A comparison of visual acuity measured by ETDRS chart and Standard Logarithmic Visual Acuity chart among outpatients

To compare the results of visual acuity (VA) measured by Early Treatment Diabetic Retinopathy Study (ETDRS) chart, 5 m Standard Logarithm Visual Acuity (5SL) chart, and 2.5 m Standard Logarithm Visual Acuity (2.5SL) chart in outpatients of age 12-80y.

Each patient (totally 2000 outpatients) had both eyes tested with ETDRS chart at 4 m, 5SL chart at 5 m, and 2.5SL chart at 2.5 m in random order. The VA values of outpatients were categorized by ages. VA values were expressed by logMAR recording method.

The mean VA results of ETDRS charts, 5SL, and 2.5SL chart were 0.52±0.28, 0.50±0.30, and 0.46±0.28 logMAR, respectively. There was a statistically significant difference in the three eye charts in the whole group (P<0.001). For all subjects, the correlation of VA tested with three charts was statistically significant (Spearman correlation coefficient=0.944, 0.937, 0.946, all P<0.001). Bland-Altman analysis shows the 95% limits of agreement between the 5SL and 2.5SL chart were -0.182 to 0.210, -0.139 to 0.251, and -0.151 to 0.235 logMAR, respectively).

The agreement between the three eye charts is not high. The VA measured by 5SL chart is slightly better than that by ETDRS chart and 5SL chart would be a suitable alternative when ETDRS chart are not available in the clinical situation. The VA measured by 2.5SL chart is about 0.5 line better than VA tested with ETDRS chart, which may overestimate VA.