The Ishihara test is a color perception test for red-green color deficiencies. The test consists of a number of colored plates, called Ishihara plates, each of which contains a circle of dots appearing randomized in color and size.Within the pattern are dots which form a number or shape clearly visible to those with normal color vision, and invisible, or difficult to see, to those with a red-green color vision defect, or the other way around. The full test consists of 38 plates, but the existence of a deficiency is usually clear after a few plates. But this test consisting only 17 plates.