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Ian L. Bailey, Marlena A. Chu, A. Jonathan Jackson, Hasan Minto, Robert B. Greer; Assessment of Vision in Severely Visually Impaired Populations. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1892.
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© ARVO (1962-2015); The Authors (2016-present)
New tests of Visual Acuity (VA) and Contrast Sensitivity (CS) have been designed to provide a simple and efficient means for testing vision in severe visual impairment. To evaluate the efficacy of these tests, we measured VA and CS in 54 subjects with a wide diversity of ocular disorders and visual capacities. Subjects with severe visual impairments were recruited from the California School for the Blind, the Orientation Center for the Blind and the San Francisco Lighthouse.
VA was measured with the Berkeley Rudimentary Vision Test (BRVT) which uses three 25cm-square hinged card-pairs; one presents four Single Tumbling E’s (STE’s) at 1m, or 25 cm; another has 4 gratings shown at 25 cm; and the third has basic vision tests of White Field Projection (WFP) and Black White Discrimination (BWD). CS was measured with the Berkeley Discs CS test which has 3 double-sided cards used to measure contrast thresholds for the detection of 5 cm discs, with 14 contrast steps to 1.95 log units. The MARS optotype CS test was used for comparison.
Binocular VA was assessed in 54 subjects. For 24, Letter Chart VA (LCVA) could be measured (9 at 4 m and 15 at 1 m); for 18, STE VA measurement was required (16 tested at 1m to 20/2000, and 2 tested at 25cm to 20/8000). Two required Grating Acuity measurement (at 25 cm to 20/16000). Eleven did not have measurable VA. (5 had WFP, 1 had BWD and 4 had Light Perception (LP) We project that, by usual clinical procedures, 20 subjects would have been categorized simply as Count Fingers (CF), and 10 as Hand Motion(HM). The BRVT system uses 13 incremental steps over the same range. BRVT test time averaged about 2 minutes. On 40 subjects, CS could be measured with both the Berkeley Discs and the MARS test. When CS was poor, higher CS scores were obtained with the Berkeley Discs, presumably because of the larger target size and simpler task. Testing was quicker with the MARS test (55 cf 71 sec)
The BRVT is shown to provide a simple and efficient means of measuring visual resolution beyond the 20/630 limit of Letter Chart VA. The BRVT uses relatively fine increments for STE VA (from 20/500 to 20/8000), and Grating VA (to 20/16,000.) Categorization using CF or HM is grossly insufficient for assessment of vision in persons with severe visual impairment. For measuring CS in persons with severe vision loss, the large area targets and simpler task of the Berkeley Discs test make it more appropriate than optotype tests.
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