Snellen chart

Snellen, Hermann (1834–1908), Dutch ophthalmologist. Snellen was director of an eye clinic at Utrecht. In 1862 he introduced a test for measuring the acuteness of vision which consisted of printed letters or words in type of various sizes. He also introduced operations for entropion and ectropion and for ptosis, the latter operation being performed by shortening the aponeurosis of the levator palpebrae superioris of the upper eyelid. Snellen is additionally famous for constructing an artificial eye consisting of two concavo-convex plates with intervening empty space.