Test type to test eyesight, England, 1920-1960
Back lit for a clearer view, this display is a chart of letters used by an optician to test a person’s sight at various distances. Such charts are perhaps the most iconic objects in sight testing. A patient with good vision should be able to read the letters at a distance of six metres. The original sight charts were developed in the 1850s by Dutch ophthalmologist Hermann Snellen (1834-1908). The letters, from largest to smallest, are all a precise shape and size. Such charts are still commonly used.
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Glossary: Snellen test types
Chart used for vision testing. The chart shows lines of black letters varying in size from large to small down the chart. Which a patient is asked to read. The optician is able to tell the level of the patient's eyesight when s/he can not read any further.