Microbial contamination of hydrophilic contact lenses: quantitation and identification of microorganisms associated with contact lenses while on the eye.

Previous studies have demonstrated the presence of microorganisms on hydrogel contact lenses under various usage conditions. We conducted this study to quantify and identify viable bacteria and fungi associated with hydrogel contact lenses while on the eye. We removed the lenses from patients' eyes using aseptic techniques and cultured them to identify loosely adherent, as well as lens bound, microorganisms. Lenses were vortexed in a transfer medium (thereafter called the lens extract) and the lenses were then incubated in an agar sandwich separately from the transfer medium. We cultured 108 lenses (82 daily wear and 26 extended wear) from 49 patients. Bacteria were cultured from 38% (41) of the lenses; for 31 of these 41 lenses bacteria were isolated only from the lens extracts (made by vortexing lenses in a transfer medium), suggesting a transient association with the lenses. No fungi were isolated. Counts of less than 10 colony forming units (CFU)/lens were observed on 89% of the lenses. Staphylococcus epidermidis were the most frequently isolated bacteria. A statistically significant relation was observed between increased CFU/lens and increased lens age for extended wear lenses (p = 0.028).