Ishihara Test

A Colorblind test using Pseudoisochromatic Plates that detects for red-green Colorblindness. Blue-yellow Colorblindness is not detected. The test consists of a number of Ishihara plates, each of which depicts a solid circle of colored dots appearing randomized in color and size. Within the pattern are dots which form a number or shape clearly visible to Color Normals, but invisible to those with a red-green CVD.

It was designed by Shinobu Ishihara – a professor at the University of Tokyo – at the request of the Japanese military in 1916, after Ishihara spent a year in Germany learning about colorblindness before the start of WWI. The tests were published publicly in 1917 and western version started to become popular in 1926. Amendments were made to the test in the following decades. Since 1951, the full test has consisted of 38 plates, but the existence of a severe deficiency is usually apparent after only a few plates. There are also Ishihara tests consisting of 10, 14 or 24 test plates, and plates in some versions ask the viewer to trace a line rather than read a number.