A1 Field, age 12, of Dubuque, Iowa, for his question:
WHAT CAUSES COLOR BLINDNESS?
Color blindness, a condition that is also called Daltonism, is not being able to tell all colors apart. Scientists believe that color blindness is inherited.
A color blind man who marries a woman with normal vision will have children with normal vision. But the defect is hidden in the daughters, and they can pass it on to their children. If a color blind man marries a woman whose father is color blind, probably half of his children will be color blind.
Most color blind persons can see only two basic colors of the rainbow and they confuse other colors. This kind of color blindness is called dichromatic vision.
Most persons with dichromatic vision can see a fairly wide range of yellows and blues. But they tend to confuse reds with greens and some reds or greens with some yellows.
Only a very few persons are truly blind to all colors. They have achromatic vision. Persons with achromatic vision see the world in shades of white, gray and black. For them, it's like looking at black and white photographs.
More men than women are color blind. More than 4 out of every 100 men are color blind, compared to only about one 1 of every 200 women.
There is no cure for color blindness.
Many animals, including cats, dogs and horses, probably do not see color as we do, the scientists tell us. But the condition is normal in their eyes and it is not a defect in their vision.
Many color blind persons do not realize that their eyesight is defective. They have learned to use the color names that everyone else uses. These persons do not know that they do not see the colors that others see. They may be hampered in their everyday activities and their condition may place them in some danger.
If a color blind person confuses red and green, for example, he may be able to tell traffic signals apart only by their brightness.
Some armed forces do not accept color blind persons for military duty.
Most persons can be easily tested for color blindness. The Hardy Rand Rittler (H R R) and Ishihara tests indicate both the type and the degree of color blindness. In these and similar tests, color triangles, squares and other shapes lie buried in a jumble of dots. These dots vary in both color and intensity. As the person identifies the colored shapes, an examiner can determine his ability to see color.
Another test, the Holmgren test, measures the ability to match colors.
John Dalton, an English chemist, was one of the first to investigate color blindness, and the condition now officially has his name. He was born in 1766 and also formulated the law of partial pressures in gases in 1802. This law states that for an ideal gas, the total pressure of a confined gas mixture equals the sum of the pressure each gas would exert alone in the same volume.