Color helps us identify objects within our visual world. We perceive color from specialized cells within our retina called cones. A person with normal color vision will have 3 specific types of cones: one cone that detects short wavelength light (blue), one that detects medium wavelength light (green) and one that detects long wavelength light (red). When all three are present and working properly, an individual is considered to have normal color vision. However, if one or more of these cones is missing, an individual is considered to be color vision deficient. If all three cones are present but one or more is abnormal, an individual may also be considered color vision deficient.
Someone who is color vision deficient can still perceive colors; however, this individual perceives them in a slightly different way and can mix up certain colors because he or she might perceive them looking the same. A color vision exam is designed to test an individual's ability to distinguish colors that are often confused. Depending on the pattern seen from testing, the doctor can distinguish what kind of color vision deficiency a patient has. It also may signify to the doctor that additional testing is needed if a certain disease process is suspected.