The authors have declared that no competing interests exist
Conceived and designed the experiments: ECK IGM DJ. Performed the experiments: ECK IGM DJ. Analyzed the data: IGM DJ. Contributed reagents/materials/analysis tools: IGM SK. Wrote the manuscript: IGM HK DJ.
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,
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.
Refractive errors can lead to visual impairment and ultimately, even blindness [
Previous epidemiological studies on refractive errors have revealed marked differences between ethnic groups in different parts of the world [
Although numerous studies have investigated ethnic variations in myopia [
Risk factors for refractive errors have been extensively investigated in previous population based studies [
Recently, time spent outdoors has been identified as a potential protective factor against myopia in children [
In the present study, we examined the prevalence of refractive errors in a representative Korean population aged 20 years old or older, selected using a stratified, multistage, clustered sampling method. We also evaluated associated risk factors, focusing on education and sunlight exposure times.
This study was based on data acquired in the Korean National Health and Nutrition Examination Survey (KNHANES). The KNHANES is an ongoing population-based cross- sectional, and nationally representative survey conducted by the Division of Chronic Disease Surveillance, Korean Center for Disease Control and Prevention. The survey consists of a health interview, a nutritional survey, and a health examination survey. The survey collected data via household interviews and by direct standardized physical examinations conducted in a specially equipped mobile examination center. In the KNHANES, the sample design and size are designed so that the survey results can be generalized to the whole Korean population.
Each year, 4,000 households in 200 enumeration districts were selected by a panel to represent the civilian, non-institutionalized South Korean population using stratified, multistage clustered sampling based on National Census Data. All members of each selected household were asked to participate in the survey, and the participation rate between 2008 and 2011 ranged from 77.8% to 82.8%.
All participants were given information about the study, and gave written informed consent. The study design followed the tenets of the Declaration of Helsinki for biomedical research and was approved by the Institutional Review Board of the Catholic University of Korea in Seoul, Korea.
Refraction without cycloplegia was measured using an auto-refractor (KR-8800®; Topcon, Tokyo, Japan) by ophthalmology residents or ophthalmologists. Refraction measurements were converted into spherical equivalents, calculated as the spherical value plus half of the astigmatic value. Myopia was defined as ≤ -0.50 diopters (D) and as ≤ -1.0 D , high myopia was defined as ≤ -6.0 D, hyperopia was defined as ≥ +0.5 D and as ≥ +2.0 D, and emmetropia was defined as between -0.5 D and +0.5 D. Astigmatism was defined as > +1.0 D. A slit-lamp examination (BM 900; Haag-Streit AG, Koeniz, Switzerland) was performed by ophthalmologists to identify pheudophakic and aphakic patients, who were excluded from the study, and to evaluate cataract status.
Demographic and socioeconomic information was obtained from a health interview. Height was measured using a wall-mounted measuring scale, and weight was measured with the individual wearing light clothing without shoes in kilograms using calibrated electronic scales. Body mass index (BMI) was calculated using the universally recognized formula: weight (kg) / height (m)2.
The educational level of participants and their parents was classified on a scale of 0 to 4, as follows: 0, no education; 1, elementary education; 2, middle school graduate; 3, high school graduate; and 4, university graduate or higher. Economic status was classified into four quartiles, which was based on personal annual income. Data on current sunlight exposure time was obtained by selecting a single question from the two questions: under 5 h, or over 5 h a day. Current smoking history was also examined by questionnaire which consisted of yes or no question.
Age- and gender-specific prevalences of myopia, hyperopia and astigmatism were assessed. The analysis of variance or chi-square test was used to compare the demographic characteristics. Logistic regression models were used to determine the risk factors for myopia, hyperopia and astigmatism in subjects aged 40 years or older. All variables for logistic regression analysis were examined for multicollinearity, and only variables with a variance inflation factor less than 10 were used. Sampling was weighted by statisticians by adjusting the oversampling and non-response rate [
Of 23,392 eligible subjects aged over 20 years, refractive error was measured for 22,562 subjects (96.5%). Of these, subjects with pseudophakic or aphakic eyes (1,206 eyes) were excluded. Thus, 21,356 subjects were included the analysis for prevalence of myopia. Analysis of risk factors for refractive errors was restricted to the subjects aged 40+ years (n = 14,285).
The demographic characteristics of 21,356 subjects enrolled in the study are summarized by refractive status in
41.0 ± 13.4 | 49.2 ± 13.7 | 63.3 ± 10.9 | <.001 | 48.6 ± 15.7 | 71.1 ± 10.1 | <.001 | |
57.3 | 55.5 | 57.8 | <.001 | 56.9 | 63.1 | <.001 | |
164.1 ± 9.1 | 162.3 ± 9.2 | 158.6 ± 9.3 | <.001 | 162.3 ± 9.4 | 156.0 ± 9.8 | <.001 | |
63.4 ± 12.4 | 62.7 ± 11.2 | 60.2 ± 11.7 | <.001 | 62.4 ± 11.6 | 57.7 ± 10.2 | <.001 | |
23.5 ± 3.5 | 23.7 ± 3.2 | 23.8 ± 3.1 | <.001 | 23.6 ± 3.4 | 23.6 ± 3.2 | .941 | |
<.001 | <.001 | ||||||
No school | 0.9 | 1.7 | 5.6 | 2.3 | 12.5 | ||
Elementary school | 9.2 | 24.4 | 47.4 | 22.3 | 55.3 | ||
Middle school | 7.0 | 13.9 | 16.6 | 11.2 | 10.1 | ||
High school | 40.4 | 37.0 | 20.4 | 34.6 | 14.7 | ||
University | 42.5 | 24.0 | 10.0 | 29.5 | 7.4 | ||
<.001 | <.001 | ||||||
No school | 8.0 | 15.6 | 26.5 | 14.2 | 32.7 | ||
Elementary school | 32.9 | 44.3 | 52.0 | 40.3 | 50.4 | ||
Middle school | 18.8 | 14.9 | 8.5 | 15.4 | 7.5 | ||
High school | 25.7 | 16.9 | 8.8 | 19.5 | 6.9 | ||
University | 14.7 | 8.3 | 4.3 | 10.6 | 2.5 | ||
<.001 | <.001 | ||||||
No school | 16.1 | 29.7 | 50.4 | 27.7 | 61.9 | ||
Elementary school | 39.8 | 44.0 | 39.6 | 40.9 | 31.9 | ||
Middle school | 18.4 | 12.6 | 5.0 | 13.8 | 2.9 | ||
High school | 20.6 | 11.3 | 4.1 | 14.3 | 2.6 | ||
University | 5.0 | 2.4 | 1.0 | 3.4 | 0.6 | ||
.004 | 0.263 | ||||||
1st quartile (low) | 23.9 | 24.9 | 24,6 | 24.3 | 25.5 | ||
2nd quartile | 24.2 | 26.8 | 25.7 | 25.3 | 25.8 | ||
3rd quartile | 26.1 | 23.4 | 25.8 | 25.3 | 24.6 | ||
4th quartile | 25.8 | 24.9 | 24.0 | 25.1 | 24.2 | ||
15.2 | 23.7 | 30.0 | <.001 | 21.1 | 27.1 | <.001 | |
20.9 | 20.6 | 16.7 | <.001 | 19.4 | 13.9 | <.001 |
Data are expressed as means ± standard deviation or frequency (%).
The ANOVA was used for continuous variables, and the Chi-square test was used for categorical variables.
Distribution of refractive error in each age group is shown in
Distribution was presented according to the age groups, and compared with those of previous studies for Korean 19 years old population in Seoul and Jeju.
19 yrs (Seou) | 19 yrs (Jeju) | 20-29 yrs | 30-39 yrs | 40-49 yrs | 50-59 yrs | 60-69 yrs | > 70 yrs | |
---|---|---|---|---|---|---|---|---|
Kurtosis | 0.43 | 0.51 | 1.08 | 5.87 | 9.54 | 19.84 | 25.68 | 17.18 |
Skewness | -0.32 | -0.60 | -1.04 | -1.88 | -2.40 | -3.10 | -3.39 | -2.74 |
Kurtosis and skewness were presented according to the age groups, and compared with those of previous studies for Korean 19 years old population in Seoul and Jeju.
The overall prevalence of myopia and high myopia was 48.1% (CI, 47.4–48.8) and 4.0% (CI, 3.7–4.3), respectively. There is no significant difference in prevalence of myopia between males and females (
20-29 | 2690 | 2123 (78.9, 77.4-80.4) | 1731 (64.4, 62.6-66.2) | 294 (10.9, 9.7-12.1) | 76 (2.8, 2.2-3.4) | 13 (0.5, 0.2-0.8) | 762 (28.3, 26.6-30.0) |
30-39 | 4381 | 3189 (72.8, 71.5-74.1) | 2385 (54.3, 52.8-55.8) | 251 (5.7, 5.0-6.4) | 122 (2.8, 2.3-3.3) | 7 (0.2, 0.1-0.3) | 972 (22.1, 20.9-23.3) |
40-49 | 4318 | 2623 (60.7, 59.2-62.2) | 1746 (40.4, 38.9-41.9) | 177 (4.1, 3.5-4.7) | 239 (5.5, 4.8-6.2) | 14 (0.3, 0.1-0.5) | 1065 (24.6, 23.3-25.9) |
50-59 | 4056 | 1322 (32.6, 31.2-34.0) | 769 (18.9, 17.7-20.1) | 63 (1.5, 1.1-1.9) | 1184 (29.2, 27.8-30.6) | 88 (2.2, 1.7-2.7) | 1248 (30.7, 29.3-32.1) |
60-69 | 3438 | 555 (16.1, 14.9-17.3) | 335 (9.7, 8.7-10.7) | 46 (1.3, 0.9-1.7) | 2018 (58.7, 57.1-60.3) | 366 (10.6, 9.6-11.6) | 1654 (47.9, 46.2-49.6) |
70+ | 2473 | 450 (18.2, 16.7-19.7) | 311 (12.6, 11.3-13.9) | 26 (1.1, 0.7-1.5) | 1527 (61.7, 59.8-63.6) | 451 (18.2, 16.7-19.7) | 1589 (64.3, 62.4-66.2) |
> 20 | 21356 | 10262 (48.1, 47.4-48.8) | 7277 (34.0, 33.4-34.6) | 857 (4.0, 3.7-4.3) | 5166 (24.2, 23.6-24.8) | 939 (4.4, 4.1-4.7) | 7290 (34.0, 33.4-34.6)) |
> 40 | 14285 | 4950 (34.7, 33.9-35.5) | 3161 (22.1, 21.4-22.8) | 312 (2.2, 2.0-2.4) | 4968 (34.8, 34.0-35.6) | 919 (6.4, 6.0-6.8) | 5556 (38.8, 38.0-39.6) |
P < .001 | P < .001 | P < .001 | P < .001 | P < .001 | P < .001 | ||
20-29 | 1148 | 894 (77.9, 75.5-80.3) | 734 (64.0, 61.2-66.8) | 100 (8.7, 7.1-10.3) | 30 (2.6, 1.7-3.5) | 3 (0.3, 0.0-0.6) | 370 (32.2, 29.5-34.9) |
30-39 | 1828 | 1312 (71.8, 69.7-73.9) | 985 (53.7, 51.4-56.0) | 94 (5.1, 4.1-6.1) | 50 (2.7, 2.0-3.4) | 2 (0.1, 0.0-0.2) | 444 (24.2, 22.2-26.2) |
40-49 | 1883 | 1157 (61.4, 59.2-63.6) | 778 (41.3, 39.1-43.5) | 83 (4.4, 3.5-5.3) | 101 (5.4, 4.4-6.4) | 6 (0.3, 0.1-0.5) | 443 (23.5, 21.6-25.4) |
50-59 | 1713 | 591 (34.5, 32.2-36.8) | 367 (21.4, 19.5-23.3) | 30 (1.7, 1.1-2.3) | 458 (26.7, 24.6-28.8) | 31 (1.8, 1.2-2.4) | 494 (28.8, 26.7-30.9) |
60-69 | 1545 | 248 (16.1, 14.3-17.9) | 146 (9.4, 7.9-10.9) | 15 (1.0, 0.5-1.5) | 876 (56.7, 54.2-59.2) | 128 (8.2, 6.8-9.6) | 741 (47.7, 45.2-50.2) |
70+ | 1082 | 179 (16.5, 14.3-18.7) | 119 (11.0, 9.1-12.9) | 2 (0.2, 0-0.5) | 666 (61.6, 58.7-64.5) | 159 (14.7, 12.6-16.8) | 715 (66.1, 63.0-68.9) |
> 20 | 9199 | 4381 (47.6,46.6-48.6) | 3129 (34.0, 33.0-35.0) | 324 (3.5, 3.1-3.9) | 2181 (23.7, 22.8-24.6) | 329 (3.6, 3.2-4.0) | 3207 (34.8, 33.8-35.8) |
> 40 | 6223 | 2175 (35.0, 33.8-36.2 ) | 1410 (22.6, 21.6-23.6) | 130 (2.1, 1.7-2.5) | 2101 (33.8,32.6-35.5) | 324 (5.2, 4.6-5.8) | 2393 (38.3,37.1-39.5) |
P < .001 | P < .001 | P < .001 | P < .001 | P < .001 | P < .001 | ||
20-29 | 1542 | 1229 (79.7, 77.7-81.7) | 997 (64.7, 62.3-67.1) | 194 (12.6, 10.9-14.3) | 46 (3.0, 2.1-3.9) | 10 (0.6, 0.2-1.0) | 392 (25.4, 23.2-27.6) |
30-39 | 2553 | 1877 (73.5, 71.8-75.2) | 1400 (54.7, 52.8-56.6) | 157 (6.1, 5.2-7.0) | 72 (2.8, 2.2-3.4) | 5 (0.2, 0.0-0.4) | 528 (20.6, 19.0-22.2) |
40-49 | 2435 | 1466 (60.2, 58.3-62.1) | 968 (39.7, 37.8-41.6) | 94 (3.8, 3.0-4.6) | 138 (5.7, 4.8-6.6) | 8 (0.3, 0.1-0.5) | 622 (25.5, 23.8-27.2) |
50-59 | 2343 | 731 (31.2, 29.3-33.1) | 402 (17.1, 15.6-18.6) | 33 (1.4, 0.9-1.9) | 726 (31.0, 29.1-32.9) | 57 (2.4, 1.8-3.0) | 754 (32.0, 30.1-33.9) |
60-69 | 1893 | 307 (16.2, 14.5-17.9) | 189 (10.0, 8.6-11.4) | 31 (1.6, 1.0-2.2) | 1142 (60.3, 58.1-62.5) | 238 (12.6, 11.1-14.1) | 913 (48.2, 45.9-50.5) |
70+ | 1391 | 271 (19.5, 17.4-21.6) | 192 (13.9, 12.1-15.7) | 24 (1.7, 1.0-2.4) | 861 (61.9, 59.3-64.5) | 292 (21.0, 18.9-23.1) | 874 (62.8, 60.3-65.3) |
> 20 | 12157 | 5881 (48.4, 47.5-49.3) | 4148 (34.0,33.2-34.8) | 533 (4.4, 4.0-4.8) | 2985 (24.6, 23.8-25.4)) | 610 (5.0, 4.6-5.4) | 4083 (33.5, 32.7-34.3) |
> 40 | 8062 | 2775 (34.4, 33.4-35.4) | 1751 (21.7, 20.8-22.6) | 182 (2.3, 2.0-2.6) | 2867 (35.6, 34.6-36.6) | 595 (7.4, 6.8-8.0) | 3163 (39.1, 38.0-40.2) |
P < .001 | P < .001 | P < .001 | P < .001 | P < .001 | P < .001 |
Prevalence is expressed as percentage and 95% confidence interval.
Prevalence was presented according to the age groups, and compared with those of previous studies for Korean 19 years old population in Seoul and Jeju.
Although the overall prevalence of hyperopia (>0.5D) was 24.2% (CI, 23.6–24.8), the age-specific prevalence was lowest at 2.8% (CI, 2.2–3.4) in the 20–29 year olds and much higher at 58.7% (CI, 57.1–60.3) in the 60–69 year olds (
Education levels by age and gender in the representative Korean population are shown in
(n = 2690) | (n = 4457) | (n = 4318) | (n = 4056) | (n = 3438) | (n = 2473) | |
No Education (%) | 0.0 | 0.0 | 0.1 (0.0-0.2) | 0.5 (0.3-0.7) | 4.7 (4.0-5.4) | 12.7 (11.4-14.0) |
Elementary School (%) | 0.5 (0.2-0.8) | 0.8 (0.5-1.1) | 6.0 (5.3-6.7) | 29.6 (28.2-31.0) | 51.6 (49.9-53.3) | 62.0 (60.1-63.9) |
Middle School (%) | 1.7 (1.2-2.2) | 2.2 (1.8-2.6) | 11.6 (10.6-12.6) | 23.1 (21.8-24.4) | 17.3 (16.0-18.6) | 9.1 (8.0-10.2) |
High School (%) | 52.1 (50.2-54.0) | 41.4 (40.0-42.8) | 46.4 (44.9-47.9) | 30.6 (29.2-32.0) | 18.6 (17.3-19.9) | 10.2 (9.0-11.4) |
University (%) | 45.7 (43.8-47.6) | 55.5 (54.0-57.0) | 35.9 (34.5-37.3) | 16.2 (15.1-17.3) | 7.9 (7.0-8.8) | 6.0 (5.1-6.9) |
(n = 1166) | (n = 1845) | (n = 1883) | (n = 1713) | (n = 1545) | (n = 1082) | |
No Education (%) | 0.0 | 0.0 | 0.0 | 0.4 (0.1-0.7) | 1.6 (1.0-2.2) | 4.7 (3.4-6.0) |
Elementary School (%) | 0.3 (0.0-0.6) | 0.8 (0.4-1.2) | 4.3 (3.4-5.2) | 19.2 (17.4-21.0) | 34.9 (32.5-37.3) | 49.9 (46.9-52.9) |
Middle School (%) | 1.6 (0.9-2.3) | 2.4 (1.7-3.1) | 8.7 (7.4-10.0) | 21.8 (19.9-23.7) | 23.0 (20.9-25.1) | 14.9 (12.8-17.0) |
High School (%) | 62.8 (60.0-65.6) | 37.0 (34.8-39.2) | 41.0 (38.8-43.2) | 32.9 (30.8-35.0) | 26.9 (24.7-29.1) | 17.8 (15.5-20.1) |
University (%) | 35.3 (32.6-38.0) | 59.9 (57.7-62.1) | 46.0 (43.7-48.3) | 25.7 (23.7-27.7) | 13.6 (11.9-15.3) | 12.7 (10.7-14.7) |
(n = 1560) | (n = 2612) | (n = 2435) | (n = 2343) | (n = 1893) | (n = 1391) | |
No Education (%) | 0.0 | 0.0 | 0.2 (0.0-0.4) | 0.6 (0.3-0.9) | 7.3 (6.1-8.5) | 18.9 (16.8-21.0) |
Elementary School (%) | 0.7 (0.3-1.1) | 0.9 (0.5-1.3) | 7.1 (6.1-8.1) | 36.8 (34.8-38.8) | 64.2 (62.0-66.4) | 70.5 (68.5-72.9) |
Middle School (%) | 1.7 (1.1-2.3) | 2.1 (1.6-2.6) | 13.5 (12.1-14.9) | 24.1 (22.4-25.8) | 13.0 (11.5-14.5) | 4.7 (3.6-5.8) |
High School (%) | 44.2 (41.7-46.7) | 44.8 (42.9-46.7) | 50.7 (48.7-52.7) | 28.9 (27.1-30.7) | 12.2 (10.7-13.7) | 4.8 (3.7-5.9) |
University (%) | 53.5 (51.0-56.0) | 52.2 (50.3-54.1) | 28.5 (26.7-30.3) | 9.6 (8.4-10.8) | 3.3 (2.5-4.1) | 1.2 (0.6-1.8) |
Prevalence is expressed as percentage and 95% confidence interval.
Both gender | (n = 2690) | (n = 4457) | (n = 4318) | (n = 4056) | (n = 3438) | (n = 2473) |
166.9 ± 9.1 | 165.3 ± 8.6 | 163.5 ± 8.3 | 161.0 ± 8.7 | 159.2 ± 8.8 | 155.7 ± 10.0 | |
Male | (n = 1166) | (n = 1845) | (n = 1883) | (n = 1713) | (n = 1545) | (n = 1082) |
174.3 ± 7.0 | 172.9 ± 6.1 | 170.6 ± 5.7 | 168.3 ± 6.1 | 166.3 ± 5.5 | 164.0 ± 6.7 | |
Female | (n = 1560) | (n = 2612) | (n = 2435) | (n = 2343) | (n = 1893) | (n = 1391) |
161.4 ± 5.9 | 159.8 ± 5.5 | 157.9 ± 5.3 | 155.7 ± 5.9 | 153.4 ± 6.4 | 149.2 ± 6.9 | |
Both gender | (n = 2690) | (n = 4457) | (n = 4318) | (n = 4056) | (n = 3438) | (n = 2473) |
13.6 (12.3-14.9) | 11.4 (10.5-12.3) | 16.3 (15.2-17.4) | 24.0 (22.7-25.3) | 33.7 (32.1-35.3) | 34.5 (32.6-36.4) | |
Male | (n = 1166) | (n = 1845) | (n = 1883) | (n = 1713) | (n = 1545) | (n = 1082) |
21.3 (19.8-22.8) | 19.0 (17.2-20.8) | 24.5 (22.6-26.4) | 32.2 (30.0-34.4) | 40.4 (38.0-42.8) | 40.4 (37.5-43.3) | |
Female | (n = 1560) | (n = 2612) | (n = 2435) | (n = 2343) | (n = 1893) | (n = 1391) |
7.9 (6.9-8.9) | 5.8 (4.9-6.7) | 9.9 (8.7-11.1) | 17.9 (16.3-19.5) | 28.2 (26.2-30.2) | 29.9 (27.5-32.3) |
0.93 (0.92-0.93) | <.001 | 0.94 (0.93-0.94) | <.001 | 1.11 (1.10-1.11) | <.001 | 1.10 (1.10-1.10) | <.001 | 1.06 (1.06-1.06) | <.001 | 1.06 (1.05-1.06) | <.001 | |
0.96 (0.89-1.04) | .337 | 1.10 (0.95-1.26) | .195 | 1.13 (1.04-1.22) | .003 | 1.01 (0.87-1.17) | .926 | 1.05 (0.97-1.12) | .220 | 0.96 (0.84-1.10) | .568 | |
1.01 (1.00-1.02) | .001 | 1.00 (1.00-1.01) | .280 | 0.99 (0.99-1.00) | .034 | 0.99 (0.99-1.00) | .327 | 0.99 (0.98-1.00) | .001 | 0.99 (0.99-1.00) | .043 | |
<.001 | <.001 | <.001 | <.001 | .489 | .717 | |||||||
< Elementary school | reference | reference | reference | reference | reference | reference | ||||||
Middle school | 1.00 (0.88-1.14) | <.001 | 1.01 (0.87-1.16) | .947 | 1.11 (0.99-1.24) | .085 | 1.13 (0.99-1.29) | .081 | 0.93 (0.84-1.04) | .206 | 0.96 (0.84-1.09) | 0.48 |
High school | 1.48 (1.32-1.65) | <.001 | 1.36 (1.19-1.56) | <.001 | 0.79 (0.71-0.88) | <.001 | 0.79 (0.69-0.91) | 0.01 | 0.94 (0.85-1.04) | .224 | 0.99 (0.87-1.12) | .862 |
University | 2.68 (2.37-3.04) | <.001 | 2.31 (1.97-2.71) | <.001 | 0.53 (0.46-0.62) | <.001 | 0.55 (0.46-0.66) | <.001 | 0.93 (0.82-1.05) | .220 | 1.04 (0.89-1.21) | .644 |
<.001 | .015 | .001 | .079 | .050 | .203 | |||||||
No school | reference | reference | reference | reference | reference | reference | ||||||
Elementary school | 0.98 (0.88-1.10) | .768 | 0.89 (0.78-1.02) | .104 | 1.22 (1.02-1.25) | .038 | 1.16 (1.02-1.32) | .026 | 1.04 (0.86-1.24) | .705 | 0.87 (0.77-0.98) | .024 |
Middle school | 1.25 (1.08-1.45) | .003 | 1.04 (0.87-1.25) | .645 | 0.96 (0.81-1.13) | .609 | 1.06 (0.87-1.30) | .539 | 0.90 (0.76-1.07) | .217 | 0.89 (0.75-1.06) | .206 |
High school | 1.48 (1.27-1.73) | <.001 | 1.11 (0.92-1.35) | .271 | 0.92 (0.77-1.10) | .366 | 1.08 (0.87-1.34) | .479 | 0.90 (0.74-1.10) | .304 | 0.95 (0.79-1.14) | .574 |
University | 1.78 (1.48-2.14) | <.001 | 1.11 (0.87-1.41) | .399 | 0.79 (0.63-0.99) | .037 | 0.89 (0.67-1.19) | .463 | 0.98 (0.81-1.20) | .869 | 0.93 (0.73-1.17) | .519 |
<.001 | .631 | .168 | .219 | .142 | .414 | |||||||
No school | reference | reference | reference | reference | reference | reference | ||||||
Elementary school | 1.07 (0.98-1.17) | .159 | 0.95 (0.85-1.07) | .387 | 1.05 (0.96-1.16) | .280 | 1.05 (0.93-1.18) | .403 | 0.94 (0.86-1.02) | .158 | 1.01 (0.91-1.13) | .831 |
Middle school | 1.30 (1.12-1.52) | .001 | 0.94 (0.78-1.13) | .498 | 0.89 (0.74-1.08) | .242 | 0.99 (0.78-1.25) | .955 | 0.96 (0.82-1.12) | .611 | 1.01 (0.83-1.22) | .956 |
High school | 1.66 (1.38-1.99) | <.001 | 1.01 (0.80-1.89) | .938 | 0.83 (0.66-1.06) | .139 | 1.17 (0.88-1.57) | .272 | 1.17 (0.97-1.42) | .095 | 1.25 (0.99-1.58) | .067 |
University | 2.24 (1.54-3.25) | <.001 | 1.24 (0.81-1.89) | .323 | 1.04 (0.66-1.64) | .872 | 1.76 (1.06-2.94) | .030 | 1.05 (0.71-1.54) | .813 | 1.11 (0.72-1.71) | 0.644 |
<.001 | .128 | .045 | .154 | <.001 | .001 | |||||||
1st quartile (low) | reference | reference | reference | reference | reference | reference | ||||||
2nd quartile | 0.92 (0.82-1.02) | .104 | 0.88 (0.78-0.99) | .038 | 1.06 (0.95-1.19) | .277 | 1.02 (0.89-1.16) | .754 | 0.91 (0.82-1.00) | .060 | 0.94 (0.84-1.06) | .308 |
3rd quartile | 1.07 (0.96-1.18) | .246 | 0.94 (0.84-1.07) | .346 | 1.12 (1.00-1.25) | .050 | 1.14 (1.01-1.30) | .039 | 0.93(0.84-1.03) | .138 | 0.95 (0.84-1.06) | .358 |
4th quartile | 1.14 (1.03-1.27) | .014 | 0.88 (0.78-1.00) | .051 | 0.96 (0.86-1.08) | .528 | 1.08 (0.95-1.24) | .233 | 0.79 (0.71-0.87) | <.001 | 0.80 (0.71-0.90) | <.001 |
0.72 (0.66-0.79) | <.001 | 0.84 (0.76-0.93) | .002 | 1.08 (0.99-1.18) | .079 | 0.94 (0.84-1.05) | .290 | 1.07 (0.99-1.16) | .103 | 1.02 (0.93-1.13) | .646 | |
0.90 (0.81-1.00) | .060 | 0.92 (0.82-1.04) | .175 | 1.08 (0.96-1.21) | .191 | 0.03 (0.90-1.17) | .667 | 1.02 (0.92-1.13) | .659 | 0.98 (0.87-1.10) | .684 |
* present over absent
Hyperopia was associated with the age (OR, 1.10; CI, 1.10-1.10), and inversely associated with high education level of high school (OR, 0.79; CI, 0.69-0.91), and university or higher (OR, 0.55 CI, 0.46-0.66). Astigmatism was associated with age (OR, 1.06; CI, 1.05-1. 06), and inversely associated with height (OR, 0.99; CI, 0.98-1.00) and higher levels of economic status (OR, 0.80; CI, 0.71-0.90) compared to lower levels.
The present study showed that the prevalence of myopia was high, particularly in the younger age groups, in Korea, in adults aged 20 years or older. In a comparison with other Asian studies with similar ages, the prevalence of myopia in 40 years or older was 34.7%, which is comparable to that in China (26.7 - 32.3%) [
2008-2011 | Korea | Korean | 14,285 | 40+c | No | < -0.5 | 34.7 | 60.7 | 32.6 | 16.1 | 18.2 | |
2006-2007 | China | Chinese | 6491 | 30+ | NA | < -0.5 | 26.7 | 22.0 | 13.8 | 14.4 | 35.1 | |
2006 | China | Chinese | 1405 | 50+ | No | < -0.5 | 32.3 | NA | 31.7 | 31.1 | 40.0 | |
2008 | Japan | Japan | 3021 | 40+ | No | < -0.5 | 41.8 | 67.8-70.3 | 42.4-49.6 | 20.8-22.1 | 13.5-24.6 | |
1996 | Singapore | Chinese | 2000 | 40+ | No | < -0.5 | 38.7 | 48.9 | 26.4 | 28.5 | 36.8 | |
2004-2006 | Singapore | Malay | 2974 | 40-80 | No | < -0.5 | 30.7 | 31.0 | 19.6 | 16.4 | 33.6 | |
2007-2009 | Singapore | Indian | 3400 | 40+ | No | < -0.5 | 28.0 | 33.3 | 23.8 | 20.3 | 26.9 | |
1996-2000 | India | Indian | 3642 | 40+ | No | < -0.5 | 34.6 | 19.2 | 38.3 | 56.0 | 54.1 | |
1995 | Mongol | Mongolian | 1800 | 40+ | No | < -0.5 | 17.2 | 15.6 | 12.5 | 21.4 | 26.5 | |
1999-2004 | U.S. | Whites | 5841 | 40+c | No | < -0.5 | 42.6 | 52.6 | 26.4 | |||
1999-2004 | U.S. | Blacks | 2343 | 40+c | No | < -0.5 | 36.5 | 44.3 | 23.9 | |||
2000-2003 | U.S. | Latinos | 5927 | 40+ | No | < -1.0 | 16.8 | 14.1-17.9 | 10.5-13.8 | 8.7-11.6 | 13.9-34.2 | |
1988-1990 | U.S. | Caucasian | 4533 | 43-84 | No | < -0.5 | 26.2 | 42.9 | 25.1 | 14.8 | 14.4 | |
1992-1994 | Australia | Caucasian | 3654 | 40+ | No | < -0.5 | 15.0 | 25.4 | 14.4 | 11.0 | 11.5 | |
1986 | Australia | Caucasian | 4744 | 40+ | No | < -0.5 | 16.9 | 23.6 | 16.3 | 12.4 | 12.8 |
a Korean National Health and Nutritional Examination Survey, b National Health and Nutritional Examination Survey, c 40+ was chosen for comparison, although total examination age range was 20+ in KNHNES and U.S. NHNES.
Age-specific prevalence data are in many ways more meaningful. The prevalence of myopia in 20-39 year-old Korean (75.1%) is higher than in age-matched black (49.0%) and white people (51.3%) in the U.S. NHANES, which used same examination methods, and a similar sampling frame (
The reason for rapid increase of myopia in Korean adults is not known. But the history of Korea provides a plausible explanation. After a period of Japanese colonization and the Second World War, Korea was impoverished, but, despite the Korean War, the Republic of Korea has undergone rapid economic development for the last 60 years, documented in a rapid increase in per capita GDP from US$ 67 in 1953 to US$ 20,050 in 2007 [
The hypothesis that education has played a crucial role is further supported by an Organization for Economic Cooperation and Development (OECD) report concerning change in education over fifty years (accessible at http://www.oecd.org/edu/skills-beyond-school/48642586.pdf). This report shows that rates of educational expansion have varied greatly among countries over recent decades. Korea has made higher education dramatically more accessible, and Korea has been transformed from a country where only a minority of students graduated from secondary school to one in which virtually all students graduate and a high proportion go on to higher education. Thus, Korea has moved from the 21st to the first rank among 25 OECD countries.
Current sun exposure time in Korean adults was inversely associated with the myopia in our study. Although higher light intensity outdoors reduces the prevalence of myopia in children through the inhibition of eye growth which is caused by the stimulated release of dopamine from the retina or increased focal depth of field by reducing image blur through pupil constriction [
The major strength of the present study is the large number of participants (21,356) and the study design using systemic stratified, multistage, clustered random sampling methods. Our study has several limitations. First, the refractive error was measured without cycloplegia, which may lead to the overestimation of the prevalence of myopia, but this is a limitation that it shares with all but one of the major studies on refractive errors in adults, including the US NHANES. Because of this concern, we did not use the data to provide prevalence estimates of refractive error for those aged 5 to 19 years (6,206 subjects). However, as shown by the comparisons to the prevalence of myopia and distribution of refractive error in 19 year-old males in Seoul and Jeju Province measured by cycloplegic autorefraction (
In conclusion, the present study provides the first population-based representative data on refractive errors in the Korean adult population. The prevalence of myopia in 40-49 year old Koreans (60.7%) was very much higher than in other countries, whereas that in 60-69 year olds (16.1%) was comparable to those in many others. This major change may be associated with the rapid economic development of Korea, and its transformation from a poorly educated country to one with amongst the highest educational standards in the world (OECD/PISA). Parallel social changes appear to have reduced the amount of time people are exposed to sunlight outdoors, and myopia in Korea is associated with higher educational level and a lower proportion of those with longer sunlight exposure times (over 5 h per day). In parallel with demonstrated secular changes in these parameters, the prevalence of myopia has increased dramatically in Korea.