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Ishihara card for testing color blindness. color blindness can be tested using Ishihara charts, named after their inventor, Japanese ophthalmologist Shinobu Ishihara (1897-1963), who devised the test in 1917. A person with normal vision will be able to see numbers, letters, or a design inscribed in the dots. A person with color blindness may only see dots with no defined image inside. Color blindness is usually caused by an inherited genetic defect in the light-sensitive cells (cones) of the eye. Color blindness can also be caused by optic injury or nerve diseases. In dichromatism, there is difficulty seeing one of the three primary colors red, blue or green. In anomalous trichomatsis, there is reduced sensitivity to certain colors. In the rarer monochromatism, there is no color vision and the world is seen in white, black and grey shades.