There are about 125 million contact lens wearers worldwide.1 Excluding the daily disposable and extended wear contact lenses, all other types of lens wear modalities require the use of a contact lens storage case for overnight storage and disinfection. However, the contact lens storage case itself can become contaminated by pathogenic micro-organisms.2
Contact lens storage case contamination is common in lens wearers, occurring in 30% to 85% of the cases.2-7 Studies have shown that lens cases receive the least cleaning attention and are the most frequently—and heavily—contaminated items compared to other lens care accessories.5,8-10
A variety of organisms have been identified in contact lens storage cases, including different types of bacteria, viruses, fungi and protozoans.2,3,11,12 These organisms include Pseudomonas, Serratia, Staphyloccus, Acanthamoeba and Fusarium species.3,5,11,13-15 Colonization of the lens storage case by pathogenic micro-organisms predisposes lens wearers to microbial or sterile keratitis.9,19-22
Poor adherence to the recommended cleaning regimen is believed to be the main cause of lens case contamination. Yet, studies have shown that even carrying out the recommended instructions does not necessarily guarantee a lens case free from contamination.21,23 Factors other than hygiene behaviors, including microbial factors such as biofilm formation and microbial resistance, may be associated with persistent microbial contamination of contact lens storage cases.24,25
Biofilm Formation in Lens Cases
Contact lens storage case.
Once bacteria enter the lens case, they may adhere to the case and switch from a planktonic (free-floating) phenotype to a sessile biofilm phenotype in response to a low-nutrient environment.24 The micro-organisms are embedded in a glycocalyx, which is a polysaccharide-containing matrix.24 Initially, this biofilm can be easily removed due to the loose attachment of cells.
But, the adhesion between microbial cells and the contact lens case surface becomes more persistent over time. The mature biofilm is significantly more resistant to antimicrobial agents than planktonic cells.26,27
Although contact lens multipurpose solutions or systems meet the international standard ISO 14729 and FDA 510(k) for adequate antimicrobial efficacy against selected reference strains of bacterial and fungal pathogens, antimicrobial efficacy varies among disinfecting solutions in vitro.6,28-31 In addition, the biocidal activity against biofilm and clinical isolates is unknown and both inherent and acquired microbial resistance may occur.23,25,32
In other words, simply soaking lens cases in disinfecting solutions may not be adequate to eliminate potentially virulent micro-organisms.7,24,32 Such factors represent a challenge in maintaining contamination-free storage cases; so, consider additional strategies to minimize storage case contamination.24,33
Today’s Approved Instructions
A recent study presented a systematic review of the Food and Drug Administration (FDA) and lens care manufacturers guidelines, and a survey of eye care practitioners’ lens case cleaning instructions for lens wearers.34 While the FDA advises lens cases be rinsed with disinfecting solution, air-dried face down after use, and replaced every three to six months, eye care practitioners and manufacturers provided less consistent advice.
For example, 20% of practitioners did not specify rinsing or air-drying lens cases. For those who recommended air-drying, 50% recommended drying cases face-up.34 There was also a large discrepancy between recommended timing of lens case replacement, ranging from one to six months between manufacturers and practitioners.
Although most of the two-flat well lens cases need to be air-dried after use, the silver-impregnated lens cases reportedly perform better when recapped, and this was not explicitly stated in the guidelines.35
The variation in advice from each source may increase wearer confusion. This perhaps explains that the major reported behaviors in lens wearers include not rinsing lens cases with disinfecting solution after use, not air-drying lens cases and not replacing lens cases regularly.5,8,36-40
In vitro studies reported that despite following the FDA and manufacturers’ recommended lens case cleaning instructions, these methods were actually not adequate in removing biofilm where a lens case is heavily contaminated.23,30 This finding confirms previous studies suggesting that even when a lens wearer follows the recommended guidelines, this may not result in contamination-free storage cases.21,23
Further, there have been controversies over whether the lens case should be cleaned with a cotton swab or toothbrush, boiled after use or microwaved; and, if so, how often.3,41-43 While these additional cleaning methods seem helpful in the attempt to reduce microbial contamination, concerns arise regarding the standardization of methods and the evidence supporting their use. In addition, their applicability across the myriad care systems and storage case types and designs, is unclear.
Although it is a responsibility of eye care professionals to deliver appropriate and consistent lens care recommendations to lens wearers, this may be challenging due to limited evidence-based lens case cleaning instructions. This suggests that we need further research to understand optimal storage case hygiene for lens wearers, and also how best to provide this information to eye care practitioners and to contact lens wearers.
Evidence-Based Guidelines: What Do We Know?
Micro-organisms recovered from a
contact lens storage case.
Microbial contamination often occurs when handling lenses, so hand-washing with soap is essential in minimizing contamination.44-46 The use of fresh disinfecting solution is recommended because topping-off the solution is associated with higher levels of contamination and lens-related complications.47,48 Simply soaking lens cases for the recommended time may not be sufficient to limit microbial contamination as discussed earlier.30 Rubbing lens cases followed by tissue-wiping is effective in removing bacterial bioburden from lens cases in vitro.30
Based on the available in vitro data, it seems reasonable that, after rinsing lens cases with fresh disinfecting solution, lens cases should be rubbed with clean fingers and further wiped with a clean tissue because such mechanical friction has been shown to reduce biofilm in lens cases.30
After the lens case has been cleaned, it needs to be air-dried face down. An in vitro study comparing the effectiveness of recapping vs. air-drying of conventional polypropylene lens cases demonstrated that recapping the lens cases resulted in significantly higher levels of bacterial recovery than air-drying cases.30 These data are consistent with epidemiological data showing that failure to air-dry lens cases is a risk factor for developing microbial keratitis.49
Lens cases air-dried face up in the bathroom were more frequently contaminated than those dried in a bedroom/office setting.50 However, air-drying location was less relevant if the cases are air-dried face down as this not only minimizes the exposure to air-borne contaminants but also promotes faster drying of lens wells, as suggested by the FDA.51
However, silver-impregnated lens cases perform better when recapped since maintaining some moisture in the lens case allows for the exchange of silver ions.35 So, recapping lids after use is recommended for silver-impregnated lens cases.
Lens storage case age is a proven risk factor for contact lens related corneal infection and older storage cases show higher levels of microbial contamination.7,49,52 Lens cases may develop moderate or heavy contamination, particularly by Gram-negative bacteria, even just after two weeks of use.52 This suggests that frequent replacement (at least monthly) of lens cases is recommended.7,52
The Challenge of Improving Lens Case Hygiene
The degree to which lens wearers’ hygiene practices coincide with practitioner advice has been defined as compliance. This rather narrow definition somewhat limits the autonomy of the lens wearer and excludes them from participating in decisions relating to their lens wear. Compliance is not a static concept; behaviors relate to perception of risks, health beliefs and values, wearer personality and the quality of the interactions between the practitioner and the wearer.
Lens wear is an ongoing activity and behaviors may change over time. Practitioners need to be aware of the factors that influence hygiene behaviour and the relevance of the mutual agreement or concordance between the wearer and the practitioner in the responsibility for outcomes in lens wear. If the wearer is excluded from the process, improving and indeed measuring compliance is difficult.
“Patient compliance” was the term originally used to describe the behavior of following recommendations prescribed by their clinicians. This implies a clinician-centered approach, and places patients in a passive role. By contrast, adherence connotes a patient’s commitment to a regimen in an active, voluntary and collaborative way. Past efforts by practitioners have generally focused on improving practice through education and information. Despite these efforts, the level of hygiene practice remains low.8,36,37,53,54 Improving contact lens case hygiene has been a difficult challenge for eye care practitioners.
The underlying causes of non-adherence to recommendations are probably diverse and complex. It may be that lens wearers follow outdated instructions, are not receiving adequate instructions from eye care practitioners in the first place, are confused by different recommendations from various sources or choose not to follow instructions due to their perception of the impact of the risk of non-adherence to recommended hygiene regimen.34,36
While this is a complex issue, it may be helpful to consider some potential issues and strategies for wearer communication and engagement.
• Lens wearers not aware of the updated or adequate instructions.
The majority of non-adherence in lens wearers appears to be due to a lack of awareness of adequate cleaning procedures or the importance of storage case cleaning.36,54 During a contact lens consultation, a practitioner is required to assess the fitting, comfort and performance of contact lenses. At the same time, the lens wearer is required to process and retain a large amount of information—e.g. lens replacement schedule, how to insert/removal lenses, how to clean, what solution to use, and so on. The volume of information for the wearer to retain can be overwhelming. On average, patients retain just 50% of verbal instructions after a consultation, and 40% to 80% of instructions are forgotten immediately under certain circumstances.55,56
The understanding of proper use of the lens products in lens wearers needs to be confirmed by the practitioners—either by asking open questions or behavioral observations such as asking the lens wearers to demonstrate how they carry out their lens care. The use of visual tools, such as demonstrating cleaning techniques for lens wearers in the clinic, and take-home instructions in addition to verbal communication, can enhance knowledge retainment.56,57
Follow-up care provides an opportunity to revisit lens wearers’ hygiene habits and their use of contact lenses, care products and, in particular, the maintenance of their lens case. An open-ended question approach helps to elicit lens wearers’ hygiene practices, understanding and concerns of lens wear; this allows for early detection and modification of any inappropriate lens care. Unfortunately, more than half of lens wearers fail to recognize the importance of follow up care.37,53 Regular follow up should be addressed by the practitioners regardless of whether or not the contact lens wearers are experienced in lens handling and satisfied with the performance of their contact lenses.
• Lens wearers can be confused with different recommendations from various sources.
Non-adherence to recommended hygiene regimens in lens wearers ranges from 50% to 79%.54 Almost one third of this non-adherence is associated with lens case hygiene, which suggests a lack of consistent education and absence of standarized guidelines as mentioned previously.34,36
We strongly urge eye care practitioners, academia and industry to collaborate to develop consistent and evidence-based cleaning guidelines. Such guidelines need to be effective in removing microbial biofilms and only require minimum additional paraphernalia, which is important for improving hygiene commitment in contact lens wearers. Manufacturers can also support the hygiene strategies by emphasizing the lens and lens case cleaning instructions on the solution bottle where they are easily accessed and highly visible.
Lens wearers commonly switch care systems due to convenience or cost issues without consulting with their eye care practitioners. In doing so, lens wearers may not realize that case cleaning procedures sometimes differ between products. So, it is essential to explain the rationale for prescribing a specific system and to specify the prescribed care system on the contact lens prescription.
• Intentional non-adherence.
It is possible that lens wearers do not perceive lens-related complications as sight threatening, and they often do not experience immediate harm from their non-compliant behavior. So, lens wearers don’t have sufficient incentive and motivation to change their behaviour.53 Inevitably, some lens wearers are always more resistant to standard care and recommendations about appropriate contact lens hygiene despite all efforts.
A large proportion of lens wearers do not follow a recommended hygiene regimen despite awareness of risk.58 One study found that intrinsic characteristics, such as the risk-taking propensity of individuals, may influence the care and maintenance of contact lenses and, even though those individuals are aware of health hazards, they still tend to perform the risky behavior.59,60
Contact lens wearers make up a different demographic compared to our other patient groups and may require alternative education approaches.37,53,61 Perhaps in the future, a tool such as a personality assessment may be useful to practitioners to help with the lens wearer selection process and the development of more targeted cleaning regimen enhancement strategies.
In summary, contact lens storage cases can become contaminated by microorganisms, resulting in microbially-driven adverse events such as corneal inflammation and infection. Current recommendations for lens case cleaning are not effective in preventing or limiting contamination and particularly in removing microbial biofilms. Limiting lens storage case contamination may reduce adverse events and result in safer contact lens wear but solving this complex problem requires collaboration between eye care practitioners, academia and industry in the development of evidence-based cleaning guidelines. Additionally, further development of lens care products, perhaps those targeting specific microbial virulence factors may assist, plus a commitment is required from advisory sources to disseminate comprehensive and consistent lens case cleaning guidelines. Finally, adherence to lens and storage case cleaning instructions depends on collaboration and understanding between contact lens practitioners and contact lens wearers.
Professor Fiona Stapleton is the Head of the School of Optometry and Vision Science at the University of New South Wales and Senior Research Associate at the Brien Holden Vision Institute at the University of New South Wales, Sydney, Australia.
Yvonne Wu is a Ph.D. candidate at Brien Holden Vision Institute and the School of Optometry and Vision Science at the University of New South Wales, Sydney, Australia.
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