title: Potential Importance of Ozone in the Association Between Outdoor Air Pollution and Dry Eye Disease in South Korea.
abstract: OBJECTIVE
  Air pollution is an important public health concern and the ocular surface is continuously exposed to pollutants in outdoor air. Ocular surface abnormalities related to air pollution are thought to be a subtype of dry eye disease (DED). However, to date, there is no large-scale study evaluating an association between air pollution and DED that includes multiple air pollutants.
  
  
  OBJECTIVE
  To investigate associations between outdoor air pollution and DED in a Korean population.
  
  
  METHODS
  A population-based cross-sectional study using data on 16 824 participants in the fifth Korea National Health and Nutrition Examination Survey was conducted from January 1, 2010, to December 31, 2012. Data analysis was conducted from September 1 to 30, 2015. Dry eye disease was defined as previously diagnosed by an ophthalmologist or the presence of frequent ocular pain and discomfort. Outdoor air pollution measurements (mean annual humidity, particulate matter with aerodynamic diameter <10 µm [PM10], ozone, and nitrogen dioxide levels) were collected from 283 national monitoring stations in South Korea.
  
  
  METHODS
  Associations of multiple air pollutants with DED were assessed from multivariable logistic regression analyses. Sociodemographic factors and previously known factors associated with DED were applied as covariates (model 1 controlled for sociodemographic factors and model 2 controlled for sociodemographic, behavioral, and clinical factors).
  
  
  RESULTS
  Among 16 824 participants (7104 men and 9720 women), higher ozone levels and lower humidity levels were significantly associated with symptoms and diagnosis of DED. In model 1, an increase in ozone levels of 0.003 ppm was significantly associated with symptoms and diagnosis of DED (symptoms: odds ratio [OR], 1.16; 95% CI, 1.02-1.30; P = .04; diagnosis: OR, 1.21; 95% CI, 1.05-1.40; P = .008), while a 5% increase in humidity levels was significantly associated with decreased symptoms and diagnoses of DED (symptoms: OR, 0.87; 95% CI, 0.77-0.98; P = .03; diagnosis: OR, 0.86; 95% CI, 0.76-0.97; P = .01). In model 2, an increase in ozone levels of 0.003 ppm was significantly associated with symptoms and diagnosis of DED (symptoms: OR, 1.17; 95% CI, 1.02-1.34; P = .03; diagnosis: OR, 1.27; 95 CI, 1.09-1.48; P = .002), while a 5% increase in humidity levels was significantly associated with decreased symptoms and diagnoses of DED (symptoms: OR, 0.88; 95% CI, 0.78-0.98; P = .045; diagnosis: OR, 0.86; 95% CI, 0.76-0.97; P = .02). In model 2, an increase in nitrogen dioxide of 0.003 ppm (OR, 1.12; 95% CI, 1.02-1.23 P = .02) was also associated with diagnosis of DED. Levels of sulfur dioxide and PM10 were not associated with symptoms or diagnosis of DED in model 1 or model 2 (P > .05 for each).
  
  
  CONCLUSIONS
  Higher ozone levels and lower humidity levels were associated with DED in the Korean population, while PM10 level was not associated with DED.
authors.affiliation: Department of Ophthalmology, Gachon University Gil Medical Center, Incheon, Korea.
authors.forename: Sung Ha
authors.initials: SH
authors.lastname: Hwang
authors.affiliation: Department of Preventive Medicine, Gachon University College of Medicine, Incheon, Korea.
authors.forename: Yoon-Hyeong
authors.initials: YH
authors.lastname: Choi
authors.affiliation: Department of Ophthalmology, Gachon University Gil Medical Center, Incheon, Korea.
authors.forename: Hae Jung
authors.initials: HJ
authors.lastname: Paik
authors.affiliation: Department of Ophthalmology, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Won Ryang
authors.initials: WR
authors.lastname: Wee
authors.affiliation: Department of Ophthalmology, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Mee Kum
authors.initials: MK
authors.lastname: Kim
authors.affiliation: Department of Ophthalmology, Gachon University Gil Medical Center, Incheon, Korea.
authors.forename: Dong Hyun
authors.initials: DH
authors.lastname: Kim