Discussion
Rigid contact lens wearers commonly rinse their lenses under tap water, and both soft and rigid lens wearers often rinse their cases in their bathroom sinks, erroneously thinking they are "cleaning" the case. This practice is often at odds with practitioner recommendations, but the advice is superseded by instructions on package inserts, which, for some brands, actually recommend rinsing the lens, the case, or both, with nonsterile water sources. Internet sites, including the Centers for Disease control and prevention (CDC) and Food and Drug Administration (FDA), send a strong message against water exposure, but then recommend to follow package instructions, making it confusing for patients to know what to do.[4,5] Contact lens and solution manufacturers, and clinicians, universally acknowledge that proper lens hygiene can reduce, but not necessarily eliminate, contact lens–related complications.[6] Nevertheless, improper lens hygiene is widespread in the general population and has been shown to result in vision-threatening infections.[7,8] Proper lens hygiene needs to include education about the dangers of tap water exposure in the setting of either soft or rigid contact lens use. This message needs to be consistent for all types of lenses to avoid confusing the average consumer.
Use of soft contact lenses has been shown in many studies to be a significant risk factor for development of ACA, but the infection has also been reported in rigid lens wearers.[9] Adherence rates of Acanthamoeba spp among hydrogel lenses vary according to the type of polymer.[10,11] Rates of adherence to rigid contacts are conflicting, with some studies reporting more adherence and some less adherence, compared with hydrogel polymers.[12,13]
In the past, use of "tap," "hot," or "distilled" water was recommended as part of the disinfection routine for all types of lenses, but current recommendations advise against the use of water during the cleaning process for soft contact lenses.1,14–17 Despite documented risks of ACA with rigid lenses, the use of tap water for rigid lenses hygiene remains controversial. Although not universally recommended,[17] some studies suggest that rinsing off the lens cleaner with water before soaking in disinfectant is acceptable.[18] Yet, it has been repeatedly shown that contact lens solutions, even in the controlled setting of a laboratory, are not necessarily effective in killing ACA.[19–23] Moreover, once a lens is contaminated by lens wear or exposure to bacteria, biofilms may form on contact lenses, which can be resistant to the antimicrobial activity of several soft contact lens care products.[12,13] The FDA does not use worn lenses for testing efficacy of disinfection products, and it is theoretically possible that the presence of biofilms generated from other organisms might render ACA even less susceptible to the disinfection capabilities of contact lens solutions.
Another common source of inadvertent exposure to Acanthamoeba spp among even compliant contact lens wearers is rinsing of the storage case with tap water. Patients are attempting to "clean" their lens cases, but in doing so, they risk contamination with pathogens.[24] Many studies have shown that the contact lens case is a source of infectious organisms.[25] Szczotka-Flynn et al.[26] have recently published an excellent review of the literature on microbial contamination of lenses, solutions, and lens cases. The group concluded that the incidence of positive microbial bioburden within storage cases ranges from 24% to 81% and most studies (72.7%) report an incidence of greater than 50%. Although lens contamination is primarily bacterial, lens cases tend to be colonized with mixed populations of bacteria, fungi, and protozoa, including Acanthamoeba. Biofilms are considered the major culprit resulting in transfer of resistant organisms from the lens case to the lens surface. It has been shown that the biofilms that form on lenses and lens cases render the disinfection solutions less effective.[12,27,28] Moreover, the biocidal properties of solutions are known to be less effective in a home setting where patient noncompliance can reduce their potency.
The potential for tragic consequences is illustrated by a case report published by Robertson et al.,[29] in which an 11-year-old boy suffered a severe Acanthamoeba infection after rinsing his orthokeratology lenses and lens case with contaminated tap water. A Scottish study demonstrated that risk factors for ACA keratitis included a failure to disinfect contact lenses, noncompliant use of chlorine tablets, and/or tap water rinsing of storage cases. They recommended that domestic tap water be avoided for contact lens and storage case hygiene.[30]
Geographical factors may also contribute to the risk of infection as several epidemiologic studies have indicated an increased risk through water supplies.[30,31]
The incidence of Acanthamoeba keratitis is significantly higher in some countries than others, with the United Kingdom having an incidence 15 times that of the United States.[31,32] Kilvington et al.[33] found that the way domestic tap water was supplied in the United Kingdom resulted in a higher incidence of Acanthameoba keratitis and noted that indirect exposure to contaminated tap water, even in compliant lens wearers, is a risk factor for infection. The epidemiological characteristics of the Chicago Acanthamoeba keratitis outbreak revealed unevenly distributed infection rates inconsistent with previously known risk factors, and the unusual geographical distribution suggested that other factors may have played a role in the infectious outbreak.[34] However, another study examining the national outbreak of Acanthamoeba in the United States concluded that the infectious outbreak of Acanthamoeba was likely a result of the combination of contamination with water or dirty hands and a solution insufficiently active against killing Acanthamoeba.[35]
Patient compliance with proper hygiene techniques is critically important for reducing contact lens–related Acanthamoeba spp infection.[2] Perhaps more critical is an initiative to establish clear standards for water exposure among solution manufacturers that are consistent with practitioner, CDC and FDA guidelines. Confusion results when an eye care provider warns against exposure of contact lenses to water but package inserts on lens cleaners recommend cleaning either the lens or the case with tap water.
This review demonstrates the inconsistencies between accepted clinical knowledge about the dangers of nonsterile water exposure for contact lenses and storage cases and the recommendations of the manufacturer. It is paradoxical that none of the soft lens solutions recommended use of water for either lenses or storage cases, yet this advice has been largely ignored for RGP lens hygiene products.
Patients who may not remember what their eye care provider recommends for a hygiene regimen are likely to read package inserts as a guide to lens care. Incongruities between clinician recommendations and written instructions on a solution package is confusing at best and vision threatening at worst in the case of ACA as in our patient. We advocate a modification of current practices within industry to include explicit warnings against use of tap or distilled water sources for cleaning contact lenses or their storage cases.
Eye Contact Lens. 2013;39(2):158-161. © 2013 Lippincott Williams & Wilkins
