Have you ever wondered if when you see red, your friend is actually seeing a different color, but you both call it the same thing? What if one day you were stripped of your ability to see one color altogether? Imagine a world where apples were no longer red and the circles on a traffic light became indistinguishable.
The idea of color is actually made up by our brains—objects don’t inherently have color to them. When two people see an apple, they may both say it is “red” without knowing if they are actually seeing the same color. The two brains could be decoding the nerve impulses differently. People who are colorblind (have a missing or faulty cone) and people who are tetrachromats (have four cones) can be diagnosed using testing of color perception.
Humans see color in terms of visible light, which comprises a range of wavelengths on the electromagnetic spectrum (from 780 nanometers to 390 nanometers), is either absorbed or reflected by an object. For example, an object that appears green absorbs all wavelengths except for the one we call green, which it would reflect. This light would pass through our pupil into the back of the eyeball where the retina, the light-sensitive eye lining, is located. In the retina there are two kinds of photoreceptors: rods and cones. The cones perceive light while the rods are implicated in night vision, and only perceive light or dark.
There are three types of cones: red, green, and blue. Each cone is activated by light that falls within its specific wavelength range. For example, the red cone is sensitive to red light, orange light, and yellow light, but it is most activated by red. Sometimes two or more cones can be activated; when yellow light shines through the eyes, both the red and green cones are activated and send nerve impulses through the optic nerve to the brain, which interprets the nerve impulses to determine the color and shape of the object. Our brains convert the wavelengths of light into the color yellow.
Color perception tests, such as the Ishihara color test, consist of a series of pictures of colored spots. A figure (usually containing numbers or shapes) is embedded in the picture as a number of spots in a slightly different color. The full set of tests has a variety of figure/background color combinations, and is most commonly used to diagnose red-green colorblindness. Another test used by clinicians to measure chromatic discrimination is the Farnsworth-Munsell 100 hue test. The patient is asked to arrange a set of colored chips to form a gradual transition of color.
While color blindness is often a sex-linked condition, color blindness can also be produced by physical or chemical damage to the eye, the optic nerve, or the brain. Brain or retinal damage caused by shaken baby syndrome, accidents, and trauma produce swelling of the brain in the occipital lobe, and may lead to color blindness. Damage to the retina caused by exposure to ultraviolet light may result in a similar disease state.
Scientists at the University of Washington and University of Florida made strides in the area of gene therapy by giving trichromatic vision to squirrel monkeys in 2009. In 2003, a cybernetic device called eyeborg was developed to allow the wearer to hear sounds representing different colors.
Color blindness may also present itself in the spectrum of degenerative diseases of the eye, and be linked to the retinal damage caused by diabetes. Low levels of vitamin A, an essential antioxidant that protects the cornea of the eye, can also result in color blindness.
While colorblindness seems to have obvious drawbacks, some studies show that colorblind people are better at penetrating certain color camouflages. Such findings may give an evolutionary reason for the high prevalence of red-green color blindness. There is also a study suggesting that people with some types of color blindness can distinguish colors that people with normal color vision cannot. And it is also important to note that color-blindness is highly sensitive to differences in material. For example, a red–green colorblind person who is incapable of distinguishing colors on printed-paper may have an easier time when viewing the same image on a computer screen or television.
While colorblindness seems to have obvious drawbacks, some studies show that colorblind people are better at penetrating certain color camouflages. Such findings may give an evolutionary reason for the high prevalence of red-green color blindness. There is also a study suggesting that people with some types of color blindness can distinguish colors that people with normal color vision cannot. And it is also important to note that color-blindness is highly sensitive to differences in material. For example, a red–green colorblind person who is incapable of distinguishing colors on printed-paper may have an easier time when viewing the same image on a computer screen or television.