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P. K. Kaiser; Comparison of Snellen versus ETDRS Protocol Visual Acuities Performed by Certified Vision Examiners. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2249. doi: https://doi.org/.
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To prospectively compare Snellen visual acuity versus "ETDRS" protocol visual acuity performed by a certified vision examiner
Prospective, consecutive, case series of patients who met the following inclusion criteria: Ability to give informed consent and not currently enrolled in a clinical trial. Visual acuity was evaluated at a single seating by same certified vision examiner in the same room with breaks allowed as needed. Vision tests carried out immediately after each other. Using best correction in trial frame, Snellen chart measured first using "Line assignment" scoring with the value of the lowest line where at least half the letters correctly identified used as the score which was then converted to logMAR for statistical analysis without taking into account differences in number of letters per line. ETDRS vision testing was performed immediately after using ETDRS chart #1 in a standard Lighthouse lightbox placed 4 meters from the patient. This was repeated with Chart #2 at 2 meters. If the patient could not read largest letters, then chart moved closer to patient.
88 eyes of 88 patients included in the study. The median age was 74 years. The mean Snellen vision was 20/86 and ETDRS was 20/72 (p<0.05). Subgroup analysis showed that the difference between Snellen and ETDRS visions was greatest in patients with poor vision (<20/200).
On average, Snellen acuities were slightly worse than equivalent "ETDRS" acuities especially with vision < 20/200. However, except for patients with poor vision, Snellen and "ETDRS" charts were comparable.
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