Korean J Ophthalmol Vol.25, No.6, 2011 7) Fundus photography A digital nonmydriatic fundus camera (TRC-NW6S, Topcon) and a Nikon D-80 digital camera (Nikon, Tokyo, Japan) were used to obtain the digital fundus images. Digital images were captured from all participants 19 years of age and older under physiological mydriasis. For each partic- ipant, one 45° nonmydriatic digital retinal image centered on the fovea (field 2) was taken per eye (2 images per person in total). Each image was graded twice (a preliminary grade and a detailed grade) using the grading protocol of the International Age-related Maculopathy Epidemiological Study Group [39]. Optic nerve configuration and any retinal pathologic findings were recorded. Patients were defined as having ear- ly AMD if they met any one of the following criteria: (1) the presence of soft indistinct drusen or reticular drusen, or (2) the presence of hard or soft distinct drusen with pigmentary abnormalities (increased pigmentation or hypopigmentation of the retinal pigment epithelium) in the absence of signs of late AMD. Late AMD included the presence of signs of wet AMD or geographic atrophy. Wet AMD was defined as reti- nal pigment epithelial detachment or serous detachment of the sensory retina, subretinal or sub-RPE hemorrhages, and subretinal fibrous scars. Geographic atrophy was defined as a circular discrete area (of 175 microns in diameter) of retinal depigmentation with visible choroidal vessels, in the absence of signs of wet AMD. In participants who had a history of diabetes mellitus or random blood glucose level of 200 mg/dL or higher and/or suspicion of diabetic retinopathy in nonmydriatic fudndus photography, 7 standard photographs from the Early Treatment for Diabetic Retinopathy Study were obtained from each eye after pharmacological pupil dilatation [40,41]. Diabetic ret- inopathy was defined as the presence of 1 or more retinal mi- croaneurysms or retinal blot hemorrhages with or without more severe lesions (hard exudates, soft exudates, intraretinal microvascular abnormalities, venous bleeding, new retinal vessels, and fibroproliferations) [42,43]. The prevalence of diabetic retinopathy was estimated in persons with diabetes mellitus. 8) Visual field test FDT (Humphrey Matrix; Carl Zeiss Meditec Inc., Dublin, CA, USA) testing with the screening program N-30-1 was performed if the participants had elevated IOP ≥22 mmHg or a glaucomatous optic disc. FDT testing was repeated once if deemed unreliable. Patients were defined as having primary open angle glaucoma (POAG) if they met any one of the fol- lowing category I or category II diagnostic criteria [44]. 9) Category I diagnosis The presence of FDT testing results, fixation error and false positive error ≤1: (1) elevated IOP ≥22 mmHg or (2) glaucomatous optic disc (loss of neuroretinal rim with verti- cal or horizontal cup-disc ratio ≥0.6 or presence of optic disc hemorrhage or presence of retinal nerve fiber layer defect or 424 asymmetry of vertical cup-disc ratio ≥0.2), (3) the presence of an abnormal FDT testing result (at least one location of re- duced sensitivity) and (4) the presence of an open angle (peripheral anterior chamber depth >1/4 corneal thickness) 10) Category II diagnosis Absence of FDT testing results or fixation error or false positive error ≥2, (1) the presence of an open angle (peripheral anterior chamber depth >1/4 corneal thickness) and (2) loss of neuroretinal rim with vertical cup-disc ratio ≥0.9, (3) asym- metry of vertical cup-disc ratio ≥0.3 or (4) the presence of retinal nerve fiber layer defect and violation of the ISNT rule. Normal tension glaucoma (NTG) was defined using the same criteria for POAG with IOP ≤21 mmHg. Primary angle closure glaucoma (PACG) was diagnosed when all of the fol- lowing four criteria were met: (1) the presence of a narrow, occludable angle (peripheral anterior chamber depth <1/4 corneal thickness), (2) elevated IOP ≥22 mmHg, (3) glaucom- atous optic disc (loss of neuroretinal rim with vertical or hori- zontal cup-disc ratio ≥0.6 or the presence of optic disc hemor- rhage or retinal nerve fiber layer defect), and (4) the presence of an abnormal FDT testing result (at least one location of re- duced sensitivity) and fixation error, false positive error ≤1. Quality control and data analysis A total of 308 surveys were conducted by four survey teams within a time span of 77 weeks. Each survey team in- cluded one ophthalmologist, one otolaryngologist, one den- tist, three nurses, two interviewers, and one coordinator. The team moved with a mobile examination unit to pre-assigned locations and performed surveys for three days. A total of 199 ophthalmology residents or ophthalmologists from 66 training hospitals participated in this project as ophthalmo- logic examiners. The quality of the survey was verified by the Epidemiologic Survey Committee of the Korean Ophthalmologic Society. Training of participating residents was periodically performed by acting staff members of the National Epidemiologic Survey Committee of the Korean Ophthalmologic Society. Data were collected using a combination of paper and digital formats. Imaging data, including fundus photographs, were retrieved directly from the imaging equipment and stored in their respective computers. All variables of interest were en- tered into a password-protected Microsoft Office Access da- tabase by a data entry clerk. For all digital information, origi- nal data were copied into external hard disks daily and writ- ten onto DVDs for storage. Statistical analyses were performed using SAS ver. 9.2 (SAS Institute, Cary, NC, USA). All estimates were obtained using the sample weight adjusted for oversampling, non- response and the Korean population in 2008 to 2009, and standard errors of estimates were estimated accounting for the complex design of the survey. Prevalence estimates for all outcomes were performed for the overall sample and then