Picture of Color Blindness
The wavelength of light that corresponds to each color differs. We perceive different colors as our eyes take in different wavelengths of light. The colors of the rainbow –- red, orange, yellow, green, blue, indigo, and violet –- follow a progression from longer to shorter wavelengths.
Color blindness is a condition in which a person experiences difficulty seeing blue, green, red, or some combination of these colors. A person with color blindness has a problem with cells that sense color in the retina. The retina is the nerve-rich part of the eye that senses light and converts it into signals that the brain perceives as color. Sometimes, these retinal cells, or the signals they send to the brain, do not function properly. Color blindness is usually congenital and inherited. Other problems with perceiving color may be due to injury, aging, disease, medication side effects, or abnormalities with the optic nerve.
Several tests may be used to assess the ability to perceive different colors. One such common test is called the pseudoisochromatic plate test or Ishihara color test. The type of color blindness one has is determined by the patterns one is able to discern on the assorted plates used for the test. The plate pictured above depicts the number 74, which should be visible within the pattern for people with normal color vision. It's not possible to correct or treat color vision problems that are inherited. Depending on the underlying cause, some types of acquired color vision problems may be treatable.