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Julie-Anne Little, Jaclyn Molloy, Kathryn J. Saunders; Paediatric Visual Acuity Tests: Their Sensitivity To Astigmatic Blur. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3602.
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Astigmatism is a frequent error of ocular focus. O’Donoghue et al. (2010) identified 24% of 6-7 year-old children had astigmatism ≥1.00D, with significantly poorer visual acuity (VA) than non-astigmatic peers. Of these, 73% had no history of spectacle wear. It is not known how paediatric acuity tests are affected by astigmatic blur. This study investigated the effects of simulated astigmatism on several paediatric VA tests.
All participants were fully corrected with trial lenses under cycloplegic conditions with a 6mm artificial pupil. Astigmatic lenses were positive cylindrical lenses: 0.75, 1.00, 1.50, 2.00, 2.50, 3.00 and 3.50DC, introduced at 90°, 180°, 45° and 135° before the right eye (RE). RE VA was measured under these astigmatic blur conditions for: the LogMAR crowded acuity test, isolated LogMAR acuity test, single letter Sheridan Gardiner (SG) chart, crowded logMAR Kay picture test and single Kay picture test.The order of testing was randomised and tests interleaved with one another for each lens power and axis orientation in a staircase procedure. Both participant and investigator were blind to the power and axis of the astigmatic lenses. All VA data are converted to LogMAR for analysis.Participants were six emmetropic adults (20-30 years of age, mean 24.5). All had a VA of at least -0.10 LogMAR RE. The testing protocol was repeated three times at weekly intervals.
Across all tests, VA decreased with increasing levels of simulated astigmatic blur. Participants demonstrated similar repeatability between and across all visits. However, the single letter SG chart was the most variable (F(5,30) = 2.64, p<0.05). For against-the-rule astigmatism, on average the astigmatism required to degrade VA to 0.3LogMAR was 1.56D for the Crowded LogMAR acuity test, 1.92DC for Single LogMAR acuity, 1.93DC for Single Letter SG, 2.61DC for Crowded Kays, and >3.50DC for Single Kays.
As expected from the logarithmic crowded design of the chart, the crowded LogMAR acuity test was the most sensitive to astigmatic blur. The single and crowded Kay pictures acuity tests were the least sensitive to astigmatic blur. Participants’ VA remained fairly good even with relatively large amounts of simulated astigmatic blur.
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