What is Colorblindness and the Different Types

http://colorvisiontesting.com/color2.htm

What Is Colorblindness
and the Different Types?
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 andCones. 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 themacula), are not much good at night but do let us perceive color during daylight
conditions.
The cones, each contain a light sensitive pigment which is sensitive over a rangeof wavelengths (each visible color is a different wavelength from approximately
400 to 700 nm). Genes contain the coding instructions for these pigments, and if
the coding instructions are wrong, then the wrong pigments will be produced,
and the cones will be sensitive to different wavelengths of light (resulting in acolor deficiency). The colors that we see are completely dependent on thesensitivity ranges of those pigments.
Many people think anyone labeled as "colorblind" only sees black and white - likewatching a black and white movie or television. This is a big misconception andnot true. It is extremely rare to be totally color blind (monochromasy - complete
absence of any color sensation). There are many different types and degrees ofcolorblindness - more correctly called color vision deficiencies.
People with normal cones and light sensitive pigment (trichromasy) are able tosee all the different colors and subtle mixtures of them by using cones sensitive
to one of three wavelength of light - red, green, andblue. A mild color deficiency is present when one ormore of the three cones light sensitive pigments are
not quite right and their peak sensitivity is shifted(anomalous trichromasy - includes protanomaly anddeuteranomaly). A more severe color deficiency ispresent when one or more of the cones light sensitive
pigments is really wrong (dichromasy - includes
protanopia and deuteranopia).
5% to 8% (depending on the study you quote) of the men and 0.5% of the women
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What is Colorblindness and the Different Types

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of the world are born colorblind. That's as high as one out of twelve men and oneout of two hundred women. I am going to limit this discussion to protans (redweak) and deutans (green weak) because they make up 99% of this group.
Protanomaly (one out of 100 males):Protanomaly is referred to as "red-weakness", an apt description of this form ofcolor 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, andyellow-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, andtherefore sees only the blue component. Hence, to him the color that normals
call "violet" may look only like another shade of blue.
Color normal

Color Deficient Dichromat(source: critiquewall.com by Paul Martin)
Under poor viewing conditions, such as when driving in dazzling sunlight or inrainy 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 failto distinguish a green traffic light from the various "white" lights in store fronts,
signs, and street lights that line our streets.
Deuteranomaly (five out of 100 males):The deuteranomalous person is considered "green weak". Similar to theprotanomalous person, he is poor at discriminating small differences in hues in
the red, orange, yellow, green region of the spectrum. He makes errors in thenaming of hues in this region because they appear somewhat shifted towards red

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What is Colorblindness and the Different Types

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for him. One very important difference between deuteranomalous individuals
and protanomalous individuals is deuteranomalous individuals do "not" have theloss of "brightness" problem.
From a practical stand point, 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 nor do their friends. The only problem they have ispassing that "Blank Blank" color vision test.
Dichromasy - can be divided into protanopia and deuteranopia (two out of 100males):These individuals normally know they have a color vision problem and it caneffect 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 thenormal viewer appear to be the same color for this two percent of thepopulation.
Protanopia (one out of 100 males):
For the protanope, the brightness of red, orange, andyellow is much reduced compared to normal. Thisdimming 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 todistinguish reds from yellows and from greensprimarily on the basis of their apparent brightness orlightness, not on any perceptible hue difference. Violet, lavender, and purple areindistinguishable from various shades of blue because their reddish components
are so dimmed as to be invisible. E.g. Pink flowers, reflecting both red light andblue 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.
In Conclusion:
It should be obvious there are several different kinds and degrees of color vision
deficiencies. Protanomalous or deuteranomalous individuals can usually pass as anormal observer in everyday activities. They may make occasional errors in color
names, or may encounter difficulties in discriminating small differences incolors, but usually they do not perform very differently from the normal except
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What is Colorblindness and the Different Types

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on color vision tests.
The protanope and deuteranope, on the other hand, can be severely color
deficient. The real problem, as a protanope or deuteranope may see it, is there
are far too many hue names (color names) used by most people without any
obvious basis for using one instead of another. Why call something "orange" when
it doesn't look different in any way from something else called green, tan, beige,
or any of several other color names?

Click here for an excellent Powerpoint
presentation
byDr.
Rabinoncolorblindness.
The presentation istechnical and mainly for the scientificcommunity.

(What is colorblindness)(Why are you colorblind)(Whatteachers should know)(A pediatric color vision test) (Evaluation of thepediatric test) (Where to purchase a color vision test) (How colorblind subjects
see the world) (Frequently asked questions) (Other helpful links)

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