title: Material properties that predict preservative uptake for silicone hydrogel contact lenses.
abstract: OBJECTIVE
  To assess material properties that affect preservative uptake by silicone hydrogel lenses.
  
  
  METHODS
  We evaluated the water content (using differential scanning calorimetry), effective pore size (using probe penetration), and preservative uptake (using high-performance liquid chromatography with spectrophotometric detection) of silicone and conventional hydrogel soft contact lenses.
  
  
  RESULTS
  Lenses grouped similarly based on freezable water content as they did based on total water content. Evaluation of the effective pore size highlighted potential differences between the surface-treated and non-surface-treated materials. The water content of the lens materials and ionic charge are associated with the degree of preservative uptake.
  
  
  CONCLUSIONS
  The current grouping system for testing contact lens-solution interactions separates all silicone hydrogels from conventional hydrogel contact lenses. However, not all silicone hydrogel lenses interact similarly with the same contact lens solution. Based upon the results of our research, we propose that the same material characteristics used to group conventional hydrogel lenses, water content and ionic charge, can also be used to predict uptake of hydrophilic preservatives for silicone hydrogel lenses. In addition, the hydrophobicity of silicone hydrogel contact lenses, although not investigated here, is a unique contact lens material property that should be evaluated for the uptake of relatively hydrophobic preservatives and tear components.
authors.affiliation: Division of Ophthalmic, Neurological and Ear, Nose and Throat Devices, Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, United States Food and Drug Administration, Silver Spring, MD, USA.
authors.forename: J Angelo
authors.initials: JA
authors.lastname: Green
authors.forename: K Scott
authors.initials: KS
authors.lastname: Phillips
authors.forename: Victoria M
authors.initials: VM
authors.lastname: Hitchins
authors.forename: Anne D
authors.initials: AD
authors.lastname: Lucas
authors.forename: Megan E
authors.initials: ME
authors.lastname: Shoff
authors.forename: Joseph C
authors.initials: JC
authors.lastname: Hutter
authors.forename: Eva M
authors.initials: EM
authors.lastname: Rorer
authors.forename: Malvina B
authors.initials: MB
authors.lastname: Eydelman
mesh_terms: D003263:Contact Lenses, Hydrophilic; D020100:Hydrogels / Q000737:chemistry*; D008422:Materials Testing; D010539:Permeability; D011310:Preservatives, Pharmaceutical / Q000032:analysis / Q000737:chemistry*; D012828:Silicones / Q000737:chemistry*; D014867:Water / Q000032:analysis
chemical_list: D020100:Hydrogels; D011310:Preservatives, Pharmaceutical; D012828:Silicones; D014867:Water