What causes color blindness? Color blindness is a genetic condition where the color sensing cones in the eye don’t function correctly. People with color blindness can see colors, but they cannot differentiate between some colors.
The cause of color blindness comes down to the cones in our eyes because they are what detect color. At the front of our eyeball is the cornea, which is a clear membrane that covers the pupil to protect it and make sure things don’t get into the eye. Behind the cornea is the pupil, which is a hole that lets light in to the eye. It can be opened and closed to adjust the amount of light that comes in. Behind the pupil is the lens, which focuses the light coming through the pupil. It can be flexed to allow us to see close up things and far away things. The lens focuses the light coming in onto the retina at the back of the eyeball. The retina receives the light, translates it into electrical signals, and sends those signals up the optic nerve to the vision processing center of the brain. This works at an astonishing speed, and the eye and the brain can process 12 images a second, each one as a separate image. That is why videos are filmed at 12 frames a second or faster, because that is what the brain processes and sees as motion.
The retina is the part that we need to look at for this question. It is made of cones and rods. We have approximately 6 million cones and 120 million rods. The rods are for detecting light, and we use them to see in low light. They are very effective at detecting light, but all they can do is register quantities of light. They are what we use at night, but because they only see the light, we cannot see colors at night. Cats and other animals that see in the dark have far more rods than we do. Cats have approximately eight times more rods than a human does.
The cones are where we detect color. We have three types of cones: ones that detect red, green, and blue. Cones need a lot more light to work than rods do, so we can only use them in bright light. The darker it gets, the less color you can see. Each cone contains a pigment. There are red pigments, green pigments, and blue pigments. Each type of pigment is sensitive to a different wavelength of light. The cones with red pigment are sensitive to wavelengths of light that peak at 560 nm. The green ones are sensitive to light that peaks at 530 nm, and the blue ones are sensitive to light that peaks at 420 nm. When light hits a cone that is sensitive to it, it is absorbed. This causes the cone to send a signal to the optic nerve, along with all of the other cones at the same time. The brain receives these signals, and it knows how many of each cone were activated and it knows the strength of each one. Different percentages of the cones being activated can create different colors, and we can see about a million shades of color just because of our three types of cones.
When someone can see all of the colors perfectly, it is called trichromacy. “Tri” means three, and “chroma” means color. If they cannot see all of the colors, they are color blind, but there are three different types of color blindness. The first type is called anomalous trichromacy. In this case, you have all of the cones in your eyes, but one of the types isn’t sensitive to the light it is supposed to register. In the worst case, that can mean you can’t see that color at all, but more often it means that you find it hard to differentiate between colors. The second type is called dichromacy. “Di” means two, so you only have two colors here. One of the cones is completely missing. And the third type is called monochromacy. “Mono” means one, and people with this only have one type of cone.
Color blindness is more common in me. 1 in 12 men have it, while only 1 in 200 women. Red-green color blindness is the most common type. You can get glasses these days that help with color blindness. They can’t fix it because the defect is in the back of the eye. These glasses work by filtering out some of the wavelengths of light that the person with color blindness confuses. So, for example, within red green color blindness, for most people, greens look more red. The glasses would block some of the red light so that they could see more green. And this is what I learned today.
Sources
https://www.allaboutvision.com/conditions/color-blindness/glasses/
https://www.aao.org/eye-health/diseases/what-is-color-blindness
https://www.aao.org/eye-health/anatomy/cones
https://www.aao.org/eye-health/tips-prevention/how-humans-see-in-color
https://www.oxfordfamilyvisioncare.com/blog/how-cones-and-rods-function-in-the-eye
https://www.nei.nih.gov/learn-about-eye-health/healthy-vision/how-eyes-work
https://en.wikipedia.org/wiki/Color_blindness
https://my.clevelandclinic.org/health/diseases/11604-color-blindness
https://medlineplus.gov/ency/article/001002.htm
Photo by Pavel Danilyuk: https://www.pexels.com/photo/a-person-holding-white-printer-paper-8204987/