CONTACT LENS CARE
More Than Just Juice: Updates in Lens Care
Today’s lens care systems are safe and effective at cleaning and conditioning lenses. So, what’s next?
By Alex Hui, OD, PhD, FAAO
Microbial keratitis, superficial punctate keratitis, fluorescein corneal staining, infiltrative keratitis, palpebral lid changes—all eyecare practitioners are aware of these and other possible contact lens complications, which range from mild to sight-threatening. All eyecare practitioners are trained to identify and manage them in routine clinical practice.
But what is often forgotten is how effective and incredibly successful modern contact lens care systems are for the majority of contact lens wearers relative to reducing the risk of these complications. There are layers of safety engineered into contact lenses and lens care solutions; it takes multiple, often extremely noncompliant, behaviors by consumers to circumvent these safety protections and cause serious complications.
The goals of modern contact lens care systems are primarily to ensure the safety of contact lens wear and to condition the contact lens for continued successful wear. Modern care systems are generally successful in achieving these goals, although the industry continues to develop and improve upon these lens care systems in the hope of improving the contact lens wearer experience. This article highlights developments that have occurred with contact lens care solutions and discusses changes in the regulatory and research environments that will give us insight into the likely future of contact lens care.
Recent Lens Care Solutions
Within the past five years, several new soft contact lens care solutions have passed through the required regulatory hurdles and been commercialized. The composition of these new products reveals some significant trends in the development of lens care solutions.
First, the selection of preservatives used in lens care solutions reflects changes in the industry’s thinking, based on research and clinical reports. There appears to be a trend toward increased use of the newer, large-molecule polyquaternium as a preservative and a corresponding drift away from the lower-molecular-weight preservative polyhexamethylene biguanide (PHMB), also known as polyaminopropyl biguanide (PAPB). PHMB, which had been a staple disinfecting agent in previous generations of care solutions, is included in only one of the newer entrants to the market. Could PHMB eventually follow in the footsteps of other preservatives, such as thimerosal and chlorhexidine, and disappear from the market (Szczotka-Flynn et al, 2013)? The trend away from PHMB could be due to evidence that it may not be well tolerated by the ocular surface, as it has been associated with corneal staining and symptoms of discomfort in contact lens wear (Jones et al, 2002; Lipener, 2009; Malet, 2014).
The recent release of a completely new hydrogen peroxide care solution, as well as an updated formulation of an existing one, demonstrates the growing importance of this segment of the market. While not as convenient as one-step multipurpose solutions due to the required additional neutralization step, hydrogen peroxide care solutions continue to be successful due to their touted biocompatibility once neutralized. Thus, they are often used as a “go-to” contact lens care solution for patients exhibiting possible care solution intolerances.
The second major trend is the shift toward dual-disinfecting care solutions. Rather than having a higher concentration of a single disinfectant, many of the new multipurpose solutions contain two preservatives, often at lower concentrations than those found in previous iterations of the products. In addition to allowing for a greater spectrum of biocidal activity, use of combined preservatives can serve as a layer of safety should one preservative be preferentially taken up into the contact lens, leaving less available in the residual care solution to adequately eliminate microbes (Jones and Powell, 2013).
The third trend in the design of care solutions has been the continued evolution of additives and conditioning agents. These additional molecules have varying roles; they are designed to remove deposits, such as proteins and lipids, and to modify the lubricity or friction of the surface (e.g., hyaluronan, HydraGlyde) (Scheuer et al, 2010). The “cocktail” of molecules added to care solutions has increased their complexity and number of components as manufacturers aim to improve comfortable wear regardless of how old a contact lens is in its wear cycle.
Regulatory Agencies: Recent Discussions to Improve Safety in Contact Lens Care
The U. S. Food and Drug Administration (FDA) plays a central role in the development of contact lens care systems because of its regulatory authority. A Contact Lens Microbiology Workshop was convened in September 2014, bringing together representatives from government, industry, optometry, and ophthalmology to discuss the microbiological challenges facing contact lens wearers and manufacturers of lens care systems (FDA, 2014). The discussion centered around three key areas that were identified as critical for long-term contact lens safety: emergence of new pathogens associated with contact lens wear, the influence of “organic soil” on disinfectant properties, and the continued problems associated with Acanthamoeba.
The emergence of new pathogens associated with contact lens wear is typically detailed through post-market surveillance. Amoebae (Acanthamoeba) and fungi (Fusarium) are particularly highlighted, as both have been associated with outbreaks of microbial keratitis in lens wearers using FDA-approved lens cleaning solutions (Chang et al, 2006; Bullock and Warwar, 2010). These two serious outbreaks in 2006 and 2007 highlighted real-world conditions encountered by consumers that were substantially different from those of the FDA testing procedures used to approve lens care solutions. As a result, the efficacy of the approved care solutions fell below that required to prevent infection (Bullock et al, 2008; Verani et al, 2009).
This naturally led to the second topic of discussion on the effects of “organic soil,” which primarily relates to the complex combination of tear-film deposits that are attracted to contact lenses and their impact on disinfection efficacy. Current disinfection efficacy testing does not include an evaluation of the impact of material deposition. The presence of additional molecules such as protein or lipid on the contact lens surface has led to variable disinfectant efficacy as well as to increased bacterial adherence (McGrath et al, 2003; Zhang et al, 2005; Hildebrandt et al, 2012). Unfortunately, lack of a standardized method to test the impact of ocular organic soil in vitro has resulted in a lack of consistency in applying the results of laboratory care solution testing to consumer performance.
The third topic focused on Acanthamoeba and the current state of knowledge of the organism. Currently, Acanthamoeba is not on the list of test organisms that are used in the panel for determining efficacy of contact lens care solutions. The experts identified the difficulty in culturing and in developing protocols for testing of this particular organism, as it can be difficult to grow and exists in different forms depending on the environmental conditions, leading to difficulties in standardizing testing against the organism.
The FDA has also begun the process of designating a new contact lens grouping system. In the original system developed by the FDA and the International Organization for Standardization (ISO), materials were placed into one of four groups (Group 1 through Group 4) depending on their water content (high >50% or low <50%) and surface charge (ionic or non-ionic); the goal of this grouping system was to provide information on the materials’ predicted preservative uptake and tear deposition characteristics to help guide practitioners in lens and care solution prescribing for particular patients (Green et al, 2012; Hutter et al, 2012). It was also used as the basis for cost-effective testing of care solution compatibility; manufacturers were not required to test every available care solution with every available contact lens, but rather they could test care solutions against “representative” lenses in each lens group (Hutter et al, 2012).
The big change in this system has been the introduction of the silicone hydrogels, which, due to their unique chemistry, do not necessarily perform as predicted when categorized according to the prior ISO/FDA classification (Hutter et al, 2012). Silicone hydrogels exhibit different types of deposition patterns than hydrogels do (Lorentz and Jones, 2007). The surfaces of many of the early silicone hydrogel lenses were also modified to allow for better wettability through a plasma oxidation processes or deposition of ultrathin coatings that, when combined with their unique hydrophobic polymers, had a profound effect on preservative interactions with the contact lenses (Jones and Powell, 2013). The new classification places silicone hydrogels within their own classification group (Group 5); within that group would be subdivisions based on water content, ionicity, presence or absence of surface treatment, and hydrophobic/hydrophilic character of the lens monomer. The goals of classifying contact lenses into these categories is to continue to allow predictions regarding preservative uptake as well as to better predict deposit-lens interactions and the effects of surfactants (Hutter et al, 2012). Table 1 shows the proposed Group 5 subdivision.
|Water content||Low||Low||Low||High||High and low|
|Surface Treatment||Yes||No||No||Yes or no||Yes or no|
|Monomer characteristic||Any||Hydrophilic||Semi-Interpenetrating network||Any||Any|
|*Adapted from Hutter et al (2012)|
Improving Contact Lens Safety: Innovative Engineering in Lens-Related Technology
The safety of contact lens wear does not need to focus solely on the disinfection properties of contact lens care solutions. Innovative engineering concepts may also help improve the overall safety of contact lens wear. Theorizing that the inner surface of a new contact lens can be contaminated by the fingers during lens application has led to creative ideas in contact lens packaging; for instance, there are now one-day contact lenses that are placed within the blister pack so that only the outer surface of the lens is handled by wearers before lens application, preventing bacterial colonization of the inner surface.
The contact lens storage case has also been investigated regarding its role in promoting safety, with antibacterial silver-impregnated cases having been already introduced to market by several companies (Amos, 2005; Amos and George, 2006). However, the ability of such cases to reduce infections on a large scale has not been well established (Dantam et al, 2012; Dutta and Willcox, 2014).
In the developmental pipeline, antibacterial surfaces being incorporated into the contact lenses themselves are beginning to gain some traction. In vitro and in vivo work has been performed with lenses incorporating melimine, a cationic peptide that can be attached to the contact lens surface to prevent microorganism colonization; it is also biocompatible with the human ocular surface (Dutta et al, 2013; Dutta et al, 2014).
Improving Performance: The Contact Lens Wearing Experience
The vast majority of contact lens wearers experience some type of contact lens discomfort during wear, and this discomfort or dryness is often cited as one of the primary reasons for discontinuation of contact lens wear (Dumbleton et al, 2013). The difficulty lies in the fact that contact lens comfort remains a complex biological and neurophysiologic phenomena, and thus no one test or battery of tests has been able to definitively identify all of the relevant factors surrounding it (Nichols et al, 2013).
What is interesting is that the thinking behind contact lens deposits and how they affect contact lens discomfort is changing. There has been some evidence that certain patterns of lipid deposits are associated with better contact lens tolerance, and differences in these deposition profiles may play a crucial part in determining wear success among patients (Subbaraman et al, 2015). This is a departure from previous conceptions of contact lens deposits in which they all were thought to be detrimental to contact lens wear and thus required removal. If certain deposits are deemed to be beneficial, then the design of care solutions will become even more complicated because they would be tasked with more selective cleaning, such that “good deposits” would be left behind and detrimental ones removed.
Contemporary contact lens care systems are expected to simultaneously disinfect and clean all contact lens types for all people, all while maintaining biocompatibility and safety—a tall order that they fulfill quite successfully. Perhaps the future of care solutions lies within a certain baseline of performance regarding health and safety, but with the potential for customization to be more useful/accepted/comfortable for certain patients who have certain characteristics.
For the industry to continue to grow, it will require cutting-edge research to identify the appropriate metrics needed for practitioners to anticipate certain types of problems and complications. Crucially, the industry also needs to develop the right types of care solutions so that identified potential complications can be nullified before they even occur.
There is currently a great deal of interest in contact lenses and lens-related technology. Innovative clinical and engineering solutions have already been proposed and implemented that have brought the contact lens wearing experience to the state that it is today. I am excited to see what changes will develop in the years to come for contact lens care. CLS
For references, please visit www.clspectrum.com/references and click on document #237.
Dr. Hui is currently a lecturer at the School of Optometry and Vision Science at the University of New South Wales in Sydney.