Introduction. Tyler H. T. Rim, 1, * Jae S. Nam, 2, * Moonjung Choi, 1 Sung C. Lee 1 and Christopher S. Lee 1. e317. Acta Ophthalmologica 2014

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1 Prevalence and risk factors of visual impairment and blindness in Korea: the Fourth Korea National Health and Nutrition Examination Survey in Tyler H. T. Rim, 1, * Jae S. Nam, 2, * Moonjung Choi, 1 Sung C. Lee 1 and Christopher S. Lee 1 1 Department of Ophthalmology, Institue of Vision Research, Yonsei University College of Medicine, Seoul, Korea 2 Department of Medicine, Yonsei University College of Medicine, Seoul, Korea ABSTRACT. Purpose: To describe the age, gender specific prevalence and risk factors of visual impairment and blindness in Korea. Methods: From 2008 to 2010, a total randomly selected national representative participants of the Korea National Health and Nutrition Examination Survey underwent additional ophthalmologic examinations by the Korean Ophthalmologic Society. Best Corrected Distance Visual Acuity was measured using an international standard vision chart based on Snellen scale (Jin s vision chart). Independent risk factors for visual impairment were investigated using multivariate logistic regression analysis. Results: The overall prevalence of visual impairment ( 20/40) of adults 40 years and older was 4.1% (95% CI, ) based on the better seeing eye. The overall prevalence of blindness ( 20/200) for adults 40 years and older was 0.2% (95% CI, ). Risk indicators of visual impairment were increasing age, low education status, living in rural area, being unemployed, being without spouse and the absence of private health insurance. The visually impaired were more likely to have eye diseases compared with the normal subjects, and they were less likely to utilize eye care. Conclusion: The prevalence of visual impairment was demonstrated to be higher while that of blindness was similar to previous population studies in Asia or U.S. Sociodemographic disparities are present in the prevalence of visual impairment and more targeted efforts are needed to promote vision screening in high risk groups. Key words: blindness Korea National Health and Nutrition Examination Survey risk factors visual impairment Acta Ophthalmol. 2014: 92: e317 e325 ª 2014 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd doi: /aos *These authors contributed equally to this work. Introduction Visual impairment and blindness are important global health issues that exert significant influence not only on the individual s quality of life, but also on the society due to its economic and social impact. Recent estimates by the World Health Organization (WHO) suggest that 285 million people are visually impaired, 121 million of which are due to uncorrected refractive errors and 39 million are blind worldwide. The WHO states that there is a paucity of population-based national data on the prevalence and causes of blindness and visual impairment in developing and undeveloped countries. Such data are essential for planning services for the realization of the goals of VISION 2020: the Global Right to Sight initiative (World Health Organization. Visual impairment and blindness. Available at ness/vision2020_report.pdf Accessed 13 November 2011). Numerous studies have been carried out to study the prevalence and socioeconomic risk factors for blindness and visual impairment across the continents, some of them also investigating the racial and ethnic differences (Munoz & West 2002; Varma et al. 2004; Maberley et al. 2006; Limburg et al. 2008; Yamada et al. 2010). In Asia, several studies have been conducted in Singapore (Saw et al. 2004; Ong et al. 2012), China (Xu et al. 2006a,b) and Japan (Iwano et al. 2004; Nakamura et al. 2010); however, there are limited national epidemiological data for the causes and prevalence of visual impairment and blindness in Asian countries. Previous research in 1971 and 1972 in Korea on eye patients reported prevalence of 4.8% for single eye blindness and 1.9% for blindness in both eyes (BS & BS 1974). Unfortunately, as this research was reported about 40 years e317

2 ago, researchers have yet to conduct a population-based study to accurately define the present state of ocular health in Korea. We investigated the independent risk factors based on a national health survey in Korea: The Fourth Korea National Health and Nutrition Examination Survey (KNHANES IV and V-1), a national representative survey conducted by the Ministry of Health and Welfare that provides data on vision status and sociodemographic factors of about adults aged over 30 years. Over the past several decades, South Korea, as well as other several Asian countries, has experienced rapid socioeconomic growth. Understanding the current status of vision-related socioeconomic disparities is important for the design, implementation and evaluation of programmes intended to reduce these disparities. Therefore, this study aims to report the prevalence of visual impairment and blindness and its association with sociodemographic factors in Korea and to provide useful data for targeted prevention. Materials and Methods Design and study population A detailed description of the sampling, enumeration, visual acuity (VA) and ocular examination procedures has already been published (Yoon et al. 2011). KNHANES IV ( ) was conducted as a national health survey in Korea that used a stratified, multistage, clustered sampling method based on 2005 National Census data to randomly select a population-based sample of individuals across 500 national districts to represent the civilian, noninstitutionalized, South Korean population, and sample design and size were estimated properly so that annual survey results could represent the whole population in Korea. Ophthalmologic interviews and examinations were conducted from July KNHANES V ( ) involved a population-based random sampling of households across 576 national districts (192 each year), which were selected by a panel to represent the South Korean population using a stratified, multistage, clustered sampling method based on 2009 National Resident demographics. All members of each selected household were asked to participate in the survey. KNHANES V-1 refers to the first year (2010) of KNHANES V. Surveys prior to KNHANES IV were able to be analyzed and could be considered a national representative sample after 3 years when the survey was completed, but rolling survey sampling methods were applied from KNHANES IV which allowed annual analysis of national representative sample data possible. All examination and health interviews by trained teams including Ophthalmology residents were conducted in mobile centres while nutrition survey was carried out in household. This survey is aimed to determine the prevalence of the vision status and common eye diseases in a population-based sample in Korea. The ophthalmologic survey was designed to continue for 5 years from July 2008 to This study includes all results of ophthalmologic survey in KNH- ANES IV and V-1 including data from a survey conducted from July 2008 to December During this period, a total of participants were recruited and received an eye examination. Ages of the study participants ranged from 3 to 95 years of age and were men and were women. Of the total participants, over the age of 30 were selected for this study. The participation rates were 74.3% (9308 of the subjects) in 2008, 79.2% ( of the subjects) in 2009, and 77.5% (8473 of the subjects) in VA testing Uncorrected VA and/or Best Corrected Distance Visual Acuity (BCVA) were measured at a distance of 4 m using an international standard vision chart based on Snellen scale (Jin s vision chart, Seoul, Korea; Jin 1997). The participant s VA was measured in each eye, right followed by left with his or her existing refractive correction if he or she had one. The participant was asked to read numbers from 0.2, proceeding to the next line if he or she read more than three letters among five letters correctly. The participant s VA was defined as the line with the smallest numbers in which he or she read more than three characters accurately. Automated refraction was performed in all participants using the autorefractorkeratometer (KR8800; Topcon, Tokyo, Japan), followed by retesting of VA after applying pinhole in patients whose VA was below 0.8 based on Snellen chart. Eye clinic use Subjects aged over 19 years were asked the question when was the last time you had an eye examination by an ophthalmologist? with possible responses of 1 month, >1 month and 1 year, >1 year and 3 years, > 3 years, and never. Definitions based on better or worse seeing eye As there is no worldwide consensus on the definition of visual impairment, we used three definitions of visual impairment and two definitions of blindness based on the VA to allow comparison with other population-based studies (Varma et al. 2004). Visual impairment definition 1: BCVA of 20/40 or worse (including 20/40). This definition of visual impairment has been used in the Beaver Dam Eye Study (Klein et al. 1991) and the Blue Mountain Eye Study (Attebo et al. 1996). Visual impairment definition 2 (U.S. definition): BCVA worse than 20/40 but better than 20/200 (not including 20/40 or >20/200). This definition has been used in the Baltimore Eye Survey (Tielsch et al. 1990), the Barbados Eye Study (Hyman et al. 2001), the Rotterdam Study (Klaver et al. 1998), Proyecto VER (Munoz et al. 2002), and the Salisbury Eye Evaluation (Munoz et al. 2000). Visual impairment definition 3 (WHO definition). BCVA worse than 20/63 but better than or equal to 20/400 (not including 20/63 but including 20/400). This definition has been used by the Baltimore Eye Survey (Tielsch et al. 1990), the Barbados Eye Study (Hyman et al. 2001), the Rotterdam Study (Klaver et al. 1998), and the World Health Organization (Available at: html). Blindness definition 1. BCVA of 20/200 or worse This definition has been used in the United States by different federal e318

3 agencies to define disability caused by blindness, as well as in most population-based studies of eye disease (Tielsch et al. 1990; Klein et al. 1991; Attebo et al. 1996; Klaver et al. 1998; Munoz et al. 2000, 2002; Hyman et al. 2001). Blindness definition 2 (WHO definition). BCVA of worse than 20/400 (not including 20/400) This definition of blindness has been used by the World Health Organization (Available at: inf-fs/en/fact145.html) and in many population-based studies (Tielsch et al. 1990; Attebo et al. 1996; Taylor et al. 1997; Klaver et al. 1998; Munoz et al. 2000; Hyman et al. 2001). Independent variables From the KNHANES IV and V-1 data set, we collected data of various sociodemographic factors, which were obtained through direct interviews using standardized questionnaires. Current age (30 39/40 49/50 59/60 69/70 or older), sex (men/women), monthly household income (lowest quintile/2nd 4th quintile/highest quintile), and highest educational level reached (elementary school graduates or lower/middle school graduates/high school graduates/university graduates or higher). residential area (urban/ rural), occupation (Administrator, Management, Professional/Business and financial operations occupations/ Sales and related occupations/farming, fishing, and forestry occupations/ Installation, maintenance, repair occupation, and technicians/labourer/ Unemployed), having a spouse (living with spouse/living without a spouse), having National Health Insurance (NHI) or Medicaid (NHI/Medicaid) and having Private Health Insurance (PHI; yes/no). Household monthly income was divided into tertiles. Income per adult equivalent was calculated using the formula household income/square root of number of persons in the household (Deaton & Lubotsky 2003). Under the NHI system, almost the entire population have been eligible for medical security (medical insurance and medical aid) in South Korea since In Korea, supplementary PHI usually covers additional medical costs and special medical needs such as hospitalization, heart and brain diseases, and cancer. The term spouse was applied to individuals who were legally married or cohabiting, the term without spouse was applied to single, divorced, or separated individuals. Statistical analysis Basic characteristics of the study population were reported by descriptive statistics. To calculate the weight of KNHANES IV in accordance with the guidelines of the 2005 Census of Korea, poststratification adjustment based on response rates and extraction rate to include the same distribution of 2005 Korean population in sex and age group of 5 years interval was performed. Finally, the sum of the weight of KNHANES IV is equal to the Korean population as of We calculated the weight of KNHANES V-1 in a similar manner based on the 2010 Korean population (in accordance with the 2010 Census of Korea) in regards to sex and age groups at 5-year intervals. Prevalence estimates for all outcomes were performed for the overall sample and then in age and gender stratified groups. Based on weight, the prevalence of visual impairment and blindness in Korea was calculated by age and gender. Data were analyzed using the survey procedure of STATA/SE version 12.1 software (StataCorp, College Station, TX, USA) to account for the sample design and sampling weight, which was adjusted for oversampling, nonresponse, and the Korean population. Multivariate logistic regression analysis was used to determine independent predictive factors for visual impairment. The adjusted odds ratios (aor) and 95% confidence interval (CI) were calculated. To evaluate the eye clinic utilization in subjects with visual impairment, the proportion of eye clinic use in visual impairment group by each definition was evaluated using unadjusted mean and adjusted mean based on linear regression analysis as the last visit to the eye clinic being <1 year, or ever been seen by an ophthalmologist. To evaluate the eye disease in subject with visual impairment, adjusted proportion of eye disease were calculated using multiple linear regression after adjusting for age, gender, household monthly income, education, residential area, occupation, spouse, and insurance status. All statistical tests were two-sided at 95% CI and were performed using the STATA/SE 12.1 software (StataCorp). Results Study population The mean age of the participants over 30 years of age was 41.1 (Standard error 14.3) years (Table 1). 43.0% were men, 73.8% were living in urban areas, and 84.1% were living with spouse. Table S3 provides the characteristics of the study population in detail. Prevalence of visual impairment and blindness Table 2 presents the prevalence of visual impairment in the better or worse seeing eyes using visual impairment definitions 1, 2 and 3. The overall prevalences of visual impairment in adults 40 years and older were 4.1% (95% CI, ) when categorized with definition (def.) 1 ( 20/40), 1.9% (95% CI, ) with definition 2 (<20/40 and >20/200) and 1.1% (95% CI, ) with definition 3 (<20/63 and 20/400) based on the better-seeing eye. Table 2 also shows the prevalence of blindness in the better or worse seeing eyes using blindness definitions 1 and 2. The overall prevalences of blindness for adults 40 years and older were 0.2% (95% CI, ) when categorized with definition 1 ( 20/200) and 0.2% (95% CI, ) with definition 2 (<20/400). Table S1 lists the prevalence of visual impairment and blindness by age and gender in detail. The prevalences of visual impairment for males 40 years and older were 2.6% (95% CI, ) with definition 1 ( 20/40), 1.2% (95% CI, ) with definition 2 (<20/40 and >20/200) and 0.9% (95% CI, ) with definition 3 (<20/63 and 20/ 400) based on the better seeing eye. The prevalences of visual impairment for women 40 years and older were 5.4% (95% CI, ) with definition 1 ( 20/40), 2.5% (95% CI, ) with definition 2 (<20/40 and >20/200) and 1.4% (95% CI, ) with definition 3(<20/63 and 20/400) based on the better-seeing eye. The overall prevalences of blindness for men 40 years and older were 0.1% e319

4 Table 1. Characteristics of study population (n = ). Number Sociodemographic factors Age Sex Men Women Monthly house income Lowest quintile nd 4th quintile Highest quintile Education Elementary school Middle school High school University or higher Residential area Urban Rural Occupation Administrator, management, professional Business and financial operations occupations Sales and related occupations Farming, fishing and forestry occupations Installation, maintenance and repair occupations/technicians Labourer Unemployed Spouse With Without NHI/Medicaid NHI Medicaid PHI Yes No NHI = National Health Insurance; PHI = Private Health Insurance. Percentage (95% CI, ) when categorized with definition 1 ( 20/200) and 0.1% (95% CI, ) with definition 2 (<20/400). Those for women 40 years and older were 0.3% (95% CI, ) when categorized with definition 1 ( 20/200) and 0.2% (95% CI, ) with definition 2 (<20/400). Factors associated with visual impairment and blindness In multivariate analysis of sociodemographic factors and health status risk factors in relation to visual impairment by definition 1, subjects who were age 60+ (aor = 7.5; 95% CI, ) were more likely to have visual impairment than those between 30 and 39 years as a reference group. Subjects who graduated middle school (aor = 0.6, 95% CI, ), high school (aor = 0.6, 95% CI, ), or university or other higher education institute (aor = 0.4, 95% CI, ) were less likely to have visual impairment compared with subjects whose maximum education reached was at most elementary school level. Subjects living in rural area were more likely to have visual impairment (aor = 2.0; 95% CI, ), and adults without aspouse(aor= 2.1; 95% CI, ) were more likely to be visually impaired than those with a spouse. Subjects without private health insurance (aor = 2.3, 95% CI, ) were also associated with increased prevalence of visual impairment. Table S2 Table 2. The prevalence of visual impairment and blindness in the better and worse seeing eye by each definition* (n = ). Visual impairment def. 1 ( 20/40) Visual impairment def. 2 (<20/40 and >20/200) Visual impairment def. 3 (<20/63 and 20/400) Blindness def. 1 (<20/200) Blindness def. 2 (<20/400) Age Total n (%) 95% CI n (%) 95% CI n (%) 95% CI n (%) 95% CI n (%) 95% CI Based on better seeing eye (3.1) (1.4) (0.9) (0.2) (0.1) (4.1) (1.9) (1.1) (0.2) (0.2) (6.3) (2.9) (1.7) (0.3) (0.3) (11.2) (5.1) (3.0) (0.5) (0.4) Based on worse seeing eye (7.3) (3.3) (2.2) (1.7) (1.4) (9.4) (4.2) (2.8) (2.1) (1.8) (13.8) (6.3) (4.2) (3.0) (2.5) (23.0) (10.2) (6.6) (4.8) (4.2) VA = visual acuity. * Visual impairment definition 1. Best-corrected VA of 20/40 or worse in the better seeing eye (including 20/40); Visual impairment definition 2. Bestcorrected VA worse than 20/40 but better than 20/200 (not including 020/40 or 20/200); Visual impairment definition 3. Best-corrected VA worse than 20/63 but better than or equal to 20/400 (not including 20/63 but including 20/400) Blindness definition 1. Best-corrected VA of 20/200 or worse in the better seeing eye; Blindness definition 2. Best-corrected VA of worse than 20/400 in the better seeing eye (not including 20/400). e320

5 provides the results of univariate and multivariate logistic regression analysis in detail. In univariate logistic regression, subjects of ages 60 years or older (OR = 9.8, 95% CI, ) were more likely to have blindness than those between 30 and 39 years as a reference group. Subjects living in rural areas were also more likely to have blindness (OR = 1.9, 95% CI, ), as were subjects without an occupation (OR = 9.4, 95% CI, ). Additionally, subjects without private health insurance were also more likely to have blindness (OR = 7.8, 95% CI, ). While patients who finished their college education did not have blindness, middle school only graduates (OR = 0.2, 95% CI, ) had a higher prevalence of blindness than high school only graduates (OR = 0.1, 95% CI, ), indicating that low education level is likely to be associated with increases in the prevalence of blindness. Eye clinic use The rate of visiting an eye clinic within the past year among the visual impairment group ranged from 23.8% to 30.6% (Fig. 1A). The rate of visiting an eye clinic ever in visual impairment group ranged from 71.7% to 77.0% Fig. 1B). Ocular comorbidities in subjects with visual impairment Eye diseases in subjects with visual impairment (def. 1) were investigated (Fig. 2). They were more likely to have anisometropia (17.2% vs. 4.8% of the normal subjects), and other diseases such as strabismus (4.8% vs. 1.1%), ptosis (16.1% vs. 9.0%), cataract (65.6% vs. 26.6%), age-related macular degeneration (ARMD; 14.4% vs. 10.8%), diabetic retinopathy (DMR; 30.8% vs. 13.3%) than the normal subjects. Subjects with more than three coexisting diseases were 27.3% compared with 11.3% of normal group. Multivariate analysis after adjusting for sociodemographic factors of eye (A) (B) Fig. 1. Eye clinic use in the visually impaired by each definition after adjusting age, sex, monthly house income, education, residential area, occupation, spouse, national insurance and private insurance status. *p < Fig. 2. Eye diseases in patients with visual impairment by definition 1 (BCVA of 20/40 or worse, including 20/40). *p < RE, refractive error; ARMD, age-related macular degeneration; DMR, diabetic retinopathy; BCVA, Best Corrected Distance Visual Acuity. e321

6 diseases contributing to visual impairment revealed that myopia (aor = 5.2, 95% CI, ) is most closely associated with visual impairment statistically, followed by cataract (aor = 3.7, 95% CI, ), anisometropia (aor = 2.3, 95% CI, ), strabismus (aor = 2.1, 95% CI, ), ptosis (aor = 1.7, 95% CI, ), and ARMD (aor = 1.3, 95% CI, ) in decreasing order. In multivariate analysis including DMR, patients with DMR were more likely to have visual impairment (aor = 2.4, 95% CI, ), compared to those without DMR, in subjects who had diabetes mellitus. Discussion The prevalence of visual impairment and blindness The prevalence of visual impairment was demonstrated to be higher, while that of blindness was similar to previous population studies performed in Asia or United States. The prevalence estimates of visual impairment in the better seeing eyes based on US definition 1 ( 20/40) in Koreans over 30 years of age was 3.1% (95% CI, ) and that of blindness definition 1 ( 20/200) in the better seeing eye was 0.2% (95% CI, ). Those of over 40 years of age were 4.1% (95% CI, ) and 0.2% (95% CI, ), respectively. Tables 3 and 4 compares the prevalence of visual Table 3. Prevalence of visual impairment in population-based studies. Year Study and population Number, age Definition of visual impairment Prevalence (%) Kumejima study (Nakamura et al. 2010) 4632, 40 years <20/63, 20/ Rural southwest island, Japan; Nakamura et al. 2010) NILS-LSA* (Japan; Iwano et al. 2004) 2263, years 20/ <20/40, >20/ <20/63, 20/ The Beijing Eye Study (China; Xu et al. 2006a,b) 4439, 40 years 20/ <20/40, >20/200 <20/63, 20/ Los Angeles Latino Eye Study (Varma et al. 2004) 6357, 40 years 20/ <20/40, >20/ <20/63, 20/ Singapore Indian eye study (Zheng et al. 2011) 3400, 40 years <20/40, >20/ Baltimore, US (White; Tielsch et al. 1990) 2911, 40 years 20/ <20/40, >20/ <20/63, 20/ KNHANES (Korea) , 30 years 20/ , 40 years 20/ , 40 years <20/40, >20/ , 40 years <20/63, 20/ Baltimore, US (Black; Tielsch et al. 1990) 2389, 40 years 20/ <20/40, >20/ <20/63, 20/ NHANES, US 5501, 40 years 20/ (corrected VA) , 12 years 20/ (uncorrected VA) * NILS-LSA = National Institute for Longevity Science-Longitudinal Study of Aging; KNHANES = Korea National Health and Nutrition Examination Survey; VA = visual acuity. Table 4. Prevalence of blindness in population-based studies. Year Study and location Number, age Definition of blindness Prevalence (%) NLIS-LSA (Japan; Iwano et al. 2004) 2263, years 20/ <20/ The Beijing Eye Study (China; Munoz et al. 2000; Ross et al. 2006) 4439, 40 years 20/ <20/ KNHANES (Korea) , 30 years 20/ , 40 years 20/ , 40 years <20/ Singapore Indian eye study (Zheng et al. 2011) 3400, 40 years 20/ Los Angeles Latino Eye Study (Varma et al. 2004) 6357, 40 years 20/ <20/ Baltimore study (White; Tielsch et al. 1990) 2911, 40 years 20/ <20/ Baltimore study (Black; Tielsch et al. 1990) 2389, 40 years 20/ <20/ KNHANES = Korea National Health and Nutrition Examination Survey. e322

7 impairment and blindness in Korea to the previous population based studies performed in Asia and United States. To compare the prevalence rates to other nations, one must consider the difference in definition of visual impairment and blindness, device used for refraction to achieve Best Corrected VA and age distribution of the population. The percentage of elderly over 70 and over 60 in this study was 15.8% and 34.7%, respectively, while those of LALES (Latinos, U.S.) were 11.8% and 31.3% (Varma et al. 2004). In National Institute for Longevity Science-Longitudinal Study of Aging (Japan), 1134 of 2263 (50.1%) were male participants, which differed in gender composition compared with KNHANES, in which 43.0% of the participants were men (Iwano et al. 2004). Despite these factors, the prevalence of visual impairment in Korea was higher than that of other Asian countries and United States, while that of blindness was similar. In terms of the WHO definition, the prevalence of blindness (based on definition 2, <20/400) in adults aged of 50 years or older in Korea was 0.3%, while that of United States was 0.4% and that of China/Mongolia was 2.3% according to Global data on visual impairment in the year 2002, which was published by WHO (Resnikoff et al. 2004). The overall prevalence of visual impairment (based on definition 3) in Korea was 0.9% in adults aged of 30 years or older, while that of United States was 1.2%, China/Mongolia 1.9% and four other Asian countries (Indonesia, Malaysia, Philippines and Thailand) 2.4%. The prevalence of blindness (based on definition 2) was 0.2% in Korea, while that of United States was 0.2%, China/Mongolia 0.6%, four Asian countries listed above 1.0% according to Global data on visual impairment in the year In 1971 and 1972, prevalence of 4.8% for single eye blindness and 1.9% for blindness in both eyes (based on blindness def. 1; <20/200, better seeing eye; BS & BS 1974) in patients with eye disease from 17 hospitals in Korea, a higher prevalence rate of blindness compared with national research in Korea from 2008 to Nevertheless, it has been about 40 years because this research was conducted and with the fact that the research was not a national population-based study, it is hard to simply compare the prevalence of blindness in these earlier studies with that of the present study. Risk factors for visual impairment and blindness The risk indicators of visual impairment in Korea and previous population-based studies are summarized in Table 5. Increasing age was the most common independent risk indicator of visual impairment which was statistically significant, followed by lowincome and low educational level. Those who were poor less educated and lacked private health insurance also demonstrated a higher prevalence of visual impairment according to the National Health and Nutrition Examination Surveys (NHANES) performed in the United States, based on the same age and protocol. Unlike this study, female and rural population did not have significant influence on visual impairment in Beijing eye study (Xu et al. 2006a,b), nor did female, household income, diabetes and hypertension in the study conducted in Japan (Iwano et al. 2004). Degree of myopia was found to be a risk factor for visual impairment in studies in Japan and Beijing. In terms of blindness, the results revealed that factors that are associated with blindness and also visual impairment. As this investigation was a crosssectional study, the causal relationship between sociodemographic factors and visual impairment/blindness, whether the sociodemographic disparities are the cause or the consequence of visual impairment/blindness, is not clear. However, the results reveal significant disparities in sociodemographic factors between the visually impaired/blindness and the normal subjects. People of older age, low educational status, living in rural areas, unemployment, living without spouse, having no PHI were more likely to have visual impairment. People of older age, low educational status, living in rural areas, unemployment were more likely to have blindness. Among all patients who underwent ophthalmologic examination, this study analyzed patients, as VA was not evaluated in 192 patients. By comparing the two groups, we discovered several sociodemographic factors that likely may have affected the patients whose eye sight was too low to be evaluated, except for the occupation factor. Especially, older age, residing in rural areas, the absence of a spouse, and not Table 5. Independent risk indicators for visual impairment in population-based studies. Risk factor Older age Low education level Unemployment Diabetes mellitus Degree of myopia History of ocular disease Separated (Divorced/Widowed) Rural residents, no PHI Study Los Angeles Latino Eye Study, Singapore Indian eye study Beijing eye study, NILS-LSA (Japan) Beaver Dam eye study, KNHANES (Korea) Singapore Indian eye study, Beijing eye study NILS-LSA (Japan), KNHANES (Korea), NHANES (US) Los Angeles Latino Eye Study, KNHANES (Korea) Los Angeles Latino Eye Study, Singapore Indian eye study NHANES (US) Beijing eye study, NILS-LSA (Japan) Los Angeles Latino Eye Study KNHANES (Korea), Los Angeles Latino Eye Study (only for blindness) KNHANES (Korea), NHANES (US) KNHANES = Korea National Health and Nutrition Examination Survey; NILS-LSA = National Institute for Longevity Science-Longitudinal Study of Aging. e323

8 covered by private health insurance while living in rural areas groups comprised nearly twice as many patients who were unable to undergo VA evaluation (refusal of examination, anophthalmia, or did not know the letters), reflective of poorer eye sight. These results can be explained in relevance to the factors related to visual impairment analyzed above and indicate that patients who are unable to undergo evaluation of VA or with low VA is more likely to be sociodemographically of a lower class. Eye clinic use Figure 1 demonstrates that the frequency of visiting eye clinic of patients with visual impairment based on definition 1 and definition 2 is less than that of people without visual impairment after adjusting for age, sex, monthly house income, education, residential area, occupation, spouse, national insurance and private insurance status. This implies that the patient group of visual impairment itself is a risk factor for visual impairment; the patients with visual impairment by definition 3 visit eye clinic more frequently than patients with visual impairment by definition 1 or 2. This is contrary to eye care utilization in the United States. which tends to have positive correlation with the severity of visual impairment (Lee et al. 2009). Possible explanation for this phenomenon is that mild visual impairment does not cause much discomfort in daily living and therefore the patients feel less need for eye care. Considering that mild visual impairment can eventually progress to become more severe, it is important to intensively screen such patients at risk and provide treatment before the condition becomes irreversible. Not only would this be beneficial for the patient, but it would also save public health care budget by intervening as secondary prevention before the condition requires tertiary prevention. Comorbidity of eye disease in those visually impaired Patients with visual impairment had more anisometropia, strabismus, ptosis, cataract, ARMD, DMR compared to the normal subjects, and 27.3% of patient with VI definition 1 had more than three eye diseases. As this was a cross-sectional study, it is difficult to clarify the causal relationship between ophthalmologic comorbidities and visual impairment. However, the fact that such high percentage of eye diseases was present in those with visual impairment reveal strong association between the two variables and therefore appropriate screening, preventive measures and early treatment of eye diseases may reduce the risk of visual impairment and blindness in Korea. Our study has several limitations. First, several previous researches have shown that differences in income nonreporting are small across levels of employment status, occupation and education (Taira et al. 1997; Ross et al. 2006), and therefore, income nonresponse is unlikely to systematically affect the results of this study. Second, a causal relationship could not be defined because this was a crosssectional study. The prevalence of blindness of Korea was similar to the result of other population based studies, while that of visual impairment was found to be higher. Sociodemographic disparities are present in the prevalence of visual impairment/blindness and subjects with visual impairment were less likely to utilize eye care. Appropriate distribution of sociodemographic resources in treating visual impairment could be promoted by introducing intensive screening of high-risk groups for visual impairment. References Attebo K, Mitchell P & Smith W (1996): Visual acuity and the causes of visual loss in Australia. 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