|Poor Color Vision
Poor color vision is an inability to distinguish among certain shades of color. Although most people call it colorblindness, true colorblindness describes a total lack of color vision. The ability to see only shades of gray is rare.
Most people with poor color vision can't distinguish between certain shades of red and green. Less commonly, people with poor color vision can't distinguish between shades of blue and yellow.
Poor color vision is an inherited condition in most cases. However, eye diseases and the effects of some medications also can cause color deficiency. Men are more likely to be born with poor color vision.
Your ability to see colors across the light spectrum begins with your eyes' ability to accurately distinguish three primary colors — red, blue and green.
Light enters your eye through your lens and passes through the
transparent, jelly-like main body of your eye (vitreous body) to color-sensitive cells (cones) in your retina at the back of your eye. Chemicals in the cones distinguish among colors and send information through your optic nerve to your brain. If your eyes are normal, you're able to distinguish hundreds of blends of colors.
If your cones lack one or more light-sensitive chemicals, you may see only two of the primary colors. The most common color deficiency is an inability to see some shades of red and green. Instead of a normal spectrum, a person with red-green color deficiency will have one or two neutral or gray areas where these two colors normally appear.
Often, a person who is red-green deficient isn't completely insensitive to both colors. Defects can be mild, moderate or severe, depending on the amount of light-sensitive substances missing from the cones. Someone with red-green deficiency may not be able to differentiate the colors of a rainbow or recognize a rose-colored sky at sunrise or sunset.
Interestingly, many people with red-green deficiency aren't aware of their problem. Their "green" may be what normal-sighted people call "yellow," but because they've always heard leaves called green, they interpret what they see as "green."
Poor color vision has several Causes:
- Inherited disorder. In most cases, the genetic information that results in color deficiency is passed along from mother to son. However, the abnormal gene passed along by the mother could come from the mother's father — maternal grandfather. In such cases both the grandfather and grandson would be affected. About one in 12 males is born with some degree of color deficiency. Most females possess genes that counteract the deficiency. Inherited color deficiency usually causes a difficulty in perceiving red and green. The severity of your color deficiency doesn't change over your lifetime. You inherit a mild, moderate or severe degree of the disorder.
- Diseases. Vision defects acquired through disease more commonly affect your perception of blue and yellow. They also may affect one eye more than the other and may get better if the underlying disease can be treated. Some conditions that can cause color deficits are diabetes, glaucoma, macular degeneration, Alzheimer's disease, Parkinson's disease, chronic alcoholism, leukemia and sickle cell anemia.
- Some medications. Color vision can be altered by certain medications, such as some drugs used to treat heart problems, high blood pressure, infections, nervous disorders and psychological problems.
- Aging. Your ability to see colors gradually deteriorates as a part of aging.
- Chemicals. Exposure to some potent chemicals in the workplace, such as carbon disulfide, fertilizers and styrene may cause loss of color vision.
When to seek medical advice :
You may have poor color vision and not know it. You also may not suspect the condition in your child until a situation causes confusion or misunderstanding — such as encountering a traffic light or trying to interpret color-coded learning materials. If your child is seeing an eye doctor for a preschool eye exam, it's a good idea to make sure your child is tested for color vision as well as for visual acuity. Even though there's no treatment for inherited poor color vision, have your child's eyes examined if you suspect you or your child has poor color vision. If the cause is some other eye illness, treating that illness may improve color vision.
If you have trouble seeing certain colors, your eye doctor can quickly and easily test to see if you have a color deficiency. Many specialists trained in eye diseases and conditions (ophthalmologists) use a book containing several multicolored dot-pattern tests to provide a simple and accurate assessment of color vision deficiencies inherited at birth. If you don't have a color vision deficiency, you'll be able to pick out numbers and shapes from within the dot patterns. However, if you do have a color vision deficiency, you'll either find it difficult to see anything among the dots, or you won't see anything at all.
No treatment can correct inherited color vision deficiencies.
If you have problems discerning shades of color, your eye doctor can determine which type of poor color vision you have and check to see if there's an associated eye disease. Eye disease isn't as common a cause of poor color vision as heredity is, but treatments that slow or reverse the course of an eye disease may improve your color vision.