Edrige-Green coloured bead test, England, 1885-1925
There are two types of red-green colour blindness: protanopia or ‘red blindness’ and deuteranopia. Protanopia is where patients can see in shades of blue and yellow but very little red. Deuteranopia is where patients cannot distinguish between reds with greens. It is more common in men and about 1% of the adult male population experiences one of these conditions. The Edridge-Green coloured bead test was a practical test for colour blindness. It was invented by F. W. Edridge-Green (1863-1953). He devised several colour blindness tests used worldwide, especially by the Armed Forces. This test consists of a wooden box. Red, yellow, green and blue beads are inserted into the appropriate holes. These beads are retrieved via a sliding draw in the base of the box. The test was made in London by Reiner & Keeler.
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The professional practice of eye and vision care. Optometry includes the correction of visual defects with lenses or glasses.
Glossary: colour blindness test
A test to find whether a person is colour blind. The most commonly used test in the world is the Ishihara test invented in 1917, where numbers are concealed within a circle of different colours.