KC Yoon, et al. Prevalence of Eye Disease in South Korea Correction of visual acuity Visual acuity ＜0.8 Ophthalmologic interview Visual acuity Auto-refraction For 5 years or older participants For 19 years or older participants Testing for strabismus & ptosis For 3 years or older participants Slit lamp examination (cataract, pterygium, depth of anterior chamber) ① IOP ≥22 mmHg or ②Suspected glaucoma on fundus examination IOP measurement Fundus photograph without pupil dilatation ① Participants with diabetes mellitus or random blood sugar ≥200 mg or ② Suspected DR on fundus examination or ③ Difficulty in checking the fundus photograph due to media opacity Visual field examination Fundus photograph after pupil dilatation abetic retinopathy and/or difficulty obtaining a fundus photo- graph due to media opacity (Fig. 1). All procedures described above except for fundus photography were performed before pupil dilatation. Examination methods and definition of eye diseases 1) Questionnaire A detailed interviewer-administered questionnaire was ad- ministered for collection of relevant sociodemographic and medical information. Collected data included marital status, education, occupation, current housing status, lifestyle fac- tors (including cigarette smoking history), optical symptoms, systemic medical and surgical history, and family history of eye diseases. 2) Visual acuity Uncorrected visual acuity and/or best-corrected distance visual acuity (BCVA) were measured at a distance of 4 m us- ing an international standard vision chart based on the LogMAR Scale (Jin’s vision chart, Seoul, Korea) [36]. Visual impairment was defined as a BCVA of 0.32 or worse in the best eye. Blindness was defined as BCVA of 0.02 or worse in the right or left eye. 3) Autorefraction An autorefractor-keratometer (KR8800; Topcon, Tokyo, Japan) was used for all measurement of refraction, which were converted to spherical equivalents calculated as the spherical value plus half of the astigmatic value. Myopia was defined as an spherical equivalents of worse than -0.75 diop- ters (D). Hyperopia was defined as spherical equivalents of worse than +1.0 D. Astigmatism was defined as a cylindrical error worse than +0.75 D. Fig. 1. Ophthalmologic ex- amination flowchart for Korea National Health and Nutrition Examination Surveys. IOP = intraocular pressure; DR = diabetic retinopathy. 4) Strabismus Testing for strabismus included the cover-uncover test, prism and alternate cover test, and/or Krimsky test. Strabismus was defined as a manifest or latent ocular deviation at dis- tance or near fixation with or without spectacle correction, esodeviation of 10 or more prism diopters, exodeviation of 15 or more prism diopters, or any vertical deviation. 5) Blepharoptosis Blepharoptosis was defined as presentation of a marginal reflex distance (MRD1) of 2 mm or less. Measurement of MRD1 was performed as follows: Positioned at the physi- cian’s eye level, participants were asked to look straight ahead and relax while focusing at a distance target. Shining the penlight into the participant’s eye, the distance from the corneal light reflex to the upper eyelid margin was measured in millimeters. 6) Slit lamp examination A structured slit-lamp examination (Haag-Streit model BQ-900; Haag-Streit AG, Koeniz, Switzerland) was per- formed by study ophthalmologists. The slit lamp examina- tion was performed for determination of diseases in the ante- rior segment of the eye (e.g., pterygium and cataract) and measurement of the IOP and anterior chamber depth using the Van Herick method [37]. Cataract was defined as a nu- clear, cortical, or posterior subcapsular cataract in at least one eye. Pseudophakic and aphakic eyes were included as oper- ated cataracts for the purpose of statistical analysis. A ptery- gium was defined as a radially oriented fibrovascular lesion crossing over the nasal or temporal limbus. Grading was based on the visibility of the underlying episcleral blood ves- sels [38]. 423