Contact lens-associated microbial keratitis is a sight-threatening condition wherein there is an infiltration of bacteria into the corneal epithelium, causing an inflammatory response that ultimately can result in corneal damage (Fleiszig and Evans, 2010). The most dreaded and shared pathogens that cause these diseases are Pseudomonas sp., Acanthamoeba sp., Fusarium sp., Staphylococcus sp., and Serratia sp. These pathogens thrive in water, food, and soil; are essentially non-pathogenic in the environment; and are often part of the normal microbiota of the eye and adnexa.
Because of the virulent profile, Pseudomonas aeruginosa is of particular concern because it can penetrate the cornea even without an epithelial break (Hoffman and Pelosini, 2016). Pseudomonas has been known to contaminate substances containing traces of organic carbon, including ophthalmic solutions such as fluorescein and ocular cosmetics and makeup such as eyeliner and mascara (Hoffman and Pelosini, 2016). Inoculation of these bacteria comes mostly from the lid margins, contact lens application, contaminated contact lens cleaning solution, or less frequently from a contact lens case (Hoffman and Pelosini, 2016; Stapleton and Wu, 2011).
Environmental factors and poor hygiene often lead to contact lens and contact lens case contamination (Stapleton and Wu, 2011). There has also been a correlation between a decreased frequency of cleaning contact lens cases and an increased level of bacterial contamination (Stapleton and Wu, 2011). Therefore, it is not surprising that the same pathogens that adhere to the contact lenses, including Pseudomonas, proliferate in the case (Stapleton and Wu, 2011).
Bacteria contamination leads to the formation of bacterial biofilm made from a polymeric extracellular matrix as the bacteria grow under a minimal nutrition environment. This makes the biofilm adhere on both the contact lens and the case. The biofilm on these surfaces will then mature, making it difficult to remove by disinfection system alone (Bispo et al, 2015; Thakur and Gaikwad, 2014).
According to a study by Szczotka-Flynn et al (2010), the frequency of contact lens case contamination is greater than that of the contact lenses themselves. By conducting a literature review, they found contamination rates as high as 81% in contact lens cases. In addition, the cases were mostly contaminated with bacteria, and the frequency of isolation of Acanthamoeba sp. was at 8% in cultures.
This same study reported that contact lens cases also tend to harbor fungi and protozoa. This was also reported in 101 study subjects. In that study, 24 and 20 contact lens cases harbored fungi and protozoa, respectively, with the highest count of 72 lens cases or 81% harboring bacteria. With that, the average incidence of contact lens case contamination due to microbes is at least 50%.
Thakur and Gaikwad (2014) tested the rate of contamination of microbes in the contact lenses, the lens cases, the tips of the lens care solution bottles, and the lens care solutions. There were 50 study participants, none of whom had any history of eye infections. The results of their study showed that contact lens cases have the highest rate of contamination at 62%, followed by contact lenses at 56%, the tips of lens care solution bottles at 48%, and lens care solutions at 42%. These contamination rates are also affected by the compliance of the users when it comes to hygiene and care for their lenses, lens cases, and solutions.
According to Wu et al (2015), there is a positive correlation between the use period of the contact lens case and the levels of microbial contamination. Contact lens cases that are less than six months old have less contamination compared with those that are older than six months. Therefore, replacement of contact lens cases on a frequent basis is recommended. In fact, the most common way to prevent microbial contamination of contact lenses has been the frequent replacement of the contact lens case (Wu et al, 2015).
It is important to educate your patients to reduce microbial contagion associated with contact lens use. Frequently replacing the contact lens case prevents the adherence of the pathogens and the formation of the biofilm. Following the manufacturers’ recommendation on the frequency of replacing the contact lens case reduces overall contamination of the contact lenses, preventing eye infections (Melton and Thomas, 2016; Epstein, 2016).
Just as we think of daily disinfection of contact lenses, maybe it is time to think about daily disinfection of contact lens cases—perhaps, even by using products intended for ocular use such as hypochlorous (HOCl) acid. With the ease of availability of HOCl acid and its well-noted broad-spectrum activity against a wide range of microbes, the use of a once-daily application after the lens case is dry would seem like a very effective manner of disinfecting the contact lens case and disrupting the associated bacterial biofilm (Wu et al, 2015; Krader, 2014; Debabov et al, 2015; Yeung et al, 2010). The chemical nature, stability, safety, and activity of HOCl acid make it a very effective oxidizing antimicrobial. And, it has been proven to be harmless and non-toxic to the eyes (Krader, 2014; Debabov et al, 2015).
The bacterial environment of the eye changes in the presence of contact lenses. It is clear that a contaminated contact lens case has the potential to act as a reservoir for microorganisms known to have catastrophic potential in the event of an infection. Most of our clinical conversations have centered around the proper use and disinfection of contact lenses, much more so compared to the disinfection of other potential sources of microbial infection such as contact lens cases.
Clinicians should look at all sources of contagions while keeping in mind the safety of their contact lenses wearers. Proper disinfection of contact lenses has been central to the conversation in contact lens use.
But, perhaps it is time to be reminded about the need to make disinfection of lens cases (Boyd, 2017) part of the conversation of daily contact lens disinfection to help prevent and manage contact lens-related eye infections. CLS
For references, please visit www.clspectrum.com/references and click on document #264.