JClin Pathol 1991;44:745-748

Colour perception in pathologists: theFarnsworth-Munsell 100-hue test

H S Rigby, B F Warren, J Diamond, C Carter, J W B Bradfield

AbstractThe value of many histological stainsdepends on the ability of the observer todifferentiate colour. This ability wasassessed in 30 histopathologists andcytopathologists of varying experienceusing the Farnsworth-Munsell 100-huetest. As a group, the pathologists perfor-med better than a reference population.Twenty eight subjects showed a wideranging ability to differentiate colour:none was colour blind. Three of the 30pathologists, however, fell below thetwentieth centile for normal subjects andonly one was aware of this deficiency!They may unknowingly misinterpretsubtle stains. Two of these three hadspecific and major defects which couldaffect their ability to interpret a widerange of less subtle stains. Those with thepoorest colour discrimination were notthose with the least experience ofmicroscopy.Pathologists should be apprised of the

importance of their ability to discrimin-ate colour, and that formal colour visiontesting of prospective histopathologistsmay be appropriate.

Departments ofPathology andOphthalmology,University of BristolH S RigbyB F WarrenJ DiamondC CarterJ W B BradfieldCorrespondence to:Dr H S Rigby, Departmentof Pathology andMicrobiology, School ofMedical Sciences, Universityof Bristol, Bristol BS8 ITDAccepted for publication20 March 1991

The interpretation of many tinctorial stainsdepends on the ability of the histopathologistto distinguish hues. It has been assumed,without formal testing, that histopathologistsare competent colour discriminators. Thereason for this study was the inability of one

of the authors to distinguish the differentialstaining of colonic mucin with the KOH AB1/mPas technique.' Correct interpretation ofthis particular dual staining method requiresthe ability to distinguish blue/purple fromred/purple to differentiate sulphomucin fromsialomucin.2 A standard test of colour vision,the Ishihara test, failed to show any differencebetween the two subjects. Therefore, a more

specific test of colour discrimination-theFarnsworth-Munsell 100-hue test was used.'This showed that the former observer hadinferior colour discrimination, in spite ofbetter visual acuity.

MethodsThe Farnsworth-Munsell 100-hue test is a

simple method for measuring colour dis-crimination. In industry it is used to testemployees in colour control laboratories

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involved in the manufacture of paints andcdyes.'The test requires each subject to sort into a

colour graded order a series of randomlyarranged coloured caps, from the whole spec-trum, into each of four black metal boxes (figs1 and 2). Each box contained discs relevant topart of the colour spectrum, plus two fixedreference coloured discs, one at each end.During the test each subject was seated at atable at a North facing window between 11.00and 12.00 hours, in an attempt to achieve theprescribed lighting conditions of Farnsworthand Munsell,' who proposed either a Northfacing window on a slightly overcast day, or aMaclaren lamp set to deliver 67400 Kelvin at25 foot-candles, or a 65000 daylight fluorescenttube. The tests were all carried out in Sep-tember.At the end of the test the four boxes were

closed and inverted individually by theexaminer. The underside of each coloured capcarried a sequential number from 1 to 85.The test score for each subject was cal-

culated as follows. The number of each capwas compared with those on the immediatelyadjacent caps. The differences between thenumber on the test cap and each of its neigh-bours were added together. A perfect score foreach cap would therefore have been 2-forexample, in the case of cap 4 the calculationwas as follows:4 - 3= 1, 5 -4 = 1, and thesum of these differences is 2. The error scorefor an individual cap is given by the differencesbetween the abnormal score and the expectedperfect score of 2.For each subject tested the error scores

were plotted on a Farnsworth-Munsell chart(fig 3). This chart comprises a central discwhich representes the entire colour spectrum.Outside this are concentric rings at error scoreintervals of 1. The innermost circle representsa perfect score of 2.Twenty eight volunteer histopathologists

and two cytopathologists (23 men and sevenwomen) were studied. These pathologistswere of varying experience and included 10consultants and two experienced non-medicalcytologists, 11 senior trainees, and sevenjunior trainees. Eleven of the subjects wereaged 20-34, 12 were aged 35-44, and sevenwere aged 45 or more years.The total number of errors made by each

pathologist was calculated and compared withthose of a standard reference population ofprospective employees in the paint and dyeindustry (Farnsworth). Any population can be

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Rigby, Warren, Diamond, Carter, Bradfield

Figure 1 Randomly arranged coloured caps of one box.

Figure 2 Perfect arrangement of coloured caps in thefour boxes.

divided into those of superior ability (less than17 errors), average ability (20-100 errors), andlow ability (more than 100 errors), based onthe total number of error scores. In the stan-dard reference population 16% were of lowability, 68% were of average ability, and 16%were of superior ability.3The error scores in each of the groups were

analysed using the Kruskal-Wallis one wayanalysis of variance.

ResultsExamples oferror charts are shown in figs 3 to 8.Taken together, nine out of 30 (30%) patho-logists had superior competence for colourdiscrimination compared with 16% of thereference population and three out of 30 (10%)had inferior competence for colour discrimina-tion compared with 16% of the referencepopulation. Eighteen (40%) of the pathologistswere of average competence for colour dis-crimination compared with 68% of thereference population.There was no statistical difference in the error

scores among the three groups- consultantsand non-medical cytopathologists, seniortrainees, and junior trainees (table 1). Similarlyno difference was seen in the error scores amongdifferent age groups (table 2), or for either sex(table 3).

Table 1 Results of error scores according to employeestatus

Consultants and non-medical cytologists Senior trainees Junior trainees

1 8 29 322 50 43 563 26 46 624 14 14 245 24 12 956 4 45 167 84 108 368 62 1089 16 1610 69 6911 80 51412 4

(p = 0-4443)

Table 2 Results of error scores according to age

20-34 35-44 45+

1 32 45 502 36 46 143 16 14 1084 8 26 695 29 12 46 43 24 627 514 95 848 108 249 16 1610 62 6911 4 5612 80

(p = 0-8838)

Table 3 Results of error scores according to sex

Women Men

1 32 162 36 43 50 244 4 695 43 246 8 267 29 168 1089 51410 4511 1212 1413 6214 5615 9516 6917 6218 8419 1420 10821 1622 8023 46

(p = 0-1852)

DiscussionThere are three facets in the histopathologist'sdiagnostic armamentarium. These are patternrecognition,4 the ability to discriminate colour,and knowledge. These abilities are never con-sidered when appointing new trainees inhistopathology. Moreover, a whole career maypass without any formal assessment of colourdiscrimination. The development of moresubtle tinctorial stains takes no account of theinability of the requesting histopathologist todistinguish their hues.We are unaware of any previous study of

colour discrimination in histopathologists.This study has shown that as a populationpathologists in Bristol performed better than astandard reference population, but threepathologists were previously unaware of their

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Colour perception in pathologists: the Fransworth-Munsell 100-hue test

Figure 3 Farnsworth-Munsell chart showing aperfect score marked atconcentric ring 2.

Figure 4 Chart ofpathologist of superiorability.

Figure S Chart ofpathologist of averageability.

Figure 6 Chart ofpathologist of low ability.

Figure 7 Chart of apathologist with apreviously known redlgreen colour blindness.

Figure 8 Chart of apathologist with apreviously unknown majordefect in colourdiscrimination.

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7

6

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low ability to discriminate hues. None of thepeople in the low ability group was a woman.The ability of pathologists to discriminatecolours was not related to age or professionalexperience.Two of the pathologists tested had specific

and major defects. One of these defects waspreviously known. The other was only recog-nised for the first time as a result of this study.The implication is that among a group ofpeople in whom the ability to discriminatecolours is a vital part of their professional lifethere will be individuals with an unrecognised

inability to do so. Pathologists with knownbipolar colour blindness have frequently adap-ted their staining techniques to become morereliant on shade. Our evidence suggests thatdifficulties will be encountered when interpret-ing certain stains if the operator's ability todistinguish colours falls below the twentiethcentile for normal. We therefore recommendthat pathologists using these new techniques1should formally assess their colour vision usingthe Farnsworth-Munsell 100-hue test. Thosewith below average ability to discriminatecolour could then seek confirmation of inter-

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Rigby, Warren, Diamond, Carter, Bradfield

pretation from more "colour able" colleagues.Those with severe colour defects should con-

sider using alternative staining techniqueswhere available.

It is paradoxical that despite advanced tech-nology employment as a mixer of paint is not

possible without formal testing of colour dis-crimination, whereas a diagnostic histopatho-logist requires no test of eyesight whatsoever.

AddendumSince the presentation of preliminary findingsat the meeting of the Pathological Society ofGreat Britain and Ireland in January 1989,5 theauthors have received anecdotal evidence ofvarying degrees of colour blindness in severaleminent past and present histopathologists. Itis the authors' intention to treat these details as

confidential, but they would be interested to

hear of any further examples.

We are grateful for the cooperation ofthe volunteer pathologistsin the south west region, to Mr C C Jeal for expert photographicassistance, and to Mr A 0 Hughes, senior lecturer in medical

statistics, for statistical help.

1 Roe R, Warren BF, Williamson RCN, Bradfield JWB.Mucin staining in transitional mucosa in right and leftcolon. JPathol 1989;157:174A.

2 Roe R, Warren BF, Williamson RCN, Bradfield JWB.Interobserver variation in colour assessment in mucinhistochemistry-an attempt at control. J Pathol 1989;157:169A.

3 Farnsworth D. Manual: The Farnsworth Munsell 100 Huetestfor the examination of colour discrimination. Baltimore:Munsell Color Co Inc, 1957.

4 Berbaum KS, Platz C. Pattern recognition. Hum Pathol1988;19:1127-31.

5 Rigby HS, Warren BF, Diamond J, Carter C, BradfieldJWB. The Farnsworth Munsell test of colour perceptionin pathologists. J Pathol 1989;158:343A.

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