The ishihara color test consists of several colored plates, each containing a circle of dots in various colors and sizes. Within the circle of dots, a numeric figure or digit is embedded as a number of spots in a different color. The digit can be seen by a person with normal color vision, but not by a person with a particular color defect (e.g. color blindness).
The complete test consists of 38 plates, but it usually only takes a few plates to discover a color vision problem.
The Ishihara test was developed in 1917 by Dr. Shinobu Ishihara, a professor at the University of Tokyo.