ADAM HART-DAVIS / SCIENCE PHOTO LIBRARY ADAM HART-DAVIS / SCIENCE PHOTO LIBRARY
Colour blindness chart. Fletcher-Hamblin colour vision test card. The card consists of five coloured dots arranged in a cross. Subjects are asked to identify which of the four outer dots has the most similar colour to the central dot. One of the outer dots is the correct answer. Another dot is deliberately disimilar and is used as a control to make sure the subject has understood the instructions. The choice of either of the other two by the subject would indicate a colour vision defect. This card is one of ten different colour combinations used in the Fletcher-Hamblin test. Colour blindness is a condition which causes confusion between red, green and yellow colours.
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