title: Lea symbols: visual acuity assessment and detection of amblyopia.
abstract: OBJECTIVE
  Lea symbols can be used for measuring visual acuity in childhood. Therefore, these symbols might be useful for early detection of amblyopia. We evaluated whether the visual acuity determined with Lea symbols (LS) corresponds to the visual acuity determined with the Landolt-C (LC).
  
  
  METHODS
  In 55 strabismic amblyopic volunteers aged 5-59 years, the monocular visual acuity of both eyes was determined using LC and LS. For comparison, the right eye of 20 healthy volunteers was examined. Single optotypes (LC, LS) were used in 55 amblyopes and crowded optotypes (LC(17.2), LC(2.6), CLS) in 40 amblyopes. The luminance of the test charts was 180-200 cd/m(2), with a contrast >85%. The refraction of the subjects was corrected beforehand.
  
  
  RESULTS
  In the 40 amblyopic eyes tested under each condition, LS exceeded CLS and LC by about 1 line (dB), LC(17.2) by 2 lines and LC(2.6) by 3 lines (mean values +/- SD: LS 0.62+/-1.8 dB, CLS 0.46+/-1.7 dB, LC 0.5+/-2. 0 dB, LC(17.2) 0.41+/-2.3 dB, LC(2.6) 0.29+/-2.3 dB). The non-amblyopic fellow eyes and healthy eyes showed smaller differences (fellow eyes LS 1.32+/-1.1 dB, CLS 1.17+/-1.1 dB, LC 1. 15+/-0.9 dB, LC(17.2) 1.05+/-0.9 dB, LC(2.6) 0.93+/-1.1 dB; healthy eyes LS 1.74+/-0.9 dB, CLS 1.58+/-0.8 dB, LC 1.48+/-0.6 dB, LC(17.2) 1.41+/-0.7 dB, LC(2.6) 1.32+/-1.1 dB). In the amblyopic eyes, the reduction of LC was more distinct than the reduction of LS. Fifty-two amblyopes had an amblyopia >1 dB of LC, LC(17.2) and LC(2. 6), while 50 had an interocular acuity difference >1 dB CLS.
  
  
  CONCLUSIONS
  Using Lea symbols, a recognition acuity can be determined and amblyopia can reliably be detected. Due to their design, the Lea symbols are particularly suitable and recommendable for application in young children. However a slight systematic difference between LS and LC has to be considered.
authors.affiliation: Department of Strabismology and Neuroophthalmology, University of Giessen, Friedrichstrasse 18, D-35385 Giessen Germany. michael.h.graef@augen.med.uni-giessen.de
authors.forename: M H
authors.initials: MH
authors.lastname: Gräf
authors.forename: R
authors.initials: R
authors.lastname: Becker
authors.forename: H
authors.initials: H
authors.lastname: Kaufmann
mesh_terms: D000293:Adolescent; D000328:Adult; D000550:Amblyopia / Q000175:diagnosis*; D002648:Child; D002675:Child, Preschool; D006801:Humans; D008875:Middle Aged; D015203:Reproducibility of Results; D014787:Vision Tests / Q000295:instrumentation*; D015349:Vision, Monocular; D014792:Visual Acuity