title: Endotoxin concentration in contact lens storage cases.
abstract: BACKGROUND
  The contamination of contact lens storage cases by gram-negative bacteria has been associated with ulcerative keratitis. This study investigated the concentration of endotoxin, a substance produced by gram-negative bacteria, in contact lens cases.
  
  
  METHODS
  The limulus amebocyte lysate (LAL) test was used to measure the concentration of endotoxin in the storage cases of 27 contact lens wearers. The units of concentration used were endotoxin units per ml (EU/ml). The type of storage solution used by each patient, as well as other aspects of lens care and use, were recorded.
  
  
  RESULTS
  Twenty-one storage cases--78% of those tested--contained measurable amounts of toxin. Two cases contained extremely high concentrations of endotoxin: 60 EU/ml and 300 EU/ml. Both cases were from persons using Opti-Free. Cases from six persons using Opti-Free accounted for five of the top seven endotoxin concentrations when cases were ranked on that basis. Fewer hours of daily lens wear and lower lens age were also possibly associated with higher concentrations of endotoxin, although those associations may have resulted by chance (p = 0.057 and p = 0.095, respectively).
  
  
  CONCLUSIONS
  The LAL test was useful in estimating the degree of contamination of cases by gram-negative bacteria. Most cases contained measurable amounts of endotoxin, indicating at least some contamination by gram-negative bacteria. The effectivity of Opti-Free in inhibition of bacterial growth in contact lens cases should be investigated further.
authors.affiliation: College of Optometry, Northeastern State University, Tahlequah, Oklahoma 74464, USA.
authors.forename: G W
authors.initials: GW
authors.lastname: Fulk
authors.forename: R D
authors.initials: RD
authors.lastname: Davis
authors.forename: M M
authors.initials: MM
authors.lastname: Abbey
mesh_terms: D018441:Biofilms / Q000187:drug effects; D018639:Contact Lens Solutions; D003261:Contact Lenses; D003320:Corneal Ulcer / Q000209:etiology / Q000517:prevention & control; D004731:Endotoxins / Q000032:analysis*; D004866:Equipment Contamination / Q000517:prevention & control; D015818:Eye Infections, Bacterial / Q000382:microbiology / Q000517:prevention & control; D006090:Gram-Negative Bacteria; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology / Q000517:prevention & control; D006801:Humans; D008033:Limulus Test / Q000379:methods; D016459:Prosthesis-Related Infections / Q000382:microbiology / Q000517:prevention & control
chemical_list: D018639:Contact Lens Solutions; D004731:Endotoxins