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Mark Bullimore, Meredith Jansen, Elli Kollbaum, Pete Kollbaum; An iPad Test of Letter Contrast Sensitivity. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5331.
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An iPad-based letter contrast sensitivity test was developed by Ridgevue Vision (ridgevue.com) consisting of two letters on each page of an iBook. The contrast decreased from 80% (logCS = 0.1) to 0.5% (logCS = 2.3) by 0.1 log units per page. Agreement and repeatability of this iPad test was compared to the Pelli-Robson Chart and the computer-based Freiburg Visual Acuity and Contrast Test (FrACT, version 3.7).
Twenty normally sighted subjects were recruited (age 21-38 years). Subjects were tested monocularly (OD) at 1 meter using the three tests following a subjective sphero-cylindrical refraction. After a 5 minute break, subjects were retested with each test in reverse order. Two different letter charts were used for both the Pelli-Robson and iPad tests, and the order of testing was varied systematically. Nominally, on all charts letters were 49 mm and background luminance was 120 cd/m2. Letter-by-letter scoring (each letter 0.05 logCS) was used for both letter tests. For the Freiburg, the target was a variable contrast Landolt C presented at eight possible orientations. The Best PEST procedure was used with 30 trials (every sixth trial at 3x threshold). Repeatability and agreement were assessed by determining the 95% limits of agreement (LoA): ±1.96 SD of the differences between administrations or tests.
All values are in log Weber contrast sensitivity. All tests showed good repeatability in terms of the 95% LoA: iPad = ±0.19, Pelli-Robson = ±0.19, Freiburg = ±0.15. The iPad test showed good agreement with the Freiburg test: iPad mean = 1.94 ± 0.15, Freiburg mean = 1.94 ± 0.07, 95% LoA = ±0.24, but the Pelli-Robson test gave significantly lower values: mean = 1.66 ± 0.04.
The iPad Letter Contrast Sensitivity Test showed similar repeatability to the other tests and may be a rapid and convenient alternative to traditional measures. The Pelli-Robson test gave lower values than the both the iPad and Freiburg tests
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