title: Free radicals and the pH of topical glaucoma medications: a lifetime of ocular chemical injury?
abstract: BACKGROUND
  Preservatives in ophthalmic preparations are known to cause ocular surface damage. Excipients can also contribute to oxidative stress in the compromised ocular surface. We evaluated commonly used topical glaucoma medications to ascertain pH levels and the intrinsic presence of free radicals.
  
  
  METHODS
  Samples of 27 topical glaucoma preparations were analysed for total free radical presence using a Randox Kit for total antioxidant status. Analytical grade indicator paper was used to ascertain pH levels.
  
  
  RESULTS
  Free radical concentrations for these 27 glaucoma preparations ranged from 0 to 4.54 mmol/l, with a median value of 0.66 mmol/l (mean value of 0.662 mmol/l, SD 0.839). Levels of pH ranged from 4.0 to 7.4, with a median value of 6.5 (mean 6.252, SD 0.826). There was no evidence of a direct correlation between these two variables (r=0.232, P=0.275).
  
  
  CONCLUSIONS
  This study is the first to document the range of pH and concentrations of free radicals intrinsically present in commonly used glaucoma medications. Long-term exposure to preservatives, free radicals, and pH levels could all contribute to ocular surface damage. The effect of excipients could be responsible for patient intolerance when changing products in the compromised ocular surface.
authors.affiliation: Tennent Institute of Ophthalmology, Gartnavel General Hospital, Glasgow, UK. davidlockington@hotmail.com
authors.forename: D
authors.initials: D
authors.lastname: Lockington
authors.forename: E C A
authors.initials: EC
authors.lastname: Macdonald
authors.forename: P
authors.initials: P
authors.lastname: Stewart
authors.forename: D
authors.initials: D
authors.lastname: Young
authors.forename: M
authors.initials: M
authors.lastname: Caslake
authors.forename: K
authors.initials: K
authors.lastname: Ramaesh
mesh_terms: D000287:Administration, Topical; D000959:Antihypertensive Agents / Q000737:chemistry*; D005128:Eye Diseases / Q000139:chemically induced; D005609:Free Radicals / Q000009:adverse effects / Q000032:analysis*; D005901:Glaucoma / Q000188:drug therapy; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009883:Ophthalmic Solutions / Q000737:chemistry*; D011310:Preservatives, Pharmaceutical / Q000737:chemistry; D011933:Reagent Kits, Diagnostic
chemical_list: D000959:Antihypertensive Agents; D005609:Free Radicals; D009883:Ophthalmic Solutions; D011310:Preservatives, Pharmaceutical; D011933:Reagent Kits, Diagnostic