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This manual presents a procedure for determining suitable optical aids for low-vision patients by means of two types of specially designed near test charts: (1) visual resolution charts consisting of groups of three circular areas; two are gray and the third one is a concentric ring target which is either resolved and therefore seen as such or is seen as a gray area. Different sizes of these test elements allow an estimation of this type of retinal resolution in an area subtending up to 10 degrees; (2) letter acuity test charts for comparison testing and the evaluation of the efficacy of the optical aid.
Both these types of tests are so designed as to represent an even progression of visual acuity steps from 35/35 to 35/1554. There is a chart for selecting the proper power of reading aids on the basis of the visual acuity findings.
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Optical Aids for Low Acuity.. AMA Arch Ophthalmol. 1958;60(3):522. doi:10.1001/archopht.1958.00940080540035