 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.Other plates are intentionally designed to reveal numbers only to those with a red-green color vision deficiency, and be invisible to those with normal red-green color vision.