Roses are red, violets are blue. But why? What makes the eye see the colors it does and how? First we must understand the basic structure of the human eye. The cornea is the outside membrane of the eye covering the iris and the pupil. The iris is the colored part of the eye and the pupil is where light enters the eye and enables us to see. Just behind the pupil is what is known as the lens, this corrects what we perceive through the eye and refracts the light we see into the retina covering the back of the eye. In the back of the eye is the optic nerve which directs the signals of what we are seeing to the brain to finish being interpreted and allows us to see everything around us.
Now, the retina is covered with tiny cells called cones and rods. Right now, we’ll only be discussing the cones, which are what give us the color vision. Humans have three types of cones that allow us to perceive colors; those cones are the yellow (or red) cones, violet (or blue) cones and green cones.
When light hits our eyes, it refracts through the lens in the eye to the retina on the cones. The various colors come from what is called the visible spectrum, which is a smaller part of an entire standard of wavelengths of different sorts, but that’s a different discussion. The visible spectrum consists of every color able to be perceived by a human being.
How does that work, one might ask? As mentioned before light passes through the cornea and the lens focuses the light onto the back of our eye. When the light hits the back of our eye the retina, covered in rods and cones, converts the “light into corresponding electrical signals” (“Light and the,”) which goes to our brain for further interpretation of the signals.
Now rods are what allow us to see detail in everything we see throughout the day. “They are responsible for our dark-adapted vision” (Nave). What this means is that at night and in dimmer lighting, we don’t see as much color vision as we do shadows and detail. Color vision requires bright light while detail and shadow vision does not need as much light. To be able to see considerable well in darkness, it rakes about “30 minutes or longer, because the rod adaptation process is much slower than that of the cones” (Nave). Also, there are many more cones than rods right around the optic nerve. However, there are no rods and cones over the optic nerve, which give every eye a blind spot.
This blind spot is where you cannot see anything, for obvious reasons considering there are no rods or cones there. The blind spot is mainly in the peripheral vision, which surprisingly enough doesn’t have color vision. The reason being is because in our peripheral vision there are far more rods than cones.
Now there can be problems with color for some people, including myself. Some people lack certain cones in their eyes or lack the use of those cones making them see colors very differently than the rest of the world. Another term for colorblindness is “Dyschromatopsia” (“Color vision: one,”). John Dalton, an English meteorologist and chemist actually had colorblindness and could only see the color yellow (“Color vision: one,”).
There are many types of colorblindness. Regular vision is trichromatic with three colors, whereas colorblindness can be dichromatic or monochromatic, with either two or one color. There are three types of dichromatic vision: deuteranopia with no green cones, protanopia with no red cones, or tritanopia with no blue cones (Lambert). People with monochromatic vision truly do see the world in black, white and grey like you would think when hearing colorblind. There are two types of this vision as well: achromatopsia, which is poor vision, and nystagmus, which gives you literal googly eyes (Lambert).
Think you’re colorblind? Take the test! See what you can see in the picture below.
Color vision: one of nature’s wonders. (n.d.). Retrieved from http://www.diycalculator.com/sp-cvision.shtml
Gouras, P. (2009). Color vision. Webvision: the organization of the retina and visual system, Retrieved from http://webvision.med.utah.edu/book/part-vii-color-vision/color-vision/
Lambert, K. (n.d.). How colorblindness works. Retrieved from http://science.howstuffworks.com/life/human-biology/colorblindness1.htm
Light and the eye. (n.d.). Retrieved from http://www.handprint.com/HP/WCL/color1.html
Nave, R. (n.d.). The rods and cones of the eye. Retrieved from http://hyperphysics.phy-astr.gsu.edu/hbase/vision/rodcone.html