Quantitative alterations of the commensal eye bacteria in contact lens wear

A study was performed on the commensal external eye flora in 34 long-term contact lens wearers and a matched control group, in order to identify the effect of lens wear. Samples were taken from the lid margin and conjunctiva by semi-quantitative, and tear film by quantitative methods. Cultured bacteria were identified with particular attention to coagulase-negative staphylococci. No qualitative alteration in the commensal bacteria was found, although lens wearers were found to have a significantly higher number of species at all sites than controls. Significant quantitative changes were identified on the lid margin, with particularly high counts in some lens wearers, and tear film. Increased numbers of bacteria obtained from the conjunctiva were not statistically significant. Quantitative changes in the tear film are thought to be secondary to changes at the lid margin, for which no explanation is apparent.