Example of an Ishihara color test plate. The number "74" should be clearly visible to viewers with normal color vision. Viewers with dichromat or anomalous trichromat may read it as "21", and viewers with achromat may see nothing.
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. There is also the smaller test consisting only 24 plates.
The plates make up several different test designs:
Transformation plates: individuals with color vision defect should see a different figure from individuals with normal color vision.
Vanishing plates: only individuals with normal color vision could recognize the figure.
Hidden digit plates: only individuals with color vision defect could recognize the figure.
Diagnostic plates: intended to determine the type of color vision defect (protanopia or deuteranopia) and the severity of it.
Ishihara Plate No. 1, presented here in black and white so that even the fully colorblind get a sense of how the test works. Look for the number represented by dots of a different color as they shift from black through grey to white.
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 ophthalmology in Germany 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 color 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.[medical citation needed]
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.[medical citation needed]