Deuteranopia – Red-Green Color Blindness
- Posted by Daniel Flück on April 17th, 2007 filed in Academic
Deutan color vision deficiencies are by far the most common forms of color blindness. This subtype of red-green color blindness is found in about 6% of the male population, mostly in its mild form deuteranomaly.
When you have a look at the color spectrum of a deuteranopic person you can see that a variety of colors look different than in a normal color spectrum. Whereas red and green are the main problem colors, there are also for example some gray, purple and a greenish blue-green which can’t be distinguished very well.
The well known term red-green color blindness is actually split into two different subtypes. On one side persons which either lack or have anomalous long wavelength sensitive cones (protan color vision deficiency), which are more responsible for the red part of vision. And on the other side deutan color vision deficiencies, which again are split into two different types:
- Dichromats: Deuteranopia (also called green-blind). In this case the medium wavelength sensitive cones (green) are missing at all. A deuteranope can only distinguish 2 to 3 different hues, whereas somebody with normal vision sees 7 different hues.
- Anomalous Trichromats: Deuteranomaly (green-weak). This can be everything between almost normal color vision and deuteranopia. The green sensitive cones are not missing in this case, but the peak of sensitivity is moved towards the red sensitive cones.
Below you can see a picture with normal colors on the left side and altered colors on the right side. The picture on the right side shows you how a person affected by deuteranopia would see the scenery (picture taken by Ottmar Liebert, some rights reserverd).
Normal Vision
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Deuteranopic Vision
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In the midst of the last century there were different researches published concerning unilateral deuteranopia. Some persons were found which had trichromatic vision in one eye and dichromatic vision in the other. The eye with dichromatic vision had a color specturm related to a deuteranopia color spectrum. One case of such a one-eyed colorblind is described in the article The Spectral Luminosity Curves for a Dichromatic Eye and a Normal Eye in the Same Person.
The one-eyed color blindness is definitely not the common case, whereas deuteranopia and especially deuteranomaly are the most observed cases of all color vision deficiencies. In 75% of all occurrences of color blindness it is a defect caused by the green sensitive cones. The following list shows the approximative rates of deutan defects in our population:
- Deuteranomaly, Male Population: 5%
- Deuteranopia, Male Population: 1%
- Deuteranomaly, Female Population: 0.35%
- Deuteranopia, Female Population: 0.1%
These numbers don’t change much, because deutan color blindness as one form of red-green color blindness is a congenital disease. Red-green color blindness is a sex-linked trait and therefore encoded on the X chromosome. Because women have two X and can overcome the handicap of one, men have only one and are therefore more often affected. This circumstance can also be read in the numbers of the table above. More details about the concrete inheritance pattern can be found at The Biology behind Red-Green Color Blindness.
If you are colorblind there is a big chance that you are red-green colorblind, usually green-weak and male. And if you are suffering from deuteranomaly I just want to let you know, that you are nothing special…
Read more about Tritanopia and Protanopia—the other two types of color blindness.
November 2nd, 2007 at 21:07
Im studying colour bilndness, Iv read several books including Diagnosis Of Defective Colour Vision by Jennifer Birch and Visual Perception a Clinical Orientation by Steven H. Schwartz, amongst others.
My question is why do dichromats and anomalous trichromats see what they see?. I understand that they either have a pigment missing or have a defective one but how does this influence the exacts colours they see?.
This what i think, a protanope should see blue and green as they are missing the red cone, i do not understand why they see blue and yellow and also why they dont see the green. Clearly my understanding is very limited and help would be much appreciated.
Thank you
November 6th, 2007 at 14:11
If you are protanopic or deuteranopic, colors along the line orange - red - green are hard to distinguish. It doesn’t mean you can’t see green. But you can’t distinguish it from orange or red.
The article about Confusion Lines of the CIE 1931 Color Space might give you a better understanding of the perception of a colorblind person.
November 25th, 2007 at 7:33
the theory is that it has to do with neurochannels that bring color information to the brain. the different wavelengths of light that are “seen” by the eyes are believed to travel to the brain through three neurochannels. One neurochannel handles red-green, one handles blue-yellow and one handles black-white. Combinations of these six colors make up all the different colors and shades that we see.
when someone is missing one or more of the cones in their eyes, it affects these channels. So missing low or mid range cones causes the red-green channel to fail. the result is that all colors that need red or green in it to form (including violet, orange, pink, etc) can not be seen. that leaves only the yellow-blue and black-white neurochannels able to do the job. thus the world is seen only in light and dark shades of blue and yellow.
same goes for blue-yellow colorblind people, who will see the world in various shades of green and red.
and people who are missing two cones, then both the yellow-blue and red-green channels fail, resulting in them seeing the world strictly in black and white.
i still don’t entirely understand the relationship between the missing cones, and the failure of the neurochannels. Logically, since there is considerable overlap of each cones scan of the visual spectrum, it seems to me that the remaining two cones should be able to process other colors. this may explain the varying degrees of colorblindness
one last thing. the names red/green/blue in reference to the cones is misleading. red cones actually peak at yellowish green, green cones peak at green and blue cones actually peak at violet. and each cone has a wide spectrum of what it ’sees’. Red cones field of vision is almost identical to green ones, just angled slightly more towards longer wavelength light.
November 25th, 2007 at 17:05
heres a link that further goes into the relationship between r/g/b cones and the red/green, blue/yellow and black/white channels.
it also helps explain why people who are missing red cones can see such colors as yellow and white
http://webvision.med.utah.edu/KallColor.html
March 31st, 2008 at 6:53
Being a person with deuteranopia and looking at the comparison images is really kind of freaky. I see them both as the same–it’s quite sobering to see evidence that confirms my visual malady.
Thanks for detailed sites like this so I can just tell the people who out me as a colorblind person to go here instead of calling everyone over and giving me a “what color is this” test so everyone can laugh at the freak.