Let me describe a condition: it is a physical disability that affects more than 20 million Americans; it is usually congenital, and almost always incurable; it is at best a nuisance, and at worst life-threatening.

You might think that such an ailment would be a major item on the agenda of the National Institutes of Health, perhaps even the subject of a Presidential Commission to seek urgent action.

No such thing. The condition I have described is colorblindness. It is strongly sex-linked. One man in 12 suffers from it to some extent, compared with only one woman in 200. The whole subject enjoys little attention.

Part of the reason for our lack of emphasis on colorblindness is its invisibility. You can't tell that a man has such a disability, although his choice of shirt and matching tie may be a bit of a giveaway. In fact, you may suffer some form of it yourself and become aware of that only in special circumstances.

In my own case I have difficulty distinguishing blues and greens, but I only notice it when playing "Trivial Pursuit," when I am never sure if I have a blue or a green question coming. A more common - and a more dangerous - form cannot distinguish red from green.

John Dalton, the chemist, a colorblind person and one of the first people to write about it, reported that "blood looks like bottle-green and a laurel leaf is a good match for sealing wax." In more modern times, sufferers are forced to distinguish the state of traffic lights by their vertical placement, and they are at risk in any situation where a red "Stop" light or a green "Go" light offers no other information to back it up.

Colorblindness originates in the retina, at the back of our eyes. The retina contains two different kinds of light-sensitive objects, each microscopic in size. The retinal rods do not perceive color at all, and they are most useful at low light levels. The retinal cones are responsible for all color vision, but they need a higher light level before they become sensitive. Recall that when on a moonlit walk your surroundings are rendered only in black and white.

In a person with normal vision, the signals generated by the cones and transmitted by nerve cells to the brain permit all color to be distinguished. If you are colorblind, however, certain colors will produce the same signals. Green and red may be confused, or pale green and yellow, or, in my case, certain greens and blues.

Unlike some other conditions, colorblindness has few compensating advantages. In a military situation, a colorblind person may detect camouflage that fools ordinary eyes, but in general, colorblindness is nothing but a nuisance.

Also, as I said at the beginning, this disability usually is incurable. It can, however, often be alleviated by the use of special eyeglasses. These contain filters that modify the light passing through them in such a way that they convert different colors to combinations that the wearer can perceive.

That's today, and even if impressive it's pretty crude. Twenty years from now we will be able to go much farther, with personalized "false color" eyeglasses. These will employ sensors and displays that transform any light falling on them into color regions for which the wearer's retina is able to generate distinguishable signals. You might argue that a person with such eyeglasses is still colorblind, because his perception of blue, green, or red will be different from yours. If you make this point, I will ask the question: how do you know that what you perceive when you see colors is at all the same as other people's perceptions?

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