Color Vision
Color Vision Abnormalities

Approximately eight percent of the male population experiences some sort of color deficiency. It is much rarer in females, effecting less than 0.5% of the population. Color �blindness� is a commonly used misnomer. In fact most people are simply color deficient. Achromasy, seeing no color at all is almost always associated with a medical condition resulting in a non-functioning of the retinal cones.

Color vision abnormalities can be classified into several distinct categories according to type and degree of the deficiency. The most widely used systems of naming and classifying color deficiencies are based on color mixing performances.

Normal Trichromatic Vision

Normal color vision is known as trichromatic vision. In this instance, the observer can match every color he or she sees with a suitable mixture of only three primary colors generally defined as red, green and blue.

Anamalous Trichromatic Vision

A person with anamalous trichromatic vision still requires the same three primaries but is deficient in one of them, thus requiring significantly different proportions than would be required by the normal observer. That person may be deficient in either red, green or blue. However red-green deficiencies make up the overwhelming majority of all color vision abnormalities found in the population. Anamalous trichromats can therefore be categorized as being protanomalous, red-deficient, deuteranomalous, green deficient, or tritanomalous, blue deficient. To emphasize, an anamalous condition is one of deficient function not without function.

Protanomaly�Red-deficient

The term �red weakness� is an accurate description of the chief characteristics of protanomaly. Red lights appear dimmer than they do to the normal observer. In a mixture of red light and green light to match a standard yellow light, the protanomalous observer requires a greater than normal proportion of red, indicating a �weakness� in the perception of red.

Deuteranomaly�Green-deficient

The name �green weakness� is sometimes applied to this condition. Here, a greater than normal proportion of green light is required in red-green mixture to match a standard yellow, indicating a desaturation of greens.

Tritanomaly�Blue-deficient

This condition is also called �blue-we akness� because a greater than normal amount of blue is required in a mixture of blue and green light to match a given blue-green. Congenital tritanomaly is extremely rare. However, impairment of blue and yellow discrimination due to changes in the ocular media with age or to changes resulting from ocular disease is more common.