Current Eye Research, 2014; 39(12): 1232–1239 ! Informa Healthcare USA, Inc. ISSN: 0271-3683 print / 1460-2202 online DOI: 10.3109/02713683.2014.907431

ORIGINAL ARTICLE

Prevalence and Risk Factors for Age-Related Macular Degeneration: Korean National Health and Nutrition Examination Survey 2008–2011 Tae Yoon La1, Eunyoung Cho2, Eun Chul Kim3, Seungbum Kang4 and Donghyun Jee1 1

Department of Ophthalmology and Visual Science, St. Vincent’s Hospital, Suwon, South Korea, 2Channing Division of Network Medicine, Brigham and Women’s Hospital and Harvard Medical School, Suwon, South Korea, 3Department of Ophthalmology and Visual Science, Buchon St. Mary’s Hospital, Suwon, South Korea, and 4Department of Ophthalmology and Visual Science, Daejon St. Mary’s Hospital, College of Medicine, Catholic University of Korea, Suwon, South Korea

ABSTRACT Purpose: To evaluate the prevalence of and risk factors for age-related macular degeneration (AMD) in a representative Korean population. Materials and Methods: A nationwide population-based cross-sectional study was conducted among the civilian, noninstitutionalized Korean population aged 40 and older (mean age, 55.7 years; 95% confidence interval [CI], 55.4–56.0). A total of 16,109 older (40 years of age) subjects participated in the Korean National Health and Nutrition Survey 2008–2011. All participants underwent standardized interviews and comprehensive ophthalmic examinations. Using physiologic mydriasis, a 45 digital fundus photograph was taken of both eyes of each participant. All fundus photographs were graded according to an international classification and grading system. Main outcome measures consisted of prevalence of early- and late-AMD. Results: Of the 16,109 subjects, fundus photographs were gradable for 14,352 (89.1%). The prevalence of earlyand late-AMD in the Korean population was 6.0 and 0.6%, respectively. The prevalence of early-AMD increased from 1.5% in those aged 40–49 years to 16.2% in those aged 70 years. After adjusting for confounders, the prevalence of early-AMD increased with increasing age (odds ratio [OR], 1.08; CI, 1.06–1.09). For late-AMD, old age (OR, 1.09; CI, 1.04–1.14), male gender (OR, 2.45; CI, 1.11–5.37), high systolic blood pressure (OR, 1.03; CI, 1.00–1.06) and high fasting glucose level (OR, 0.97; CI, 0.94–0.99) were significant risk factors. Smoking was not associated with either early- or late-AMD in this Korean population. Conclusions: The present study provides the first population-based data on the prevalence of and risk factors for AMD in a representative Korean population. The prevalences of early- and late-AMD in this population were 6.0 and 0.6%, respectively. The prevalence of AMD in Koreans is higher than for those in other Asian countries and similar to that of Caucasians in Western countries. Keywords: Age-related macular degeneration, Korean, prevalence, risk factor, smoking

INTRODUCTION

and severe visual loss in older populations in both Western and Asian countries.1 The disease is reported to be more frequent in Caucasians than in Asians, conceivably because Asians have more retinal and

Age-related macular degeneration (AMD) is recognized as the leading cause of irreversible blindness

Received 12 August 2013; revised 28 February 2014; accepted 15 March 2014; published online 21 April 2014 Correspondence: Donghyun Jee, MD, PhD, Department of Ophthalmology and Visual Science, St. Vincent’s Hospital, College of Medicine, Catholic University of Korea, 93-6 Ji-dong, Paldal-gu, Suwon, Gyeonggi-do 442-723, South Korea. Tel: +82 312497343. Fax: +82 312496225. E-mail: [email protected]

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Age-Related Macular Degeneration in Korea choroidal pigmentation, which is protective against oxidative insults.2 Population-based data regarding the prevalence of AMD provide important information regarding different patterns of AMD in various countries. However, population-based study regarding the prevalence of AMD for Korean population has not been available yet. Epidemiological studies have revealed a number of AMD-associated risk factors, including age, gender, smoking, and hypertension.3–7 While age and smoking have consistently been found to be risk factors for AMD, other risk factors, for example, cardiovascular disease and diabetes, have been identified with inconsistent results.8,9 A possible reason for such inconsistencies may reside in insufficient numbers of study participants. Therefore, risk factors need to be determined in studies with sufficiently large numbers of participants. In the present study, data from a survey using a systematic stratified, multistage sampling methodology were utilized to (i) examine the prevalence of AMD and (ii) evaluate its associated risk factors in a relatively large, older (40 years of age) Korean population.

MATERIALS AND METHODS Study Population This study was based on data from 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 amasses data via household interviews and by direct standardized physical examinations conducted in specially equipped mobile examination centers. The KNHANES methodology has been described in detail previously.10–12 A total of 4000 households in 200 enumeration districts are selected annually by a panel that represents the civilian, noninstitutionalized South Korean population. A systematic stratified, multistage clustered sampling method, based on the National Census Data, was used. All members of each selected household were asked to participate in the survey. The participation rate between 2008 and 2011 ranged from 77.8 to 82.8%. All participants gave informed consent. This 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. !

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Data Collection Digital fundus images were obtained under physiological mydriasis using a digital fundus camera (TRC-NW6S, Topcon, Tokyo, Japan). For each participant, a 45 digital retinal image, centered on the fovea, was obtained for each eye (two images per person in total). Each image was graded twice—one preliminary and one detailed—using the international classification and grading system.10,13 Two different graders analyzed fundus photograph images, and a trained senior grader who is an ophthalmologist was consulted in case of disagreements. These graders were masked to the clinical status of the subjects. Early-AMD was defined by the presence of soft, indistinct, or reticular drusen; any type of drusen plus hyper- or hypopigmentary changes of the retinal pigment epithelium (RPE) in the macula; or soft drusen over an area of 500 mm in diameter in the absence of signs of late-AMD in the macula. Late-AMD was defined as the presence of wet or dry (geographic atrophy) AMD. Wet AMD was defined as RPE detachment, serous detachment of the sensory retina, presence of subretinal or subretinal pigment epithelial hemorrhages or subretinal fibrous scars. Dry AMD was defined as a circular discrete area 175 mm in diameter of retinal depigmentation with visible choroidal vessels. For subjects with AMD lesions in one eye only or asymmetric AMD lesions in both eyes, AMD was defined according to the more affected eye. Ratio for bilateral AMD was defined bilateral any AMD over any AMD, bilateral earlyAMD over early-AMD and bilateral late-AMD over late-AMD. Mixed type of AMD was defined as coexistence of early- and late-AMD in different eyes of the same subject. Blood pressure was measured with a sphygmomanometer with the patient in a sitting position. Three measurements were made at 5-min intervals. The average of the second and third measurements was used in the analysis. Blood samples were collected in the morning after fasting for at least 8 h. Fasting glucose, hemoglobin A1c, total cholesterol and triglycerides were measured at a central, certified laboratory.3 The presence of diabetes mellitus was defined as a fasting glucose of 126 mg/dL or if the individual was prescribed antiglycemic medication. The presence of hypertension was defined as systolic blood pressure 140 mmHg and diastolic blood pressure 90 mmHg or if the individual was prescribed antihypertensive medication. Hypercholesterolemia was defined as a total cholesterol concentration 240 mg/dL or if the individual was prescribed anticholesterol medication. Heart problems were defined as a history of myocardial infarction or angina. Body mass index was calculated by dividing weight by height squared (kg/m2), after height and weight were obtained using standardized techniques

1234 T. Yoon et al. and equipment. Demographic and social factor data were based on the health interview. Age was classified with the interval of 10 years. Smoking status was classified by self-reporting method as current smoker and ever smoker. Alcohol use was evaluated and grouped as ever drinker or never drinker, using self-report.11

Statistical Analyses Age- and gender-specific prevalences of earlyand late-AMD with 95% confidence intervals (CIs) and standard errors were assessed. Analysis of variance (ANOVA) and chi-square tests for complex samples were used to compare demographic characteristics. Logistic regression models for complex samples were used to determine the risk factors for early- or late-AMD. Risk factors were adjusted by age and gender at first and then were adjusted by all possible risk factors using multivariable analysis. Age was treated as continuous variable in the model. All variables for logistic regression analysis were examined for multi colinearity, and only variables with a variance inflation factor 510 were used. Data for the annual surveys conducted during 2008–2011were combined. Analyses were performed using SPSS version 18 (SPSS, Inc., Chicago, IL, USA) software.

RESULTS Fundus photographs were gradable for 14,352 of the 16,109 (89.1%) study participants. No fundus photography was performed if the following are applied:

small pupil (36.7%), cataract (28.4%), poor patient cooperation (13.3%), corneal opacity (5.9%), patient refusal (5.7%), or miscellaneous other reasons (10.0%). Demographic characteristics of the 14,352 subjects are summarized according to the status of AMD in Table 1. There was a significant difference of age, gender and smoking status among three groups: no AMD, early-AMD and late-AMD (p50.001, p50.001 and p = 0.001, respectively). Table 2 shows the crude prevalence of early- and late-AMD by age and gender. Prevalence of earlyAMD was 6.0% (95% CI, 5.6–6.5) and that of late-AMD was 0.6% (CI, 0.5–0.8). The prevalence of early-AMD was higher in females (6.7%) than males (5.2%; p = 0.001), whereas that of late-AMD was higher in males (0.8%) than females (0.4%) (p = 0.002). The prevalence of AMD increased sharply with age—for example, for early-AMD, 1.5% in those aged 40–49 years and 16.2% in those aged 70+ years (p50.001). The age-adjusted prevalence of early-AMD was 7.0% and that of late-AMD was 0.7%. Bilateral early- and late-AMD rates were 40.2 and 18.1%, respectively (Table 3). The crude prevalence of early-AMD increased from 4.6% in 2008 to 7.2% in 2011 (p for trend50.001), whereas the prevalence of late-AMD showed no liner increase over time (p = 0.052, Table 4). Age-adjusted prevalence of early-AMD significantly increased from 5.7% in 2008 to 9.0% in 2011 (p for trend50.001, Table 4). Early-AMD was significantly associated with old age (odds ratio [OR], 1.08; CI, 1.07–1.09), high fasting glucose level (OR, 0.99; CI, 0.99–1.00 for mg/dL increase) and high HbA1c (OR, 0.82; CI, 0.73–0.93 for 1% increase) in a model adjusted for age and gender. Multivariable analysis after adjusting all possible factors listed in Table 5 indicated that the

TABLE 1. Demographic and clinical characteristics, according to early- and late-age-related macular degeneration (AMD) status and participation status, as reported in the Korean National Health and Nutrition Examination Survey 2008–2011. Characteristics

No AMD (n = 13,223)

Age (years) Male (%) Current smoker (%) If-ever smoker (%) Systolic blood pressure (mmHg) Diastolic blood pressure (mmHg) Hypertension (%) Heart problems (%) Stroke (%) Fasting glucose (mg/dL) HbA1c (%) Diabetes (%) Total cholesterol (mg/dL) Triglyceride (mg/dL) Hypercholesterolemia (%) Alcohol use (%) Body mass index (kg/m2)

54.3 48.2 23.2 45.9 122.1 78.7 25.5 2.8 2.1 100.9 6.2 9.9 193.3 147.9 15.4 85.0 24.0

(0.2) (0.4) (0.5) (0.5) (0.2) (0.2) (0.5) (0.2) (0.1) (0.3) (0.0) (0.3) (0.4) (1.5) (0.4) (0.4) (0.0)

Early-AMD (n = 1,034) 64.7 41.8 17.7 40.3 127.0 77.4 41.2 5.1 3.8 100.9 6.1 12.4 192.3 137.8 15.2 75.0 23.6

(0.4) (1.8) (1.5) (1.9) (0.7) (0.4) (1.8) (0.9) (0.7) (0.9) (0.1) (1.2) (1.4) (4.0) (1.6) (1.6) (0.1)

Late-AMD (n = 95) 65.0 67.5 33.4 66.2 131.7 78.3 38.8 6.2 3.9 95.5 5.8 8.4 196.7 152.6 18.7 87.2 23.2

(1.7) (5.8) (6.3) (5.9) (2.4) (1.3) (6.0) (3.3) (2.0) (1.3) (0.1) (3.8) (5.7) (14.6) (5.4) (4.2) (0.4)

p 50.001 50.001 0.001 50.001 50.001 50.001 50.001 0.001 0.003 50.001 50.001 0.129 50.001 50.001 0.795 50.001 50.001

Participants (n = 14,352) 54.9 47.9 22.9 45.7 122.5 78.6 26.5 2.9 2.2 100.9 6.2 10.0 193.0 147.3 15.4 84.4 24.0

(0.2) (0.4) (0.5) (0.5) (0.2) (0.2) (0.5) (0.2) (0.1) (0.3) (0.0) (0.3) (0.4) (1.5) (0.4) (0.4) (0.0)

Nonparticipants (n = 1,757) 62.8 48.6 23.9 49.6 127.4 78.2 36.2 4.1 4.2 104.3 6.5 13.4 193.6 148.9 16.8 78.1 23.8

(0.5) (1.4) (1.4) (1.5) (0.7) (0.4) (1.4) (0.2) (0.5) (0.9) (0.1) (1.1) (1.2) (3.4) (1.2) (1.2) (0.1)

p 50.001 0.688 0.496 0.019 50.001 50.001 50.001 0.020 50.001 50.001 50.001 0.001 50.001 50.001 0.293 50.001 50.001

Data are expressed as weighted means or weighted frequency (%) with standard errors. Current Eye Research

Age-Related Macular Degeneration in Korea

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TABLE 2. Prevalence of early- and late-age-related macular degeneration (AMD), stratified according to age and gender, as reported in the Korean National Health and Nutrition Examination Survey 2008–2011. Age

n

Total 14,352 Males 6,156 Females 8,196 p Both genders 40–49 4,232 50–59 3,963 60–69 3,424 70+ 2,733 p for trend Male 40–49 1,847 50–59 1,668 60–69 1,516 70+ 1,125 p for trend Female 40–49 2,385 50–59 2,295 60–69 1,908 70+ 1,608 p for trend

Early-AMD (n = 1,034)

Late-AMD (n = 95)

Wet AMD (n = 72)

Dry AMD (n = 24)

Any-AMD (n = 1129)

6.0 (5.6–6.5, 0.2) 5.2 (4.6–5.9, 0.3) 6.7 (6.1–7.4, 0.3) p = 0.001

0.6 (0.5–0.8, 0.1) 0.8 (0.6–1.2, 0.1) 0.4 (0.2–0.6, 0.1) p = 0.002

0.5 (0.4–0.6, 0.1) 0.7 (0.5–1.0, 0.1) 0.3 (0.2–0.5, 0.1) p = 0.011

0.1 (0.1–0.2, 0.0) 0.2 (0.1–0.3, 0.1) 0.1 (0.0–0.2, 0.0) p = 0.155

6.6 (6.2–7.1, 0.2) 6.1 (5.5–6.8, 0.3) 7.1 (6.5–7.8, 0.3) p = 0.033

1.5 4.7 10.7 16.2

(1.1–2.0, 0.2) (4.0–5.5, 0.4) (9.5–12.1, 0.7) (14.5–18.1, 0.9) p50.001

0.2 0.4 1.0 1.7

(0.1–0.4, 0.1) (0.2–0.8, 0.1) (0.6–1.6, 0.2) (1.2–2.3, 0.3) p50.001

0.2 0.4 0.8 1.1

(0.1–0.4, 0.1) (0.2–0.7, 0.1) (0.5–1.4, 0.2) (0.8–1.7, 0.2) p50.001

0.0 0.0 0.2 0.7

(0.0–0.0, 0.0) (0.0–0.3, 0.0) (0.1–0.5, 0.1) (0.4–1.1, 0.2) p50.001

1.6 5.1 11.8 17.9

(1.3–2.2, 0.2) (4.4–6.0, 0.4) (10.5–13.2, 0.7) (16.1–19.8, 0.9) p50.001

1.3 4.9 10.6 13.1

(0.8–2.1, 0.3) (3.9–6.1, 0.6) (8.8–12.6, 1.0) (11.1–15.5, 1.1) p50.001

0.4 0.6 1.7 2.3

(0.2–0.8, 0.1) (0.2–1.3, 0.2) (1.0–2.9, 1.7) (1.5–3.4, 0.5) p50.001

0.4 0.5 1.3 1.4

(0.2–0.8, 0.1) (0.2–1.2, 0.2) (0.7–2.5, 0.4) (0.8–2.4, 0.4) p50.012

0.0 0.1 0.4 0.9

(0.0–0.0, 0.0) (0.0–0.7, 0.1) (0.1–1.1, 0.2) (0.1–1.8, 0.3) p50.001

1.7 5.4 12.3 15.4

(1.1–2.5, 1.7) (4.4–6.7, 0.6) (10.4–14.4, 1.0) (13.2–17.8, 1.2) p50.001

1.6 4.6 10.9 18.0

(1.1–2.3, 0.3) (3.6–5.7, 0.5) (9.2–12.8, 0.9) (15.6–20.7, 1.3) p50.001

0.0 0.3 0.4 1.4

(0.0–0.0, 0.0) (0.1–0.7, 0.1) (0.2–1.2, 0.2) (0.9–2.2, 0.3) p50.001

0.0 0.3 0.4 1.0

(0.0–0.0, 0.0) (0.1–0.7, 0.1) (0.1–1.1, 0.2) (0.6–1.8, 0.3) p50.001

0.0 0.0 0.0 0.5

(0.0–0.0, 0.0) (0.0–0.0, 0.0) (0.0–0.2, 0.0) (0.2–1.2, 0.2) p50.001

1.6 4.8 11.3 19.4

(1.1–2.3, 0.3) (3.8–6.0, 0.5) (9.6–13.3, 0.9) (16.9–22.1, 1.3) p50.001

Crude prevalence was expressed as weighted estimates (%) (95% confidence intervals, standard errors [%]).

TABLE 3. Prevalence of bilateral age-related macular degeneration (AMD), presented according to age and gender, in a representative Korean population.

Total Male Female p 40–49 50–59 60–69 70+ p for trend

Bilateral AMD/any AMD

Bilateral early-AMD/ early-AMD

Bilateral late-AMD/ late-AMD

Mixed AMDa/ any AMD

40.8 (37.4–44.3, 1.7) 31.9 (27.2–37.1, 2.5) 47.8 (43.1–52.7, 2.4) p50.001 16.4 (9.1–27.8, 4.7) 33.0 (25.8–41.1,3.9)) 41.8 (36.3–47.6, 2.9) 51.6 (46.1–57.1, 2.8) p50.001

40.2 (36.6–43.9, 1.9) 29.8 (24.8–35.3, 2.7) 47.7 (42.8–52.7, 2.5) p50.001 16.5 (8.8–28.9, 5.1) 31.9 (24.7–40.1, 3.9) 41.2 (35.5–47.2, 3.0) 51.1 (45.2–57.1, 3.0) p50.001

18.1 (9.6–31.5, 5.5) 19.7 (9.0–37.8, 7.3) 15.0 (5.3–35.5, 7.4) p50.654 0.0 (0.0–0.0, 0.0) 20.5 (3.1–67.4, 17.3) 20.4 (7.0–46.5, 10.1) 20.7 (10.2–37.5, 7.0) p50.685

2.6 (1.7–3.9, 0.6) 3.6 (2.0–6.1, 1.0) 1.9 (1.0–3.4, 0.6) p50.121 1.7 (0.4–6.9, 1.2) 2.0 (0.6–6.6, 1.2) 2.4 (1.1–5.3, 1.0) 3.4 (1.9–5.9, 1.0) p50. 729

a

Mixed AMD was defined as coexistence of early- and late-AMD in different eyes of the same subject. Crude prevalence was expressed as weighted estimates [%] (95% confidence intervals, standard errors [%]).

TABLE 4. Prevalence of early- and late-age-related macular degeneration (AMD), stratified according to examination years, in the Korean National Health and Nutrition Examination Survey 2008–2011.

Early-AMD Late-AMD Age-adjusted early-AMD Age-adjusted late-AMD Number of participants Age of participants Subjects aged 70+ years (%) Current smoker (%)

2008

2009

2010

2011

p for trend

4.6 (3.6–5.7, 0.5) 0.7 (0.5–1.2, 0.2) 5.7 0.8 2074 55.2 (0.4) 14.1 (0.9) 23.2 (1.1)

5.2 (4.5–6.1, 0.4) 0.4 (0.2–0.6, 0.1) 6.2 0.5 4379 55.6 (0.3) 15.3 (0.7) 22.6 (0.7)

6.2 (5.4–7.2, 0.5) 0.5 (0.3–0.8, 0.1) 7.7 0.6 3870 55.7 (0.4) 15.6 (0.9) 24.4 (1.0)

7.2 (6.4–8.1, 0.4) 0.8 (0.6–1.3, 0.2) 9.0 1.0 4029 56.0 (0.3) 16.2 (0.8) 22.1 (0.9)

50.001 0.052 50.001 0.064

Prevalence was expressed as weighted estimates (%) (95% confidence intervals, standard errors [%]).

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50.001 0.461 0.232

1236 T. Yoon et al. TABLE 5. Associations with early- and late-age-related macular degeneration (AMD) in the Korean National Health and Nutrition Examination Survey 2008–2011. Early-AMD Age- and genderadjusted OR

Characteristics Age Gender (male versus female) Current smokera If-ever smokera Systolic BP (mmHg) Diastolic BP (mmHg) Hypertensiona Heart problema Strokea Fasting glucose (mg/dL) HbA1c (%) Diabetesa Total cholesterol (mg/dL) Triglyceride (mg/dL) Hypercholesterolemiaa Alcohol usea Body mass index (kg/m2)

1.08 0.93 1.03 0.88 1.00 1.00 1.08 1.09 0.95 0.99 0.82 0.80 1.00 0.99 0.80 0.98 0.98

p

Late-AMD

Multivariate analysis

p

Age- and genderadjusted OR

p

Multivariate analysis

p

(1.07–1.09) 50.001 1.08 (1.06–1.09) 50.001 1.08 (1.06–1.10) 50.001 1.09 (1.04–1.14) 50.001 (0.79–1.09) 0.368 0.81 (0.53–1.23) 0.313 2.73 (1.63–4.55) 50.001 2.45 (1.11–5.37) 0.026 (0.81–1.31) 0.828 1.25 (0.81–1.92) 0.311 1.73(0.97–3.10) 0.064 1.36 (0.33–5.58) 0.666 (0.68–1.14) 0.328 0.85 (0.56–1.31) 0.472 1.76 (1.01–3.07) 0.047 0.75 (0.24–2.30) 0.614 (0.99–1.00) 0.999 1.00 (0.99–1.01) 0.665 1.01 (1.00–1.03) 0.044 1.03 (1.00–1.06) 0.025 (0.99–1.01) 0.547 1.01 (0.99–1.02) 0.589 1.01 (0.99–1.03) 0.519 1.00 (0.97–1.05) 0.834 (0.91–1.28) 0.364 1.16 (0. 86–1.55) 0.328 0.99 (0.61–1.59) 0.953 0.71 (0.34–1.46) 0.345 (0.75–1.60) 0.642 1.39 (0.76–2.53) 0.291 1.18 (0.39–3.57) 0.763 2.08 (0.39–10.99) 0.387 (0.61–1.49) 0.831 1.21 (0.58–2.52) 0.619 0.82 (0.28–2.35) 0.706 1.31 (0.30–5.72) 0.723 (0.99–1.00) 0.046 1.00 (0.99–1.01) 0.573 0.98 (0.96–0.99) 50.001 0.97 (0.94–0.99) 0.014 (0.73–0.93) 0.002 0.81 (0.66–1.00) 0.050 0.46 (0.25–0.82) 0.009 0.78 (0.25–2.44) 0.666 (0.63–1.02) 0.073 0.80 (0.53–1.22) 0.301 0.52 (0.19–1.39) 0.191 1.12 (0.12–10.82) 0.922 (0.99–1.00) 0.672 1.00 (0.99–1.01) 0.408 1.01 (1.00–1.01) 0.173 1.01 (0.99–1.03) 0.352 (0.99–1.00) 0.114 1.00 (1.00–1.00) 0.988 1.00 (1.00–100) 0.691 1.00 (0.99–1.01) 0.596 (0.62–1.03) 0.085 0.71 (0.49–1.05) 0.086 1.18 (0. 59–2.35) 0.640 1.00 (0.28–3.56) 0.999 (0.80–1.19) 0.800 0.90 (0.67–1.22) 0.504 1.68 (0.81–3.47) 0.161 1.85 (0.58–5.94) 0.299 (0.95–1.00) 0.092 0.97 (0.93–1.02) 0.221 0.94 (0.86–1.03) 0.175 0.97 (0.83–1.14) 0.749

a

Present over absent. Prevalence was expressed as weighted estimates [%] (95% confidence intervals, standard errors [%]). Risk was expressed as odds ratio with 95% confidence intervals.

prevalence of early-AMD increased with increasing age (adjusted OR, 1.08; CI, 1.07–1.09, Table 5). Late-AMD was significantly associated with old age (OR, 1.08; CI, 1.06–1.09), male gender (OR, 2.73; CI, 1.63–4.55), smoking status (OR, 1.76; CI, 1.01–3.07 for ever smokers), high systolic blood pressure (OR, 1.01; CI, 1.00–1.03 for 1 mmHg increase), high fasting glucose level (OR, 0.98; CI, 0.96–0.99 for 1 mg/dL increase) and high HbA1c (OR, 0.46; CI, 0.25–0.82 for 1% increase) in a model adjusted for age and gender. Multivariable analysis after adjusting all possible factors listed in Table 5 indicated that age (adjusted OR, 1.09; CI, 1.04–1.14), male gender (adjusted OR, 2.45; CI, 1.11–5.37), high systolic blood pressure (adjusted OR, 1.03; CI, 1.00–1.06) and high fasting glucose level (adjusted OR, 0.97; CI, 0.94–0.99) were risk factors for late-AMD (Table 5).

DISCUSSION The present study provides prevalence data on AMD, data that are essential for planning eye healthcare services in Korea. The prevalence of early- (6.0%) and late-AMD (0.6%) in the Korean population is comparable to that of Caucasians in the United States (7.6 and 1.3% for early- and late-AMD, respectively)14 and higher than that for African Americans (3.0 and 0.1% for early- and late-AMD, respectively). When compared with other Asian countries, the figures are higher than those for China (1.4–3.0 and 0.1–0.2% for early- and late-AMD, respectively)15,16 and Japan

(3.5 and 0.5% for early- and late-AMD, respectively)17 and comparable to or lower than those for India (5.7–8.9 and 1.4–1.8% for early- and late-AMD, respectively)18–20 (Figure 1). The traditional notion that the prevalence of AMD is lower in Asians than in Caucasians has not been shown to be true for the Korean population. Moreover, the findings in the present study show that the prevalence of AMD is higher in Koreans than in four other ethnic groups (Caucasians, Blacks, Hispanic, and Chinese) reported in the multiethnic study of atherosclerosis (MESA).21 However, the results of MESA may be underestimated, since MESA participants comprised a selectively healthy population, free of clinical cardiovascular disease – an important risk factor for AMD. The results of previous major population-based studies are summarized in Table 6.14–17,20–25 Age-specific prevalence data are meaningful in many ways. A further examination of our data reveals that age-specific prevalence of early-AMD in Korean adults exhibits different patterns from those of adults from other Asian and Western countries. The prevalence of early-AMD in Koreans increases sharply – from 1.5% in 40–49-year-olds to 16.2% in 70+-year-olds (Table 2). ORs for those aged 50–59, 60–69 and 70+ years compared to those aged 40–49 years were 3.34 (95% CI, 2.38–4.69), 8.16 (95% CI, 5.90–11.30) and 13.23 (95% CI, 9.65–18.13), respectively. The prevalence of AMD in 70+-year-old Koreans was 10.8 times higher than that of 40–49-year-old Koreans. This ratio is higher than that of China (2.7 times),15 Japan (1.4 times),17 Singapore (5.6 times),22 Current Eye Research

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FIGURE 1. Prevalence of early-age-related macular degeneration (AMD), according to age groups, in major population-based studies.

TABLE 6. Reported prevalence of early- and late-age-related macular degeneration (AMD) from major population-based studies. Prevalence of AMD Study KNHANES 2008–2011 KNHANES 2010–2011 Handan eye study Beijing eye study Funagata study Hisayama study Singapore Malay eye study APEDS NHANES NHANES MESA MESA MESA MESA Los Angeles Latino eye study

Year

Country

2008–2011 Korea 2010–2011 Korea 2006–2007 China 2001 China 2000–2002 Japan 1998 Japan 2004–2006 Singapore 1996–2000 2005–2008 2005–2008 2000–2002 2000–2002 2000–2002 2000–2002 2000–2003

India US US US US US US US

Ethnicity

Number

Korean Korean Chinese Chinese Japan Japan Malay

14,352 7899 6830 4376 1625 889 3280

Indian Whites Blacks Whites Blacks Hispanics Chinese Latinos

3723 2947 1114 2299 1583 1274 691 6357

Age (yr)

Mean age (yr)

40+ 54.9 (0.2) 40+ 55.2 (0.2) 30+ 51.8 ± 11.7 40+ 56.1 ± 10.5 35+ 60.1–70.6 50+ 65.2 ± 8.9 40–80 58.0–59.4 40+ 40+ 40+ 45–85 45–85 45–85 45–85 40+

53.2–54.7 56.3 (0.4) 56.3 (0.4) 63.0 ± 10.2 62.4 ± 9.9 61.6 ± 10.2 62.4 ± 10.2 54.6 ± 10.7

Early Late (%) (%) 40–49 50–59 60–69 6.0 6.7 3.0 1.4 3.5 12.7 4.9

0.6 0.7 0.1 0.2 0.5 0.9 0.7

1.5 1.4 2.3 0.7 3.0 NA 1.7

8.9 7.6 3.0 4.8 2.1 4.0 3.6 9.4

1.8 1.3 0.1 0.6 0.4 0.2 1.0 0.4

4.5

4.7 5.1 4.7 1.5 3.4 9.1 2.8

10.7 12.0 6.3 1.5 4.3 10.3 6.4

9.1

11.7 17.8 11.6 5.0 5.5 13.3 2.1 5.9 4.5 11.8 5.0 11.1 11.4 20.0

3.0 1.4 1.8 0.4 2.0 0.5 6.2

70+

2.8 2.4 2.4 2.0 8.3

16.2 18.2 6.1 2.9 3.0 18.9 9.6

KNHANES, Korean National Health and Nutritional Examination survey; APEDS, Andhra Pradesh eye disease study; NHANES, US National Health and Nutritional Examination survey; MESA, multiethnic study of atherosclerosis.

India (4.0 times)20 and the United States (Latinos, 3.2 times).23 As yet, the precise reason(s) for such an highly age-sensitive increase of AMD among Koreans than other countries is unknown. Further studies aimed at investigating this disparity are needed in the future. Bilateral AMD is important because those with bilateral AMD have the potential risk for bilateral !

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visual impairment or blindness. We found 40.2% of early-AMD and 18.1% of late-AMD had the bilateral AMD. In addition, the rate of mixed AMD, which was defined as coexistence of early- and late-AMD in different eyes of the same subject, is very low (2.6%). This finding suggests the possibility that mechanism for early- and late-AMD might be different.

1238 T. Yoon et al. The prevalence of early-AMD among Koreans increased from 4.6% in 2008 to 7.2% in 2011. This finding may be partially explained by the fact that the average age of participants was significantly increased during this time. Since the prevalence of AMD increases sharply with age, the differences in prevalence between examination years may be due to differences in age distributions. After age-adjusting, this increasing trend persisted. It is known that Korea is the one of countries where population is aging fast.26 Whether the prevalence of AMD in the Korean population has increased or decreased is, as yet, not completely known. Considering that KNHANES is an ongoing survey, with 4000 households receiving ophthalmic examinations annually, accumulated data from KNHANES are expected to provide a better trends regarding the prevalence of AMD in Korea. Recently, Cho et al. reported the prevalence of early-AMD (6.7%) and late-AMD (0.7%) in Korean representative population.22,25 One unique strength of the present study is observation of the increase in prevalence over examination period. Prevalence of AMD in the study of Cho et al. is slightly higher than that in the present study. This is not surprising because the examination of AMD in the study of Cho et al. was performed in more recent period. A number of epidemiological studies have reported smoking to be the most consistent risk factor for AMD.15,17,27,28 However, we found no significant association between smoking and AMD in the Korean population, although smoking has marginal association with late-AMD only in age- and genderadjusted regression analysis. This finding is in agreement with the results of a previous clinic-based study of the Korean population, although hospital-based study samples do not provide dependable information about the general community.29 The reason for such a finding is unclear. The effect of smoking on AMD among the Korean population may be somehow different or influenced by other environmental factors, such as diet. In Korean populations, early-AMD was more prevalent in females, whereas late-AMD was more prevalent in males. In addition, any gender was not associated with early-AMD and the male gender was a significant risk factor for late-AMD in multivariate analysis. Although a proportion of current smoker in persons with late-AMD was higher in males (47.2%) than in females (6.0%), the male gender was still a strong independent risk factor, even after adjusting smoking factor for late-AMD. This finding implicated that the male gender may be inherently more susceptible to the development of late-AMD due to undiscovered biological mechanism of male. Systolic blood pressure was associated with late-AMD in this study. This is consistent with the age-related eye disease study.30 In the present study,

diastolic blood pressure or hypertension was not associated with the prevalence of any type of AMD, implying the possible barotraumas of high blood pressure to the retinal or choroidal vessels. Interestingly, high levels of fasting glucose and hemoglobin A1c were inversely associated with both early- and late-AMD in age- and genderadjusted regression model, although most of this effect disappeared after adjusting other possible risk factors. Moreover, fasting glucose level for late-AMD showed independent inverse association even after multivariable adjustment. The exact reason for this was not found. Further studies evaluating the association of glucose level and AMD were warranted. The strengths of the present study versus other population-based studies are its study design, which makes use of a nationwide, stratified, multistage, clustered sampling method and a relatively large number (14,352) of participants (Table 6). The limitations of this study are that a significant number of eligible subjects did not participate. Considering that non-participants are older than participants and older population is more likely to have AMD, this may result in a possible underestimation of the prevalence of AMD. Another limitation is that the cross-sectional design could preclude causality inferences. In summary, the present study provides important information regarding the prevalence of and risk factors for AMD in a representative Korean population. The prevalence of early- (6.0%) and late-AMD (0.6%) in the Korean population is higher than for other Asian countries and comparable to Caucasians in Western countries. We found the increase in prevalence over the examination period. Even after adjusting for age, the increasing trend persisted. Further study to elucidate the cause of this trend is needed in the future. Earlyand late-AMD were found to be associated with increased age, but smoking was not associated with any type of AMD in this representative Korean population.

ACKNOWLEDGEMENTS This study was supported in part by a fund from Industry-Academic Cooperation Foundation (5-2013D0383-00002) in Medical College, Catholic University of Korea.

DECLARATION OF INTEREST The authors report no conflicts of interest. No author has a financial or proprietary interest in any material or method mentioned. Current Eye Research

Age-Related Macular Degeneration in Korea

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Prevalence and risk factors for age-related macular degeneration: Korean National Health and Nutrition Examination Survey 2008-2011.

To evaluate the prevalence of and risk factors for age-related macular degeneration (AMD) in a representative Korean population...
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