a color-blindness test using a series of plates (Ishihara plates) in which numbers or letters are formed by dots of a given color against a background of dots of varying degrees of brightness and saturation. A modification of the earlier Stilling Color Vision Test, the Ishihara test was devised in 1916 for use by the Japanese army. It first became available commercially in late 1917 and reportedly is now the most widely used color-blindness test. [Shinobu Ishihara (1879–1963), Japanese ophthalmologist]