To see how color blindness is experienced, click here .
What is color?
When we see different colors, we are perceiving differences in the type of light that is reaching our eyes.
The way we see different colors is something like the way we hear different sounds as being "low" or "high." This is called pitch, and it corresponds to the frequency of the sound.
The keys on the left side of a piano keyboard make low-frequency sounds, for example, and the frequency of the sound gets higher as one plays keys further to the right. There is a similar order to the colors we see.
The colors of every rainbow always appear in the same order: red, orange, yellow, green, blue, and violet. The different colors in each part of the rainbow correspond to a different wavelength of light. Reddish colors are long in wavelength and bluish colors are shorter. And just as there are many notes on the piano, there are many wavelengths of light corresponding to different colors.
How does the eye normally see colors?
The eye is often compared to a camera. The front of the eye contains a lens that focuses images on the inside of the back of the eye. This area, called the retina, is covered with special nerve cells that react to light.
These retinal nerve cells include the rods and cones. The rods and cones react to light because they contain pigments that change when light strikes them.
There is only one kind of pigment in the rods, and it reacts the same way to any wavelength of light. The rods do not have anything to do with color vision. They are very sensitive to light, however, and it is the rods that allow us to see at night.
The cones are responsible for color vision. There are several kinds of pigments present in three types of cone cells. Some cones react to short-wavelength light, others react to medium wavelengths, and others react to higher wavelengths.
When the rods and all the types of cones are working together, the eye sees all possible colors. It is something like the way a painter can mix just a few colors together and make paint of every possible color.
What is color blindness?
If there is some problem with the pigments in the cones, the eye will not see colors in the usual way. This is called color deficiency or color blindness.
If just one pigment is missing, the eye might have trouble differentiating similar colors. In some eyes, none of the pigments are present in the cones, so the eye does not see color at all. This most severe form is known as achromatopsia.
Eye doctors have special tests designed to check the ability of the eye to see colors and to tell the difference between different colors.
Why do some people have color deficiencies?
When someone has color deficiencies, it is usually because their eyes do not make all the pigments needed for color vision. This is usually because part of the genetic code for the pigment is incorrect or missing from the person's DNA. This is a condition that is usually inherited. The way it is passed through the DNA means that men are color-blind more often than women.
Are problems with color vision a sign of other health problems?
Even a very small error in the genetic code for the visual pigments can cause color blindness. It does not usually cause any other health problem. However, there are some health conditions that can affect color vision. If you notice that your color vision is changing, it is very important to schedule an appointment with your eye doctor as soon as possible.
The kind of color "blindness" that is present at birth does not lead to additional vision loss or total blindness. But because the cone cells of the retina are also used to see fine details, people who are color blind tend to have vision that is less sharp. The rod cells also tend to be "overloaded" by bright light, so tinted eyeglasses often help color-blind people to see better.
If you think you have a problem with color vision, you should schedule an appointment with an eye doctor right away. The doctor will be able to tell you whether you are seeing colors properly and what to do if you are not.
The Achromatopsia Network is a volunteer project that offers information about color blindness and provides a network for communication among color-blind people. It can be reached on the Internet at www.achromat.org or by writing to Frances Futterman, P.O. Box 214, Berkeley, CA 94701-0214.
Click here to make an appointment now . Or call 216/444-2020 or 1/800-223-2273 Ext. 42020 to schedule an appointment with a Cole Eye Institute ophthalmologist.
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