title: Bacterial populations on 30-night extended wear silicone hydrogel lenses.
abstract: OBJECTIVE
  Ocular infection and inflammation during hydrogel lens extended wear is often associated with colonization of the lenses with bacteria. This study compares colonization of a high Dk silicone hydrogel contact lens (lotrafilcon A) worn on a 30-night extended wear basis to a low Dk HEMA-based lens (etafilcon A) worn on a 6-night extended wear schedule.
  
  
  METHODS
  The group wearing the low Dk/t soft contact lens (n = 63) replaced their lenses weekly and the group wearing high Dk/t soft contact lenses replaced their lenses monthly (n = 64). Lens allocation was assigned randomly at enrollment. Worn lenses, from one eye only, were collected aseptically and placed in sterile vials. Microbial growth on various media was enumerated and the number of colony forming units (cfu) per lens was calculated in categories of normal ocular microbiota (such as coagulase-negative staphylococci and Propionibacterium spp.) and known ocular pathogens (such as Staphylococcus aureus and gram-negative bacteria). The proportion of samples colonized with these bacteria and the extent of colonization were compared between the two groups. The proportion of sterile lenses was calculated, and the types of bacteria on each lens group were compared.
  
  
  RESULTS
  No differences between the low and high Dk/t Soft contact lens groups were observed in the proportion of lenses colonized by Propionibacterium spp. (48% vs 43%, P = 0.4) or coagulase-negative staphylococci (47% vs 54%, P = 0.2). Similarly, no differences were found for lenses colonized by S. aureus (0% vs 2%, P = 0.1) or gram-negative bacteria (3% vs 2%, P = 0.8). The types of bacteria isolated from the high and low Dk/t lenses were similar. There were no differences in the number of sterile samples (28% vs 27%, P = 0.8) from each group.
  
  
  CONCLUSIONS
  These findings suggest that high Dk/t silicone hydrogel materials are colonized by similar numbers and types of microorganisms during extended wear compared to HEMA-based material. Most lenses were colonized by commensal bacteria during 30-night extended wear with high Dk/t lenses and during 6-night extended wear with low Dk/t lenses. The incidence of sterile samples was the same between the high and low Dk/t soft contact lens groups.
authors.affiliation: Cornea and Contact Lens Research Unit, School of Optometry, University of New South Wales, Sydney, Australia.
authors.forename: L
authors.initials: L
authors.lastname: Keay
authors.forename: M D
authors.initials: MD
authors.lastname: Willcox
authors.forename: D F
authors.initials: DF
authors.lastname: Sweeney
authors.forename: C A
authors.initials: CA
authors.lastname: Morris
authors.forename: N
authors.initials: N
authors.lastname: Harmis
authors.forename: K
authors.initials: K
authors.lastname: Corrigan
authors.forename: B A
authors.initials: BA
authors.lastname: Holden
mesh_terms: D000328:Adult; D001419:Bacteria / Q000254:growth & development* / Q000302:isolation & purification; D015169:Colony Count, Microbial; D003262:Contact Lenses, Extended-Wear / Q000382:microbiology*; D005260:Female; D006801:Humans; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate; D008297:Male; D012826:Silicone Elastomers
chemical_list: D012826:Silicone Elastomers; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate