A N N 0 I'ATIONS

17. Einhorn, M., Davidsohn, I . ( 1964) 'Hepatotoxicity of mercaptopurine.' Jurrrtrol o/ /he .-ltmvicun Medical Associu/ioti. 188, 802.

18. Clarysse. A. M.. Cathey. W. J.. Cartwright. G . E., Wintrobe. M. M. (1969) 'Pulmonary disease com- plicating intermittent therapy with methotrexate.' Jortrml of /he Americati Midicol Associarion, 209, 1861.

19. Robertson, J. H. (1970) 'Pneumonia and niethotrexate.' BririsA M ~ ~ I i c o l Jortrtiul. 2, 156. 20. Duttera, M. J., Bleyer, W. A,. Pomeroy. T. C.. 1-eventhal, C. M., Leventhal. B. G . (1973) 'Irradiation.

21. Fairley, K. F.. Barrie. J . U., Johnson, W. (1972) 'Sterility and testicular atrophy related to cyclo-

22. De Groot, G . W., Faiman. C., Winter. J . S. D. (1974) 'Cyclophosphamide and the pre-pubertal gonad.'

23. Hoover. R.. Fraumeni, J. F. (1973) 'Rish o f cancer in renal-transplant recipients.' Lunce/. 2. 55.

methotrexate toxicity. and the treatment of meningeal leukaeniia.' Laticer. 2, 702.

phosphamide therapy.' Lairce.r, 1. 568.

Jorrrtiol of Pediufrics, 84, 123.

CONGENITAL COLOUR BLINDNESS A N D ITS DETECTION IN CHILDREN

TtiE detection of congenitally abnormal colour vision seems to be a neglected part of the general (and indeed sometimes of the ophthalmic) assessment of a child. This may be because congenital colour blindness is thought to be rare; or because if the visual acuity is normal the colour sense is also assumed to be so; or it may be thought that the tests employed are inapplicable to young children. These assumptions are not justified.

The report The Edircarion of'the C ' , S i d l j , t/umIicuppe(P gives several distance visual acuity tests which may be used in children from the age of 28 years. N o mention is made of screening colour vision in the pre-school child.

The use of colour is stressed in teaching nursery and infant school children, and the detection and diagnosis of a congenital abnormality affecting one boy in I2 is a responsibility which should not be ignored. The term 'colour blindness' is worth retaining if only to remind paediatricians, ophthalmologists and educationalists of this ever-present problem; it should be more accurately described as congenitally defective colour vision.

The Phj.siologicu1 Backgroirricl Light is that small part of the electro-magnetic spectrum (from 380 t o 7S9nm) capable

of exciting the photoreceptor cells of the retina. from which arise and are transmitted electrical impulses for interpretation i n the visual cortes. The perception of light has two qualities-that of brightness and that of colour. To these must be added form sense, in order to achieve visual sensation. The classtcul YOLNC;-HELM~IOLTZ theory of trichromatic colour vision postulates the existence o f thrce types of retinal cone cells, each containing a different photopigment. Each pigment \ h o ~ s ;I spectral absorption curve corresponding to red or green or blue. ( C R A \ v w R D 2 has dcscribecl the current concepts of this theory.) HERISG'S opponent theory challenged t h i h . He ahsurnes there are three pair5 ot' primary colour sensation-red-green, yellow-blue and black-white. Within each pair the component5 are antagonistic and, depending on whether ;I catabolic or an anabolic pixices5 occurred, one primary sensation would arise from each pair.

There appears to be a separate retino-cortical pathway, apart from that for colour. which conveys the sensation of brightne\\ o r luminosity. The cells involbed i n this channel and in the opponent sensation processes are thought to be, firstly, those of the retina. excluding the photo-receptors. and secondly, thohe of the lateral geniculate nucleus. All these views are melded today in the trichromatic opponent theory o f colour vision. which postulates three types of cones-red. blue and green. They provide both luminance signals

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DEVELOPMENTAL MEDICINE AND CHILD NEUROLOGY. 1975, 17

and chromatic signals; the latter are adapted into antagonistic red-green and yellow-blue channels. MACNICHOL et gives a comprehensive review of the electro-physiological and neuro-physical evidence for this integrated theory.

The Incidence and T\pes of Colotir Bliiirltiess The severity of defective colour vision in a child may range from the total inability to

recognise any colour (achromatopsia) to slight, but anomalous, trichromatic vision. The forms of colour blindness and the incidence of the common types in male Caucasians are given in the Table.

TABLE Forms and incidence of common t y p s of colour blindness in Caucasian males

I .4tlot?lnlolrs

trictirotiiutistii Dic/lrotIlotislil

Protons Protanomaly 1 ",: Protanopia 1 ( I , ,

Dcwfotis Deuteranoniily 5 ' I , , Deuteranopia 1 " , )

Triratis Tritanomaly Tri tanopia

~~ ___________ Motiochrotnatism

Rod Monochromat Cone Monochromat

I

The anomalous trichromat uses three primary colours to match a test hue(like thenormal), but with an excess of red, green or blue for the protanomalous, deuteranomalous and tritanomalous trichromat respectively. The dichromat uses only two primary colours in colour matching. The protanope lacks the visual sensation of red, the deuteranope green and the tritanope blue. Monochromatic subjects are extremely rare. For the achromat the world is seen as in a black and white film. The rod monochromat, unlike the cone mono- chromat who sees well in daylight, has poor visual acuity, usually painless photophobia and sometimes nystagmus, because of poor cofie function.

Both the colour-weak and colour-blind have been grouped together as protans when the defect is for red, as deutans when it is for green and as tritans when it is for blue. HEATH^ has described well the misinterpretations by protans and deutans of everyday colours, and our understanding of their problems has been enlarged by descriptions from rare subjects with congenital monocular defective colour vision. The inheritance of protanomaly, deuteranomaly and tritanomaly is by an X-linked recessive trait. K A L M U S ~ gives a full account of the genetics of colour blindness, including the probable mechanisms in tritanopia and achromasy. I t is still not clear where the defect occurs in the colcur visual pathway which results in colour blindness.

The Methods of' Testiiig Coloiir Visioii The earlier a diagnosis of colour blindness can be made, the earlier will parents and

teachers understand and be able to help the child. Diagnostic clues may appear if, when the child is learning to talk and expanding his colour vocabulary, he frequently misnames colours. In infant school, inability to sort out and match coloured objects should alert the teacher. Subjective tests consist of the spectral denomination tests and the pigment denomi- nation tests. Both types may be used with older children and adolescents, but the pigment denomination type is better with the pre-school child.

Spectral denomination tests range from simple naming of colours in a projected visible spectrum to the various lantern tests and the anomaloscope. There are two kinds of pigment

248

denomination tests: the FARNSM~ORI 11-MLIvsEI.1. tests and the pseudo-isochromatic (PIC)

or 'confusion' tests. Best known of the latter is the I S H I H A K A chart. More recently introduced are those by Dvorine, Tokyo Medical College. and Hardy-Rand-Rittler.

The Farnsworth-Munsell 100-hue and the Farnsworth dichotomous tests require the subject to arrange in order. according to hue, a series (either 85 or IS) of coloured discs set i n numbered plastic caps. The error score. calculated from the cap number. is entered on a circular graph and. depending upun the number of errors plotted o n \ariou.i axes. the colour defect can be diagnosed quantitatively. For screening purposes the Farnsworth dichotomous (Dl j ) test may be used for older children and to this the 100-hue test would be complementary.

To detect congenital colour blindness i n the pre-school child, use i s made of the pseudo- isochromatic principle: i t should he possihle to identify a dichromatic child earlier than one with anomalous trichromasy. The P I C ' charts have it number. letter. symbol or winding path. composed of coloured dots. which must be distinguished from the deliherately confusing background of pseudo-isocliromaric (o r apparently similar) dots. The coloured wool tests. like the Holmgren test. are not now recommended.

Fcasihle Tests ,fhr Screetiitig /Or R~~rl-Grceti Dqfec,t.s The validity of the results of testing young children for congenital colour defects is

debatable and there is scope for clinical comparison between the tests available. For instance, Cox" screened 270 children. using the lshihara illiterate plateh, and found on re-examination two to three years later that a third of those earlier identified as colour blind were in fact normal. T H U L I N ~ ~ and S L O A S ~ found the illiterate plates useful for screening, but H E A T H 4 suggests the PI(' cliarts using geometric figures were often successful. GAR DINER^ described a PIC' colour test relying on matching patterns (letter\), but this and the geometric figure recognition tests (particularly the H-R-R test) introduce the relative abilities of children to discriminate and match forms. The tests' validity might be improved if the children to be tested are first taught to identify the shapes, for ccimplt., triangles, circles and the letters used in the STYCAR test for children aged three years.

Although perceptuo-motor ability must be gauged when using the Ishihara illiterate plates, this test would seem to be the most practical to use. It should be pos.iible to increase the interest of the child, and so his co-operation. by making a game out of tracing the pathway with stylus or camelhair brush; f o r example, instead of X at each end of the pathway there could be a picture of ;I house and a child, or dog and its hennel, and the child being tested is asked to show the path that a lost child or dog would take to reach home. In this way nursery- and infant-school teachers may be able ro help in screening. particularly for dichromats.

For the older child, the H-R-R ;tiid the Farnsworth Dlj tests ;ire useful quantitative supplementary procedures. KALMUS" stresses certain fundamental criteria that must be observed in conducting these tests. The instruction3 for the test must be carefully followed. and the correct illumination must be uled. The PIC charts are designed for use i n illuminant C: this is approximated by diffuse Northern daylight. N o test should be done in sunshine. o r the early morning or late afternoon. o r i n a room with strongly coloured walls. Never should testing be done in ordinary tungsten light. A Macheth Easel lamp is the recom- mended source of artificial daylight, hut ;I dnylight fluorescent tube is the usual (commonly found) compromise. The plates should not ht. handled o r allowed to fade. The recommended

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DEVELOPMENTAL MEDICINE AND CHILD NEUROLOGY. 1975, 17

viewing distance should be observed and spectacles, if worn, should be non-tinted. Failure to follow strict testing conditions may have accounted in the past for incorrect diagnoses and even dubious occurrence rates of the various forms of colour blindness.

Rapport must be present between child and examiner in order to avoid difficulties in comprehension, and thus unresponsiveness. The examiner should understand the test and the intellectual ability possessed by the child.

The Importance of Early Diagnosis A diagnosis of colour blindness in the older child is important because of the implications

for vocational guidance. As TAYLOR’O notes, certain occupations such as navigation, traffic control, radio-telegraphy, post-office and railway electrical work, the police and commis- sions in the armed services, are precluded by colour blindness. Difficulties in pursuing other careers like medicine, dentistry, applied physics and chemistry, colour printing, photography and television, and industrial design, may be overcome by an awareness on the part of the patient, parent and teacher of the precise nature of the defect, together with a determination to overcome it. In the young, great emphasis is placed upon the use of coloured materials and objects in pre-school, infant and junior school education. Specific use may be made of colour in elementary arithmetic (as in ‘Cusenaire’ rods and ‘Unifix’ cubes); and in the Gattegno reading-scheme, words and groups of letters within words are printed in different colours. A child with an unsuspected colour vision defect may be misjudged by an unaware teacher as lacking intellectual prowess. Such misjudgement may result in frustration on the part of both, in ridicule from classmates, and in an attempt by the child to erect a psychological ‘cover’ which may be manifested as boredom, inattention and disobedience.

Wlia: to Tell the Parents and Teacher It is to be hoped that defective colour vision will be detected in the pre-school child aged

three to five years. The siblings, present and future, of a proband should be examined. The mechanism of inheritance should be discussed with the parents. All those concerned with a colour-defective child must understand that there is no means of curing the defect. Those responsible for a child with protanomalous or deuteranomalous trichromasy should understand the difficulties he will encounter, which will vary with the severity of the defect. Thus while being able to see all colours, he will be unsure about pastel blue-green tints and dark shades of green and brown. Usually environmental clues, including comparison colours, will allow him to compensate satisfactorily for the defect-often parent and child alike may be quite unaware of its presence. It is difficult for the child to identify within the blue end of the visible spectrum the several hues such as lavender, indigo and violet. Because both red-‘weak‘ and green-‘weak‘ individuals may call an amber light red when it is seen beside a green light and green when it is seen beside a red one, the obvious safety implications must be explained.

The handicap of the dichromatic child is more severe; for the protanope and deuteranope, red, orange, yellow and green all appear to have the same hue, and all the hues at the short-wavelength end of the spectrum are called blue. He has only brightness and saturation of colour to add to his other environmental clues and is prone to mistakes. For example, he would have difficulty in selecting the right hue to colour a picture showing apples, cherries or strawberries, and equal difficulty in identifying these fruits against their foliage.

250

ANNOTATIONS

The paediatrician or ophthalmologist who may have detected and later precisely diag- nosed the condition can, by counsel. contribute to the understanding. education and everyday compensation of the child with congenital defective colour vision.

Moorfields Eye Hospital, City Road, London EClV 2PD.

Hcw WILLIAMS

R E F t RENCFS 1. The Education o /!he Visually Hundicaprcd (1072) London: H.M.S.O., p. 12. 2. Crawford. R. H. (1965) 'Sketch of the preqent position of the Young-Helmholti thcork of colour vision.'

I n de Reuck, A. V. S. , Knight, J. (Ed.;.) C(J/OIW Vision: P/ l? .s i fh,q' arid E.vpcrin:cw!ul Psjdlo1og.v. Ciba Foundatior Symposium. Boston: l.~t!lc. Brown.

3. MacNichol, E. F., Feinberg. R.. Harosi. F. I . (1973) 'Colour diwrimination proce\scs in the retina.' Colorrr 73. London: Adam Hilger, p. 191.

4. Heath, G . G. (1964) 'Colour vision.' I n Hirsch. M. J . , Wick. R. E. (Eds.) Vi.cion o/ (%i/m'rcn: an Uplo- nie!ric Syniposiuni. London: Hamniond. Hamniond and Co., p. 291.

5. Kalmus. H. ( 1965) Dingnosis uric/ Grrwrics of Dt~/kttiw Co!or/~ Visioiz. Oxford : Pergainon. 6. Cox, B. J. ( 1971) 'Validity of a prexhool colour vision test.' Journal y/'Schoo/ Hrulrh . 41, 163. 7. Thi!lir?e, IH. C. (1972) 'Colour blindne\s in children. The importance and feasibility of early recognition.'

8. Sloan, L. L. (1963) 'Testing for deficient colotir perception in children.' ltt!cwio!iunu/ O)pht/iu/nio/ogy Clinical Pediairics, 11, 295.

Clinirs. 3. 697. ... . ~ _ ~

9. Gardiner, P. - ( 1973) 'A colour vision te\t for young children and the handicapped.' Developmen!ul

10. Taylor, W. 0. G. (1971) 'ETects on eniplo!n:ent of defects in colour vision.' Rritivlr Jor/nrul of Ophlhnl- Medicine and Child Ntwdog?. , IS, 337.

rTlolog.l*, 55, 753.

PARENTAL RESPONSE TO HANDICAPPED CHILDREN THERE has been considerable interest in parents' adaptation to a signiticantly handicapped childl--lO. The young professional will gain from digesting R I C H M O N D ~ and MAC KEITH'O, who have recently pointed out some of the variability among responses of parents t o a handicapped child. There are two con\iderations which may also be helpful.

First is the special meaning that the child and his handicap have to the individual parent. Every child has some specific conscious and unconscious meanings to the family: for example, the first-born male has always had special meaning. and ii child born after con- siderable difficulty with frustrating attempts at conception will have special meaning. The sex of the child, o r circumstances surrounding the conception also may be significant to individual parents. One clue to the special meaning of a child is his or her name and why it was chosen.

Secondly, the particular handicap may have specific meanings t o the parents. This usually reflects experiences parents have had with people with the same handicap. The parents' stereotype of mental retardation o r cerebral palsy or some other such handicap may be bleak and depressing. Parents may have ideas that mentally retarded children will completely stop learning at some future age, or will be sexually promiscuous, or must live in an institution, and so on. Even when these preconceptions have been discussed, their effective component may continue to influence the parents' adaptation to their child.

Parents also vary in their capability to adapt to stress. Having a child with a serious chronic handicap is a stressful event and leads 011 to a chronically stressful situation.

Basically, it is helpful to know the parents as people. I t is helpful to know what kind of childhood the parents had and what important events have taken place in their past and how they responded to these, for example whether by specific defensive maneuvres such as denial, o r reaction formation, depression or intellectualization. The task is to understand

251