Ishihara's charts and test
Test for colour blindness using pseudochromatic charts. The charts consist of fields of dots and figures of the same colour, but vith varying degreees of colour saturation and lightness. On these fields are dotshaped letters of other colours that are easily readable by people with a normal vision. The letters cannot be seen by colur blind patients - or, in som cases, only by them. They also give a good indication of what form of colour blindness the viewer has. The full test consists of thirty-eight plates, but the existence of a deficiency is usually clear after no more than four plates.
Several names are associated with such charts. Ishihara’s chart and test is a modification of Stilling’s test. Inherited defects of colour vision affects about 8% of men and 0.5% of women.
Stilling’s test, named for Jakob Stilling, is entered on whonamedit.com as Reuss’ test, under August Ritter von Reuss, Austrian ophthalmologist, 1841-1924. Ishihara’s original hand-painted charts are still at the University of Tokyo. The plates are still considered the best screening test for congenital color blindness.
In the introduction to his book, Ishihara writes: «This series of plates is intended to discover quickly and accurately congenital colour-blindness, the most common form of colour-blindness, and is in use to test the sight of railway employees, candidates for the navy, and others.
Acquired colour-blindness, being of secondary significance, has been disregarded in arranging these plates, for it is a symptom that appears at the time of some ailments in the optic nerve, retina, etc., and usually accompanied with other more serious visual defects, and therefore we can presume it to be a disqualification for railway and naval service.
Congenital colour-blindness is of two kinds; total colour-blindness and red-green blindness, and these have each two forms; complete and incomplete...»
«. . .Among those congenitally colour-blind, the complete total colour-blind are rare, and as they have very bad central vision, accompanied with photophobia and nystagmus, there is practically no necessity to subject them to the test for colour-blindness.» Etc.
- S. Ishihara:
Tests for Colour-Blindness. Tokyo, Handaya Company, 1917. 15th edition, 1960. Ishihara Pseudoisochromatic Charts for Color Blindness. Tokyo, Kanehara & Co, 1925.
This 5th edition is the first international edition.