Patent Application: US-39713989-A

Abstract:
the computer - assisted moving eye campimetric device is a computer display of a moveable test grid having a central reference spot . the patient &# 39 ; s eye is kept focussed on the spot by giving the patient the task of keeping the moving spot in a circle by operating a hand held mouse . with the patient &# 39 ; s eye correctly focussed on the reference spot , target elements in the field of vision are successively illuminated and the patient reacts by pressing a button on the mouse . failure to react indicates impaired vision at that point in the patient &# 39 ; s visual field . the results are held in the computer memory and plotted out as a map of the patient &# 39 ; s effective field of vision .

Description:
the test has been designed on an ibm at personal computer with enhanced graphics display ( ega ) and the software written in basic . it is implemented with the subject &# 39 ; s eye at a fixed distance from the computer screen and it is possible to test the central 30 degrees using a 12 inch monitor with a user to screen distance of 24 cms . the background and foreground colours for the test can be selected from a palette of 10 shades . an entirely new method is used to hold fixation . unlike previous tests in which a subject &# 39 ; s eye is fixed on a central stationary target , the test does not require an immobile eye . the fixation point essentially consists of a spot whose radius can be varied from 1 to 8 pixels . at its minimum value it subtends 1 . 3 degrees and at its maximum , 1 . 9 degrees , useful in patients with poor visual acuity . the fixation stimulus is initially surrounded by a circle whose movement the subject is able to control using the computer &# 39 ; s mouse . the fixation spot oscillates in a horizontal direction across the screen and must be maintained inside the circle for the presentation of test stimuli to proceed ( fig1 ). if the spot touches the circle , an unpleasant noise is emitted by the computer and the appearance of the test stimulus is delayed . the ease with which this task can be accomplished can be altered by varying the speed of movement of the spot ( 5 possible speeds ) or its size relative to the circle . these conditions can be altered either automatically by the computer or manually in a preliminary test immediately prior to the examination . if necessary the size of both the spot and the circle can be increased to accommodate patients with poor central vision . in this way fixation is maintained at a satisfactory level . typically , the spot oscillates for about 5 seconds during which time a test stimulus appears . the stimulus is visible for a preset time . then the spot disappears for a time interval and reappears at another randomly selected position on the screen , where it oscillates again . the sensitivity of the test can be set by selecting one of eight stimuli which are solid circles effectively subtending from 0 . 1 to 1 . 2 degrees . the size of the circle can also be varied . while the subject &# 39 ; s eye is focussed on the fixation target , test stimuli are silently presented on the computer screen in predetermined positions in a random order . the subject signals awareness of their presence by pressing a button on the mouse , a rewarding sound is emitted and the stimulus is recorded as seen . if the subject fails to respond in a preset time interval the stimulus silently disappears and is recorded as missed . if the button is pressed when no stimulus is present this is judged to be a fixation loss and the appearance of the next stimulus is delayed until fixation is deemed to be satisfactory these illegal responses also signalled by annoying beeps and recorded as a measure of patient reliability . the duration of the stimulus presentation and the time between successive presentations can be specified prior to examination . if these are then found to be unsuitable they can easily be altered and the test restarted . the stimulus should appear at a time after the reappearance of the fixations spot which exceed the time which the oscillating spot would take to leave , the circle , if the patient leaves the circle unmoved . this ensures that the patient &# 39 ; s fixation on the spot is being maintained . for an average patient the time is usually from 0 . 5 to 2 . 0 seconds . a longer time of from 1 . 5 to 3 . 0 seconds may be more appropriate for a patient of impaired vision , since he is likely to take longer to find the fixation spot . the test is interrupted if the patient sees the stimulus first , without having seen the fixation spot . missed stimuli can be retested at the same size to verify their non - visualisation or retested at a larger size to assess the depth of a defect . the procedure is repeated until all stimuli have been presented and the results can be save to disk , plotted , or viewed on the screen . the location of test points in the visual field are chosen by defining an array of points , known as the test grid ( fig2 ). the program offers a choice of four basic test grids which can be modified to suit individual patient requirements . the most complex of these consists of 96 points arranged in polar formation , with radius r , ranging from 2 . 3 cm to 13 . 9 cm and meridian , theta , from 0 to 360 degrees in 22 . 5 degree intervals . the grid therefore subtends the central 30 degrees with points situated approximately every 4 . 7 degrees , when viewed at a distance of 24 cms . points can easily be added to or deleted from this grid using a cursor , with a maximum of 100 points . points are added by pressing the add and deleted by using del . the degree of eccentricity and the meridian of the cursor position within the grid are displayed in order to facilitate precise positioning of test stimuli in the visual field . for each test point four test attributes can be set : size , colour , duration of presentation , and delay before presentation . the fixation point is located at the centre of the grid and similarly its size , colour and duration before stimulus presentation can be set . an area effectively four times the size of the computer screen is used , with fixation point and test stimulus being moved into the screen area by a suitable offset . ( fig3 ) the test results are plotted on a scaled down version of the test grid with patient details , test attributes and numerical test results plotted beneath ( fig4 ). points seen on their first presentation are displayed as small horizontal lines , whilst those seen on successive presentations are shown as increasingly larger and thicker crosses . points not seen on the final presentation are shown as solid squares . the results can be viewed on the screen and a hardcopy obtained if necessary . from the resulting visual field pattern the ophthalmologist is able to recognise any abnormality . the program is menu driven and requires a password for access . the appropriate test screen is set from the specified machine parameters -- namely graphics standard and screen dimensions and the user is then presented with the following menu : individual test parameters from a previously selected test may be altered without executing the entire test selection procedure and the modified test saved to disk . a demonstration of the test may be given to the patient and a training period is allowed for familiarisation with test equipment and method . at this stage the difficulty of the test can be tailored to suit the individual patient with the relevant parameters altered either automatically or manually . the test can be paused , restarted or aborted at any time without losing partial results . the response or absence of response to each test stimulus is recorded with the size of the stimulus presented . patient progress can also be viewed at any time during the test . the test has been developed for use on the ibm personal computer and exact compatibles . a 12 inch monitor with enhanced colour display and ega graphics card are required for high resolution colour graphics ; however the test will support cga standard graphics and a monochrome monitor with subsequent reduced resolution and range of colour . a microsoft mouse is used for optimum patient interaction , but keyboard and joystick versions of the test would be possible . an epson compatible printer provides a hardcopy of the test results . standard screen luminance levels can be set prior to the examination using a photometer . a headrest assembly ensures that patient &# 39 ; s eye remains at a fixed distance from the computer screen throughout the test . in spite of the fact that this test uses an entirely new method to test the visual field , it furnishes very similar results to conventional methods ( fig5 ). in the examination of 16 eyes in 10 normal volunteers , the blind spot was accurately and reproducibly located at 15 degrees in all cases and the average testing time was 3 . 2 ±/- 1 . 2 . ( sd ) mins . the time taken to perform visual field examination is very dependent on the number of stimuli tested , patient dexterity and patient co - operation . all individuals tested had normal visual fields and were tested using 26 , 0 . 1 degree stimuli . using the format of a game helps to maintain a child &# 39 ; s interest and consequently improves fixation . the story of the game can be adapted to suit each individual child , but essentially , subjects are instructed that the spot inside the circle must not be allowed to escape and if the see any &# 34 ; other subjects &# 34 ; on the screen coming to rescue it , these can be captured by pressing a button on the mouse . children who have been tested have enjoyed the game - like aspects of the procedure and have had no difficulty in maintaining their interest for its duration . their fixation was also good , with no real opportunity for their eye to wander due to the design of the test . because the accuracy of the test is so dependent on the co - ordination of the patient , a short demonstration / training program has been developed to be executed prior to the examination , enabling the user to finely tailor the level of difficulty of the test to suit the individual patient . the speed of the fixation target is important . if it moves too slowly then the patient finds the test procedure simple and his attention starts to wander . this can result in a loss of fixation . conversely , if the fixation target moves too quickly then the patient may not be able to keep the circle over it and he quickly loses interest , again resulting in a loss of fixation . during the demonstration period , the computer monitor &# 39 ; s the patient &# 39 ; s success at keeping the circle over the fixation target , increasing the fixation speed if the test appears too easy and decreasing it if it appears too difficult . the level of difficulty of the test can further be altered by changing the size of the circle . these parameters do not make the test more difficult visually , but rather increase its concentration requirements and maintain fixation at a satisfactory level . although the test has been developed for use primarily in children , it could also be useful in adults and is considerably less expensive than most currently available automated perimeters . it could therefore make visual field examination available in situation where conventional methods are not possible . 1 . harrington , d . o . 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( 1986 ). a rapid technique for kinetic visual field determination in young children and adults with central retinal lesions . doc . ophthamol . proc . series 49 , 495 , 501 .