Color Blindness Health Article

Definition

The term color blindness describes a deficiency in discriminating various colors. It is a misnomer because most color-blind people do, in fact, see colors. The deficiency is a lack of perceptual sensitivity to certain colors. A rare few may not see colors at all.

Description

Normal color vision requires the use of special cells, called cones. They are wavelength receptors located at the back of the eye on the retina. Most of us are trichromats, which means that we have three types of cones, commonly called red, green, and blue cones. They are long, medium, and short wavelength receptors, respectively. The interplay among these cones enables us to see a large spectrum of colors. A defect in any of these types of cones will result in deficient color vision. Most color- deficient individuals are dichromats. They are not entirely blind to color, rather they get some colors confused with each other. For example, they may see certain colors (like red and green) as very similar, whereas people without the deficiency would easily be able to differentiate these colors.

The following are three basic types of color deficiency:

• Protanopia and deuteranopia (commonly called red/green color blindness). Red/green color blindness is the most common deficiency, affecting about 10% of Caucasian males and 0.5% of females. People with protanopia have fewer red cones; blue-green and red- purple appear gray to them. Deuteranopes have fewer green cones; green and purple-red appear gray to them.
• Tritanopia (commonly called Blue color blindness). People with tritanopia have fewer blue cones; blue and yellow appear as white or gray to them. Such people are very rare and have poor blue and/or yellow perception. As many females as males have this deficiency. It usually appears in people who have physical disorders, such as liver disease or diabetes mellitus.
• Achromatopsia (commonly called total color blindness). Total color blindness—vision only in black, white, and shades of gray—can be caused by monochromacy (a retina that has only one type of receptor) or from acquired brain damage. Monochromacy is a very rare hereditary disorder. It affects one person in 33,000 in the United States, males and females equally. They usually have poor visual acuity and extreme sensitivity to light. Their vision is significantly impaired and they protect their light-sensitive eyes by squinting in even ordinary light.