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M. D. Willcox, J. Diec, N. Carnt, V. Evans, T. Nadvilath, S. Iskandar, H. Zhu, B. A. Holden; Contact Lens Case Contamination During Daily Wear of a Silicone Hydrogel Lens. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1511.
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For the past 20 year there has been no reduction in the rate of keratitis associated with lens wear. Poor contact lens case hygiene is often reported to predispose to keratitis, but there have been few reports of the contamination of cases during use with silicone hydrogel lenses. This study determined the type and frequency of contamination of contact lens cases during use of a daily wear monthly disposable basis and using various disinfecting solutions.
Contact lens cases were from 160 subjects (N=40 each solution) who wore comfilcon A lenses and had disinfected their lenses using either Aquify (PHMB disinfectant), Optifree Express (Polyquad/Aldox), Optifree Replenish (Polyquad/Aldox) or ClearCare (H2O2). Cases were collected after 1 month of use on two occasions and sampled for the presence or absence of microbes using standard microbiological tests. Microbes were also identified. Differences in the frequency of case contamination and the types of microbes contaminating were tested using logistic regression with robust estimate of variance to adjust for repeated observations of a user.
Overall, 86% of cases were contaminated. Cases were most frequently contaminated with Gram-positive bacteria, followed by Gram-negative bacteria, and then fungi. For overall contamination, cases with Optifree Express were less contaminated (76%) than Aquify (93%; p=0.016). Furthermore, cases with Optifree Express had less Gram-negative contamination (7%) than Aquify (30%; p=0.002), ClearCare 32%; p=0.001), or Optifree Replenish (45%; p<0.001). Frequency of contamination of cases by Gram-positive bacteria or fungi were not different. There were higher numbers of Gram-negative bacteria contaminating cases with Optifree Replenish (63,197 ± 140,652 cfu) than Optifree Express (14 ± 58; p<0.001), ClearCare (14,834 ± 59,642; p=0.001), or Aquify (25,288 ± 106,801; p=0.001).
Contact lens case contamination is very common. However, the type of disinfecting solution used can affect the frequency and type of microbes that contaminate cases.
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