CL Case Hygiene: Evidence-based Guidelines & Impact of Care Systems
By Loretta B. Szczotka-Flynn, OD, PhD
Much has been said about lens care systems and how they impact the cleanliness of worn lenses, but less is known about the impact of hygiene practices on lens storage cases. The storage case is very likely the incubator for microorganisms to attach to and proliferate into biofilm, and the lens then acts as a vector to transfer the organisms to the ocular surface. Indeed, the same strain of bacteria isolated in contact lens-associated microbial keratitis has been isolated from the patient's lens storage case (Mayo, 1987).
A literature review revealed that well over half of all lens cases assessed across various studies were microbially contaminated (Szczotka-Flynn, 2010). Most case contamination involves bacteria, and many studies document contamination rates as high as 81%. However, unlike lens contamination which is almost exclusively bacterial, when contamination is detected within storage cases, the microorganisms involved are usually mixed contaminants of bacteria, fungi and protozoa (Clark, 1994; Gray, 1995; Larkin, 1990). Additionally, in those studies that specifically culture for the presence of Acanthamoeba sp., the frequency of isolation is approximately 8 percent (Szczotka-Flynn, 2010).
Biofilms are resistant matrices of microorganisms and secreted polysaccharides that shield bacteria and fungi from host defenses and antimicrobials. They are considered the major culprit in resistant case contamination and it has been shown that biofilm—or even surface attached bacterial cells—established within the lens case are more resistant (compared to free-floating planktonic cells) to the biocide properties of lens care products (May, 1995).
The guidelines for storage case hygiene historically have not been uniform among manufacturers. At best, the U.S. FDA recommends rinsing with the storage solution, drying face down, and replacing the case every 3-6 months (fda.gov/ForConsumers/ConsumerUpdates/ucm164197. htm). There is no guidance on if or how to rub the inside of the lens case to dislodge biofilm. Recently, researchers from the Brien Holden Vision Institute in Australia has published a series of articles that provide evidence on best practices for lens case hygiene. Wu and colleagues have studied the various lens case cleaning steps to isolate the most effective methods which should lead to cleaner storage cases. The group specifically studied the profile and frequency of microbial contamination of storage cases, (Wu, Zhu, Harmis; OVS 2010) the effect of lens case drying position (up or down) on contamination levels, (Wu, Zhu, Willcox; OVS 2010) and the efficacy of common cleaning practices on the removal of biofilm in storage cases (Wu IOVS 2010, Wu AAO abstract 2010).
My summary of Wu and colleagues' most relevant and salient findings are as follows: As has been reported previously, over half of used lens cases are contaminated, and in well-type cases the upper inner rim has greater rates and more pathogenic organisms compared to the lower inner base (Wu, Zhu, Harmis et al; OVS 2010). Case contamination is associated with age of the lens case, with significantly lower contamination rates in cases that are under 9 months of age, supporting the recommendation for shorter periods of use (Wu, Zhu, Harmis et al; OVS 2010). Drying cases face down reduces the level of case contamination (Wu, Zhu, Willcox et al; OVS 2010). Digital rubbing the inside of the lens case as well as wiping the case with tissue significantly reduce more biofilm compared rinsing, air-drying, or recapping cases (Wu et al, IOVS 2010).
Care systems can also influence case contamination. With regards to peroxide based systems, some studies found that the use of peroxide decreases bacterial contamination, (Larkin, 1990; Wilson, 1990) others show no difference from MPDS systems (Willcox; OVS 2010), and others associate greater case contamination with peroxide care systems compared with chemical disinfection (Gray, 1995). In fact, Gray and colleagues noted that microbial contaminants contain catalase which breaks down hydrogen peroxide to water and oxygen—these microbes may become preferentially selected to a resistant population after repeated exposure to peroxide (Gray, 1995).
A common theme in many publications is the ability of certain polyquaternium-myristamidopropyl dimethylamine (Aldox) preserved care solutions to effectively destroy biofilm. In 2008, Vermeltfoort and colleagues (Vermeltfoort, 2008) published a biofilm model to determine the efficacy of chemical disinfection systems against biofilms grown in lens cases and on bacterial transmission from the biofilm laden case to lenses stored within the case. Compared to biguanide preserved multipurpose care solutions, they found that a polyquaternium-myristamidopropyl dimethylamine preserved care solution was the most effective. Subsequently, Willcox and colleagues (OVS 2010) found that a polyquaternium-myristamidopropyl dimethylamine preserved care solution reduced the rates of gram negative bacterial contamination in cases compared to other products, although there were differences between various polyquaternium-myristamidopropyl dimethylamine preserved products. In one of Wu's recent articles, (IOVS 2010) soaking cases with formed biofilms in a polyquaternium-myristamidopropyl dimethylamine preserved MPDS for 6 hours removed “the majority” of biofilm. This data is in concert with data from our laboratories where certain polyquaternium-preserved products have been shown to be more effective than other MPS products tested against both bacterial and fungal biofilms formed on silicone hydrogel contact lenses. (Szczotka-Flynn, Cornea 2009; Ho, 2011).
Data drawn from Table 4 in Szczotka-Flynn L, Pearlman E, Ghannoum M. Microbial Contamination of contact lenses, lens care solutions, and their accessories: a literature review. Eye Contact Lens. 2010;36(2):116-129.
Percent of contaminated cases and/or residual solution within cases as found across various studies published between 1986-2008. Each bar represents a different study.
Therefore, evidence-based guidelines in the best care practices for contact lens storage cases conclude the following: Digitally rub or wipe and rinse the inside of the case, air dry face down, replace regularly, and use an effective disinfecting solution. CLS
For references, please visit www.clspectrum.com/references.asp and click on document SE2011.
Dr. Szczotka-Flynn is a professor at the Case Western Reserve University Department of Ophthalmology & Visual Sciences and is director of the Contact Lens Service at University Hospitals Case Medical Center. She has received research funding from Alcon, Ciba Vision, CooperVision and Vistakon.