Colour blindness

The original card version of this test was designed to be carried out in a room adequately lit by daylight. The presence of direct sunlight or artificial light may produce some discrepancy in the results because of some alteration in the appearance of shades of colour.

Colour vision tests

The most commonly used test to determine whether and how a person is colour-blind was developed by Shinobu Ishihara, a professor of the University of Tokyo, Japan, who designed a series of plates as a test for colour blindness. The test involves the patient being able to distinguish a number within the coloured field at the centre of each chart.