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F. Lu, H. Ma, D. Xu, G. Wang, C. Wang, J. Qu; Acuity Reserve and Critical Print Size for Chinese Characters . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4582.
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Purpose: Acuity reserve is defined as a ratio of a given print size to the near acuity threshold for a reading letter or character. This study was to determine the acuity reserve at a critical print size (the smallest print size with a highest reading speed similar to larger print sizes) for reading of Chinese characters. Methods: Thirty–seven year 2 university students with a corrected visual acuity of at least 20/20 (both distant and near VA) were evaluated for near acuity threshold using charts of Chinese characters (all composed of 5 strokes "song" fonts). The students were then assigned to 2 groups based on their near acuity threshold. Each group read a range of different sizes of Chinese characters and the reading speed related to the acuity reserve for each print size was analyzed. Results: The near acuity threshold for Chinese characters was 2.5pt in 19 subjects (Group 1) and 2.2pt in 18 subjects (Group 2). In Group 1, subjects with the 4 acuity reserves at 3.64:1, 3.03:1, 2.63:1 and 2.22:1 achieved a corresponding reading speed (words/min.) as 584 ±11.84, 632±10.88, 574±8.98 and 562±6.79. In Group 2, subjects with the 4 acuity reserves at 3.50:1, 3.03:1, 2.56:1 and 2.33:1 achieved a corresponding reading speed as 596 ±10.69, 646 ±7.01, 597 ±10.76 and 585 ±9.62. The highest reading speed was achieved when the acuity reserve was 3.03:1 in both groups. The reading speed reduced when the acuity reserve was smaller than 3:1. The highest reading speed is up to 632 words /min for Group 1 and 646 words/min for Group 2 with an acuity reserve at 3:1. Conclusions:The critical print size for Chinese characters is a reading size corresponding to an acuity reserve at 3:1 among people with normal vision. These results provide a reference to standardize print sizes of Chinese characters at different levels of visual acuity.
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