Snellen Eye Chart Model 10 Foot

Snellen Eye Chart To test visual acuity, position the patient 10 or 20 feet in front of the Snellen eye chart (depending on model chosen). Test, eye chart: This test measures how well you see at various distances. The eye chart itself -- the usual one is called Snellen's chart -- is imprinted with block letters that line-by-line decrease in size, corresponding to the distance at which that line of letters is normally visible. The letters on Snellen's chart are, not surprisingly, called Snellen's test type. Each block letter is quite scientific in design (so that at the appropriate distance the letter subtends a visual angle of 5 degrees and each component part subtends an angle of 1 minute). The chart and the letters are named for a 19th-century Dutch ophthalmologist Hermann Snellen (1834-1908) who came up with them as a test of visual acuity. Visual acuity refers to the clarity or clearness of the vision, a measure of how well a person sees. The word "acuity" comes from the Latin "acu