CONTACT LENS CARE
A New-generation Multipurpose Disinfecting Solution
Evolution in lens materials and pathogens means multipurpose solutions need to change to continue meeting the needs of contact lens wearers.
By J. James Thimons, OD, FAAO
A few years ago, I had the unfortunate experience of working directly with several of the patients involved in the Acanthamoeba and Fusarium keratitis outbreak that led to recalls of multipurpose disinfecting solution (MPDS). After that experience, my goal as the optometric medical director at our consulting practice was to never have another sight-threatening episode secondary to contact lens care solution failure. Although I think that is an achievable goal, it demands that we set a higher bar for the MPDS products we recommend to our patients.
The microbial environment is constantly evolving. Changes in patients' lens care habits, as well as water management systems and average temperatures, challenge a lens care solution's ability to kill pathogens before they are introduced into the eye. Growing resistance is also a problem. Methicillin-resistant Staphylococcus aureus (MRSA), once virtually unknown outside the hospital setting, is now a leading cause of endophthalmitis, post-LASIK microbial keratitis and death by infection in the United States (Klevens et al, 2007). Therefore, we need multipurpose disinfecting solutions that are effective against today's microbes.
In addition, it is not enough to assess MPDS efficacy under ideal conditions. The pristine environment of controlled laboratory testing is not representative of the broad range of hygiene and lens care behaviors that we see in our practices. We know patients do not always soak their lenses overnight, nor do they follow our instructions about rubbing, rinsing, using fresh solution every day, and drying and regularly replacing lens cases. A survey found that more than one-third of contact lens wearers never washed their hands before handling their lenses (Stone, 2007). In the AOA's latest Eye-Q survey, 23 percent of respondents reported soaking or cleaning their lenses in tap water, and 12 percent admitted storing them in something other than a contact lens case.
Educating our patients is part of the answer, but I do not believe we will ever achieve 100 percent adherence. In addition to better education, we need lens care systems that can tolerate some nonadherence without compromising efficacy.
Until recently, the care solutions on the market were tested for compatibility only with conventional soft lenses. Silicone hydrogel (SiHy) is now the most commonly prescribed contact lens material, so clearly we need care systems designed to work well with these new materials. Because of their increased oxygen transmissibility, SiHy lenses were expected to reduce the risk of corneal infection, but large epidemiological studies have shown similar rates of microbial keratitis with these lenses compared with hydrogels. This points to the need for more data about lens material-care solution responses.
We have also seen, in my opinion, controversial reports that staining or superficial punctate keratitis (SPK) are more frequent with certain MPDS-SiHy combinations. Although care solution-related transient SPK is not the defining factor for ocular health, in my opinion, it does affect comfort and visual performance, so I believe we should choose MPDS products that are compatible with newer materials and offer a workable interface to the corneal surface and the tear film.
Addressing the Gaps
RevitaLens Ocutec (Abbott Medical Optics) is a new MPDS that attempts to directly address these gaps in the marketplace. Although we have limited feedback from patients using this product, the laboratory and clinical trial data are encouraging.
RevitaLens was tested with the leading brands of silicone hydrogel materials and approved for use with all soft lenses, including silicone hydrogels. It has excellent, broad-spectrum coverage with a rapid kill rate for the standard-panel organisms against which all MPDS products must be tested (Kilvington et al, 2011). In fact, its biocidal efficacy is similar to that of hydrogen peroxide systems (Kilvington et al, 2011).
Importantly, the method used to test this care system gives me confidence that it will provide sufficient microbial protection, even for patients who do not follow my care instructions. In a study that looked beyond the standard microbial panel at resistant organisms, such as MRSA, and clinical isolates typically found in contact lens cases, such as Staphylococcus marcescens, Delftia acidovorans and Stenotrophomonas maltophilia, RevitaLens demonstrated superior antimicrobial efficacy compared with the leading MPDS (Figure 1) (Zhu et al, 2010).
Figure 1. RevitaLens Ocutec offered superior antimicrobial efficacy against resistant clinical isolates and microbes commonly found in contact lens cases.
RevitaLens also performed well in tests designed to simulate partial evaporation of the solution, maintaining 100 percent biocidal efficacy even at four times the concentration (Figure 2) (Powell et al, 2010). In the past, we have seen that temperature and light can degrade an ophthalmic compound (latanoprost), even in its original bottle, due in part to evaporation (Morgan et al, 2001). In the context of contact lens wear, opportunities for evaporation of care solutions in the lens case are numerous, particularly when patients underfill lens wells, reuse or top off solution or leave lens caps off. The Powell et al (2010) data reinforce that the failure of ReNu MoistureLoc under such conditions likely contributed to the Fusarium outbreak.
Figure 2. As the solution became more concentrated with evaporation, there was no significant loss in efficacy for RevitaLens Ocutec (P< 0.05).
RevitaLens is labeled with a rub-and-rinse regimen, but as an MPDS, it has passed the standalone tests for efficacy without rubbing. I always instruct patients to rub their lenses, because, in my opinion, the manual removal of proteins and buildup is very important for comfort and clarity of vision. Again, recognizing that a certain percentage of patients will likely disregard my instructions, I am more comfortable with a care solution designated as MPDS, meaning it is effective regardless of the regimen.
Meeting Today's Challenges
Our expectations of contact lens care systems today are high. Meeting the first goal of producing a strong antimicrobial solution is relatively easy. Maintaining that efficacy against a broad range of real-world pathogens and environmental and compliance challenges is more difficult. To do all of that while maintaining the comfort and quality of lens wear that patients expect is even more challenging.
RevitaLens has been engineered to meet all of these goals. It holds the promise of giving us greater confidence that its predicted efficacy in the laboratory will be maintained in the real world of clinical practice. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #193.
|Dr. Thimons is in private practice at Ophthalmic Consultants of Connecticut in Fairfield. He is a consultant to Abbott Medical Optics (AMO) and receives lecture or authorship honoraria from AMO, Alcon, Allergan, Inspire, Konan, Optovue, TLC and Zeiss. You can reach him at (203) 366-8000 or www.occeye.com.|