clicks the mouse or button as above. The computer again records the position of the second mini-projector display relative to the first. This is repeated until all the test points are covered. The computer then draws the test result on the computer screen. The test can be accepted or discarded and the test can be repeated as required depending on the satisfaction of the operator. After finishing testing with red before the right eye, the filters are reversed so as the red before the left eye and the green before the nght eye and the testing process is repeated as above. The tests for the red filter before right eye and red filter before the left eye are stored in the computer memory. Either eye test can be viewed separately or the two eyes viewed together with the patient data on the computer screen. The test result can be pnnted (figure 9) or saved along with any previous test/s data.

12 B) Large screen display. data show of large TV-scree The patient and test data is entered in the usual way. If a previous test file is present then this is loaded as above. The patient puts his chin-rest at its central position and a head strap is used to steady the head when appropriate. The red filter is dialled before the right eye and the green before the left eye. The testing distance will be according to the screen display size and can be calculated by the software. On the testing screen, lines of the Hess test (figure 1) are displayed in green colour so these are seen only, by the eye with the green filter and not with the eye with the red filter. The computer screen cursor shape is complementary to the shape of computer targets display at the testing points, but of red colour.

The computer then draws a green-target (for example a circle or a spot of certain size) at the first test point. The patient is asked to move the screen cursor by moving the mouse or track ball (or similar device) and tries to super-impose the red cursor (for example in the shape of a circle or a spot) on the green target displayed at the testing point. Once the patient is satisfied that the objects appear to superimpose, he/she clicks the mouse or a button and a sound is emitted indicating this action. The computer records the position of the cursor and its position relative to the green target at the test point when the button or the mouse was clicked. Then the computer displays the green object at the next testing point and the patient repeats the above action of moving the red cursor to superimpose it on the displayed green target, until all the points are tested and recorded by the computer. The computer then draws the test result on the computer screen. The test can be accepted or discarded by the operator and the test can be repeated as required. After this the filters are switched so that the red filter is before the left eye and the green before the right eye and the 1 n testing process is repeated. The tests for the red filter before right eye and red filter before the lefl eye are stored in the computer memory. Either eye test can be viewed separately or the two eyes viewed together with the patient data on the computer screen. The test result can be printed or saved along with any previous test/s data- In case of data show or large TV, with a TV-computer adapter, the testing distance is adjusted according to the actual display dimensions (and not computer screen size). The testing distance calculations will be part of the software after entering the display horizontal and vertical parameters. The testing process is as outlined above.

Once enough test data of different clinical conditions is accumulated, the program can then be taught to suggest a diagnosis recommend of surgical or clinical management.

The above device can also be used to test for visual field defects. This is achieved via appropriate computer software. The computer program flashes lights of different sizes and intensities at different locations to the inside of the hemisphere using one of the mini-projectors (in case of the hemispheric display) or directly onto the screen in large screen display - The patient just clicks the mouse or button when he detects the Rash of light and in this case recorded by the computer as detected by the patient at that location with stimulus size and intensity. If no button is pressed then this will be recorded as missed. Tests could be performed using different combinations of lightspot sizes. locations and intensities. The patient fixation can be monitored via the digital camera at the centre of the hemi-dome or screen. The result of the test can be printed or saved in a file as appropriate.

14

Claims

1. Automatic Strabismus Assessor (ASA) is a computer controlled display device consists of both hardware and software components: the hardware consists of a computer system with colour monitor, keyboard, and printer; an input device such as trackball or similar; a secondary display used for the testing; digital camera with lens; adjustable chin-rest; and eyepieces assembly; the software, on the other hand, is used for the testing process. ASA as claimed in Claim 1 wherein the secondary display used for testing is in form of a hemisphere, computer screen, projected computer display, a TV screen with TV-computer adapter, or similar computer controlled display. ASA as claimed in Claim 2 wherein in case of hemisphere secondary display two mobile computer controlled miniprojectors fixed inside the dome and project targets to the inside of the dome any where 360' around and up to 60' from the centre.

4. ASA as claimed in Claim 3 3 wherein case of hemisphere secondary display a light is used to uniformly illuminate the inside of the dome.

5. ASA as claimed in Claim 4 wherein the eyepieces assembly contains occluders, red filters, green filters, and plus lenses in front of the right and the left eyes.

6. ASA as claimed in Claim 5 wherein the digital camera lens, which is connected to a digital camera connected to the computer, is attached to the centre of the secondary display used for testing for taking photos of the eye during the testing process and monitoring eye fixation.

7. ASA as claimed in Claim 6 wherein a LCD screen is used to monitor patient eye fixation during testing.

C 8. ASA as claimed in Claim 7 wherein the strabismus angle can be measured in strabimsus patients using digital image analysis techniques of eye images taken by the digital camera during cover test in the primary position and at eccentric positions of gaze.

9. ASA as claimed in Claim 8 wherein the degree of eye movements can be assessed using digital image analysis techniques of eye images taken by the digital camera at the primary position and at eccentric positions of gaze.

10. ASA as claimed in Claim 9 wherein testing of the patient for ocular motility defects where under-action or over-action of particular extraocular muscles can be recorded according to Hess test principles using red-green dissociation.

11. ASA as claimed in Claim 10 wherein visual field test can be performed with the appropriate software.

12. ASA as claimed in Claim I I wherein patient and test data can be saved, retrieved, or printed ASA as claimed in Claim 12 wherein as enough tests data is acquired in different pathological conditions it is then possible for the program to suggest diagnosis and recommend the amount of strabimsus surgery required based,on the test findings.

16 t Amendments to the claims have been filed as follows CLAIMS:

1. Automatic Strabismus Assessor (ASA) comprising of a computer controlled display device consists of both hardware and software components: the hardware consists of a computer system with colour monitor, keyboard, and printer; an input device such as trackball or similar; a secondary display for computer generated targets used for testing; digital camera with lens; adjustable chin-rest; and eyepieces assembly; the software, on the other hand, is used for the testing process.

ASA as claimed in Claim I wherein the secondary display used for testing is in form of a hemisphere, computer screen, projected computer display, a TV screen with TV-computer adapter.

ASA as claimed in Claim 2 wherein in case of hemisphere secondary display two mobile computer controlled mini-projectors fixed inside the dome and project targets to the inside of the dome any where 360' around and up to 60' from the centre.

ASA as claimed in Claim 3 3 wherein case of hemisphere secondary display a light is used to uniforinly illuminate the inside of the dome.

5. ASA as claimed in Claim 5 wherein the digital camera lens, which is connected to a digital camera connected to the computer, is attached to the centre of the secondary display used for testing for taking photos of the eye during the testing process and monitoring eye fixation.

6. ASA as claimed in Claim 6 wherein a LCD screen is used to monitor patient eye fixation during testing.

9-7 t 7. ASA as claimed in Claim 7 wherein the strabismus angle can be measured in strabismus patients using digital image analysis techniques of eye images taken by the digital camera during cover test in the primary position and at eccentric positions of gaze. ASA as claimed in Claim 8 wherein the degree of eye movements can be assessed using digital image analysis techniques of eye images taken by the digital camera at the primary position and at eccentric positions of gaze.

9. ASA as claimed in Claim 9 wherein testing of the patient for ocular motility defects where under-action or over-action of particular extraocular muscles can be recorded according to Hess test principles using red-green dissociation.

10. ASA as claimed in Claim 10 wherein visual field test can be performed with the appropriate software.

11. ASA as claimed in Claim 12 wherein as enough tests data is acquired in different pathological conditions it is then possible for the program to suggest diagnosis and recommend the amount of strabismus surgery required based on the test findings.

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