title: Determinants of posterior corneal biometric measurements in a multi-ethnic Asian population.
abstract: OBJECTIVE
  To describe the corneal and anterior segment determinants of posterior corneal arc length (PCAL) and posterior corneal curvature (PCC).
  
  
  METHODS
  Cross-sectional, population-based study of 1069 subjects (1069 eyes) aged 40-80 years, from three major Asian ethnic groups. All underwent anterior segment optical coherence tomography imaging and analysis with Zhongshan Angle Assessment Program. Our main outcome measures were determinants of PCAL and PCC using adjusted, multivariate linear regression analysis, adjusted for confounders to obtain the estimated marginal means (EMM) with standard error (SE).
  
  
  RESULTS
  The overall mean (± SD) of PCC was: 6.51±0.39 mm; and PCAL was: 12.52±0.59 mm. Malays had a relatively longer PCAL (EMM = 12.74 mm, SE = 0.04 mm) than Chinese (EMM = 12.48 mm, SE = 0.03 mm, P<0.001), and Indians (EMM = 12.42 mm, SE = 0.03 mm, P<0.001). Anterior segment parameters had weak-moderate correlations with PCAL, which included: anterior chamber depth (ACD) (r = 0.55, P<0.001), PCC (r = 0.27, P<0.001), anterior corneal curvature (ACC) (r = 0.14, P<0.001) and central corneal thickness (CCT) (r = -0.07, P = 0.023). In multivariate analysis, anterior segment parameters explained only 37.6% of the variance of PCAL, with ACD being the most important determinant (partial R2  = 0.300; P<0.001). The determinants of PCC included ACC, PCAL and CCT (explaining 72.1% variation of PCC), with ACC being the most important determinant (partial R2  = 0.683; P<0.001).
  
  
  CONCLUSIONS
  There was moderate correlation of PCAL with ACD, but anterior segment parameters accounted for only a small proportion of the variation in PCAL. The significant differences in PCAL and PCC amongst different Asian ethnic groups suggests that there is a need to consider this factor when planning for anterior segment surgeries such as endothelial keratoplasty.
authors.affiliation: Singapore National Eye Centre, Singapore, Singapore; Singapore Eye Research Institute, Singapore, Singapore.
authors.forename: Marcus
authors.initials: M
authors.lastname: Ang
authors.affiliation: Singapore National Eye Centre, Singapore, Singapore.
authors.forename: Wesley
authors.initials: W
authors.lastname: Chong
authors.affiliation: Singapore Eye Research Institute, Singapore, Singapore.
authors.forename: Huiqi
authors.initials: H
authors.lastname: Huang
authors.affiliation: Singapore National Eye Centre, Singapore, Singapore; Singapore Eye Research Institute, Singapore, Singapore; Department of Ophthalmology, National University of Singapore, Singapore, Singapore; Office of Clinical Sciences, Duke- National University of Singapore Graduate Medical School, Singapore, Singapore.
authors.forename: Tien Yin
authors.initials: TY
authors.lastname: Wong
authors.affiliation: State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Guangzhou, China.
authors.forename: Ming-Guang
authors.initials: MG
authors.lastname: He
authors.affiliation: Singapore National Eye Centre, Singapore, Singapore; Singapore Eye Research Institute, Singapore, Singapore; Department of Ophthalmology, National University of Singapore, Singapore, Singapore.
authors.forename: Tin
authors.initials: T
authors.lastname: Aung
authors.affiliation: Singapore National Eye Centre, Singapore, Singapore; Singapore Eye Research Institute, Singapore, Singapore; Office of Clinical Sciences, Duke- National University of Singapore Graduate Medical School, Singapore, Singapore.
authors.forename: Jodhbir S
authors.initials: JS
authors.lastname: Mehta
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001699:Biometry; D002681:China / Q000208:ethnology; D003315:Cornea / Q000473:pathology*; D003316:Corneal Diseases / Q000175:diagnosis* / Q000601:surgery; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D007194:India / Q000208:ethnology; D016014:Linear Models; D008296:Malaysia / Q000208:ethnology; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D012846:Singapore; D041623:Tomography, Optical Coherence