Color Blindness
Introduction to Color Blindness
When we see different colors, we are perceiving differences in the 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, indigo, 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?
Think of your eye as 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.
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.
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;
however, they are very sensitive to light and allow us to see at night.
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 seeing certain
colors. Red-green colorblindness - where red and green might look the same - is
the most common form of colorblindness, followed by blue-yellow colorblindness.
Patients who have blue-yellow colorblindness almost always have red-green
colorblindness, too.
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.
Next: What is color blindness? »
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