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What colorblindness is:
- Color blindness (color vision deficiency) is a condition
in which certain colors cannot be distinguished, and is most commonly
due to an inherited condition. Red/Green color blindness is by far the
most common form, about 99%, and causes problems in distinguishing reds
and greens. Another color deficiency Blue/Yellow also exists, but is
rare and there is no commonly available test for it.
- Depending on just which figures you believe, color
blindness seems to occur in about 8% - 12% of males of European origin
and about one-half of 1% of females. I did not find any figures for
frequency in other races. Total color blindness (seeing in only shades
of gray) is extremely rare.
- There is no treatment for color blindness, nor is
it usually the cause of any significant disability. However, it can
be very frustrating for individuals affected by it. Those who are not
color blind seem to have the misconception that color blindness means
that a color blind person sees only in black and white or shades of
gray. While this sort of condition is possible, it is extremely rare.
Being color blind does keep one from performing certain jobs and makes
others difficult.
Life's minor frustrations
(and occasional dangers) for the color blind:
- Weather forecasts - especially the Weather
Channel - where certain colors just can not be distinguished on their
weather maps. Also, maps in general because of the color coding on the
legends.
- Bi-color and tri-color LEDs (Light Emitting
Diodes): Is that glowing indicator light red, yellow, or green?
- Traffic lights, and worst of all, Caution lights:
Color blind people always know the position of the colors on the traffic
light - in most states, Red on top, Yellow in the center, Green (or
is that blue?) on the bottom. It isn't good when we go to a city or
state where they put traffic lights horizontal - it takes a couple of
days to get used to that one! But caution lights present an entirely
different problem. In this situation there is only one light; no top
or bottom, no right or left, just one light that is either red or yellow
- but which is it?
- Getting in the sun with your girlfriend: So,
you're out in the boat or on the beach with your girlfriend and soaking
up the rays. But I can't tell until far too late if I'm getting red
- or if she is. If I can tell it's red, by that time it's fire engine
red and a painful sunburn is already present.
- Color observation by others: "Look at
those lovely pink flowers on that shrub". My reply, looking at
a greenish shrub "What flowers?"
- Purchasing clothing: I've got some really neat
colors of clothes. Not everyone appreciates them like I do though; they
seem to think the colors are strange. I just don't know why!
- Kids and crayons: Color vision deficiencies
bother affected children from the earliest years. At school, coloring
can become a difficulty when one has to take the blue crayon -and not
the pink one- to color the ocean.
- Test strips for hard water, pH, swimming pools,
etc.: A color blind person is generally unable to :
- interpret some chemical reactions
- see that litmus paper turns red by acid
- identify a material by the color of its flame
such as lead blue or potassium purple
- interpret the chemical testing kits for swimming
pool water, test strips for hard water, soil or water pH tests -
all of which rely on subtle color differences and a band of similar
colors to compare against.
- Cooking and foods:
- When cooking, red deficient individuals cannot
tell whether their piece of meat is raw or well done. Many can not
tell the difference between green and ripe tomatoes or between ketchup
and chocolate syrup.
- Some food can even look definitely disgusting
to color deficient individuals. For example, people with a green
deficiency cannot possibly eat spinach which to them just look like
cow pat. They can however distinguish some citrus fruits. Oranges
seem to be of a brighter yellow than that of lemons.
- Are you wearing lipstick? Many color blind
people cannot tell whether a woman is wearing lipstick or not. More
difficult to handle for some is the inability to make the difference
between a blue-eyed blonde and a green-eyed redhead.
Clinical information about
color blindness:
- Cones (color sensitive receptors) containing single
visual pigments selective for red, green, and blue light, are present
in the normal human eye. Disturbances of color vision will occur if
the amount of pigment per cone is reduced or if one or more of the three
cone systems are absent.
- Although defective color vision may be acquired as
a result of another eye disorder, the vast majority of color blind cases
are hereditary - present at birth. The gene for this is carried in the
X chromosome. Since males have an X-Y pairing and females have X-X,
color blindness can occur much more easily in males and is typically
passed to them by their mothers.
- Color blindness is rooted in the chromosomal differences
between males and females. Females may be carriers of color blindness,
but males are more commonly affected.
- Color blindness is a malfunction of the retina, which
converts light energy into electircal energy that is then transmitted
to the brain. This conversion is accomplished by two types of photoreceptor
cells in the retina: rods and cones.
- The cones are responsible for encoding color. Each
cone contains structures or visual pigments sensitive to one of three
wavelengths of light: red, green, and blue. Normal persons are able
to match all colors of the spectrum by mixtures of only three fundamental
color sensitivities. Hence, the huge variety of colors we perceive stems
from the cone cells' response to different compositions of wavelengths
of light.
- Defects in color vision occur when one of the three
cone cell color coding structures fails to function properly. One of
the visual pigments may be present and functioning abnormally, or it
may be absent altogether.
- For practical purposes, all color-deficient individuals
have varieties of red or green deficiency. Blue deficiencies are very
rare. Color deficient patients are not completely red or green blind.
Compared to persons with normal color vision, they have some trouble
differentiating between certain colors, but the severity of the color
deficiency is variable.
- Color blindness is normally diagnosed through clinical
testing. (See the Ishihara color test -
the one most common test used) Although there is no treatment for color
blindness, most color deficient persons compensate well for their defect
and may even discover instances in which they can discern details and
images that would escape normal-sighted persons. At one time the U.S.
Army found that color blind persons can spot "camouflage"
colors where those with normal color vision are fooled by it.
How color blindness works:
- The human eye sees by light stimulating the retina
(a neuro-membrane lining the inside back of the eye). The retina is
made up of what are called Rods and Cones. The rods, located in the
peripheral retina, give us our night vision, but can not distinguish
color. Cones, located in the center of the retina (called the macula),
are not much good at night but do let us perceive color during daylight
conditions.
- Many people think anyone labeled as "colorblind"
only sees black and white - like watching a black and white movie or
television. This is a big misconception and not true. It is extremely
rare to be totally color blind. There are many different types and degrees
of colorblindness, really they are "color deficiencies" since
virtually no one is truly blind to all colors.
- People with normal cones and color vision are able
to see all the different colors and subtle mixtures of them by using
cones sensitive to one of three wavelength of light - red, green, and
blue.
- A mild color deficiency is present when one or more
of the three cones functions "poorly". A more severe color
deficiency is present when one of the cones does not function at "all"
or is missing.
- Protanomaly (one out of 100 males):
Protanomaly is referred to as "red-weakness", an apt description
of this form of color deficiency. Any redness seen in a color by a normal
observer is seen more weakly by the protanomalous viewer, both in terms
of its "coloring power" (saturation, or depth of color) and
its brightness. Red, orange, yellow, yellow-green, and green, appear
somewhat shifted in hue ("hue" is just another word for "color")
towards green, and all appear paler than they do to the normal observer.
The redness component that a normal observer sees in a violet or lavender
color is so weakened for the protanomalous observer that he may fail
to detect it, and therefore sees only the blue component. Hence, to
him the color that normals call "violet" may look only like
another shade of blue.
Under poor viewing conditions, such as when driving in dazzling sunlight
or in rainy or foggy weather, it is easily possible for protanomalous
individuals to mistake a blinking red traffic light from a blinking
yellow or amber one, or to fail to distinguish a green traffic light
from the various "white" lights in store fronts, signs, and
street lights that line our streets. Do not let them adjust the color
on the television, because it will look far to redish or violet for
the rest of the family members.
- Deuteranomaly (five out of 100 of males):
Let the deuteranomalous person adjust your television and he would add
more green and subtract red. He is considered "green weak".
Similar to the protanomalous person, he is poor at discriminating small
differences in hues in the red, orange, yellow, green region of the
spectrum. He makes errors in the naming of hues in this region because
they appear somewhat shifted towards red for him - difficulty in distinguishing
violet from blue.
From a practical stand point though, many protanomalous and deuteranomalous
people breeze through life with very little difficulty doing tasks that
require normal color vision. Some may not even be aware that their color
perception is in any way different from normal. The only problem they
have is passing a color vision test.
- Dicromasy - can be divided into protanopia
and deuteranopia (two out of 100 males):
These individuals normally know they have a color vision problem and
it can effect their lives on a daily basis. They see no perceptible
difference between red, orange, yellow, and green. All these colors
that seem so different to the normal viewer appear to be the same color
for this two percent of the population.
- Protanopia (one out of 100 males):
For the protanope, the brightness of red, orange, and yellow is much
reduced compared to normal. This dimming can be so pronounced that reds
may be confused with black or dark gray, and red traffic lights may
appear to be extinguished. They may learn to distinguish reds from yellows
and from greens primarily on the basis of their apparent brightness
or lightness, not on any perceptible hue difference. Violet, lavender,
and purple are indistinguishable from various shades of blue because
their reddish components are so dimmed as to be invisible e.g. Pink
flowers, reflecting both red light and blue light, may appear just blue
to the protanope.
- Deuteranopia (one out of 100 males):
The deuteranope suffers the same hue discrimination problems as the
protanope, but without the abnormal dimming. The names red, orange,
yellow, and green really mean very little to him aside from being different
names that every one else around him seems to be able to agree on. Similarly,
violet, lavender, purple, and blue, seem to be too many names to use
logically for hues that all look alike to him.
Some of the information on this page was taken from:
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