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D. Ah-Kine Ng Poon Hing, J. J. Vaidhyan, A. Pathak, N. Quinn, L. Deng, S. Lyons, B. Moore; Comparison of Visual Acuity Measured With Lea Symbols and Lea Numbers at Different Test Distances. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4852.
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© ARVO (1962-2015); The Authors (2016-present)
Traditionally, visual acuity (VA) has been measured at 6 meters (m) in adults and at 3m for children. The Lea Symbol and Lea Number tests are frequently used to assess VA in children. VA is often measured at closer distances in the pediatric and non-verbal populations to improve testability. The purpose of this study is to compare the visual acuity of adults with normal VA at different distances using the Lea Symbol and Lea Number charts.
25 optometry students participated in the study. All subjects had best-corrected Snellen VA of better than 20/25 at each session to be included in the study. LogMAR charts, calibrated for 4m with 7 optotypes per line, were constructed and supplied by the Goodlite Co. The middle 5 optotypes were scored to ensure constant crowding. Visual acuity of the right eye of each subject was tested at distances of 3.2, 4, 5 and 6.4m. Stimuli presentation was randomized for both chart distance and optotype. Four measurements (two per session separated by one week) were obtained for each chart. Repeated measures of ANOVA and multiple comparisons were utilized in the statistical analysis.
The mean LogMAR VA for Lea Numbers was -0.104 at 3.2m, -0.099 at 4m, -0.117 at 5m, -0.096 at 6.4m. There were no significant differences between distances (p-values>0.03). The mean LogMAR VA for Lea Symbols was -0.113 at 3.2m, -0.128 at 4m, -0.145 at 5m, -0.117 at 6.4m. For Lea Symbols, VA measured at 5m was significantly different than that measured at 6.4m (p=0.007) and 3.2m (p=0.002). There was no difference between acuities at 4m and 6.4m or between 4m and 5m (p-values>0.05).
In adult subjects, VA measurements using the Lea Number chart were similar at all distances. Differences when using the Lea Symbol chart exist, but are not clinically significant, since the greatest differences were equivalent to less than 2 optotypes. Further studies are necessary to evaluate the differences in testing distance in the pediatric population.
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