The term "colorblindness" (or "color blindness") is incorrect in most cases, according to the website Colour Blindness and Medicine. Most people who are said to be colorblind can see some color, but have a deficiency that prevents them from seeing all colors accurately. Colorblindness comes in seven varieties, and although many people believe that this condition can only be found in men, some women also have color deficiencies. In the developed world, about 8 percent of men and 0.4 percent of women are colorblind.
The first case of colorblindness was described in the late 18th century by chemist John Dalton, who was himself blind. Dalton is more commonly known for developing the atomic theory, but the first paper he ever wrote described colorblindness in himself and his brother. His research started the ball rolling on this condition in the scientific community, and today, some call colorblindness Daltonism in honor of his first description.
Achromatopsia Gene Discovery
True or full colorblindness, called achromatopsia, is the complete inability to see color. According to the Gale Encyclopedia of Children's Health, the gene that causes this condition was discovered on chromosome 2 in 1997. With this condition, both parents must carry the gene, but neither are colorblind. Their children have a 25 percent chance of developing achromatopsia if this is the case, as well as a 50 percent chance of carrying the gene and passing it on to their own children.
Ishihara Color Test
One of the first and most popular tests for colorblindness is the Ishihara Color Test, which was developed in 1917 as people began to study this condition more. These colored plates contain random dots that are colored in patterns. With normal vision, patients see certain numbers in the dots or do not see anything at all. However, if a patient has certain kinds of colorblindness, different numbers will appear in the dots or no numbers will appear at all.
Since first being described in the late 1700s, several types of colorblindness have been discovered and classified. Along with achromatopsia, patients can have protanopia, deuteranopa or tritanopia. With protanopia and deuteranopa, the red-green channels of sight do not work, making it difficult to distinguish those two colors. Tritanopia is a problem with the blue channel of sight, making it hard to distinguish between shades of blue and between shades of yellow.
Although most people associate colorblindness with heredity, there are other causes as well, which doctors have found after studying the condition during the past several decades. Color vision can change with certain medical conditions. When a disease attacks the eye's retina, it causes tritanopia. On the other hand, when a disease affects the optic nerve, it causes problems with red-green colorblindness.