title: Ethnic differences of intraocular pressure and central corneal thickness: the Singapore Epidemiology of Eye Diseases study.
abstract: OBJECTIVE
  To determine the ethnic differences in the distribution of intraocular pressure (IOP) and central corneal thickness (CCT) in a multi-ethnic Asian population by self-reported ethnicity and genetic ancestry.
  
  
  METHODS
  Population-based, cross-sectional study.
  
  
  METHODS
  A total of 10 033 adults (3353 Chinese, 3280 Malays, and 3400 Indians) aged >40 years.
  
  
  METHODS
  Participants underwent standardized systemic and ocular examinations and interviewer-administered questionnaires for risk factor assessment. The IOP readings were obtained by Goldmann applanation tonometry (Haag-Streit, Konig, Switzerland) before pupil dilation. The CCT was measured with ultrasound pachymetry. Genetic ancestry was derived using principal component (PC) analysis. Regression models were used to investigate the association of IOP and CCT with potential risk factors and genetic ancestry.
  
  
  METHODS
  Intraocular pressure and CCT.
  
  
  RESULTS
  After excluding participants with a history of glaucoma surgery or medication, refractive surgery, corneal edema, or corneal dystrophy, IOP and CCT readings were available for 3251 Chinese, 3232 Malays, and 3317 Indians. The mean IOP readings in the Chinese, Malay, and Indian participants were 14.3±3.1, 15.3±3.7, and 15.8±2.9 mmHg, respectively (P < 0.001). The prevalence of participants with IOP ≥21 mmHg was 2.6% in Chinese, 6.2% in Malays, and 4% in Indians (P < 0.001). In the multivariate regression analysis, the Malay and Indian participants on average had 0.81 and 1.43 mmHg higher IOP levels, respectively, than Chinese (P < 0.001). The mean CCT reading was 552.3±33.4 μm in Chinese, 540.9±33.6 μm in Malays, and 540.4±33.6 μm in Indians (P < 0.001). The percentage of participants with CCT <555 μm was 52.8% in Chinese, 68.5% in Malays, and 66.2% in Indians (P < 0.001). The IOP and CCT levels are significantly correlated with genetic ancestry in our South East Asian population.
  
  
  CONCLUSIONS
  Chinese have the thickest CCT but lowest IOP among the 3 major ethnic groups. In addition, there is a higher proportion of Malays with IOP ≥21 mmHg and CCT <555 μm compared with the Chinese or Indians. This disparity across ethnic groups should be taken into account by future studies investigating IOP and CCT as risk factors or diagnostic tests for glaucoma in Asian populations.
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore.
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Chua
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore; Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore and National University Health System, Singapore.
authors.forename: Yih Chung
authors.initials: YC
authors.lastname: Tham
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore; Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore and National University Health System, Singapore.
authors.forename: Jiemin
authors.initials: J
authors.lastname: Liao
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore.
authors.forename: Yingfeng
authors.initials: Y
authors.lastname: Zheng
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore; Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore and National University Health System, Singapore.
authors.forename: Tin
authors.initials: T
authors.lastname: Aung
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore; Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore and National University Health System, Singapore; Duke-National University of Singapore Graduate Medical School, Singapore.
authors.forename: Tien Yin
authors.initials: TY
authors.lastname: Wong
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore; Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore and National University Health System, Singapore; Duke-National University of Singapore Graduate Medical School, Singapore; Saw Swee Hock School of Public Health, National University of Singapore and National University Health System, Singapore. Electronic address: ching-yu_cheng@nuhs.edu.sg.
authors.forename: Ching-Yu
authors.initials: CY
authors.lastname: Cheng
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D044466:Asian People / Q000706:statistics & numerical data*; D002681:China; D003315:Cornea / Q000033:anatomy & histology*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007194:India; D007429:Intraocular Pressure / Q000502:physiology*; D008296:Malaysia; D008297:Male; D008875:Middle Aged; D012044:Regression Analysis