Encyclopedia - Color Blindness

What is color blindness?
What causes color blindness?
How is color blindness detected?

What is color blindness?

Color blindness — or, to use the formal medical term, color vision deficiency — is any abnormality of the color vision system that causes a person to see colors differently than most people or to have difficulty distinguishing among certain colors.

What causes color blindness?

Color vision deficiency is can be caused by:

Inherited defects of the color-sensitive pigments of the cone cells, which are concentrated in the macula, the central area of the retina (See Anatomy of the Eye)
An abnormality of the cone cells
A reduced number of cone cells
Injury or certain diseases of the retina or optic nerve

Total color blindness, in which the world is seen only in black, white and gray, is very rare. Most persons with color vision deficiency have vision that is adequate for most purposes but cannot distinguish certain colors. Reduced discrimination of wavelengths within the middle part of the visual spectrum hinders the person’s ability to see green. Reduced discrimination in the long parts of the spectrum results in difficulties seeing the red family of colors. A rarer form is blue deficiency, or tritanopia, which may be inherited but can result from the toxic effects of drugs or poison or deterioration of the retina or optic nerve.

Inherited color vision deficiency usually is gender-based, with the majority of sufferers being male. Some women may carry the gene defect and pass it on to their children. The overall incidence of color vision deficiency for whites of European origin is 8 percent for males and 1 percent for women. The incidence is lower for Asians and Native Americans and lowest of all for blacks.

How is color blindness detected?

Color vision deficiency is detected by tests that use special color plates under daylight conditions. The test usually is conducted during the childhood years. It is also performed when an adult applies for a job in which color vision is essential, such as airline pilot. The exact degree of color vision deficiency can be determined by a test that requires the arrangement of sequences of colored chips or by an instrument called an anomaloscope, which shines a mixture of red and green lights. The person being tested adjusts the mixture until it appears the same as a fixed spot of yellow light. An adjustment that yields a mixture that is too red or too green indicates the presence and severity of color vision deficiency.

Many people with color vision deficiency are not aware of the problem because it does not interfere with everyday living. It can be detected during employment tests for an occupation requiring normal color vision. Such positions include airline pilot, commercial artist, marine pilot, color photographer, or electrician, where the ability to distinguish color-coded wires is important. There is no treatment for the condition.