title: [Selection of Chinese characters for visual acuity charts using psychophysical methods].
abstract: OBJECTIVE
  This study investigated the legibility in use of psycho-physical methods to select Chinese characters for visual acuity charts.
  
  
  METHODS
  Twenty-eight subjects with the raw visual acuity or best corrected visual acuity of -0.11 ± 0.06 (LogMAR) were recruited for this study. Ninety Chinese characters with similar Fourier frequency spectrum were used as candidates for the selection of visual targets. Thirty-seven Chinese characters with each consisted of horizontal, vertical and oblique strokes were selected from these candidates. Six different-sized BMP images for each selected Chinese character were made based on the average visual acuity threshold of all the selected characters. The accuracy rate for all subjects to read each size of the BMP images was averaged. Graphs correlating the font sizes with the accuracy rates were formed using Weibull function imitation, which provided a visual acuity (VA) threshold and slope for each Chinese character selected.
  
  
  RESULTS
  Among the 37 Chinese characters selected, 17 had a VA threshold 6.16 ± 0.54 (unit: arc) and 20 had a VA threshold of 8.20 ± 0.71. The slope for characters with low stroke number and medium stroke number was 5.91 ± 2.18 and 11.18 ± 3.55, respectively. Based on the similarity in VA thresholds and slopes, 10 Chinese characters were finally determined as the visual targets for a lower stroke-number Chinese visual acuity chart (tb: 5.84 ± 0.36, β: 4.72 ± 0.85). Another 10 characters "rdquo; (tb: 8.38 ± 0.24, β: 10.47 ± 3.9) were determined as the visual targets for a medium stroke-number Chinese visual chart.
  
  
  CONCLUSIONS
  Analysis using Fourier frequency spectrum provides an objective method in the selection of Chinese characters for Chinese visual acuity charts. A psychological test for this selection would further confirm the legibility of the method used in this study.
authors: School of Ophthalmology and Optometry, Wenzhou Medical College, Wenzhou 325027, China.
authors: Chen-xiao
authors: CX
authors: Wang
authors: Fan
authors: F
authors: Lü
mesh_terms: D000328:Adult; D002681:China; D005260:Female; D006801:Humans; D007802:Language; D008297:Male; D011932:Reading; D017550:Spectroscopy, Fourier Transform Infrared; D014792:Visual Acuity; D014796:Visual Perception; D055815:Young Adult