As patients increasingly choose to wear – and sleep in – silicone hydrogel lenses, the incidence of infections is on the rise. Multi-purpose disinfecting solutions could provide a higher level of care.
Approximately 125 million people around the world wear contact lenses1 and the vast majority of them regularly care for their lenses with a multi-purpose solution (MPS) 2 – a single solution to rinse, disinfect and store lenses.
The antimicrobial efficacy of the multi-purpose disinfecting solutions (MPDS) based lens care system is the key to the safe use of contact lenses. However the efficacy of MPDS solutions also face a number of challenges, including the need for compatibility with new contact lens materials, the emergence of resistant pathogens, and poor patient compliance with cleaning regimens, lens handling and wear.
Global trends indicate a shift towards silicone hydrogel lenses and now represent 36 per cent of all soft contact lenses prescribed3. Many of these lenses are worn during sleep, which significantly increases the risk of microbial keratitis3.
What is required is an advanced multi-purpose disinfecting solution to deliver broad-spectrum, peroxide-quality disinfection, even under non-compliant conditions without compromising comfort…
In recent years, there have been two outbreaks of infections associated with the fungus Fusarium and the free-living amoeba Acanthamoeba. Severe reduction of disinfecting solution efficacy upon partial evaporation was considered a key factor in the Fusarium-related keratitis cases4-7. These events have cast doubt on the effectiveness of MPS, as well as the current methods and standards that evaluate their ability.
The common consensus is that more robust testing methods and standards are required to assess the microbiological efficacy of MPDS cleaning systems.
Poor Compliance
Numerous studies have shown that poor patient compliance is a major factor implicated in contact lens-related ocular infections and is estimated to be responsible for more than 80 per cent of all contact lens-related problems8.
Non-compliant behaviour typically starts with the failure to adhere to the manufacturers’ recommended use of MPS or other disinfection systems. Specifically, such non-compliance issues include the reuse and ‘topping off’ of solutions, underfilled contact lens case wells and failure to recap or secure the lens case during soaking, resulting in partial evaporation of the solution.
These conditions can all have a significant effect on the concentration and antimicrobial efficacy of the MPDS. The formation of a microorganism-protective film from an evaporated solution also hampers efficacy of the MPDS9.
Advanced Solutions Needed
Newer, more complex contact lens solutions should be recommended to maintain efficacy and face the challenges of emerging pathogens and user noncompliance in real world conditions. In short, an advanced multi-purpose disinfecting solution to deliver broad-spectrum, peroxide-quality disinfection, even under non-compliant conditions without compromising comfort. Solutions of this quality offer excellent lens cleaning with advanced protein and lipid removal and low rates of corneal staining and adverse events for both silicone hydrogel and conventional contact lenses10-13.
Typically, MPDS is composed of a preservative, a buffer system and other agents to aid lens comfort and cleaning. Advanced interactive systems consisting of disinfectants that work in concert with the chelating agent ethylenediamine tetra-acetic acid (EDTA) and a buffering system that includes boric acid, perform all the functions essential to contact lens care. While the dual disinfecting agents provide excellent antimicrobial activity, a citrate buffer prevents the uptake of polyquaternium-1 by contact lenses. The EDTA and the buffering system work together to chemically bind proteins to prevent their attachment to the lens surface.
Rigorous Testing
To be certain of efficacy, any MPDS solution recommended to your patients should pass the most rigorous ‘stand alone’ test (inoculum challenge) of the International Standards Organization (ISO) used by the U.S. Food and Drug Administration (FDA) for testing contact lens solutions. Because the “rub & rinse” regimen removes four times more unwanted deposits from contact lenses compared to rinsing alone and is strongly recommended by the FDA, the MPDS you recommend should be labelled with rub-rinse regimen.15
Resistant Against Pathogens
Even though Acanthamoeba is not among the organisms that solutions are required to be tested against, it is important, given recent outbreaks of Acanthamoeba keratitis that an effective MPDS reduces Acanthamoeba trophozoites (amoeboid form) and resistant cysts.14
Furthermore, the MPDS you recommend should be effective against clinical isolates, including a methicillin-resistant S. aureus, S. marcescens, D. acidovorans, S. maltophilia, and Candida albicans, P. aeruginosa 037 and 142, S. marcescens 035, acineto sp 008, P. fluorescens 029, S. aureus 110, and F. solani 004 and 005.
Another cause for concern is the pathogenic bacterium Stenotrophomonas maltophilia (formally known as Pseudomonas maltophilia). The ability of S. maltophilia to survive and replicate in certain MPDS may result in an increased risk of bacterial keratitis and may provide a food source for the growth of Acanthamoeba in contact lens storage cases resulting in an increased risk of amoebic keratitis.
Nikolic and colleagues demonstrated that all PHMB-containing MPDS result in ≥3.6 log10 kill rates for S. maltophilia strains by 6 hours of exposure time with no re-growth over the ensuing 28 days.16 In contrast, a MPDS based on PQ-1 and Aldox (myristamidopropyl dimethylamine) not only failed to kill the bacterium but actually supported growth in the formulation. 16
Efficacy Under Noncompliance
Importantly, an effective MPDS must be designed to maintain biocidal efficacy against leading pathogens even under noncompliant conditions. It must not lose Fusarium efficacy upon evaporation or alexidine upon partial evaporation.
Corneal Staining
Corneal staining can occur with some contact lens-solution combinations and can be a sign associated with cytotoxicity and solution hypersensitivity. Other signs and symptoms, including limbal redness, burning or stinging sensations, may accompany staining. Additionally, corneal infiltrates are three times more likely to occur in eyes that exhibit toxic staining as compared to unaffected eyes.17 Furthermore, epithelial toxicity may lead to symptoms of ocular surface discomfort or dryness and these symptoms may motivate some contact lens wearers to discontinue lens wear.18
It is therefore essential to choose an MPDS solution that has clinically demonstrated low-level side effects and high levels of long term wearing comfort.
Professional Advice Required
Regular and thorough lens care is essential to prevent eye infections and discomfort. While patient education is integral to achieving a high standard of lens care, so too is your patients’ choice of disinfecting solution.
As an eye care professional, it is your responsibility to recommend the highest quality solution that delivers high kill rates that exceed the standard requirements against the pathogenic bacteria and fungi and also effectively kills Acanthamoeba and Fusarium. Importantly, the MPDS you recommend must maintain its efficacy even under robust conditions of partial evaporation. Moreover, it must be compatible with both silicone hydrogel and conventional lens materials and effectively remove protein and lipids from the lens surface. The solution you recommend should be formulated to help minimise ocular sensitivities, be gentle on ocular tissues, associated with low corneal staining and adverse events, and potentially reduce SICS.
It is only by improving comfort levels and reducing the risk of ocular infections that the contact lens market will continue to grow.
