Each cone interprets only one color-red, green or blue.
Color blindness, also known
as color vision deficiency, is the inability to distinguish colors and shades
or to recognize them at all. It occurs when the color-sensing cones
of the retina
are absent or do not function properly.
About 8 percent of males and
1 percent of females are color-blind to some degree. Most color-blind people
in distinguishing among various shades of the same color or seeing some colors
as brightly as others; the inability to distinguish any colors at all and see
the world in black-and-white is rare.
Most color blindness is inherited and present
at birth. But acquired color blindness can result from cataracts, retinal or
optical nerve disease, use of certain medications or simply the normal aging
process -- as we age, the normally clear lens
begins to darken, making it harder to differentiate one dark color from
Normally, the pigments of
each cone correspond to one of the primary colors of light – red, blue and
green. In color blindness, there is a broad range of variances in these cones,
including unbalanced proportions of cones for each color, absence of cones for
one or more colors, and malfunction of cones for one or more colors. If no
functioning cones are present, the rods
take over in sensing lightness and darkness that enhance peripheral vision and
vision in dim light.
While people with color
blindness may have trouble distinguishing any or various colors or shades, the
most common inherited form is “red/green” color blindness, in which there are
problems seeing shades of red or green. For instance, red might appear as
yellow or invisible or that pastel shades of yellow and green are
indistinguishable. Another common form is blue/yellow color blindness.
Color blindness is usually
detected during a routine eye exam. Children should be tested for color
blindness beginning at age 4. It cannot be prevented, but poses no threat to
overall health. Although it may be inconvenience to some people, it presents no
handicap on everyday life.
While color blindness cannot
be cured, there are many methods of coping with and compensating for the
difficulties it presents, such as:
- Tinted contact lenses can make some colors appear dimmer or brighter, and may help some with
certain color vision deficiencies. Some color-blind people claim that
wearing a lens in one eye helps their vision and functioning, although
there is no evidence indicating that the lenses actually allow them to see
more colors. The lenses may blur vision and distort depth perception,
creating potentially dangerous situations.
- Electronic Eyes
are hand-held devices that identify colors. In
such devices, color sensors activate an audio synthesizer that speaks the
color aloud. The sensors, however, cannot read text.
If your child is
color-blind, you can make modifications to help him/her identify colors. This
includes activities such as labeling clothing, accessories and other items to help with
coordination, and teaching how to recognize brightness and location of green,
yellow and red positions on traffic lights and the meaning of signs by shape.
You may also have to make adjustments in
reading materials at school. Be on alert for books that use colored print and
colored backgrounds and inform teachers that color-oriented and color-coded
school assignments are not appropriate for your child.