Comparison of Intra–Subject Variability of Visual Acuity Measured With Lea Symbols and Lea Numbers to Adult Standards

Abstract

Abstract: : Purpose: Visual acuity is an important indicator of visual function and is often used to guide clinical decisions. However, repeated visual acuity measurement yields varying results even in the absence of any pathological or physiological changes. Many studies have quantified normal variability using adult standard optotypes, however this not been investigated using pediatric optotypes. The purpose of this study is to compare the normal intra–subject variability of Log MAR visual acuity using Lea Numbers and Lea Symbols to Sloan and Landolt C charts. Methods: 25 optometry students participated in this study. Best–corrected visual acuity of better than 20/25 was verified at the beginning of each session. Visual acuity of the right eye was tested at 3, 4, 5 and 6 meters with distance and chart type randomized. A total of four measurements (two per session separated by 1 week) were obtained for each chart type at each distance. All charts were of Log MAR design with 7 optotypes on each line. The middle 5 optotypes were scored to ensure constant crowding. The standard deviation of the four measurements for each subject was calculated and the average standard deviation was utilized to construct a 95% (+/–1.96 SD) confidence interval. Results: The 95% confidence interval for Lea symbols was +/– .113 logMAR at 3M, +/– .119 at 4M, +/– .139 at 5M, and +/– .117 at 6M. The 95% confidence interval for Lea Numbers was +/– .084 logMAR at 3M, +/– .109 at 4M, .130 at 5M, and .100 at 6M. The 95% confidence interval found for Landolt C to be +/– .135 logMAR at 3M, +/– .119 at 4M, +/– .118 at 5M, and +/– .097 at 6M. The 95% confidence interval for Sloan letters was +/– .076 logMAR at 3M, +/– .082 at 4M, +/– .093 at 5M, and +/– .083 at 6M. Conclusions: Variability of repeated visual acuity measurements with the adult acuity charts falls well within the previously reported ranges. Variability for the visual acuity with pediatric charts evaluated was never greater than +/– .046 logMAR (2.3 letters) from the adult charts showing strong agreement of variability.

Keywords: visual acuity • clinical (human) or epidemiologic studies: systems/equipment/techniques