The Ishihara booklet or cards should be stored out of direct light to prevent fading of the color plates.
Ishihara is printed by different printers and the saturation of colors differs in printing, hence some books look easy to read and some hard.
The doctor will ask you to look at a series of circles (also called plates) with dots of different colors and sizes. Some of the dots form shapes or one- or two-digit numbers. If you have trouble seeing red and green, those shapes will be hard to see, or you may not see them at all.
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