Bacterial populations on high‐Dk silicone hydrogel contact lenses: effect of length of wear in asymptomatic patients

BACKGROUND: Ocular infection and inflammation during extended wear with hydrogel lenses are often associated with contamination of the lenses with bacteria. This study examines the colonisation of a high-Dk silicone hydrogel contact lens worn on a 30-night extended wear basis (continuous wear) during asymptomatic lens wear. METHODS: Worn lenses were collected aseptically and placed in sterile vials. Microbial growth on various media was enumerated and the number of colony-forming units per whole lens was calculated. The proportions of samples contaminated with the bacteria and the extent of contamination were compared after one month, six months and two years of continuous wear with monthly replacement. The proportion of lenses that were sterile was calculated. RESULTS: The most frequently isolated and most numerous microbes that colonised the contact lenses during wear were the coagulase-negative staphylococci (in particular Staphylococcus epidermidis), followed by Propionibacterium sp. The frequency of isolation of the majority of bacterial isolates did not increase over time. Generally, lenses were sparsely colonised during asymptomatic wear. CONCLUSION: Up to two years continuous wear of silicone hydrogel lenses of the type used in this study does not appear to alter the types and number of bacteria that colonise the eye during wear, when lenses are replaced on a monthly schedule and the patients remain asymptomatic.