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L Dong, BS Hawkins, MJ Marsh; Consistency Between Visual Acuity Scores Obtained at Different Test Distances: Theory versus Observations in Multiple Studies . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3823.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To investigate the consistency of visual acuity (VA) scores measured at two different distances using original or modified Bailey-Lovie (ETDRS) charts. Methods: Best corrected VA scores measured at two different distances for the same eyes at the same examinations were collected from 4 sets of randomized clinical trials among patients with choroidal neovascularization (CNV) secondary to age-related macular degeneration (AMD), ocular histoplasmosis, or idiopathic CNV. Within each trial, the pairs of VA scores were compared using paired t-test. Regression analysis was used to describe the relationship between scores at the closer and the farther distance. Findings were compared with a published study among young healthy subjects. Results: After adjustment for test distance, VA scores obtained at the closer distance were systematically lower than those obtained at the farther distance in all 4 data sets. In the Submacular Surgical Trials Pilot Study, the average discrepancy between 2-meter and 0.5-meter VA scores was 7.5 letters (95% CI [6.6 to 8.5]). In the Macular Photocoagulation Study ancillary study, the discrepancy between 10-foot and 5-foot VA scores was 3.1 letters (95% CI [2.4 to 3.9]). In the Laser to Drusen Trial pilot study, the discrepancy between 3.2-meter and 1-meter VA scores was 7.3 letters (95% CI [5.7 to 8.8]). In the Treatment of Age-related Macular Degeneration with Photodynamic Therapy Study, the estimated discrepancy between 2-meter and 1-meter VA scores was 8.2 letters. Reduction in visual angle at closer test distance may account for some of the discrepancy, but does not explain it completely. The data did not support attribution of the discrepancy to features of the macular lesion, poor accommodation of the elderly AMD population, or the test charts. Conclusion: VA scores at distances less than 2 meters were lower than expected in 4 different studies. The discrepancy observed among patients with CNV in the central macula was consistent with findings from a study among healthy young subjects, suggesting that the phenomenon is real and common.
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