TOPIC: Hydrogen Peroxide Versus MPS

point

Peroxide Systems Provide Maximum Disinfection Efficacy

BY CHARLOTTE JOSLIN, OD, PHD

Contact lens wear is a safe alternative for refractive error correction. In fact, recent estimates by Stapleton et al (2009) demonstrate that the cumulative risk of visual loss from daily wear contact lens use is substantially lower than the one-time risk from LASIK. Schein et al (2007) expressed similar sentiments comparing contact lens and LASIK risk, challenging assumptions by Mathers and colleagues (2006) in calculation of cumulative risk.

Most Serious Lens Wear Risk

Despite this assurance, microbial keratitis (MK) represents the most serious complication of contact lens use. Over the past two decades, even with the development of new care systems, lens modalities, and materials such as silicone hydrogels, MK risk remains unmodified and continues to be associated with overnight lens use and poor hygiene — risk factors that were identified more than 20 years ago.

Building evidence that atypical organisms are increasingly common causes of MK makes the question of whether multipurpose systems were previously effective disinfectants moot. Two recent worldwide solution recalls resulted from the association with MK subtypes caused by amoeba and fungal organisms, following two decades without a major solution recall. In each outbreak, controlling for the solution used, hygiene was a risk factor, indicating that inadequate hygiene increased risk regardless of solution. This is interesting considering that sub-optimal hygiene is and always has been common among even healthy lens users and could not have changed rapidly enough at the population level to cause the outbreaks. Current lens care systems including hydrogen peroxide, while not previously associated with Acanthamoeba keratitis, are now proving ineffective in Chicago and elsewhere (Gupta, 2009). In fact, Shoff et al (2008) demonstrated using recent Acanthamoeba clinical and tap water isolates that only a simulated two-step peroxide system has total efficacy against Acanthamoeba organisms, and recent Centers for Disease Control and Prevention (CDC) outbreak investigation laboratory work supports these results (Johnston et al, 2009).

Preventing MK

If environmental causes are indeed increasing the organism load (Joslin et al, 2006), then it is vital to:

1. Educate patients to improve lens-related hygiene.

2. Use lens care systems with maximum efficacy against Acanthamoeba.

3. Develop products with improved disinfection efficacy.

Hydrogen peroxide-based solutions have the greatest efficacy against all bacterial, fungal, and amoebic pathogens of MK. Given that Acanthamoeba is likely the most resistant organism associated with contact lens wear and continues to cause MK despite recent recalls, we should strongly consider increasing hydrogen peroxide use until more effective solutions are developed.

Still, even hydrogen peroxide is ineffective if contact lens hygiene is inadequate. So we must take responsibility through marketing opportunities and in the office to educate patients and to improve awareness about appropriate lens-related hygiene to prevent disease and to maintain contact lens safety. CLS

For references, please visit www.clspectrum.com/references.asp and click on document #163.

Dr. Joslin is an epidemiologist and an assistant professor of Ophthalmology and Visual Sciences at the University of Illinois at Chicago, Chicago, IL. She is a Diplomate of the American Academy of Optometry in the Section on Cornea, Contact Lenses and Refractive Technologies. She is also a consultant or advisor to Bausch & Lomb.

counterpoint

Multipurpose Solutions: Safe, Efficacious, and Simple

BY CRAIG A. WOODS, PHD, FAAO

Regardless of your point of view, contact lenses need to be cared for. Every day, practitioners decide which care system to prescribe to their patients, a decision that should not be made lightly. The primary consideration must surely be what is in the best interest of each patient. That consideration alone is complex, but could be broken down into:

• What is safe?
• What is efficacious?

Today, we have a basic choice: whether to prescribe a multipurpose disinfecting solution (MPS) system or a hydrogen peroxide-based system (HPB).

Keeping Things Simple

The real issue may be how compliant your patients will be with the system. Aiding compliance could be the key, and the key to compliance is keeping things simple. Simple lens care systems are more likely to be used correctly. So maybe we should expect a lens care system to be safe, efficacious, and simple.

Simplicity with contact lens wear is achieved by requiring patients to perform the fewest steps possible, hence the development of "one-step" systems.

MPS systems have a demonstrated ability to disinfect. With only rare reports of complications, they are safe and efficient. Also, you couldn't find a simpler process: rub and rinse with the MPS system and place the lenses into the lens case with fresh MPS; in the morning, remove, rinse, and apply the lenses.

The alternative to using an MPS system, which we agree are simple and successful, would be to offer patients HPB systems. These systems are either "two-step" systems, which require additional steps to enact neutralization, or they have been adapted to match the simplicity of the one-step MPS systems. If our goal is simplicity for the sake of aiding compliance, use of the one-step HPB systems would be preferred. So, we are left to choose between MPS systems and the one-step HPB systems.

However for HPB systems to be effective, lenses need to be exposed to the hydrogen peroxide for a significant amount of time. One-step HPB systems require that the neutralization step begins immediately, which means that the lens may not be immersed long enough in the disinfecting peroxide. Essentially, one-step HPB systems may compromise disinfecting power for the goal of improved compliance.

MPS Benefits Outweigh Risks

Much has been published about the corneal physiological response induced by particular combinations of lenses and MPS systems — a review of the literature may lead you to believe that we have actually learned how to induce corneal staining, which is apparent after two hours of lens wear and gone before six hours of lens wear. We still do not fully understand this phenomena and should not assume that this reaction occurs for all lenses, all MPS systems or for all patients.

Public health reporting is sensitive enough to highlight events such as those that occurred in Chicago and Florida over the past few years. In the grand scheme of things, I hold the view that although these events were horrendous for the individuals involved, they are not relevant to a review of the performance of MPS systems or preference for a lens care system as a whole.

Finally, let's remember in this cost conscious world, where some patients will do whatever it takes to save money, MPS systems are significantly cheaper than peroxide systems. Also, patients find ocular exposure to hydrogen peroxide distressful (it does occasionally happen!), which will always consume valuable chair time.

The Bottom Line

MPS lens care systems are the number-one choice around the world for a reason: They are successful in what they are designed to do, which is namely to deliver clean, disinfected contact lenses that are comfortable to wear, with minimal fuss. CLS

Dr. Woods is the Research Manager at the Centre for Contact Lens Research, School of Optometry, University of Waterloo, Ontario, Canada.