About
Color Blindness:
Color
blindness, or color vision deficiency, in humans
is the inability to perceive differences
between some or all colors that other people can
distinguish. It is most often of genetic nature,
but may also occur because of eye, nerve, or brain
damage, or due to exposure to certain chemicals.
Color blindness is usually classed as a disability;
however, in selected situations color blind people
may have advantages over people with normal color
vision. There is anecdotal evidence that color
blind individuals are better at penetrating color
camouflage.
There
are many types of color blindness. The most common
are hereditary (genetic)
photoreceptor disorders, but it is also possible
to acquire color blindness through damage to the
retina, optic nerve, or higher brain areas. Higher
brain areas implicated in color processing include
the parvocellular pathway of the lateral geniculate
nucleus of the thalamus, and visual area V4 of
the visual cortex.
The
different kinds of inherited color blindness
result from partial or complete loss of
function of one or more of the different
cone systems. When one cone system is compromised,
dichromacy results. The most frequent forms
of human color blindness result from problems
with either the middle or long wavelength
sensitive cone systems, and involve difficulties
in discriminating reds, yellows, and greens
from one another. They are collectively
referred to as "red-green color blindness",
though the term is an over-simplification
and somewhat misleading. Other forms of
color blindness are much more rare. They
include problems in discriminating blues
from yellows, and the rarest forms of all,
complete color blindness or monochromacy,
where one cannot distinguish any color
from grey, as in a black-and-white movie
or photograph.
The
Ishihara color test, which consists of
a series of pictures of colored spots,
is the test most often used to diagnose
red-green color deficiencies. A figure
(usually one or more Arabic digits) is
embedded in the picture as a number of
spots in a slightly different color,
and can be seen with normal color vision,
but
not with a particular color defect. The
full set of tests has a variety of figure/background
color combinations, and enable diagnosis
of which particular visual defect is
present. The anomaloscope, described above,
is also
used in diagnosing anomalous trichromacy.
For
more information on color blindness please click
here.
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Example
of an Ishihara color test plate. The numeral "2" should
be clearly visible to viewers with normal
color vision. |
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