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Seeing color is important in our lives. When light passes through a prism (a clear glass object with many sides), it separates light passing through it into the colors of the rainbow. Every color has a different wavelength. The human eye and brain together translate light into color. The light receptors within the eye send messages to the brain, producing the sensation of color.
The initial process occurs in the retina of the eye. The retina contains millions of cells called photoreceptors that are sensitive to light. We have two types of photoreceptors, some shaped like rods and some like cones. These photoreceptors process light into nerve impulses and pass them along to the cortex of the brain via the optic nerve.
Rods, which transmit mostly black and white information to the brain, help your eyes adjust when you enter a darkened room.
Cones in each eye transmit the higher level of light intensity that creates the sensation of color.
There are three types of cone cells, each sensitive to the long, medium or short wavelength of light (red, blue and green). These cells, working with the connecting nerve cells, give the brain information to interpret and name colors. Humans can see 7,000,000 colors. What about animals? Well, most animals see fewer colors than we do, but some see more. Birds can see five to seven colors. Crocodiles can only see black and white and shades of gray.
Color blindness, more correctly called color vision deficiency, describes problems in recognizing various colors and shades of color. Normal color vision requires specialized receptor cells called cones, which are in the retina of the eye. The three types of cones correspond to red, blue and green, which help us to see a wide range of colors. An abnormality or lack of any of the types of cones results in color blindness, which affects 9% of humans. Color blindness is not a form of blindness at all, but a problem in seeing color. With this problem, the person cannot distinguish some colors, such as red and green or blue and yellow. Red/green color deficiency is the most common form of colorblindness. Blue color blindness is the inability to distinguish both blue and yellow, which are seen as white or gray. Total color blindness (achromatopsia) is the complete lack of cones in the retina and is very rare.
Humans are born colorblind because the cones do not begin functioning until a baby is about four months old. One male in twenty suffers from some form of colorblindness, but only one in several hundred females are color blind. Colorblindness is usually inherited, that is, a genetic defect. Not all color deficiency is due to heredity. Aging, certain medications, and retinal or optic nerve disease may interfere with normal color vision.
There is no cure for color deficiency that has been present since birth. Some cases of color deficiency that begin later in life may be helped with surgery, changing medication, or treating the eye disease that caused the color deficiency. If one cannot distinguish colors, one should see an eye doctor for evaluation. Diagnosing colorblindness early may prevent learning problems during the school years.