Korean J Ophthalmol Vol.25, No.6, 2011 Epidemiological studies provide information on the pre- vention, treatment, and minimization of the impact of dis- eases on society. In the past two decades, a wide range of epi- demiologic studies in ophthalmology have provided im- portant information on the pattern of visual impairment and the major eye diseases that cause such vision loss [1]. Although several epidemiological studies of several age-re- lated eye diseases (e.g., glaucoma, age-related macular de- generation, and cataract) have been conducted in Korea [2-4], these studies were hospital-based or were conducted primarily in urban areas. Data on the prevalence of diseases based on the number of hospital visits or surveys conducted in limited areas are easy to obtain; however, substantial dif- ferences may exist between such data and that obtained in large-scale population studies, which are more accurate and can represent entire populations. Large-scale population-based studies conducted over the past two decades in many countries, including the United States [5-14], Western Europe [15-17], Australia [18-21], Japan [22-26], Singapore [27-30], and China [31-35], have been used to guide public health policy and plan preventive strategies. However, these studies were conducted mostly with regard to major age-related eye diseases, such as cata- ract, glaucoma, age-related macular degeneration, and dia- betic retinopathy, which are major causes of vision loss. Nation-wide epidemiological studies of all age groups for the prevalence of common eye diseases have not been performed. The Korea Center for Disease Control and Prevention (CDC) conducted a series of Korea National Health and Nutrition Examination Surveys (KNHANES) in 1998, 2001, 2005 and 2007-2009 for examination of the general health and nutrition status of Koreans. As of the fourth KNHANES (2007-2009), an annual total of 4,600 households were se- lected, and the participating household members were inter- viewed regarding health and nutrition and underwent a basic health examination that included blood pressure measure- ments, blood and urine collection, a pulmonary function test, and a dental examination. Since the Korean Ophthalmologic Society has participated in this survey since 2008, oph- thalmologic interviews and examinations were also con- ducted with the same participants. The purpose of this study is to investigate the national prevalence of common eye diseases in South Korea based on the survey data obtained from the KNHANES and to analyze the prevalence of diseases according to age and gender. Data Received: July 18, 2011 Accepted: September 23, 2011 Corresponding Authors: Se Woong Kang, MD, PhD. Department of Ophthalmology, Samsung Medical Center, Sungkyunkwan University School of Medicine, #50 Irwon-dong, Gangnam-gu, Seoul 135-710, Korea. Tel: 82-2-3410-3562, Fax: 82-2-3410-0074, E-mail: swkang@skku.edu. Kyung Won Oh, PhD. Division of Chronic Disease Surveillance, Korea Centers for Disease Control & Prevention, #187 Osongsaengmyeong 2-ro, Gangoe-myeon, Cheongwon 363-951, Korea. Tel: 82-43-719-7460, Fax: 82-43-719-7527, E-mail: kwoh27@korea.kr 422 obtained from KNHANES may offer further insight into the etiology, ethnic differences, and public health impact of the most common eye diseases affecting Korean people living in Asia. Materials and Methods Study design and population The KNHANES is an ongoing population-based, cross- sectional epidemiological survey conducted in South Korea. Annually, 4,000 households in 200 enumeration districts were selected by a panel to represent the civilian, non-in- stitutionalized South Korean population using the stratified, multistage clustered sampling method based on the 2005 National Census Data. In KNHANES, sample design and size are estimated so that annual survey results represent the whole population in Korea. Therefore, annual survey re- sults can be used as statistics to represent the overall Korean population. All members of each selected household were asked to participate in the survey, and the rate of partic- ipation in the past several cycles ranged from 79% to 84%. From July 2008, ophthalmologic interviews and examina- tions have been conducted. All examination and health in- terviews were conducted by trained teams in mobile cen- ters, while nutrition surveys were performed in individual households. This survey is aimed to determine the prevalence of the following vision status and common eye diseases in a pop- ulation-based sample of Koreans: visual impairment and blindness, refractive errors, strabismus, blepharoptosis, cata- ract, pterygium, diabetic retinopathy, age-related macular de- generation (AMD), and glaucoma. The ophthalmologic sur- vey was designed to be conducted over 5 years from 2008 to 2013. The present study includes interim data from a survey conducted from July 2008 to December 2009. Examination procedures Examination procedures were stratified according to age group. Participants aged 3 to 4 years old only underwent test- ing for strabismus and blepharoptosis. Autorefraction and visual acuity testing and testing for strabismus and blephar- optosis were performed among the participants ranging in age from 5 to 18 years old. The participants over 19 years of age underwent full ocular examinations, including autore- fraction and visual acuity testing, testing for strabismus and blepharoptosis, slit lamp examinations, measurement of in- traocular pressure (IOP), and fundus photographs. IOP was measured with a Goldmann applanation tonometer. For par- ticipants meeting the glaucoma suspicion criteria, frequency doubling perimetry (FDT) was carried out. Phamacological pupil dilatation was performed for participants who had a history of diabetes mellitus or random blood glucose level of 200 mg/dL or higher and/or fundus photograph suspected di-