title: Microbial contamination of contact lenses, lens care solutions, and their accessories: a literature review.
abstract: OBJECTIVE
  A contact lens (CL) can act as a vector for microorganisms to adhere to and transfer to the ocular surface. Commensal microorganisms that uneventfully cohabitate on lid margins and conjunctivae and potential pathogens that are found transiently on the ocular surface can inoculate CLs in vivo. In the presence of reduced tissue resistance, these resident microorganisms or transient pathogens can invade and colonize the cornea or conjunctiva to produce inflammation or infection.
  
  
  METHODS
  The literature was reviewed and used to summarize the findings over the last 30 years on the identification, enumeration, and classification of microorganisms adherent to CLs and their accessories during the course of normal wear and to hypothesize the role that these microorganisms play in CL infection and inflammation.
  
  
  RESULTS
  Lens handling greatly increases the incidence of lens contamination, and the ocular surface has a tremendous ability to destroy organisms. However, even when removed aseptically from the eye, more than half of lenses are found to harbor microorganisms, almost exclusively bacteria. Coagulase-negative Staphylococci are most commonly cultured from worn lenses; however, approximately 10% of lenses harbor Gram-negative and highly pathogenic species, even in asymptomatic subjects. In storage cases, the incidence of positive microbial bioburden is also typically greater than 50%. All types of care solutions can become contaminated, including up to 30% of preserved products.
  
  
  CONCLUSIONS
  The process of CL-related microbial keratitis and inflammation is thought to be preceded by the presence or transfer or both of microorganisms from the lens to the ocular surface. Thus, this detailed understanding of lens-related bioburden is important in the understanding of factors associated with infectious and inflammatory complications. Promising mechanisms to prevent bacterial colonization on lenses and lens cases are forthcoming, which may decrease the incidence of microbially driven CL complications.
authors.affiliation: Departmentsof Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, Ohio, USA. loretta.szczotka@uhhospitals.org
authors.forename: Loretta B
authors.initials: LB
authors.lastname: Szczotka-Flynn
authors.forename: Eric
authors.initials: E
authors.lastname: Pearlman
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Ghannoum
mesh_terms: D001419:Bacteria / Q000302:isolation & purification; D018441:Biofilms; D018639:Contact Lens Solutions; D003261:Contact Lenses / Q000382:microbiology*; D004340:Drug Contamination; D004866:Equipment Contamination / Q000517:prevention & control; D005123:Eye / Q000382:microbiology; D006090:Gram-Negative Bacteria / Q000302:isolation & purification; D006801:Humans; D007634:Keratitis / Q000209:etiology / Q000382:microbiology; D054158:Orthokeratologic Procedures / Q000009:adverse effects; D013210:Staphylococcus / Q000302:isolation & purification
chemical_list: D018639:Contact Lens Solutions