Anti-microbial efficacy of the silver-impregnated contact lens storage cases

Abstract

Microbial keratitis is a serious sight threatening complication of contact lens wear. The pathogenic organisms associated with microbial keratitis have been identified in contact lens storage cases. The contaminated storage cases might act as a reservoir for the microorganisms which could gain access to the ocular surface through contact lens wear. Recently, silver-impregnated storage cases were introduced to limit microbial contamination. This thesis describes in-vitro and in-vivo anti-microbial efficacy of three commercially available silver-impregnated contact lens storage cases, namely i-clean®, MicroBlock and Nano-case®. A reliable test method was developed for comparing the efficacies of these cases against planktonic microorganisms based on a modified version of stand-alone test procedure recommended by ISO 14729 for the testing of contact lens care products. Further, the silver release from these cases has been quantified using inductively-coupled plasma mass spectrometry. The surface activity of these storage cases was investigated by considering their ability to inhibit bacterial biofilm formation, additionally confocal laser scanning microscopy was used to visualise their surfaces for bacterial viability and x-ray photoelectron spectroscopy to detect the presence of silver-ions on their surface. For a comprehensive understanding of the entire lens care system, the performance of these storage cases was tested under the influence of multi-purpose disinfecting solution, contact lenses and organic soil. Based on these observations, in-vivo studies were conducted to evaluate the performance of silver-impregnated cases in use. This thesis demonstrated differences in efficacy of silver-impregnated storage cases against different groups of microorganisms, in their planktonic and sessile form of growth. Further, the use of silver-impregnated cases along with the recommended disinfection system in the presence of contact lenses and organic soil also revealed remarkable differences in their anti-microbial activity. The results from in-vivo studies illustrated decreased levels of microbial recovery with silver-impregnated storage cases, which indicates that their use may add an additional level of safety to contact lens wearers. Further studies are required to establish whether use of such cases might limit the contact lens adverse responses associated with microbial contamination and to determine whether such benefits are maintained in community studies.