Set of eight Ishihara charts for testing colour-blindnes, c 1959.
© Science Museum / Science & Society Picture Library
Most colour blindnes is inherited, and affects more men than women. Colour blindnes usually involves confusion between red, green and yellow. Dr Shinobu Ishihara, Profesor Emeritus of the University of Tokyo, Japan, designed this series of plates as a test for colour blindnes. The test involves the patient being able to distinguish a number within the coloured field at the centre of each chart.