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A. Pathak, D. Ah-Kine Ng Poon Hing, J. Vaidhyan, N. Quinn, L. Deng, B. Moore, S. Lyons; Comparison of Standard and Modified Procedures for Measuring LogMAR Visual Acuity Using Four Visual Acuity Charts. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1169.
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LogMAR visual acuity charts are the recognized standard for measuring visual acuity (VA). The length and complexity involved in completing the standard procedure for measuring LogMAR VA is difficult for young children. The purpose of this study is to compare LogMAR VA measured by standard and modified procedures in adult subjects using 4 visual acuity charts: Lea Symbols (LS), Lea Numbers (LN), Landolt C (LC) and Sloan Letters (SL).
50 optometry students separated into two groups participated in the study. Group 1 completed the VA measurements using the standard procedure of reading all optotypes on each acuity chart until threshold was reached. Group 2 completed a modified procedure whereby the first two optotypes of each line were read until one was answered incorrectly. The subject then read every optotype beginning at the preceding line. 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 4 meters (m) with 7 optotypes per line were constructed and supplied by the Goodlite Co. The middle 5 optotypes were scored to ensure constant crowding. VA of the right eye of each subject was tested at 4m, with each chart presented randomly. 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.
In Group 1, the mean LogMAR VA was LS -0.156, SL -0.140, LN -0.125 and LC -0.119. In Group 2, the mean LogMAR VA was LS -0.128, SL -0.119, LN -0.099 and LC -0.095. In both groups, LS was significantly different from LC and LN (p<0.001) but not from SL. The difference between LS and LC was less than 2 optotypes. Group 2 had better VA on each chart than Group 1. These differences were not statistically significant (p>0.2), amounting to a difference of less than 2 optotypes per chart.
In adults, both procedures for measuring LogMAR VA can be used with similar results for LS, LN, LC and SL. Differences between the groups and between acuity charts exist but are not clinically significant.
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