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V. Dobson, E. M. Harvey, C. E. Clifford-Donaldson, J. M. Miller; Best-corrected Lea Symbols Acuity versus Best-corrected ETDRS Letter Acuity in a Population of Children With a High Prevalence of Astigmatism. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5510.
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© ARVO (1962-2015); The Authors (2016-present)
: To compare visual acuity (VA) results obtained with the Lea Symbols logMAR distance VA chart and the ETDRS logMAR distance VA chart in kindergarten and 1st grade children who are members of a Native American Tribe with a high prevalence of astigmatism.
Subjects were 216 children 5.4-9.2 years of age who attended kindergarten or 1st grade on the Tohono O’odham Reservation during the 2005/06 school year. Based on cycloplegic refraction 115 children (53.2%) had astigmatism ≥ 1.00 D (cylinder range: 0.00 to 6.75 D). While wearing spectacles containing best correction, each child had right eye VA tested with the Lea Symbols chart at 3 m and with the ETDRS chart at 4 m. VA was scored as the smallest optotype size at which the child correctly identified, by naming or matching to symbols or letters on a lap card, at least 3 out of a maximum of 5 optotypes. VA results were converted to logMAR values prior to analyses.
Correlation between Lea Symbols VA and ETDRS VA was 0.78 (p<0.001), with Lea Symbols scores ranging from 20/10 to 20/100, and ETDRS scores ranging from 20/12 to 20/100. Mean Lea Symbols VA (0.16 logMAR [20/29], SD 0.17) was approximately one-half line better than mean ETDRS VA (0.20 logMAR [20/32], SD 0.18) (t(215)=5.86, p<0.001). Difference between Lea Symbols and ETDRS VA was correlated with ETDRS VA results (r=0.37, p<0.001), with an average difference of 0.03 (1.5 letters) for acuity scores of 20/40 or better, increasing to a difference of 0.14 (1.5 lines or 7 letters) for acuity scores worse than 20/40.
In this population of young children, in whom the primary source of reduced best-corrected VA is astigmatism-related amblyopia, VA measured with the Lea Symbols chart was, on average, one-half line better than VA measured with an ETDRS chart. It is not likely that this difference is due to a simple factor such as difference in test distance (3m vs 4 m), differences in the height or width of equivalent optotypes on the two charts, or differences in the number of optotypes used on the two charts (4 vs 10 optotypes), because the VA difference between tests varied as a function of VA level. Thus, for children with near-normal VA, the Lea Symbols test provides a good estimate of ETDRS VA. However, in children with mild to moderate astigmatism-related amblyopia, the Lea Symbols test overestimates ETDRS VA by an average of 1.5 lines.
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