title: Prevalence and risk factors of lens opacities in rural populations living at two different altitudes in China.
abstract: OBJECTIVE
  To investigate the prevalence of and risk factors for lens opacities in populations living at two different altitudes in China.
  
  
  METHODS
  A total of 813 subjects aged ≥40y in Lhasa (Tibet Autonomous Region, China. Altitude: 3658 m) and Shaoxing (Zhejiang Province, China. Altitude: 15 m) were underwent eye examinations and interviewed in this cross-sectional study. Participants' lens opacities were graded according to the Lens Opacities Classification System II (LOCS II) and the types of opacities with LOCS II scores ≥2 were determined. Univariate and stepwise logistic regression were used to evaluate the associations of independent risk factors with lens opacities.
  
  
  RESULTS
  Lens opacities were significantly more prevalent in the high-altitude than in the low-altitude area (χ (2)=10.54, P<0.001). Lens opacities appear to develop earlier in people living at high than at low altitude. The main types of lens opacity in Lhasa and Shaoxing were mixed (23.81%) and cortical (17.87%), respectively. Independent risk factors associated with all lens opacities were age, ultraviolet (UV) radiation exposure, and educational level. Compared with participants aged 40-49y, the risk of lens opacities increased gradually from 2 to 85 times per 10y [odds ratio (OR)=2.168-84.731, P<0.05). The risk of lens opacities was about two times greater in participants with the highest UV exposure than in those with the lowest exposure (OR=2.606, P=0.001). Educational level was inversely associated with lens opacities; literacy deceased the risk by about 25% compared with illiteracy (OR=0.758, P=0.041).
  
  
  CONCLUSIONS
  Old age, higher UV exposure and lower educational level are important risk factors for the development of lens opacities. Lens opacities are more prevalent among high-altitude than low-altitude inhabitants.
authors.affiliation: Department of Ophthalmology, the Fourth Affiliated Hospital of China Medical University, Shenyang 110005, Liaoning Province, China.
authors.forename: Jia-Ming
authors.initials: JM
authors.lastname: Yu
authors.affiliation: Department of Ophthalmology, the Fourth Affiliated Hospital of China Medical University, Shenyang 110005, Liaoning Province, China.
authors.forename: De-Qi
authors.initials: DQ
authors.lastname: Yang
authors.affiliation: Department of Ophthalmology, the Fourth Affiliated Hospital of China Medical University, Shenyang 110005, Liaoning Province, China.
authors.forename: Han
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Ophthalmology, the Fourth Affiliated Hospital of China Medical University, Shenyang 110005, Liaoning Province, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Xu
authors.affiliation: Department of Environmental Health, School of Public Health, China Medical University, Shenyang 110122, Liaoning Province, China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Gao
authors.affiliation: Department of Environmental Health, School of Public Health, China Medical University, Shenyang 110122, Liaoning Province, China.
authors.forename: Li-Wen
authors.initials: LW
authors.lastname: Hu
authors.affiliation: Department of Environmental Health, School of Public Health, China Medical University, Shenyang 110122, Liaoning Province, China.
authors.forename: Fang
authors.initials: F
authors.lastname: Wang
authors.affiliation: Department of Environmental Health, School of Public Health, China Medical University, Shenyang 110122, Liaoning Province, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Ophthalmology, the Fourth Affiliated Hospital of China Medical University, Shenyang 110005, Liaoning Province, China.
authors.forename: Qi-Chang
authors.initials: QC
authors.lastname: Yan
authors.affiliation: Department of Ophthalmology, the Fourth Affiliated Hospital of China Medical University, Shenyang 110005, Liaoning Province, China.
authors.forename: Jin-Song
authors.initials: JS
authors.lastname: Zhang
authors.affiliation: Department of Environmental Health, School of Public Health, China Medical University, Shenyang 110122, Liaoning Province, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
keywords: altitude; cataract; lens opacities; risk factor; ultraviolet exposure