Anomalous Trichromacy

Protanomaly is referred to as "red-weakness" — an apt description of this form of color deficiency. The red cone's sensitivity is shifted toward the green part of the spectrum. Any redness seen in a color by a normal observer is seen more weakly by the protanomalous viewer, both in terms of its "coloring power" (saturation, or depth of color) and its brightness. Red, orange, yellow, and yellow-green appear somewhat shifted in hue towards green, and all appear paler than they do to the normal observer. The redness component that a normal observer sees in a violet or lavender color is so weakened for the protanomalous observer that he may fail to detect it, and therefore sees only the blue component. Hence, to him the color that normals call "violet" may look only like another shade of blue.

• Often confused with deuteranomaly
• Red appears darker and less saturated
• Traffic lights and danger signals may be harder to see

Deuteranomaly is a type of anomalous trichromatic vision in which the green-sensitive cones have decreased sensitivity. It is an X-linked trait, affecting about 5% of white males and 0.25% of females in the United States, and is the most common color vision deficiency. It is an inherited disorder of color vision, caused by a gene located on the X chromosome, in which a person has all three of the retinal pigments in the cones, but the sensitivity of the green-sensitive cones is decreased. People with deuteranomaly have difficulty distinguishing greens from reds, and may confuse greens with yellows or reds with purples.

• Most prevalent form of color blindness
• Affects ~5% of all males worldwide
• Greens and yellows appear very similar

Tritanomaly involves an abnormal blue cone and is very rare. It is a rare type of anomalous trichromatic vision in which the third, blue-sensitive, cones have decreased sensitivity. Less than about 0.01% of people are affected by it. However, it is known that reds and greens are unaffected, and some yellows may be visible on the lower end of the spectrum with this disorder. What is known about protanomaly and deuteranomaly suggests that tritanomaly is caused by defective S photopigment. It is known that persons affected by this condition have difficulty distinguishing between yellow and blue.

• Not sex-linked — affects males & females equally
• Can be acquired from aging or disease
• Blue and green appear very similar