Investigating colour vision

Ishihara colour vision tests

This is the most common method of testing colour vision. It was first developed in Japan in 1917 and is used worldwide in schools, industry and medicine.

Whether a person's vision is defective and the type of defect can be ascertained according to the numbers which they can or cannot read on the test cards.

The test consists of up to 36 cards. A person making up to 4 errors is classed as normal. Eight or more errors indicate defective colour vision. In cases of 5-7 errors, additional tests should be undertaken.