Complete color blindness is called monochromacy, and it’s so rare that only one person in 33,000 has it. For most people with color blindness, it only affects certain colors, and a few factors determine which ones and why, so let’s take a closer look at the different types of color blindness.
To understand color blindness, it’s important to know how color vision works in the first place. One step in the vision process is light hitting the photoreceptors in our eyes, which come in two types: rods and cones. Rods are good for distinguishing between the amount of light we’re seeing (important for things like night vision), while cones detect differences in color.
Someone with normal color vision has three types of cones that absorb light from different parts of the visible spectrum. Some process short (blue) wavelengths, some process medium (green) ones, and some process long (red) ones. It’s a little like the way the tiny red, green, and blue phosphors on old TV sets could combine to produce millions of colors.
Most color blindness is the result of a mutation on the X chromosome. Because it’s a recessive gene, women, with two X chromosomes, have two chances to have the gene for normal color vision, while men only have one. The sons of a woman who has a copy of the color blindness gene but isn’t colorblind herself have a 50% chance of being colorblind. This is why one in about a dozen men is colorblind but only one in every 200 women is!
While there’s one way for color vision to go right (called trichromacy), there are quite a few ways for it to go wrong. Someone with anomalous trichromacy has all the types of cones but some of them misfire, resulting in limited color vision almost to the degree of someone with dichromacy (completely missing one type of cone).
Red-green color blindness is the most common, possibly because it happens whether it’s the red cones (protanomaly/protanopia) or the green cones (deuteranomaly/deuteranopia) that misfire or are absent. Either way, the result is a landscape of dull brownish-yellows, and this is the type of color blindness that affects more men than women.
Less common (only 5% of all cases of color blindness) is blue-yellow color blindness (tritanopia if the relevant cones are missing or tritanomaly if they’re just misfiring), which doesn’t come from the X chromosome and is therefore split evenly between the sexes. The result is a palette of pinks, teals, and browns (more so with tritanopia).
Rarest of all is monochromacy, which could happen because no cones work, only one type works so there’s no contrast to create color perception, or there’s a problem with how the brain processes visual information from the retinas. Monochromacy tends to be accompanied by weak central vision, severe sensitivity to light, and involuntary eye movements.
In recent years, some colorblind people have discovered a wider spectrum of color thanks to special glasses. They don’t help all forms of color blindness, only the types where all cones are present but some are misfiring, and even then only when the overlap between two types of cones isn’t too great.
The glasses work by blocking out wavelengths of light that have the greatest overlap between misfiring cones and the other cones, which increases contrast and helps train the cones to only respond to the correct wavelengths of light. We highly recommend checking out some videos of colorblind people trying these glasses on for the first time — or checking out the glasses if you’re colorblind yourself!
Not everyone who has color blindness is aware of it. If you want to check how strong your color vision is, that’s something we can screen for in an eye exam. Not being able to see all the colors might seem like a minor issue compared to full blindness, but it does make some everyday tasks more challenging. The first step towards overcoming these challenges is diagnosis!