Korean J Ophthalmol Vol.25, No.6, 2011 Table 10. Prevalence of glaucoma according to age and gender Age group (yr) Total 19-29 30-39 40-49 50-59 60-69 ≥70 No 10,035 1,457 2,017 2,095 1,720 1,585 1,161 Total Prev (%) 1.4 0.3 0.7 1.0 2.3 2.2 4.9 SE (0.1) (0.1) (0.2) (0.2) (0.4) (0.4) (0.7) No 4,284 646 848 898 737 682 473 Male Prev (%) 1.6 0.1 1.0 1.4 2.8 2.5 5.7 SE (0.2) (0.1) (0.4) (0.4) (0.7) (0.7) (1.2) No = number of participants; Prev = prevalence; SE = standard error. No 5,751 811 1,169 1,197 983 903 688 Female Prev (%) 1.1 0.5 0.2 0.5 1.9 1.9 4.4 SE (0.2) (0.3) (0.1) (0.2) (0.5) (0.5) (0.9) p-value <0.05 0.22 <0.01 <0.05 0.20 0.41 0.40 Japan [22-26,48,56], Singapore [27-30], China [31-35,46] and Taiwan [61,62]. However, even within a single Asian country, significant racial/ethnic variations may exist. The present study is the first investigating the prevalence of eye diseases in South Korea based on nationally representative data. The 10th Revision of the World Health Organization International Statistical Classification of Diseases, Injuries and Causes of Death defines visual impairment as a BCVA less than 20 / 60 but 20 / 400 or better in the best eye, and blindness is defined as a BCVA of worse than 20 / 400 in the best eye. The United States criteria define visual impairment as a BCVA of less than 20 / 40 but better than 20 / 200, and blindness as a BCVA of 20 / 200 or worse. Using the United States standard, the prevalence of visual impairment was 0.97% to 2.34% in White Americans over 40 years of age [10] and 5.3% in African Americans over 65 years of age [8]. In a Japanese population of subjects over 40 years of age, the prevalence of visual impairment and blindness were 1.28% and 0.15%, respectively [25]. The prevalence of visual im- pairment and blindness in China was reported as 1.1 % and 0.3 %, respectively, in subjects over 40 years of age, accord- ing to the World Health Organization definition [31]. In our study, when we defined visual impairment and blindness as a BCVA of 0.32 or worse and 0.01 or worse, respectively, the prevalence of visual impairment and blindness in the subjects over 40 years of age was 0.9% and 0.1%, respectively, sim- ilar to the prevalence reported from China. 430 Fig. 7. Prevalence of glaucoma accord- ing to age and gender. The prevalence of myopia has been reported as 25% in Western Europe [45], 26% in the United States [45], 38% among Chinese individuals [46], and 41% to 43 % in Japan [47,48]. In the present study, the prevalence of myopia in adult Koreans over 40 years of age was 35.7%, which was higher than those of Western Europe and United States and similar to those reported in China and Japan. Changes in the prevalence and value of refractive errors do occur with age starting in childhood [49]. Many studies have reported a de- crease of the prevalence of myopia and a simultaneous in- crease in the prevalence of hyperopia with increasing age [50-52]. Results of our study were in agreement with those findings. In this study, the overall prevalence of strabismus in the 3 to 5 and 6 to 11 year age groups was 1.8% in South Korea. The prevalence of strabismus has been reported as 2.3% in subjects 2 to 5 years of age in the United Kingdom [53], 3.1% in subjects 4 to 7 years of age in the United States [54], 2.7% in subjects under the age of 7 years in Sweden [55], and 1.3% in subjects 6 to 12 years of age in Japan [56]. There is a sig- nificant ethnic component influencing the distribution of strabismus: Studies in Asian populations have reported an esotropia to exotropia ratio of less than 1, while in European populations, the ratio was greater than 1 [53-56]. Our study demonstrated an esotropia to exotropia ratio of less than 1, similar to results from other Asian countries [56]. Blepharoptosis, drooping of the upper eyelid, is one of the most common upper eyelid diseases. Symptoms relate to im-