Comparison of Lea single symbols and Landolt single optotypes

Purpose Lea (LH) symbols seem to be favourable for visual acuity assessment in childhood. The symbols of the LH test are well standardized and applica ble to preschool children. We compared the visual acuity determined by LH s ingle symbols (LH) and the acuity measured with the Landolt-C (LC). Patients and methods 138 cooperative subjects aged 7 to 91 years were exami ned. Their visual acuity was either normal or reduced due to various etiolo gies. Their refractive error was corrected. The monocular LW and LC were de termined by a 3/4 criterion (study 1). In 19 healthy subjects aged 21 to 58 years, acuity was reduced stepwise by 5 different calibrated occlusives (s tudy 2). A Lighthouse single symbol book (LH symbols) was used at a distanc e of 3 m. LC was determined at a distance of 5 m, The luminance of the test field was 180-200 cd/m(2). The right eye of each patient and the amblyopic eye of the squinting patients was taken for statistical evaluation. The st rabismic patients' interocular differences of LC and LH were compared. Results Within study 1, LC ranged from 0.02 to 2.0 and LH from 0.03 to 2.5. LH overestimated LC by 1.4 lines on an average (t-test p < 0.0001). The re gression equation IgLH = 0.95 IgLC + 0.11 describes a high correlation (r = 0.95) between LH and LC. The relations between LPI and LC of 43 strabismic amblyopic patients and the remaining subjects did not significantly differ . Due to the criterion of an interocular LH-difference >1 line, 85.7% resp. 90% of the strabismic amblyopic patients with an interocular LC difference >1 resp >2 lines were detected. In study 2, LC ranged from 0.1 to 1.6, LH from 0.12 to 2.0. The mean difference LH-LC was 1.3 lines. The regression e quation was IgLH = 0.91 IgLC + 0.08 (r = 0.95). Conclusion LH symbols allow a reliable measurement of recognition acuity. D ue to the design of the symbols, they are excellently suitable for applicat ion to preschool children. Age related normal values should be established. The systematic difference between the LC acuity and the LH acuity measured with the Lighthouse LW single symbol book by 1.4 lines has to be considere d.