Sloan letters, designed by American ophthalmologist Louise Sloan in 1959, are a set of optotypes used to test visual acuity generally used in Snellen charts, logMAR charts and ETDRS charts. These letters, unlike the ones used in older Snellen charts, are designed to give acuity testing results that are comparable to tests made using Landolt rings.
Sloan letters, designed by American ophthalmologist Louise Sloan in 1959, are a set of optotypes used to test visual acuity generally used in Snellen charts, logMAR charts and ETDRS charts. These letters, unlike the ones used in older Snellen charts, are designed to give acuity testing results that are comparable to tests made using Landolt rings.
Source: Wikipedia "Sloan letters" · CC BY-SA 4.0
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