title: Phosphate concentration in artificial tears.
abstract: BACKGROUND
  Irrigating solutions and eye drops may contain phosphates as part of their buffer system. In the presence of epithelial keratopathy, a high concentration of phosphate favours corneal calcification. Knowledge of the phosphate concentration in artificial tear products helps to prevent this sight-threatening complication. This study gives an overview on the amount of phosphate contained in artificial tears.
  
  
  METHODS
  Fifty-nine samples of commercially available artificial tear preparations were tested. The quantification of phosphate was performed using the molybdate method on a Modular P autoanalyzer.
  
  
  RESULTS
  Twenty-six of 59 (44%) artificial tear products had a phosphate concentration above physiological levels (>1.45 mmol/l). A phosphate concentration above 25 mmol/l was found in nine products (15%), a concentration higher than 50 mmol/l in three (5%).
  
  
  CONCLUSIONS
  Many artificial tear formulations contain unphysiological levels of phosphate, but very high concentrations are found only in a few products. These preparations have the potential to favour the formation of insoluble crystalline calcium phosphate deposits when used on a damaged corneal surface, and should therefore be used cautiously.
authors.affiliation: Department of Ophthalmology, University of Zürich, Zürich, Switzerland. wolfgang.bernauer@hin.ch
authors.forename: W
authors.initials: W
authors.lastname: Bernauer
authors.forename: M A
authors.initials: MA
authors.lastname: Thiel
authors.forename: U M
authors.initials: UM
authors.lastname: Langenauer
authors.forename: K M
authors.initials: KM
authors.lastname: Rentsch
mesh_terms: D001322:Autoanalysis; D009883:Ophthalmic Solutions / Q000737:chemistry*; D010710:Phosphates / Q000032:analysis*
chemical_list: D009883:Ophthalmic Solutions; D010710:Phosphates