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D.K. DeCarlo, G. McGwin, Jr., A. Xie, C. Owsley; Relationship Between ETDRS and Projected Snellen Visual Acuity in Patients With ARMD . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3474.
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Snellen acuities have long been the standard for visual acuity (VA) measurement and legal blindness (LogMAR 1.0 or worse) determination. Increasingly, vision rehabilitation specialists have been using LogMAR charts, such as the ETDRS chart since they are better suited for measuring acuities worse than 20/100 than typical Snellen charts. The purpose of this project is to determine whether or not VA measured by ETDRS and Snellen charts are equal in patients with advanced ARMD.
26 patients enrolled in a study on vision rehabilitation had best–corrected visual acuities measured OD, OS, and OU using a projected Snellen chart at 6 meters (m) and with the ETDRS chart (using letter–by–letter scoring) at 1, 2 and 4m. Contrast sensitivity was measured at 1m using the Pelli–Robson chart. Statistical analysis consisted of t–tests and Pearson correlations.
Participants were mostly female (61%) and white (92%) with an average age of 84 years. Correlations were strong between Snellen and ETDRS acuities at all test distances, however the correlations were stronger at longer distances. Patients were further divided into those who scored higher versus lower than the median on contrast sensitivity (CS) and the correlations were similar.
VA measured by ETDRS and projected Snellen charts correlate well, especially at longer distances, which is true for patients regardless of contrast sensitivity level. However, VA obtained via the ETDRS charts is somewhat better than that obtained via the Snellen chart. Thus, certification of a patient as legally blind is more likely with the Snellen chart than with the ETDRS chart. Using the ETDRS chart may deny some patients of legal blindness status and the associated rights and privileges.
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