Typical contact lens wearers have poor contact lens case maintenance habits. This leads to up to 80% of cases becoming infected with unwanted microbes (Wu et al, 2010; Panthi et al, 2009). Case contamination frequently results from hand inoculation, which can subsequently lead to contact lens contamination and serious ocular infections, such as microbial keratitis (Dantam et al, 2012; Dutta and Willcox, 2014).
The advent of daily disposable contact lenses has eliminated contact lens storage for about 28% of U.S. contact lens wearers; however, daily disposable contact lenses are not an option for all wearers, and they will likely never be the best modality for every patient (Nichols, 2016).
Therefore, contact lens case innovations are needed to help combat the near certainty that our patients’ cases will become contaminated. One of these technical advances will likely revolve around creating contact lens cases that have their own antimicrobial activities independent of those of care solutions (Amos and George, 2006; Dantam et al, 2012).
Silver-impregnated contact lens cases are currently the only U.S. Food and Drug Administration-cleared antimicrobial cases (Dutta and Willcox, 2014). These contact lens cases continuously release silver cations into solution, which subsequently damage bacterial “nucleic acids, membranes, and cell walls” (Dutta and Willcox, 2014). Silver is effective at killing common gram-negative bacteria (P. aeruginosa and S. marcescens), gram-positive bacteria (S. aureus), and fungi (C. albicans) (Dantam et al, 2011; Dantam et al, 2012; Dutta and Willcox, 2014).
Silver-containing contact lens cases are more effective when stored wet, which is in contrast to conventional lens cases and is a potential advantage for some patients (Dantam et al, 2012). Because silver is continuously released from the case, these lens cases needs to be replaced about monthly to maintain their antimicrobial activities (Dantam et al, 2011).
Tran et al (2016) were the first to report on selenium-containing contact lens cases. Their preliminary research tested the antimicrobial properties of a copolymer called “organoselenium polypropylene,” a material that could easily be made into a safe contact lens case. Selenium is a catalytic molecule that produces superoxide molecules, which also damage bacterial cell membranes (Dutta and Willcox, 2014; Tran et al, 2016). The authors found that the organoselenium polypropylene copolymer was able to produce a nearly 100% reduction in common gram-negative and gram-positive challenge organisms, which is much more effective compared to the silver-containing cases (Tran et al, 2016).
Because selenium is catalytic, when incorporated into a contact lens case, it can theoretically last the life of the case. The authors provide support for this theory with their finding that their copolymer was still highly antimicrobial after eight weeks (Tran et al, 2016). While this product is not yet commercially available, these promising results certainly warrant additional study.
Silver-impregnated lens cases are able to reduce microbial load on contact lens cases. With the recent advent of a selenium-containing copolymer, the next generation of antimicrobial cases is likely on the way (Dutta and Willcox, 2014; Tran et al, 2016).
While there has been limited research on antimicrobial contact lens cases, other substances (e.g., copper, antimicrobial peptides, and hydrophobic polymers) have been utilized to make contact lenses and other medical devices more resistant to microbes, and these materials may also make their way into contact lens cases (Dutta and Willcox, 2014). With that said, more research is needed to determine whether these agents can be made into safe and effective antimicrobial contact lens cases. CLS
For references, please visit www.clspectrum.com/references and click on document #254.
Dr. Pucker is currently an assistant professor at the University of Alabama at Birmingham. He has also received research funding from Alcon. You can reach him at email@example.com.