Dr Pray's astigmatic letters (visual acuity chart)

Catalogue Number: 2006
Dr Pray's astigmatic letters (visual acuity chart)
Category: Equipment
Sub-Category: Visual Acuity, Contrast sensitivity tests
Designer/inventor: PRAY O M
Year Of Publication/Manufacture: late 19th C
Time Period: 19th C
Description Of Item: Still white card 278 mm x 450 mm, with two horizontal hinged folds and four lines of three letters of equal size constructed from black stripes that vary in orientation for each letter. Metal reinforced hole for hanging the chart. Headed 'Dr Pray's astigmatic letters'. The orientations of the stripes in degrees are 180, 165, 150, 135, 120, 105, 90, 75, 60, 45, 30 and 15
Historical Significance: The chart is designed to measure the power and axis of astigmatism. It was devised by Dr O M Pray, a USA ophthalmologist from Brooklyn, before 1869. Pray died in 1869. His death was noted at the 6th meeting of the American Ophthalmological Society held on July 21 1869. Pray's 'Letters for Astigmatism' were presented to the same meeting by Dr Noyes. This was about the same time as Dr John Green, also a US ophthalmologist, perfected the block and fan test for astigmatism (1868). A chart to the same design as Pray's was made by the American Optical Company up to about 1945. (See BOA Museum catalogue). The BOA example bears the name American Optical Company at the bottom of the chart, which this example does not. This version may be earlier than the AO one.
Condition: Good but some mottling
Location: Archive room. North wall slat board

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