title: Contact lens material characteristics associated with hydrogel lens dehydration.
abstract: OBJECTIVE
  To determine the association between material dehydration and hydrogel contact lens material characteristics, including water content and ionicity.
  
  
  METHODS
  Water content and refractive index data were derived from automated refractometry measurements of worn hydrogel contact lenses of 318 participants in the Contact Lens and Dry Eye Study (CLADES). Dehydration was determined in two ways; as the difference between nominal and measured (1) water content and (2) refractive index. Multiple regression models were used to examine the relation between dehydration and material characteristics, controlling for tear osmolality.
  
  
  RESULTS
  The overall measured and nominal water content values were 52.58 +/- 7.49% and 56.88 +/- 7.81% respectively, while the measured and nominal refractive indices were 1.429 +/- 0.015 and 1.410 +/- 0.017. High water content and ionic hydrogel lens materials were associated with greater dehydration (p < 0.0001 for both) than low water content and non-ionic materials. When dehydration was assessed as the difference in refractive index, only high water content was associated with dehydration (p < 0.0001).
  
  
  CONCLUSIONS
  High water content and ionic characteristics of hydrogel lens materials are associated with hydrogel lens dehydration, with the former being more strongly associated. Such dehydration changes could in turn lead to important clinical ramifications such as reduced oxygen transmissibility, greater lens adherence and reduced tear exchange.
authors.affiliation: The Ohio State University, 320 West Tenth Avenue, Columbus, OH 43210, USA.
authors.forename: Padmapriya
authors.initials: P
authors.lastname: Ramamoorthy
authors.forename: Loraine T
authors.initials: LT
authors.lastname: Sinnott
authors.forename: Jason J
authors.initials: JJ
authors.lastname: Nichols
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D003261:Contact Lenses; D003430:Cross-Sectional Studies; D003890:Desiccation; D005260:Female; D006801:Humans; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate / Q000737:chemistry*; D008297:Male; D009994:Osmolar Concentration; D012029:Refraction, Ocular / Q000502:physiology; D012044:Regression Analysis; D014867:Water / Q000032:analysis*
chemical_list: D014867:Water; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate