New computer controlled color vision test Károly Ladunga*, Klára Wenzel, Gyorgy Abrahám**

Transcription

1 New computer controlled color vision test Károly Ladunga*, Klára Wenzel, Gyorgy Abrahám** *Department of Precision Mechanics and Optics Technical University ofbudapest, Hungary **Coloryte Hungary Inc. ABSTRACT A computer controlled color discrimination test is described which enables rapid testing using selected colors from the color space of normal CRT monitors. We have investigated whether differences in color discrimination between groups of normal and color deficient observers could be detected using a computer-controlled test of color vision. The test accurately identified the differences between the normal and color deficient groups. New color discrimination tests have been developed to more efficiently evaluate color vision. Coloryte Inc. All rights reserved. Keywords: color vision test, color deficiency, CRT. 1. INTRODUCTION 1.1 Disturbance to visual function in color deficiency Color deficiency is mostly a genetic defect. 8% of men and 0.5%of women are color- deficient. There are more than 100 professions from which color-deficient people are excluded. In several countries it is difficult for people with color-deficiency to get a driver's license, especially a professional one. In recent times the amount and significance of information sent by color has grown. It was observed that color-deficiency has a negative effect on clear sight and noticing details. 1.2 Disadvantages of recent clinical color vision tests Clinical color vision testing has some limitations in the diagnosis of color deficiency. Ishihara plates often detect abnormalities, but they are not quantitative and can not demonstrate progress or regression in color discrimination ability. The Fransworth- Munsell test can be made semi-quantitative, and is especially useful in acquired defects of tritan type.24 However, without computer-aided scoring, it is time consuming to evaluate. Various lantern and other tests have been proposed but have not proved generally useful.78 One difficulty facing all present methods is that in many cases, patients using specially colored filters are able to pass the test, although they have poor color discrimination ability. Considerations such as these have led us to consider the use of CRT monitors as a medium for color vision testing. The immediate advantages are that that the test patterns can be changed both temporally and spatially Purpose The purpose of the current study was to develop a rapid computer controlled color vision test, which is able to establish the diagnosis of color discrimination ability. Two stipulations were made. The results of the test should not be effected by an observer wearing colored filter lenses and should give information about the extent of defect. Our test has been developed to produce an optimal clinical vision test, and preliminary results are presented. 2. METHODS 2.1 Designing pseudo-isochromatic plates Pseudoisochromatic plates are designed to present apparently or falsely equal colors, which are chosen to fall within the color zones where the defective observers are most likely to be confused.' The test stimulus consists of spatially discrete patches of varying size and luminance, presented on a black background. (Fig. 1) The luminance of each individual patch varied randomly. In Photon/cs, Dev/ces, and Systems, Miroslav Hrabovsk', Pavel Tománek, Miroslav Miler, Editors, Proceedings of SPIE Vol (2000) X/OO/$

2 A subset of patches formed the target, having the form of numbers and letters. The chromaticity of the target patches differed from that of the field patches, and was varied along a curve in color space described later. The outer diameter of the target is seen in an 8 visual angle. The test randomly generates up to 99 different combinations of numbers to prevent memorization. The plates generated gradually increase in difficulty. (Fig. 1) During the test the subjects indicate verbally the numbers which they can identify, the experimenter pressing a button on their behalf to indicate their response. Each plate was presented for a maximum of 10 seconds. If the character has been well recognized than the operator proceeds to the next plate until the patient can not detect or did not respond in the allowed time or an incorrect response was recorded. Fig.1. Designing changeable difficulty pseudo isochromatic plate 2.2 Designing variable difficulty pseudo isochromatic plates The result of the test is the subject's color discrimination threshold measured using the computerized test described herein. The software generates pseudo isochromatic plates, which appear on the monitor screen. Pseudoisochromatic plates are constructed to present luminance distribution of the dots being mostly equal in the target and the background. Luminance values vary among the dots. We use an experimental formula to determine the colors of a monitor to produce the same target and background luminance stimuli to the patient. Red and green guns of the monitor are adequate to produce plates to measure the red-green discrimination ability. In this case the formula is the following'0: Const = (g * Green)2 + Re d2 Cont: Constant, presents the degree of stimuli produced by luminance Green: DAC value ofthe green gun ofthe monitor (0-255) Red. DAC value ofthe red gun ofthe monitor (0-255) g: Constant Only different luminance monitor greens are used in the background. Mixing red and green colors based on the experimental formula produces the dots ofthe characters. Fig. 2 shows the colors used in the plates. The difficulty ofthe actual plate depends on the mixing rate ofgreen and red colors. The result is calculated in percent and automatically saved by the software. 2.3 Relative intensity measurement A calibration method has been developed to evaluate the (g) constant in the equation called the relative intensity measurement. Adjustable luminance red and green rectangles connect to each other in center of the screen at a 40 visual angle. (Fig 3.) Before 502

3 rm Green DAC values Fig 2. Colors used in the plates beginning the test patient adjust the luminance of the rectangles to see the same level of luminance in both of them.' The value of the (g) constant can be easily calculated (g = RedlGreen). Where (Red/Green) is the quotient of the DAC values of red and green guns of the monitor (0-25 5). Using colored filters or lenses for color visioncorrection9 traditional tests can be passed by color deficient subjects because the luminance of painted isochromatic plates is changed by the filters. Patients forced to for the relative intensity calibration compensates the changed ratio of the background and targetluminance to avoid this problem. Fig.3. Relative intensity measurement to evaluate the (g) constant in the equation System parameters The digital to analog converters of many simple systems have only 256 levels, and a theoretical analysis of the resulting limitations suggests that color vision testing with a simple system is impracticable.6 We have used such a simple and inexpensive system, and this paper demonstrates that minimal difference in DAC outputsand the disturbance of dots produce color changes that are so small that they are bellow the resolution of human color vision. The stimuli were generated using a Pentium-lOO computer. and presented on a Daewoo 14' monitor in a darkened room. The system allowed the output of each gun

4 of the monitor to be specified with a precision of 8 bit, which is adequate for measuring thresholds of normal subjects under our experimental conditions. The monitor was calibrated. 3. RESULTS We tested a total of 39 color deficient patients and 25 control subjects with normal color vision. Before beginning the computer test, we tested subjects with Ishihara plates. The results of the test have been plotted in (Fig. 4). The difference in red-green color discrimination ability between the control group and patients is clearly seen. ' as u /U j U, o 30 CL Color detkieiit aiiettts (39 (Oflifol group (normal oior vision (25)) 15 ' Number of patients Fig. 4. Measured data DISCUSSION Traditional dotted test-books can be used only for screening between normal and color deficient people. The proposed computer test result gives more than a superficial evaluation of the state of an observer's color vision. It can be utilized as screening test for color vision anomalies and will give a quantitative (extent of defect). Because of a higher degree of convenience and simplicity of administration, computer controlled polychromatic charts for detection of defective color vision has been popular. This is a fast and low cost solution to aid diagnosis of color-deficient people, which can be used in almost any location. 5. ACKNOWLEDGEMENT This work was supported by Coloryte Inc. We are grateful to Dr. Zs. Czibók for access to her patients and facilities, the staff at the company for their help, to our volunteers for their cooperation and to I. Kucsera and P. Rosalio for comments on the text. 6. REFERENCES 1. LeGrand H. Hardy, Gertrude Rand, M. Catherine Rittler. "Tests for the Detection and Analysis of Color-Blindness", Journal of the OpticalSociety ofamerica. April, Fletcher R. and Voke J. (1985) Defective Color Vision, Huger, Bristol. 3. Pokorny J., Smith V. C., Verriest G. and Pinckers A. J. L. G. (1979) Congenital and Acquired Color Vision Defects. Grune & Stratton, New York. 504

5 f ç OMSU1J Q jsunja-q2.iomsu1j Sfl0UI0Oq3ip SS 10J UOIS!A umo3 j 'uo!s!a P!P q UOHOJAI f U pu thtts 1 1 IIPV 'SS1d E861'UOPUOT 0 'upv )I ZflpUflJ PU S f(ud 10103,, UO!S!A qim 1ndwoD soqd19 'usx ujj UO!SLA Jdj dd oze-ioe uosicj J '1 wv r JqpU j 1 lojoj,, sjd jouqvzpi,'d '6 JA 'V JUSO)J pu U1AiIjflS d o dpq su!d qut '861 dd LiL-1t7 j)jufl9 UOD u 0 Xiwiojoj,, q E MU 'ldiou!1d mpaiqj t uqiqv pu su poqj 'g'o sajavjd qai yow1vytpdq PZUM 'upiijnoo soudzs souvc 1OJ UDjJ,\J PS to!do ui"i /IDd) '(ci700o/6f1h 661 pzu '9upijiO unp 'joi uqiqy ijqi s szpuiq S1ZSA9UJZS 'isiui pu 1 D 'U!PQ UC11UnH U2d 66d '(wzio 6661 uwdinb JOJ u!jns1jai 001 nq T idq og wy ' '06i dd 9Lc-89c 1 A 'Z M njq uoo 'wsrwoiipouow '9661 t-1e ioj uiao1dw io ui(jipoj ioio ''8861 UOTS!J4 pu wojpqiz poip) coc