A comparison of Lea Symbol vs ETDRS letter distance visual acuity in a population of young children with a high prevalence of astigmatism

Purpose To compare visual acuity results obtained by use of the Lea Symbols chart with results obtained with Early Treatment Diabetic Retinopathy Study (ETDRS) charts in young children who are members of a population with a high prevalence of astigmatism. Methods Subjects were 438 children ages 5 through 7 years who were enrolled in kindergarten or first grade on the Tohono O'odham Reservation: 241 (55%) had astigmatism ≥1.00 D in one or both eyes (range, 0.00-6.75 D). While wearing best correction, each child had right eye visual acuity tested with the 62 cm by 65 cm Lea Symbols chart at 3 m and with the 62 cm by 65 cm ETDRS chart at 4 m. Visual acuity was scored as the smallest optotype size at which the child correctly identified 3 of a maximum of 5 optotypes. ETDRS visual acuity also was scored based on the total number of letters that the child correctly identified. Results Correlation between Lea Symbols visual acuity and ETDRS visual acuity was 0.78 ( p < 0.001). Mean Lea Symbols visual acuity was one-half line (0.04-0.06 logMAR) better than mean ETDRS visual acuity ( p < 0.001). The difference between Lea Symbols and ETDRS visual acuity was not correlated with the mean of the Lea Symbols and ETDRS visual acuity scores, which ranged from −0.3 logMAR (20/10) to 0.74 logMAR (20/110). Conclusions In this population of young children, in whom the primary source of reduced visual acuity is astigmatism-related amblyopia, the Lea Symbols chart produced visual acuity scores that were about 0.5 line better than visual acuity scores obtained with ETDRS charts.