Procedures for Testing Color Vision Report of Working Group 41 (1981) / Chapter Skim
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3. Color Vision Tests
3. Color Vision Tests
Pages 14-80
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From page 14... ...
Pseudoisochromatic plates were f irst introduced by Stilling (18733. The success of tests of this kind depends on the inability of color-defective observers to discriminate between certain colors.
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for use in diagnosing acquired color vision defects. GENERAL DESCRIPTION OF TYPES OF COLOR VISION TESTS Anomaloscopes Anomaloscopes are optical instruments in which the observer must manipulate stimulus control knobs to match two colored fields in color and brightness.
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However, when used by a skilled examiner, the anomaloscope has advantages as a diagnostic instrument that far outweigh any inconveniences in training. Plate Tests In a plate test, the observer must identify a colored symbol embedded in a background (most pseudoisochromatic plates)
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Arrangement tests may be designed for evaluation of fine hue discrimination (FM 100-hue test) ; for evaluation of color confusion (Farnsworth Panel D-IS, Lanthony Desaturated Panel, Lanthony New Color Test)
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Lantern tests do not specifically screen for color defect, although it is expected that color-defective observers will not perform as well as observers with normal color vision. HOW TO EVALUATE A COLOR TEST Reliability and Validity Evaluation of a new color test requires knowledge of its reliability and its validity.
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Specific Procedures for Calculating Different Types of Tests Plate Tests The appropriate procedure is to compare K coefficients for reliability and validity. Evaluation of reliability should compare test and retest data; evaluation of validity should compare plate test data and anomaloscope data.
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It is appropriate to use scatter-plot and correlational analyses to compare match midpoints and matching ranges of two anomaloscopes that have identical mixture primaries and test wavelengths. In order to compensate for scale differences, however, the data must either be converted to the comparable scale units devised by Willis and Farnsworth (1952)
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compared two lamps manufactured in the United States -- the GE Chroma 70 and the Verd-A-Ray Cr iticolor Fluorescent -- with the Macbeth Easel Lamp, which was designed for use with screening plate tests. While the lamps gave similar screening data on the AO B-R-R and Panel D-15 tests, and similar total error scores on the FM 100-hue and ISCC tests, the classification data varied among the three illuminants.
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From page 22... ...
Error scores on the FM-100 hue test vary with the level of illumination. Above 100 lux, Increased zilum~nat~on can improve the error scores of observers whose chromatic discrimination was below average at a lower level.
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The distance of the illuminant from the material determines the level of illuminance and the area of illumination. Plate tests should be presented at a distance of about 75 cm.
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Data from Verriest (1963~. EXISTING TESTS: AVAILABILITY, PRACTICALITY, AND PPOCEDtJRES Anomaloscopes Nagel Model T Made by Schmidt and Haensch, Berlin, Germany Available in Canada from Imperial Optical Company, Ltd.
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If the normal match, or one close to it, is accepted the next step is to evaluate the range of acceptable red-green ratio values. For a normal observer this range will be small (between 0 and S scale units)
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The match midpoints of the range are calculated and may be converted to anomalous quotients or comparative scores. Many laboratories simply report the instrument scale units, including the usual normal range.
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Comparative scale units (CSU) range from zero at the green primary to 100 at the red primary, with the normal match at 50.
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The distributions of matching ranges and mid~atching points for normal and anomalous trichromats are shown in Figure 3-1 where the percentage 1
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Fl - , r al nF PA n 15 n 5 10 15 20 25 30 35 1 - ' MATCHING WIDTH (MIXTURE SCALE UNITS) FIGURE 3-1 Norms for the Nagel Model I anomaloscope.
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The mean normal match on a given Nagel Model T anomaloscope varier between 40 and 50 scale units. When converted to anomalous quotients, the total range of the match midpoints for normal observers was O.80 to 1.20.
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is matched to a mixture of yellow and blue. At scale zero, the mixture field appears yellow and changes continuously to white and then blue at scale 80.
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Anomalous quotients may be calculated, but they cannot be compared with anomalous quotients derived from other Pickford-Nicolson anomaloscopes or from the Nagel anomaloscope. An alternative method of expressing the equation of a given observer relative to that of a population of normal observers is to use the statistical properties of the distribution of match midpoints made by normal observers (Pickford, lasso.
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From page 33... ...
The Engelking-Trendelenburg and Pickford-Lakowski equations have been most useful in identifying acquired color vision defects. The Engelking-Trendelenburg equation is not suitable for diagnosis of tritanomaly, and neither equation will differentiate a tritanope from an incomplete tritan.
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ad 40 ad 30 cat It ~ 20 A UJ ad 10 o R-G Y-B _ N 127 N 124 1 .-n. ~ G-8 m..~: ~ Lm 9 6 3 0 3 6 99 6 3 0 3 6 99 6 3 0 3 6 9 JND SCALE UNITS | | -G n G-S N 127 N 125 ~ ~ ~~U L0 1 24 6 8 1 2 4681012+ 1 24 6 8101214+ JND SCALE UNITS ; FIGURE 3-2 Norms for the Pickford-Nicolson anomaloscope.
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40 . 60 JND SCALE UNITS 80 FIGURE 3-3 Distribution of match midpoints on the Rayleigh equation for anomalous trichromats (mean age is 20)
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. 1 Ail ~ 80 o 20 40 JND SCALE UNITS 60 FIGURE 3-4 Distribution of matching ranges on the Rayleigh equation for anomalous trichromats (mean age is 20 ~ using the Pickford-Nicolson anomaloscope.
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The matching ranges are asymmetric for all three equations. Match midpoints and matching ranges of the Rayleigh equation for anomalous trichromats are shown in Figures 3-3 and 3-4.
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When an anomaloscope is purchased or introduced into a laboratory or clinic, the first step is to establish norms for the instrument. Matching ranges are established for all normal observers who are working in the laboratory or clinic, and others may be invited to participate.
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He may be perturbed or confused by the examiner's assertion. Color terms used by dichromats and many anomalous trichromats depend on the luminance relations between the two halves of the field.
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Pseudoisochromatic Plates American Optical Color Vision Test Pseudo-Isochromatic Plates for Testing Color Perception by American Optical Corporation, Buffalo, NY 14215 15 plates Available from: 1. American Optical Co., Catalog t13375 AO Color Test, Buffalo, NY 14215 2.
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From page 41... ...
The major discrepancy is in the number of normal observers who are misclassified. The AO plates have been compared to other plate tests (Chapanis, 1948, 1949; Hardy et al., 1954b; McCulloch et al., 1959; and Steen and Lewis, 1972.
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If the observer makes an incorrect response to screening plates 3 to 6 (screening plates for red-green defects) , the examiner proceeds to plates 7 to 16, the diagnostic plates for red-green color defects.
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for reliability of screening, qualitative diagnosis {protan, deutan, blue-yellow defect) , and quantitative diagnosis (severity)
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is distributed among anomalous trichromats and dichromats. The grade Mild is strongly associated with simple anomalous trichromats; the conditional K on ~mild.
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The remaining 14 plates are based on pseudoisochromatic principles and are of the vanishing type. Twelve of these plates are screening plates (plates 2 to 5 and 8 to 15~; two are diagnostic plates (plates 6 and 71.
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Qualitative classification i" good according to Frey (19637. The value of K is reduced primarily by those color-defective observers who are unclassified, the conditional K is 0.97.
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However, the F2 plate should be used to screen for red-green defects only in young populations without eye disease, since Pinckers (1972) noted that observers with acquired color vision defects fail the F2 plate by failing to see either the blue, or the green, or even both squares.
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The numerals are in script, and some Americans may be confused by their appearance. An instruction manual is provided, but no sample scoring sheet accompanies the plates.
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The values of ~ for qualitative classification are variable and are reduced primarily by those color-defective observers for whom no classification is made. Provided a classification is made, the conditional K ranges from 0.61 to 1.00.
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If the observer fails both protan and deutan classification plates he is classified as unsevered red-green defect. Total color blindness, tritan, or acquired color defects are suspected if an observer fails demonstration plate 2 or 3.
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The Tokyo Medical College test for color blindness is designed to screen red-green and blue-yellow defective color vision and to differentiate between protan and deutan defects. The test consists of double-digit numerals in standard Arabic form.
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Umazume and Matsuo (1962} reported greater success with the qualitative diagnostic plates, but their data do not allow calculation of K Quantitative classification is poor, primarily because simple anomalous trichromats are distributed in all three severity categories; however, only simple anomalous trichromats are classified as mild (conditional K ~ 1.0~.
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Validity of both of these slides was evaluated (Paulson, 1973~. Slide 71-21-21 was administered to 34 normal observers, 161 protans, and 215 deutans.
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Thus the test may be criticized on the grounds that the observer may have failed the test because of slight error in color naming rather than defective color perception; even a few normal observers will call one of the reds, "orange. " Second, although Army Regulation 601-270 states that the observers are not to be advised in advance as to the colors used in the test , the f act that the three colors in the test are red, green, and yellow inevitably becomes general knowledge.
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. Among anomalous trichromats, however, 31 percent of protanomalous and 51 percent of deuteranomalous trichromts fail the test; classification of those who fail is correct for only 40 percent of the protanomalous and 72 percent of the deuteranomalous trichromats.
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General Description. The Titmus Color Perception Test consists of a slide containing reproductions of Ishihara pseudoisochromatic plates.
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Observers classified as color defective by the Ishihara failed both blocks 2 and 3 while those classified as color defective by both Ishihara and the Farnsworth Panel D-15 failed three blocks (2, 3, plus one other) on the Titmus Pediatric Color Perception Test.
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The test consists of 15 colored caps placed in a box, with one reference cap at a fixed location. The samples are chosen to represent approximately equal hue steps in the natural color circle and are similar in chrome to those of the FM 100-hue test.
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, and Verriest and Caluwserts (1978~. Quantitative classification shows that, in general, simple anomalous trichromats pass while extreme anomalous trichromats and dichromats fail.
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Dichromats who fail the test make multiple (6 to 12} crossovers and connect specific caps at the beginning of the series with specific caps at the end of the series; the axis of theme parallel crossover lines determines whether the observer is a protanope or deuteranope. Color-defective observers who pass the test (anomalous trichromats)
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From page 61... ...
100-hue test wa s designed to test hue discrimination among people with normal color vision and to measure the areas of color confusion in color-defective observers. The test cons ists of 85 movable color samples arranged in four boxes of 21 or 22 colors each.
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Observers with normal color vision may make some errors in all four boxes {Figure 3-5~. The distribution of error scores is asymmetric and for young observers has a range of 0 to 150 {Figure 3-6~.
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The average error scores of color-defective observers indicate the severity of the defect (Taylor, 1966; Lakowski, 1971~. Lakowski's data are shown in Figure 3-10.
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The FM 100-hue test is not designed for the screening of color defect. Farnsworth suggests that error scores for normal observers should be classified only in three categories (superior, average, and inferior}, and that error scores should not be regarded as representing a continuous scale of performance.
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65 ~ 'I ' ' ~ ' ~ ' - ~~ ~~ ~ ~~ /~ ~~ : r , ; Fat ~ '~PA 4- c h'' ~ 82 ERRORS'- "1 a~ //////: fif:J~ 1 ~ i:~\ :\~ ~ , ~,/~ =_ ~ ~ P ~ At ~ '' ~156 ERRORS- ~ ., an_ ~~ - ~ ~~ ,4~ ~ \'\: ~ . FIGURE 3-7 Example of FM 100-hue test profile for representative protanomalous trichromat, extreme protanomalous trichromat, and protanope (students of mean age 20~.
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~ lo Hi\\' ~ ~ 'a'\ t ' · / ,' / / / 'at/ ~- -'! ' ~ ad FIGURE 3-8 Examples of FM 100-hue test profile for representative deuteranomalous trichromat, extreme deuteranomalous trichromat, and deuteranope (students of mean age 20~.
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From page 67... ...
It is appropriate to use error scores quantitatively in comparing two eyes of an individual with an acquired color defect (Aspinall, 1974b}; in following temporal changes of an acquired color defect (Chisholm et al., 1975~; and in comparing the errors in different quadrants (Helve, 1972; Smith et al., 1976~.
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The test is used in conjunction with the standard panel (Farnsworth Panel D-15 Test) and was designed specifically for acquired color vision defects.
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69 151 10 5 o 15 ~ 10 Ad lo C, CY LL 5 o 15 10 DA o 0 100 200 300 400 0 'I 1 _ 1 o 100 200 300 400 0 D _ 1 515 o 100 200 15 10 15 r PA 1 100 200 EDA 15 10 300 400 , 1 EPA 100 200 300 400 o 1 _ 300 400 0 E RR ORS p 100 200 300 400 FIGURE 3-10 Distr ibution of FM 100-hue test scores for anomalous trichromats and dichromats (students of mean age 20 ~ . Based on data from Lakowski (1971)
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From page 70... ...
noted that 82 percent of observers with congenital red-green color defects failed the Lanthony Desaturated Panel, including 98 percent of the dichromats and 70 percent of the anomalous trichromats. Qualitative classification was excellent for dichromats, but only 78 percent of the anomalous trichromats were correctly classified.
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From page 71... ...
This procedure differs from that used in the Farnsworth Panel D-15 in that the observer chooses the starting cap; there is no fixed starting cap. Furthermore, since the classification phase follows the separation phase, there may not always be 15 colored caps remaining, although there may be some gray caps In that group.
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Sahlgren's Saturation Test was designed to evaluate the loss in saturation discrimination that is characteristic of acquired color vision defects. The 12 caps include five greenish blue and five bluish purple samples of varying saturation plus two gray caps.
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From page 73... ...
Scores for observers with congenital color defects ranged from 0 to greater than 50; 45 percent of the observers with congenital color defects had an abnormal score. Scores for observers with acquired color defects ranged from 0 to greater than 50; 90 percent of the observers with acquired color vision defects had an abnormal score.
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A demonstration of the eight colored lights is given at the brightest of the eight luminances. The examiner then turns the luminance knob to the dimmest of the eight luminances and presents the eight colored lights consecutively, I1 to l8.
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The part-score for each of the eight colored lights is obtained by counting the correct response, starting from luminance level 8 and continuing to lower luminance levels until an error occurs. Correct responses at still lower levels are not counted.
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Some of them are very difficult even for those with normal color vision. Administration is complicated for the examiner because the five rotating discs {containing the colored filters, the modifying filters, and the apertures)
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From page 77... ...
Unlike other lanterns that use lights that simulate navigational, aviation, or railroad signal lights, the Farnsworth Lantern uses specific red, green, and white lights that are confused by people with more severe color vision defects. The reason for this choice was as follows.
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The Holmgren Wool Test was one of the original tests designed to screen red-green color defects. The test consists of 75 small strands and three large strands of colored wools.
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From page 79... ...
Congenital red-green color-defective observers select colors in the blue-green and red regions: dichromats select two or more colors at all saturation levels; anomalous trichromats select two or more colors at medium saturation levels. The actual colors chosen are diagnostic of the color defect: nos.
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From page 80... ...
All deuteranopes were correctly classified. Deuteranomalous trichromats were classified correctly as such in 90 percent of cases and were incorrectly classified as deuteranopes in 10 percent of the cases.
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