Red-green blindness confined to one eye.

We report experimental studies of an individual with different types of color vision in his two eyes. The left eye is typically deuteranomalous, with good wavelength discrimination. The right eye is typically deuteranopic. both in its wavelength discrimination and in its color matching functions. Luminosity curves of left and right eyes are indistinguishable, both being within the normal range. Binocular matches show that the colors seen with the dichromatic eye range from “orange” (610 nml at long wavelengths to “greenish blue” (473 or 474 nm) at short wavelengths. Possible physiological and genetic mech&ms are-discussed. The nature of the link between deuteranopia and normal color vision has been a central problem in color theory for more than a hundred years, and many experiments have attempted to clarify it. Thanks to the investigations of Pitt (1935) and others, reviewed by WimeroiI (1970), it is now possible to specify which colors deuteranopic observers confuse with which: which greens, for instance, a deuteranope will confuse with a given red or purple. But these experiments have left unanswered a still more basic question: just what color sensations does a deuteranope experience? Does he see red as green, or green as red, or both as yellow or some other color? It is useless to put this question directly to the deuteranope, for since the deuteranope knows nothing of the normal observer’s color sensations, there is no guarantee that when he uses a particular color name the color sensation intended is the one to which a normal observer would apply the term. Clearly too, normal observers, lacking access to the deuteranope’s experience, can never learn which of their own color sensations are available to him. For i~o~tion about the colors seen by deuteranopes, we have to rely mainly on certain rare individuals whose deuteranopia is confined to one eye, the other eye being more or less normal. For these unilateral color blinds it is a simple matter to identify, among a range of colors viewed monocularly with the normal eye, the particular color that matches a test coior viewed by the color-blind eye. From the binocular matches of a unilateral deuteranope the normal ~d~vidual can perhaps learn which ofI% own color sensations are experienced by deuteranopes. Although the special importance of unilateral congenital red-green blindness has long been recognized (Judd, 1948), only four unilaterally dichromatic cases have been reported up to now, and probably only one of these is a deuteranope. The earliest case is the one studied by van Hippei (1880, 1881) and by Holmgren (1881) and discussed more recently by Walls and Mathews (19523. Both von Hippel and Holrngren found evidence of substantially reduced sensitivity to long wavelengths in the red-green blind eye, so this observer was probably a unilateral protanope. A second case of unilateral red-green blindness. possibly congenital, was reported by von Neipperg in 1932 but was not extensively studied. In a third case (Sloan and Wollach, 1948), the coIorblind eye appears to have been truly deuteranopic: the other eye exhibited a relatively slight deutan-like deficiency. All of these unilateral dichromats, and others too (Judd, 1948), saw with their dichromatic eyes colors ranging between blue at the short wavelength end of the spectrum and yellow at the long wavelength end, and this fact has had considerable influence on the theory of color blindness (see, for instance, Judd, I949; Graham, 1965).