Color vision is the ability of the visual system to recognize colors. For color perception sensory cells, the cones are responsible. They absorb the three different wavelengths of light: blue, green and red.
8% of men and at least 1% of women are affected by a disorder of the red-green color sense which can be congenital or acquired. Although the eyes function normally, there is a weakness for red or green color. There is a red blindness (protanopia) when the red cones fail, the failure of the green cones leads to a green blindness (deuteranopia).
The affected patients confuse colors or can`t see part of the light spectrum. Often one does not notice these color vision deficiency since it is congenital. But misidentifications of colors can have unpleasant consequences. Aptitude tests for police officers, pilots or professional drivers are obligatory to determine the extent of color vision deficiency.
To analyze color vision deficiency, patients use the anomaloscope to mix the spectral colors red and green to make yellow. This process is compared with normal values to determine the degree of abnormality. Furthermore, so-called pigment panels are used carrying a number made of various color splashes. The number is placed on a background of different-colored or gray splashes. Using this method, a color impaired patient will not be able to read the correct number.