Purpose.: To examine prevalence of refractive errors and its associated factors, such as body stature and educational level, among 19-year-old males in Seoul, Korea. Methods.: A population-based cross-sectional study was performed in male subjects (n = 23,616; age = 19 years) who were normally resident in Seoul for male compulsory conscripts during the study period (2010). Refractive examination was performed with cycloplegia. Height, weight, and educational level were examined. Myopia was defined as a spherical equivalent less than −0.5 diopters (D) and high myopia less than −6.0 D. The association of myopia with body stature and educational level was analyzed using logistic regression analysis. Results.: The prevalence of myopia in 19-year-old males in Seoul was 96.5%. The prevalence of high myopia was 21.61%. Body stature was not significantly associated with myopia. Four- to 6-year university students (odds ratio [OR] 1.69; P < 0.001) and 2 to 3-year college students (OR 1.68; P < 0.001) showed significantly higher risk for myopia than those with lower academic achievement (< high school graduation). Conclusions.: The 19-year-old male population in Seoul, Korea, demonstrated a very high myopic prevalence. Myopic refractive error was associated with academic achievement, not with body stature.

Purpose.: To assess the prevalence and risk factors of myopia in 19-year-old males in Jeju, a rural area of Korea. Methods.: A total of 2805 subjects were included. Refractive examination was performed with cycloplegia to test for myopia (<−0.5 diopters [D]) and high myopia (<−6.0 D). Possible associated factors were evaluated including height, weight, educational level, and color vision deficiency. Results.: The prevalence of myopia and high myopia were 83.3% and 6.8%, respectively, in 19-year-old males in Jeju. University students in their fourth to sixth years showed a higher risk for myopia (odds ratio [OR] 2.04; 95% confidence interval [CI], 1.52–2.71, P < 0.001) than those with lower academic achievement. Conclusions.: The prevalence of myopia was relatively high (83.3%) in a rural area of Korea, while the rate of high myopia was relatively low (6.8%) compared with that (20.6%) in an urban area of Korea.

To examine the prevalence and risk factors of refractive errors in a representative Korean population aged 20 years old or older. A total of 23,392 people aged 20+ years were selected for the Korean National Health and Nutrition Survey 2008–2011, using stratified, multistage, clustered sampling. Refractive error was measured by autorefraction without cycloplegia, and interviews were performed regarding associated risk factors including gender, age, height, education level, parent's education level, economic status, light exposure time, and current smoking history. Of 23,392 participants, refractive errors were examined in 22,562 persons, including 21,356 subjects with phakic eyes. The overall prevalences of myopia (< -0.5 D), high myopia (< -6.0 D), and hyperopia (> 0.5 D) were 48.1% (95% confidence interval [CI], 47.4–48.8), 4.0% (CI, 3.7–4.3), and 24.2% (CI, 23.6–24.8), respectively. The prevalence of myopia sharply decreased from 78.9% (CI, 77.4–80.4) in 20–29 year olds to 16.1% (CI, 14.9–17.3) in 60–69 year olds. In multivariable logistic regression analyses restricted to subjects aged 40+ years, myopia was associated with younger age (odds ratio [OR], 0.94; 95% Confidence Interval [CI], 0.93-0.94, p < 0.001), education level of university or higher (OR, 2.31; CI, 1.97–2.71, p < 0.001), and shorter sunlight exposure time (OR, 0.84; CI, 0.76–0.93, p = 0.002). This study provides the first representative population-based data on refractive error for Korean adults. The prevalence of myopia in Korean adults in 40+ years (34.7%) was comparable to that in other Asian countries. These results show that the younger generations in Korea are much more myopic than previous generations, and that important factors associated with this increase are increased education levels and reduced sunlight exposures.

To investigate the association between 25-hydroxyvitamin D and diabetic retinopathy (DR). A population-based cross-sectional study using a nation-wide, systemically stratified, multistage, clustered sampling method included a total of 18,363 subjects aged ≥40 years who participated in the Korean National Health and Nutrition Examination Survey during 2008–2012. All participants participated in standardized interviews, blood 25-hydroxyvitamin D level evaluations, and comprehensive ophthalmic examinations. Seven standard retinal fundus photographs were obtained from both eyes after pupil dilatation. DR was graded according to the modified Airlie House classification system. The blood 25-hydroxyvitamin D levels were 19.2 ng/mL in men and 17.9 ng/mL in women. After adjusting for potential confounders, including age, sex, diabetes duration, hemoglobin A1c levels, and hypertension, the odds ratios (OR) for any DR and proliferative DR among men decreased significantly in the highest blood 25-hydroxyvitamin D level quintile relative to the lowest quintile (OR, 0.37; 95% confidence interval [CI], 0.18–0.76; P for trend = 0.004 and OR, 0.15; 95% CI, 0.03–0.83; P for trend = 0.043). This study provides the first epidemiologic findings of the inverse relationships of blood 25-hydroxyvitamin D levels with any DR and proliferative DR only in men. Considering anti-angiogenic and anti-fibrotic action of vitamin D, further studies including longitudinal and interventional analysis are warranted.