Hi there! Thanks for your question! To understand colorblindness, we must understand a little about how the eye works and a little bit about light.
The human eye has a lining on its back surface that detects light. The lining is made up of several special cell types called neurons. The neurons that specifically sense light are called "photoreceptor cells". The photoreceptors come in 2 kinds: the "rods" and "cones". The rod cells work best in low-light conditions, and provide mostly back-and-white vision. The cones on the other hand work well in bright light and can detect colors. There are 3 different kinds of cones, and they respond each best to different colors. If you have ever seen a "spectrum" of light, it looks like a rainbow, spanning from red to violet.
Light travels like a wave, and the waves of different colors carry different energy, so they have different "wavelengths"; violet has the shortest wavelength and carries the most energy, while red has the longest wavelength and so the least amount of energy. This explanation of light and wavelengths is just to explain that the 3 types of cone cells are named S (for Short wavelengths of light, like violet), M (for Medium wavelengths like green) and L (for, you guessed it, Long wavelengths of light like red). The cones are very complex in design, and have in them special molecules called "photopigments". These photopigments can respond to a tiny bit of light, and are the beginning of a process to translate the light into an electrical signal that is then sent to other neurons, and eventually to the brain where we figure out what our eyes are seeing!
When there are problems with the cones, people can have problems with their color vision. This is called "color-blindness". Most color blindness has a genetic cause, meaning that people are born with changes in their DNA code that will cause problems with their cone cells.
There are 3 different classifications of colorblindness: monochromacy, dichomacy and "anomalous trichromacy". Monochromacy is rare, and is also called "total color blindness". It occurs when 2-3 of the cone types are missing or don't work at all. Dichromacy is more common, and is when one of the cone types is absent or not functioning. For example, someone with this might not be able to tell green and red apart because they lack green (M) cones. Anomalous trichromacy is more common yet, and it occurs when one of the 3 types of cones has an altered (or "anomalous") sensitivity or response to light. This result is a milder color-blindness, such as having a difficult time distinguishing red and green hues. Some types of dichromacy and anomalous trichomacy occur more often in males.
Doctors, especially eye specialists, can test for color blindness. They might use a test where the patent tries to see a colored pattern, like a number, in a colored field of spots. If they cannot see the number, it means they have a difficult time distinguishing certain colors from each other. Different colored tests can help to distinguish which type of color blindness the patient has. Tests like this can be found in books and online colortest
but everyone should go to their doctor for a real test if they are concerned about color blindness.
There are no known cures for color blindness, but most people are able to adapt and function fine with some deficiency in distinguishing colors. Some careers, such as pilot, may require unimpaired color vision. It is important that people keep in mind people with color-blindness when they are designing illustrations, especially in PowerPoint presentations and scientific figures.
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