7 years ago
Friday, 23 January 2009
Attention contact lens wearers!
Have you ever wondered how your contact lens (CL) solution rates in anti-bacterial effectivity when compared to other CL solutions? Or whether the silver impregnation of a CL case enhances the anti-bacterial effectivity of the case? If you have then read on...
All CL wearers are vulnerable to contaminating bacteria regardless of rigorous CL cleaning practices. To minimise the time and tediousness of cleaning CLs, manufacturers of CL solutions have experimented with the ingredients of their solutions and other factors such as composition of CL cases, cleaning techniques and time required to soak CLs in CL solutions. A 2008 study examined the killing effectivity of three multi-purpose CL solutions, and the effectivity of silver impregnations in CL cases. Details of solutions used in this study were given, including their shelf name, manufacturer and active ingredients. However, to make this blog-post non-discriminatory against the different CL solutions on the market, and as you can never be fully certain whether published studies testing products from pharmaceutical companies provide unbiased results, I decided to re-name the CL solutions but include their respective active ingredients. This way you can check to see whether the CL solution you use contains the important active ingredients.
Three different CL solutions (see table below) were tested for their anti-bacterial effectivity. Biofilms (a layer of bacteria which forms on the surface of an object) of bacteria* were grown on CL cases and incubated with each CL solution and 0.9% sodium chloride (a control). Similarly, planktonic bacteria* (bacteria floating freely in solution) were tested by suspending the bacteria in each CL solution. The killing effectivity of both types of bacterial forms were tested. Additionally, the numbers of live and dead bacteria transmitted from CL solution to lens were measured using both bacterial counts and microscopy (fluorescence). The effectivity of silver impregnated CL cases was also tested.
Summary of results: The results showed that:
(1) Solution A had the highest killing effectivity for both biofilm and planktonic bacteria.
(2) The silver impregnation of CL cases with added CL solution increased the killing effectivity of one type of bacteria (Pseudomonas aeruginosa) but not the other.
(3) Solution A transmitted the lowest number of bacteria from solution to CL and silver impregnation of the CL case did not make any difference when solution A was used.
Conclusions: Solution A has the most effective anti-bacterial effectivity as seen in this study. Silver impregnation of CL cases is useful in enhancing anti-bacterial effectivity but is redundant if solution A is used. According to the paper, other researchers have found opposing results however these studies were not carried out in “real-life” conditions ie. other studies carried out their incubations of CLs in CL solution for 7 days as opposed to over-night which is more realistic of a CL wearer.
* Bacteria tested include Staphylococcus aureus and Pseudomonas aeruginosa.
(1) Vermeltfoort PBJ, Hooymans JMM, Busscher HJ and Van der mei HC (2008) Bacterial transmission from lens storage cases to contact lenses - Effects of lens care solutions and silver impregnation of cases. Journal of Biomedical Materials Research part B 87(1) p.237-243.
(2) Image: Wikimedia Commons