The Ishihara Test is a color perception test used to detect deficiencies for which colors?

The Ishihara test is a color perception test for red-green color deficiencies, the first in a class of successful color vision tests called pseudo-isochromatic plates ("PIP"). It was named after its designer, Dr. Shinobu Ishihara, a professor at the University of Tokyo, who first published his tests in 1917.

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. The full test consists of 38 plates, but the existence of a severe deficiency is usually apparent after only a few plates. Proper testing technique is to give only three seconds per plate for an answer, and not allow coaching, touching or tracing of the numbers by the subject.

Since its creation, the Ishihara Color Blindness Test has become commonly used worldwide because of its easy use and high accuracy. In recent years, the Ishihara test has become available online in addition to its original paper version. Though both media use the same plates, they require different methods for an accurate diagnosis.