Equivalent legibility font size for traditional Chinese character compared to early treatment diabetic retinopathy study near visual acuity

PURPOSES: To investigate the legibility of a standardized logarithmic print size of traditional Chinese (TC) characters and compare it with Early Treatment Diabetic Retinopathy Study (ETDRS) near chart. MATERIALS AND METHODS: A total of 1243 commonly used TC characters were chosen and divided into three groups according to its stroke complexity: Group A with 2-9 strokes, Group B with 10-17 strokes, and Group C with 18-25 strokes. For each group of characters, near charts were created using randomly chosen characters arranged in decreasing logarithmic size. In a well-illuminated room, healthy controls were fully corrected to test both ETDRS near chart and our set of TC near charts. The smallest legible font sizes (SLFS) in TC near charts were recorded and analyzed. RESULTS: Forty-two healthy eyes (21 participants) (age 29 +/- 8.9 years old) were included. The mean near best-corrected visual acuity (nBCVA) in ETDRS chart was 0.06 +/- 0.05 logMAR. We found that the mean SLFS in TC charts (0.33 +/-; 0.09 logMAR) was significantly larger than the nBCVA in ETDRS chart (P < 0.001). The SLFS of Group B and the SLFS of Group C was significantly larger than that of Group A (P < 0.001). CONCLUSION: According to our results, to recognize TC characters, normal-sight readers need a 0.22-0.30 logMAR (1.7-2.0 fold) enlargement of the acuity size measured by ETDRS near chart. The low-stroke TC charts may provide a new method to assess the postsurgical outcomes for comparable functional visual acuity in reading TC characters.