Causes and Risk Factors for Color Blindness
Color deficiency is usually a hereditary condition. The trait is passed on the X chromosome, and because males only have one X chromosome, it is easier for them to inherit color vision deficiency.
A mother who carries one normal X chromosome and one X chromosome with a mutation of red and/or green pigments is not affected, but her son has a 50 percent chance of having a color vision deficit. Fathers cannot pass it to their sons, because they supply only a Y chromosome to the genetic mix, but they can pass the gene to their daughters who carry the gene but do not manifest a color deficit.
For a woman to inherit a color vision deficiency, she must have a mother who is a carrier and a father who is color deficient. The odds of this occurring are very slim.
Color vision deficiency can be acquirednot only as a result of diseases or conditions of the retina, optic nerve, or more posterior visual pathways in the brainbut also as a result of exposure to toxins and certain drugs. Macular degeneration, optic neuritis, and strokes that affect certain areas of the occipital lobe, for example, can affect color perception. Head injuries, systemic diseases that damage nerves (e.g., multiple sclerosis), heavy metal poisoning, and certain medications (e.g., antimalarials) also can affect color vision adversely. Unlike congenital color vision defects, acquired defects often affect visual acuity, are asymmetric from eye to eye, and may change as the disease changes.
Signs and Symptoms of Color Blindness
Children with achromatopsia demonstrate poor vision and an inability to tolerate bright light at a very young age. A child who is having trouble in school should be evaluated for vision problems, including color vision deficiency.
Milder forms of color vision deficiency are more subtle, and many people never realize that they have a problem seeing colors. Routine color vision testing of all children will identify those having a color vision problem at an early age. Anyone who notices a change in color perception should see an eye care specialist immediately.
Diagnosis of Color Blindness
Inherited color vision deficiency is usually diagnosed in early childhood using simple screening tests. The Hardy-Rand-Rittler (H-R-R) and Ishihara Color Plates are used to evaluate the type and degree of color deficiency. In these tests, the person is asked to identify the colored shapes or numbers that lie within a jumble of dots and vary in color and intensity. The physician detects and categorizes the deficiency based on the person's responses.
The D–15 and the Farnsworth-Munsell 100-hue disk-matching test evaluate the ability to identify gradations of color by placing discs in order.
Treatment for Color Blindness
Congenital (inherited) color vision deficiency cannot be treated or cured. Measures can be taken, however, to compensate for it. Some people develop their own system of recognizing colors by their brightness or location, such as the positions of red, yellow, and green in a traffic light.
Specialized glasses and tinted lenses that "normalize" colors are also available. Complete achromats can use strong magnifiers to read and perform near tasks and use sunglasses to reduce light sensitivity.
Acquired color vision deficiency requires treatment of the underlying cause. In many cases, normal color perception returns when the underlying condition has been resolved.
Color Blindness Prevention
Inherited color vision deficiency cannot be prevented.