title: Distribution and associated factors of optic disc diameter and cup-to-disc ratio in an elderly Chinese population.
abstract: BACKGROUND
  Glaucoma is the second leading cause of blindness worldwide and East Asian people account for almost half of those affected. Vertical elongation of the optic cup is a characteristic feature of glaucoma. However, there is a significant overlap in the vertical cup-to-disc ratio (VCDR) between normal eyes and eyes affected by glaucoma. The purpose of this study was to determine the distribution of VCDR and vertical disc diameter (VDD) and their predictive factors in a population of elderly Chinese residents in Taiwan.
  
  
  METHODS
  Four hundred and sixty elderly Chinese residents aged 72 years and older in the Shihpai district, Taipei, Taiwan participated in this study. Slit lamp biomicroscopic measurement of the VCDR and VDD after pupil dilation with a 78 diopter lens was performed by one glaucoma specialist. Multiple linear regression analyses were used to fit the best model for independent variables.
  
  
  RESULTS
  The VCDR was recorded for 438 right eyes and 430 left eyes. After excluding participants with glaucoma, the mean ± SD VCDR was 0.44 ± 0.17 for both eyes, and the 97.5(th) percentile was 0.8. A greater VCDR was associated with a longer axial length [VCDR = -0.47 + 0.04(axial length)] under multiple regression analysis. The VDD was obtained for 420 right eyes and 406 left eyes. The mean ± SD VDD for all participants was 1.77 ± 0.22 mm for the right eye and 1.79 ± 0.22 mm for the left eye. A higher body mass index (BMI) and a longer axial length were significantly associated with a larger VDD under multiple regression analysis. [VDD = -0.05 + 0.07 (axial length) + 0.06 (obesity); if BMI <24, then obesity = 0; if BMI ≥ 24, then obesity = 1]. A larger VDD was associated with a larger VCDR (p < 0.001) and the VCDR could be predicted by the equation VCDR = -0.07 + 0.3VDD.
  
  
  CONCLUSIONS
  A greater VCDR was related to a longer axial length. A greater VDD was related to a higher BMI and a longer axial length.
authors.affiliation: Department of Ophthalmology, Taipei Veterans General Hospital, Taipei, Taiwan, ROC; School of Medicine, National Yang-Ming University, Taipei, Taiwan, ROC; Community Medicine Research Center and Institute of Public Health, National Yang-Ming University, Taipei, Taiwan, ROC.
authors.forename: Tung-Mei
authors.initials: TM
authors.lastname: Kuang
authors.affiliation: Department of Ophthalmology, Taipei Veterans General Hospital, Taipei, Taiwan, ROC; School of Medicine, National Yang-Ming University, Taipei, Taiwan, ROC.
authors.forename: Catherine Jui-Ling
authors.initials: CJ
authors.lastname: Liu
authors.affiliation: Department of Ophthalmology, Taipei Veterans General Hospital, Taipei, Taiwan, ROC; School of Medicine, National Yang-Ming University, Taipei, Taiwan, ROC.
authors.forename: Yu-Chieh
authors.initials: YC
authors.lastname: Ko
authors.affiliation: Department of Ophthalmology, Taipei Veterans General Hospital, Taipei, Taiwan, ROC; School of Medicine, National Yang-Ming University, Taipei, Taiwan, ROC.
authors.forename: Shui-Mei
authors.initials: SM
authors.lastname: Lee
authors.affiliation: Department of Ophthalmology, Taipei Veterans General Hospital, Taipei, Taiwan, ROC; School of Medicine, National Yang-Ming University, Taipei, Taiwan, ROC.
authors.forename: Ching-Yu
authors.initials: CY
authors.lastname: Cheng
authors.affiliation: Community Medicine Research Center and Institute of Public Health, National Yang-Ming University, Taipei, Taiwan, ROC. Electronic address: pschou@ym.edu.tw.
authors.forename: Pesus
authors.initials: P
authors.lastname: Chou
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D044466:Asian People; D015992:Body Mass Index; D005260:Female; D005901:Glaucoma / Q000175:diagnosis*; D006801:Humans; D008297:Male; D009898:Optic Disk / Q000033:anatomy & histology*; D013624:Taiwan
keywords: Chinese population; elderly patients; vertical cup-to-disc ratio; vertical disc diameter