Dutch #ophthalmologist whose #SnellenChart imprinted with lines of black letters is used for test…

Dutch #ophthalmologist whose #SnellenChart imprinted with lines of black letters is used for testing #VisualAcuity .

Test types were invented in 1843 by Heinrich Kuechler (1811-1873) and were improved by the Vienna oculist Eduard Jaeger Ritter von Jaxtthal (1818-1884) in 1854. Shortly after this Snellen invented his chart of square shaped letters. This chart soon gained acceptance around the world. The #Snellen fraction is a ratio, for instance 20/20 or 20/100 (metric equivalent 6/6, 6/30), measuring the acuity of a person's #eyesight compared to a standard observer with good normal acuity. 20/20 means he can resolve 2 target features at 20 feet.

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