Red color blindness is a disorder that affects the way an individual perceives color. The retina detects colors through cone cells. There are three types of cones in the human eye, each containing a specific photo-pigment that is most sensitive to particular wavelengths of light, i.e. red, blue or green. In individuals affected with protanopia, there are no working red cone cells. This results in the patient perceiving red light as black. In the milder condition of protanomaly, the red cone photo-pigment is abnormal. Red, orange, and yellow appear greener and colors are not as bright.
The disorder is much more prevalent in men. It affects one in ten males and only about one in two hundred females. Prevalence also differs between races, with northern European populations showing a higher incidence of the disease. The disorder only affects the perception of color and does not affect visual acuity. However, it can still negatively affect the quality of life in affected individuals. Children are particularly inconvenienced by the disorder as most educational aids in classrooms are color-coded. Hence it is important that the condition is properly diagnosed. Several different tests can be used to diagnose color vision defects. The Ishihara plate test, for example, uses colored circles which contain a collection of dots in different colors and sizes. The dots form a shape that while clearly visible to most people, would be difficult to identify for those with color vision defects. The Farnsworth-Munsell 100 Hue Test is another widely used analysis that measures the ability to discriminate between subtle color changes. While there is no cure for the disorder, certain contact lenses and glasses may help users perceive colors more accurately.