I hadn’t originally planned on writing anything here on this site. Nonetheless, I had been reading for some time and had found information on all kinds of conditions, common and rare, but literally nothing about a condition I experience, along with nearly 8 percent of men and 0.5 percent of women. It’s color blindness, more accurately known as color vision deficiency.
What is it?
Basically, color blindness is a condition which affects the colors you see. It’s not related to sharpness of vision at all. You can have 20/20 vision and still be color blind. It is also completely separate from visual processing disorders, which are a brain-based condition that affect what you see but not the colors in which you see it. In almost all cases, color vision deficiency is inherited, although some organic solvents such as toluene (a common ingredient in adhesives) can temporarily induce color blindness. (1) The most common cause of color blindness is a mutation in the gene encoding the cone of that color.
Why are men more likely to be color blind than women?
The most common form, by far, is red-green color blindness. This is encoded by a recessive gene on the X chromosome. If you’ve got two X chromosomes, you will need two copies of the color blindness gene to be affected. If you’ve got an X and Y chromosome, and if anything funny’s going on the X chromosome, you’ll have no choice but to express it, as there’s no other X chromosome to overwrite the error. The Y chromosome doesn’t carry any genes related to color blindness.
Are you at risk?
By far the most common form of inheritance pattern for red-green color blindness is affected males and carrier females. If you’re a mother and your father was color blind, then half your sons can be color blind too. If those sons have children of their own, all the daughters will carry the color blindness gene, but none of your grandsons will be color blind. Blue color blindness is inherited the same way as cystic fibrosis and other recessive conditions.
Are there many forms of it?
Indeed there are. Generally, it’s divided into red-green and blue-yellow colorblindness:
Red-green:
- Protanopia: This is a loss of the red cones and is the form I have. About 1 percent of men have this.
- Deuteranopia: Loss of the green cones. Also experienced by 1 percent of men.
- Protanomaly: Here, you’ve got three cones, but the red one doesn’t work quite the way it should. This leads to slight weakness seeing red (for example in dim lighting), and affects 1 percent of men.
- Deuteranomaly: Similar to the above but with a weakness in the green cones. This is the most common form of color blindness, affecting around 6 percent of men and .4 percent of women.
Blue-yellow:
- Tritanopia: Loss of the blue cones. This is very rare, and the “female advantage” doesn’t apply here. This gene is on chromosome 7, and therefore affects both sexes equally.
- Tritanomaly: This affects the blue cones and affects around 0.01 percent of people. (2,3)
- It’s also possible to lack cones entirely, which leads to grayscale vision. This however is very rare.
What’s it like to be color blind?
It’s actually quite interesting. While I can’t exactly speak for those who experience deuteranopia or one of the other forms of color blindness, I can speak from my experiences. I personally cannot distinguish between red text and black text or distinguish pink from various shades of blue. Same goes for purple; I can’t distinguish that from blue at all. But the most famous case is my complete inability to distinguish green and orange (it all looks orange to my eyes), which may seem rather inconsequential until you consider things in the woods meant to be seen are typically bright orange (think chainsaws, flagging tape, hunting uniforms…). It also means there are a good many occupations into which I cannot enter. These include pilot, fireman, policeman, and ship’s captain, for example.
While that hasn’t exactly been a personal problem, as I’ve never had any desire to enter these fields (I’ve stuck to scientific research), there are other things I do from day to day where distinguishing colors is important. Think about graphs, for example. How do most people keep categories apart? By using colors, of course. Certain colors are fine, but others aren’t, so sometimes I have to ask somebody to interpret graphs for me. pH indicator paper can also be a bit of a challenge; I am not very capable of distinguishing between acids and bases without some outside help or a pH meter. Whenever I do a titration, I always do a rough run first, just to make sure I know what I’m looking for. For example, it is said that phenolphthalein (a common pH indicator), changes from colorless to pink to purple, but that is meaningless to me. Instead I’ll see the indicator go from colorless to grey to red to dark blue.
Arguably the most dangerous characteristic of my color blindness, however, is difficulty (note: I said difficulty, not impossibility) distinguishing traffic lights, especially at night. The red and the yellow lights look nearly identical, and the green light looks nearly identical to that of an LED street light. Thankfully, I can take public transit most of the time in the city, and driving in the country at night is not a problem, so some minor behavioral changes can make all the difference.
A more humorous instance of where color blindness may become apparent is not knowing whether a hat’s green or brown (as a result, buying matching clothing could be interesting…), or the last time I marked my students’ lab reports with a black pen instead of a red one by accident!
Be aware that for many people, including myself, the exact perception of color depends on how it’s displayed. I might be unable to distinguish two colors if they are shown on-screen but have no trouble distinguishing them when they’re printed. Or I might be able to tell that a stop sign is red but be unable to distinguish between a red and a black pen.
If you want a rough approximation of what it’s like to be red-green color blind, try removing the magenta cartridge from your printer, and go ahead and print a picture.
References:
- A. Cavalleri, F. Gobba, E. Nicali, V. Fiocchi. Arch. Environ. Health. 55, 399 (2000)
- R.W. Pickford. Nature. 160, 335 (1947)
- Kalloniatis, Michael; Luu, Charles (July 9, 2007). “The Perception of Color”. In Kolb, Helga; Fernandez, Eduardo; Nelson, Ralph. Webvision: The Organization of the Retina and Visual System. PMID 21413396.
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I'm a country chemist with an M.Sc. in inorganic chemistry, currently doing a PhD in materials science. I am also an inorganic chemistry TA with protanopia and (recently learned) cPTSD. I'm also an amateur hurricane tracker with 13-years experience, along with being a sailor, canoeist, hiker, and general outdoorsman.
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