The Ishihara test is a colour perception test for red-green colour deficiencies. In other words the Ishihara test is used to detect daltonism (colour blindness of basis colours: red, blue and green). It was named after its designer, M.D., Dr. Med. Sc. Shinobu Ishihara, a professor emeritus at the University of Tokyo and member of the Japan Academy, who first published his tests in 1917.
The test consists of a number of coloured plates, called Ishihara plates, each of which contains a circle of dots appearing randomized in colour and size. Within the pattern are dots which form a number or shape clearly visible to those with normal colour vision, and invisible, or difficult to see, to those with a red-green colour 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. There is also the smaller test consisting only 14 plates or 24 plates.
The plates make up several different test designs:
- Transformation plates: individuals with colour vision defect should see a different figure from individuals with normal colour vision.
- Vanishing plates: only individuals with normal colour vision could recognize the figure.
- Hidden digit plates: only individuals with colour vision defect could recognize the figure.
- Diagnostic plates: intended to determine the type of colour vision defect (protanopia or deuteranopia) and the severity of it. Protanopes, who do not see red. Deuteranopes, who do not see green.
Born in 1879 to a family in Tokyo, Dr.Shinobu Ishihara began his education at the Imperial University where he attended on a military scholarship. Ishihara had just completed his graduate studies in opthalmology in German when war broke out in Europe and World War I had begun. While holding a military position related to his field, he was given the task of creating a colour blindness test. Ishihara studied existing tests and combined elements of the Spilling test with the concept of pseudo-isochromaticism to produce an improved, more accurate and easier to use test.
Since its creation, the Ishihara Colour Blindness Test has become commonly used worldwide because of its easy use and high accuracy. It is the most popular used daltonism test in the world.