Zone Medical now has an effective range of Visual Test Charts to help diagnose visual impairement be it near and far vision and colour blindness.
Some of these charts include the Snellen Chart: acuteness of the vision as determined by a comparison with the normal ability to define certain letters at a given distance, and the Ishihara colour blindness test.
The test consists of a number of colored plates, called Ishihara plates, each of which contains a circle of dots appearing randomized in color and size. Within the pattern are dots which form a number or shape clearly visible to those with normal color vision, and invisible, or difficult to see, to those with a red-green color vision defect, or the other way around. The full test consists of 38 plates, but the existence of a deficiency is usually clear after a few plates. There is also the smaller test consisting only 24 or 18 plates.