Microbial colonization in lens cases may act as a reservoir for microbes that cause microbial keratitis, increasing the chance of transmission of the microbes to lenses and ultimately to the ocular surface (Vermeltfoort et al, 2008; Szczotka-Flynn et al, 2010). Increased contamination of lens cases is associated with contact lens-induced infiltrative events (Willcox and Holden, 2001) as well as with contact lens-induced ocular discomfort, dryness, and ocular injection (Midelfart et al, 1996).

Antimicrobial lens cases have been developed using several antimicrobial agents such as silver, selenium, and silica (Bôas et al, 2018; Amos and George, 2006) to reduce lens case contamination. In vitro, antimicrobial lens cases reduce contamination against a broad range of microbial species (Bôas et al, 2018; Amos and George, 2006; Qu et al, 2013; Dantam et al, 2011; and others. Full list available at www.clspectrum.com/references .). Lens cases impregnated with silver have demonstrated robust antimicrobial activity against both International Organization for Standardization reference strains of microbes and clinical strains of Gram-positive and -negative bacteria (Bôas et al, 2018; Qu et al, 2013). Silver ions kill bacteria using multiple mechanisms that may reduce resistance to the ions and offer a supplementary advantage compared to other systems (Cavicchioli et al, 2010; Sambhy et al, 2006; Dallas et al, 2011). Compared to non-silver cases, silver lens storage cases reduce the rate and quantity of organisms.

The Studies

Flat case designs have been previously evaluated; however, barrel case designs have not. One study examined the rate and level of microbial contamination of silver-impregnated and non-silver (control) barrel lens storage cases in vivo used in conjunction with the respective multipurpose disinfection solution over a two-month period (Datta et al, 2020). The frequency, type, and level of microbial contamination was evaluated from collected lens cases using viable culture and standard identification methods. Participants’ lens-related hygiene compliance was evaluated with questionnaires.

Of the 48 daily wear lens wearers who completed the study, 27% of silver and 35% of control lens cases (P > 0.05) were contaminated, primarily with Gram-positive bacteria. The overall rate of microbial contamination of the silver barrel lens cases was 27%. This is consistent with prior studies with a commercially available silver lens case, in which 26% to 38% were contaminated (Amos and George, 2006). Compared to prior studies with different combinations of silver cases and multipurpose solutions, the frequency of Gram-positive bacteria, predominantly coagulase-negative staphylococci, in both silver and control barrel lens cases was significantly lower (Amos and George, 2006). No Pseudomonas aeruginosa nor Serratia marcescens (Gram-negative pathogenic bacteria often isolated from cases of those who have microbial keratitis) were recovered from lens cases (McLaughlin-Borlace et al, 1998; Jalbert et al, 2000; Stapleton et al, 2007). Note that lens cases were not screened for Acanthamoeba.

Hydrogel lenses were associated with higher levels of contamination in silver lens cases compared to silicone hydrogel lenses. The authors proposed that hydrogel lenses may take up silver and sequester it away from microbes. Because bacteria are food for Acanthamoeba, this finding may be associated with the increased risk of Acanthamoeba keratitis with certain disinfecting solution and Group IV lenses (Carnt et al, 2018). This study demonstrated that barrel cases can decrease the overall rate and level of bacterial contamination. Future research is needed to validate whether the use of silver-impregnated barrel cases can lower the rate of adverse events during lens wear. CLS

For references, please visit www.clspectrum.com/references and click on document #300.