title: Oxygen permeability of soft contact lenses in different pH, osmolality and buffering solution.
abstract: OBJECTIVE
  To determine the effect of pH, osmolality, and buffering system on the oxygen permeability (Dk) of soft contact lenses.
  
  
  METHODS
  Two hydrogel lenses (nelfilcon A and etafilcon A) and 2 silicone hydrogel lenses (lotrafilcon A and balafilcon A) were used in the study. These lenses were incubated in phosphate-buffered saline (PBS) and borate-buffered saline (BBS) solutions adjusted by 0.8 pH increments to a pH in the range of 5.8-9.0 or in hypotonic (280 mOsmol/kg), isotonic (310 mOsmol/kg) and hypertonic (380 mOsmol/kg) PBS solutions. Polarographic method was used for measuring the Dk and lenses were stacked as 4 layers to correct the boundary effect.
  
  
  RESULTS
  Dk values of all contact lenses measured in BBS solutions were more stable than those in PBS solutions. Especially the etafilcon A lens showed a relative big change compared with other types of contact lenses at the same conditions. When the osmolality of PBS solution increased from hypotonic to hypertonic, Dk of all contact lenses decreased. Variations in Dk existed depending on lens materials, etafilcon A lens was the most affected and nelfilcon A was the least affected by osmolality.
  
  
  CONCLUSIONS
  From the result obtained, it is revealed that Dk of contact lenses is changed by the pH, osmolality, and buffering condition of tear. Thus, Dk of contact lens can be varied by the lens wearers' physiological and/or pathological conditions.
authors.affiliation: Department of Optometry, Seoul National University of Science and Technology, Seoul 139-743, Korea.
authors.forename: Se Eun
authors.initials: SE
authors.lastname: Lee
authors.affiliation: Department of Optometry, Seoul National University of Science and Technology, Seoul 139-743, Korea.
authors.forename: So Ra
authors.initials: SR
authors.lastname: Kim
authors.affiliation: Department of Optometry, Seoul National University of Science and Technology, Seoul 139-743, Korea.
authors.forename: Mijung
authors.initials: M
authors.lastname: Park
keywords: buffer solutions; osmolality; oxygen permeability; pH; soft contact lens