March 20, 2018
First, visualize what the world might look like without color. While many of us go on in our lives in a world of color, the simple fact that different colors appear different to each one of us is an interesting and complex process. Science explains that the reason humans see colors is that there are cells in the retina in the back of the eye called photoreceptors. These photoreceptors, called rods and cones because of their shape, capture the light that goes into our eyes, and through a complex chain of chemical reactions, send our brain a signal that we are seeing is in color. The electromagnetic spectrum is a map of all the types of light that we can identify; it separates all the types of light by wavelength because that directly relates to how energetic the wave is. More energetic waves have shorter wavelengths while less energetic waves have longer wavelengths. Not all light is in the visible spectrum, which is the light you can see. There are many kinds of electromagnetic waves that you can’t see.
The light we are actually seeing is similar to the colors of the rainbow. The colors of the rainbow–red, orange, yellow, green, blue, indigo, and violet–make up the visual spectrum of colors. It might be hard to imagine, but all visible light is made up of the colors of the visual spectrum, each color having its own unique wavelength. These unique wavelengths determine the shades and hues of the colors we see. The human eye can see 10 million different shades of colors.
Since this is such a complex process, where the photoreceptors capture the light, transmit the signal to the brain and then the brain interprets the signals, things can go wrong. Science explains that about 95% of humans see colors virtually the same way, but about 5% of men and 1% of women see the world a little differently. The original term for those who see colors differently was, “color blind.” This is misleading because these individuals actually see colors, but in a different way. As eye doctors, we like to say “color deficient” to describe this group that sees colors differently. We also like to test color vision routinely and there are special color vision tests that we use to determine an individual’s color vision. Color vision tends to become less sensitive as we age and this decreased sensitivity can mean a more serious eye condition is beginning.
In animals, there is often significantly less of the cone shaped photoreceptors. Animals that hunt in the dark, where there is the absence of visible colors, rely more on the rod shaped photoreceptors which are thought to detect motion and increase visibility in the dark. The cones are responsible for seeing colors and therefore, many animals are thought to see far less color than humans see.
Most color deficiencies are genetic. Some color deficiencies, however, are due to disease processes. These problems due to disease processes are very often found when one notices changes in the color vision. Changes in color perception can be the first sign of diseases of the eye like cataracts or macular degeneration.
Testing your color vision, therefore, is one way to keep up your eye health. It is also important to know if you are color deficient because there are many careers and hobbies that you might not be able to participate in. Many professions–electricians, pilots and military, for example, require you to pass the color vision test. As eye doctors, we provide genetic counseling to those patients who are color deficient so they know what to look for if they have children. As eye doctors, our go-to tool to test color vision is the Ishihara color vision test, with many small color bubbles and a hidden number in the middle.
There are many such tests available online these days, including EyeQue’s color vision test. It’s fun and easy, and a great way to monitor more about your eyes from the comfort of your own home.