Primary Open-Angle Glaucoma in a Population Associated with High Prevalence of Primary Angle-Closure Glaucoma The Kumejima Study Shunichi Yamamoto, MD, 1 Shoichi Sawaguchi, MD, PhD, 1 Aiko Iwase, MD, PhD, 2 Tetsuya Yamamoto, MD, PhD, 3 Haruki Abe, MD, PhD, 4 Goji Tomita, MD, PhD, 5 Atsuo Tomidokoro, MD, PhD, 6 Makoto Araie, MD, PhD 6,7 Purpose: To evaluate the prevalence of and risk factors for primary open-angle glaucoma (POAG) in a rural population of southwestern Japan. Design: Population-based cross-sectional study. Participants: All residents 40 years of age and older in Kumejima, Okinawa, Japan. Methods: Of the eligible 4632 residents 40 years of age and older, 3762 subjects (participant rate, 81.2%) underwent screening examinations, including visual acuity (VA) measurement, slit-lamp examination, Goldmann applanation tonometry, gonioscopy, undilated stereoscopic fundus photographs, autorefractometry, noncontact specular microscopy, pachymetry, and visual field (VF) testing using frequency-doubling technology. If glaucoma or other related ocular disorders were suspected, subjects were referred for definitive examinations including VF testing with the Humphrey Field Analyzer. The diagnosis of POAG was based on the criteria of the International Society for Geographical and Epidemiological Ophthalmology. Main Outcome Measures: Prevalence and risk factors of POAG. Results: The prevalence of POAG was 4.0% (95% confidence interval [CI], 3.4%e4.7%); 82% of patients had an intraocular pressure (IOP) less than 22 mmHg, resulting in a prevalence of 3.3% (95% CI, 2.8%e3.9%). Because of POAG, 3 subjects had a VA worse than 20/400 in only 1 eye, and 1 subject had VA loss of worse than 20/400 bilaterally. The average IOP values (mean  standard deviation) were 14.93.2 and 14.63.3 mmHg in the right and left eyes, respectively; the IOP values were higher in patients with POAG (15.43.3 and 15.23.3 mmHg, respectively) than in subjects without glaucoma (14.83.1 and 14.43.1 mmHg, respectively; P<0.045, Student t test). Multivariate analysis showed that male gender (P ¼ 0.003), older age (P<0.001), higher IOP (P<0.001), longer axial length (P<0.001), and thinner central cornea (P ¼ 0.006) were associated with POAG. Conclusions: High prevalence rates of POAG (4.0%) and POAG with normal IOP levels (3.3%), which were comparable with those on the Japanese mainland, were found in a southwestern rural island of Japan, where the prevalence of primary angle-closure glaucoma (previously reported as 2.2%) was considerably higher than on the Japanese mainland (0.6% in the Tajimi Study) or other countries. The risk factors for POAG included male gender, older age, higher IOP, myopia, and a thinner cornea. Ophthalmology 2014;-:1e8 ª 2014 by the American Academy of Ophthalmology. Glaucoma is a leading cause of visual impairment world- wide. 1,2 Primary open-angle glaucoma (POAG) is the most common type of glaucoma in many population-based stud- ies, 3e24 although the prevalence rates differ among studies from a low of 0.5% 6 to very high at 8.8%. 10 Racial variations also have been identified, with high prevalence rates in black people and low prevalence rates in Asian and white populations. 25,26 In a population-based study of glaucoma on the main is- land of Japan (the Tajimi study), 27,28 a relatively high prev- alence (3.6%) of POAG with an intraocular pressure (IOP) lower than 22 mmHg (normal-tension glaucoma [NTG]), and relatively low prevalence (0.6%) of primary angle-closure glaucoma (PACG) were estimated. Recently, a similarly high prevalence of NTG (2.7%) was reported in Korea, 22 suggesting that there are common high prevalence rates of POAG with normal IOP in those East Asian countries. However, more recently, a high prevalence (2.2%) of PACG was estimated in a population-based study per- formed in Kumejima, a rural southwestern island of Japan. 29 Ethnic or genetic differences between the Japanese mainland and the southwestern islands and differences in refractive 1 Ó 2014 by the American Academy of Ophthalmology ISSN 0161-6420/14/$ - see front matter Published by Elsevier Inc. http://dx.doi.org/10.1016/j.ophtha.2014.03.003