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I. Falkenstein, D. E. Cochran, S. P. Azen, L. Dustin, A. M. Tammewar, I. Kozak, W. R. Freeman; Comparison of Visual Acuity Measurements in Macular Degeneration Patients Tested With Snellen and LogMAR (ETDRS) Charts. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2148.
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To compare the visual acuity (VA) results measured with Snellen and ETDRS charts in eyes with and without age-related macular degeneration (ARMD).
104 participants (190 eyes) randomly selected from a University retina practice, 80 participants (142 eyes) had some degree of ARMD. VA was measured in each patient using standard procedure with both Snellen and ETDRS charts in random order. Visual acuity measured by both charts was recorded in logMAR notations for statistical analysis.
Overall, the mean Snellen VA was 0.78 logMAR (=20/120), and the mean ETDRS VA in the same eye was 0.54 logMAR (=20/70). In the low vision group (< 20/200) - all patients with ARMD, the average difference in number of lines was considerably larger than in the good vision range (>20/30). On average 20/200 on Snellen was 20/95 on ETDRS in the same eye (>3 lines difference), and 20/30 on Snellen was 20/25 on ETDRS in the same eye (<1line difference).
Our results show poor agreement between Snellen and ETDRS chart, more pronounced in the group with poor vision. ETDRS measurements yielded better visual acuity, particularly in participants with vision below 20/200 (representing ARMD patients). We suggest taking these findings into consideration when comparing outcomes in clinical practices (which typically measure VA using Snellen charts) with outcomes from clinical trials (which typically measure VA using ETDRS charts).
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