Ishihara color test

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Example of an Ishihara color test plate. The numeral "74" should be clearly visible to viewers with normal color vision. Viewers with dichromat or anomalous trichromat may read it as "21", and viewers with achromat may see nothing.

The Ishihara Color Test is a test for red-green color deficiencies. It was named after its designer, Dr. Shinobu Ishihara, a professor at the University of Tokyo, who first published his tests in 1917. ^[1]

The test consists of a number of colored plates, called Ishihara plates, each of which contain a circle of dots appearing randomized in color and size. Within the pattern are dots which form a number visible to those with normal color vision and invisible, or difficult to see, for those with a red-green color vision defect. The full test consists of 38 plates, but the existence of a deficiency is usually clear after a few plates. Testing the first 24 plates gives a more accurate diagnosis of the severity of the color vision defect.

Common plates include a circle of dots in shades of green and light blues with a figure differentiated in shades of brown, or a circle of dots in shades of red, orange and yellow with a figure in shades of green; the first testing for protanopia and the second for deuteranopia.

Presented here in black and white so that even the fully colorblind get a sense of how the test works. Look for the number represented by dots of a different color.