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In 1960, Alpern, Falls, and Lee reviewed the extensive literature on congenital monochromatism and then described the visual characteristics of five patients with typical total monochromacy.1At the time these data were presented, one of us (H.F.F.) made a plea for eyes of this kind which might become available for histological examination. One such case has now been described, but the eyes were only obtained 40 hours after death, at which time considerable autolysis of the photoreceptor layer had already occurred.2In the case to be presented, the eye was fixed immediately after surgical enucleation. While we had no psychophysical measurements on this observer at that time, we have since obtained good measurements of the color vision and dark adaptation characteristics of her remaining eye. The present paper will describe the results of both the histological examination and the psychophysical measurements. Report of Case A 69-year-old white woman

1. Atypical (blue cone) monochromats show two action spectra when tested by the increment threshold method of Stiles with `central' fixation. One spectrum peaks near 450 nm and has the spectral characteristics of normal blue cones. The other resembles rhodopsin (π0) modified slightly by photostable macular pigment. 2. Under some circumstances such observers are dichromats. There is a neutral point (matched to Illuminant `C') in the neighbourhood of 460-470 nm. 3. The spectral colour matching functions using two primaries have been measured on three such subjects. They can be fit reasonably well, although imperfectly, by linear combinations of π0 and π1. The chromaticity co-ordinates have been calculated according to the convention of W. D. Wright and compared to the results predicted from π0 and π1. The comparison suggests that part of the imperfections of the colour matching function fit is due to prereceptor differences (e.g. macular pigment) between the blue-cone monochromats and the hypothetical π0, π1 observer. 4. Colour matches made at high light levels continue to hold when the intensity of the field is reduced below the cone threshold. 5. Therefore one of the visual pigments participating in the colour matches has an action spectrum which is not measurably different from that of the rod pigment rhodopsin. 6. Increment threshold measurements show that the mechanism which has the rhodopsin action spectrum has the directional sensitivity of cones, not rods. 7. Blue test threshold during dark adaptation after a full bleach follow a bipartite exponential recovery curve. The first exponential has a time constant of 1 min, the second 2 min. By comparing these curves to the increment thresholds it is possible to relate the first to the π1, the second to the π0 cones. 8. Using a broad band blue gelatin filter in the measuring light of the retinal densitometer and studying the same retinal region tested in 7 it is possible to follow the regeneration of a pigment after a full bleach which has an exponential recovery with a time constant of 1·0 min. With a yellow green filter in the measuring light the exponential recovery observed after a full bleach has a time constant of 2·0 min. 9. One of the two visual pigments participating in the colour matches resides in receptors which have the action spectrum, the directional sensitivity and probably the dark adaptation curve of normal blue cones. 10. The other resides in receptors which have the action spectrum of normal rods but the directional sensitivity and the dark adaptation curve of normal red and green cones.

SummaryThe different varieties of congenital dyschromatopsias are inherited following different modes. The dyschromatopsias of the protan and deutan type, as well as the atypical achromatopsia (blue mono-cone monochromacy), are sex-linked recessive, the tritanopia probably autosomal dominant and the typical achromatopsia surely autosomal recessive. The mode of transmission of the tritanomalia is still dubious.Concerning the localisation of the genes on the X chromosome, the bilocular theory for the deutan and protan genes is accepted at the present time. These genes form a cluster with the genes of hemophilia A and G6PD deficiency. It is possible that this cluster is situated on the short arm of the X chromosome or on the long arm near the centromeric region. The exact situation will be known very soon, when the interpretation of the results of the cellular hybridisation, which are still discordant, will be well established.

Resume A l'aide d'un banc d'optique, de filtres interferentiels et d'un photometreapapillotement de Bechstein, presentant un champ d'observation de 1° 30′ entoured'un champ peripherique d'adaptation de 30° et de meˆme luminance, nous avons determine,adeseclairements retiniens de 55 et de 415 trolands, des courbes spectrales iso-energetiques d'efficacitelumineuse relativeacelle d'une radiation de 552 nm chez 25 sujets protanopes, 23 protanomaux, 24 deuteranopes, 27 deuteranomaux, sept achromates typiques et un achromate atypique du type “blue mono-cone monochromacy”. Le materiel de comparaison est constituepar un groupe de 25 sujets normaux de meˆmeaˆge moyen. Tous les groupes de sujets anormaux presentent des courbes moyennes tres significativement differentes de celle du groupe de sujets normaux. Les groupes protan ont des facteurs moyens augmentes en decade 552 nm et diminues au-delade 552 nm, tandis que les groupes deutan ont des facteurs moyens diminues en decade 552 nm et augmentes au-delade 552 nm. Par contre, il n'y a que des differences minimes et non-significatives entre la fonction moyenne d'un dichromatisme et celle du trichromatisme anormal correspondant. La comparaison entre les deux niveaux d'eclairement retinien montre que le “phenomene inverse de Purkyne” des sujets normaux est retrouvechez les sujets deutan et retrouvepartiellement chez les sujets protan. La dispersion des valeurs individuelles au sein des groupes protan et deutan n'est jamais plus petite que la dispersion normale ; celle parmi les sujets protan est particulierement grande entre 567 et 641 nm et celle parmi les sujets deutan est particulierement grande entre 489 et 567 nm. Toutefois, les trichromates anormaux ne presentent pas de correlation significative entre le quotient d'anomalie et les facteurs pour 489 et 616 nm. Ce n'est que chez un achromate typique et au seul niveau de 55 trolands que la courbe coincide convenablement avec la fonction scotopique V ′(λ) de la C.I.E.; chez les autres achromates typiques l'accord n'est obtenu que si la fonction V ′(λ) est corrigee pour une absorptiona50 pour cent de la pigmentation maculaire normale. Ce meˆme resultat est donnepar l'achromate atypique au niveau de 55 trolands, tandis que celui de 415 trolands donne une fonction “bleue” culminanta450 nm. Apres une legere correction faisant coincider la courbe moyenne de nos sujets normaux avec la fonction photopique V (λ) de la C.I.E., nous avons calculeune fonction moyenne protan V p (λ), un peu differente de la fonction W p de Judd, ainsi qu'une fonction moyenne deutan V d (λ).

Introduction Cone dysfunction syndrome is the term used in the present investigation to designate a generalized disturbance of the cone system resulting in subnormal visual acuity, defective color vision, and absence of the photopic flicker electroretinogram; concomitant signs may include nystagmus and photophobia. The fundus is normal or may show a variety of lesions which cannot be considered pathognomonic of the condition. The bestknown form of the syndrome is congenital and is commonly referred to as total color blindness, monochromacy, or typical achromatopsia—terms which place emphasis upon the severe loss of color vision. Although it is now apparent that the incidence of generalized cone pathology is much greater than previously assumed,1-3a lack of awareness of the clinical symptomatology has resulted in frequent misdiagnoses. Many of the patients to be reported had earlier diagnoses of optic atrophy, macular degeneration, cerebral pathology, albinism, congenital nystagmus, or merely "unexplained amblyopia." The