The prescribing of spectacles / by Archibald Stanley Percival.

  • Percival, A. S. (Archibald Stanley), 1862-
Date:
1910
Catalogue details

Licence: In copyright

Credit: The prescribing of spectacles / by Archibald Stanley Percival. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    Landolt has provided us with some more accurate test types, formed of broken rings resembling the letter C ; the gap subtending an angle of 1' at the assigned distance of 5 metres. The sizes of the figures are so arranged that, at 5 metres distance, each of them corresponds to a different acuteness of vision (T, '15, 2, '3, '4, '5, 6, '7, •8, -9, 1, 1'25, 1-5, 175, 2 {Fig. 4). O o 0.15 0.2 O o 03 0.4 0.5 0.6 0.7 O O O C o o o 0.8 0.9 1 1.25 1.5 1.75 2 Fig. 4.—(In this figure the sizes of the test types have been reduced, so that the distance at which they should be viewed is 5 feet.) When the patient cannot see the CO m. line of Snellen's types at the prescribed distance of 6 m., he is allowed to approach the types until he can see the largest letter. If this occur at 3 m. we enter his uncorrected vision as When Landolt's types are used his vision would be noted as /o or '06. The system of radiating lines in the diagram (Fig. 5) is a most useful test for astigmatism, and is hence called the astigmatic fan. The method of using it is explained