NEW RESEARCH being published in response to the pandemic has helped to fill gaps in knowledge about the activity of contact lens solutions against emerging pathogens.

GUIDELINES AND TESTING

Before contact lens cleaning solutions reach the market, they must go through regulatory approval, demonstrating a minimum established antimicrobial activity generally described by International Standards Organization (ISO) guidelines. The most important guideline for contact lens solutions is ISO 14729, which details the microbiological testing that solutions need to pass to be labeled as disinfectants, including information on the test organisms, the test procedures, and evaluation criteria (ISO, 2017). For example, as part of testing, it is expected that a solution is exposed to a set number of microorganisms, and the effectiveness of its disinfection is evaluated by capturing the number of viable microorganisms at certain time points after exposure.

The intrinsic property of a disinfecting solution to reduce microorganism numbers is evaluated using the “stand-alone” test, in which microorganisms are exposed to the solution on their own with no other actions, such as rinsing. The assumption is that the stand-alone test evaluates what the solution can do on its own.

Not all solutions are able to demonstrate sufficient reduction in microorganism count using the stand-alone method for all organisms specified in the guidelines. In these situations, solutions may be further evaluated for approval with the “regimen procedure,” which incorporates the recommended steps that would be done if the solutions were used in practice as directed, including rubbing and rinsing of contaminated contact lenses (ISO, 2017).

Moreover, since studies have shown that the presence of a contact lens can reduce the antimicrobial efficacy of some contact lens solutions (Gabriel et al, 2018), an additional standard, ISO 18259, was developed to assess the impact of contact lenses and contact lens cases on solution antimicrobial efficacy (ISO, 2019). Health Canada has also published its own guideline, “Safety and Effectiveness Requirements for Contact Lens Disinfectants,” with the most recent revision taking effect in 2018 (Gabriel et al, 2018).

All of these guidelines specify testing against numerous named bacteria (such as P. aeruginosa, S. aureus, and S. marcescens) and molds/fungi (including C. albicans and F. solani) and are required to demonstrate 99.9% and 90% reduction in recoverable microorganisms, respectively, when used as directed. Health Canada also includes a suggestion for testing against Acanthamoeba, while acknowledging that there may not currently be an agreed-upon method to test contact lens solutions against the protozoan species.

VIRUCIDAL TESTING

Interestingly, current guidelines do not cover virucidal testing and, therefore, they do not include a methodology or performance criteria for solutions challenged by viruses. Historically there was a recommendation to test the virucidal activity of CL solutions, with the U.S. Food and Drug Administration (FDA) requiring evidence of the virucidal efficacy of CL care products against the herpes simplex virus (FDA, 1985).

However, in the 1990s, testing against viruses was no longer considered essential, so specific literature or guidelines describing methodologies to test virucidal activity of CL care products date from the 1980s and early 1990s. The lack of any guidance for testing solutions for virucidal activity represents, at a minimum, a concern—not only in light of discussion of potential SARS-CoV-2 transmission through the eye during the COVID-19 pandemic, but also considering the potential for transmission of known ocular viruses such as adenovirus and herpes simplex virus.

Several recent laboratory-based studies have looked into the potential of contact lens solutions to remove or deactivate surrogate coronaviruses of the SARS-CoV-2 virus (Yasir et al, 2022; Nogueira et al, December 2022; Nogueira et al, April 2022). The use of surrogate coronaviruses, such as the seasonal human coronaviruses HCoV-229E and HCoV-OC43 strains (Nogueira et al, December 2022; Nogueira et al, April 2022) or the coronavirus mouse hepatitis virus (Yasir et al, 2022), allows for evaluation of potential effects against the SARS-CoV-2 virus without exposing researchers to the potentially higher levels of risk. Similar expected results are due to similarities in viral structures owing to their all belonging in the same virus family (Nogueira et al, April 2022).

Interestingly, studies conducted in two worldwide laboratories reached strikingly similar results. Namely, multipurpose or non-oxidative solutions that utilize active ingredients such as polyquaternium-1, alexidine, or polyhexamethylene biguanide as disinfection agents are ineffective against these viruses in stand-alone tests, leading to continued recovery of virus particles and demonstrating no intrinsic anti-coronavirus activity (Yasir et al, 2022; Nogueira et al, April 2022).

However, it appears that simply rinsing contact lenses with multipurpose solution, or even with saline, is sufficient to remove the virus particles, suggesting that the viruses are not strongly adherent to the contact lenses tested and that effective removal can be achieved by following manufacturers’ cleaning and disinfection regimens, including rubbing and rinsing (Yasir et al, 2022; Nogueira et al, December 2022).

These studies are also complemented by one published study on the effectiveness of these solutions against the SARS-CoV-2 virus itself, obtained via positive residual diagnostic material (Veugen et al, 2022). Multipurpose solutions were found to have little effect in reducing the SARS-CoV-2 counts, but the counts could be significantly reduced by following the manufacturer’s instructions, again due to simply rubbing and rinsing the lenses (Veugen et al, 2022).

Across these studies, oxidative, non-multipurpose systems based on hydrogen peroxide or povidone iodine were more than effective against these viruses, reducing them below limits of quantification after following manufacturers’ instructions (Yasir et al, 2022; Nogueira et al, December 2022; Nogueira et al, April 2022; Veugen et al, 2022).

CLEANING AND DISINFECTION

The American Optometric Association and the American Academy of Optometry have published their guidance on the proper safe handling of multiuse contact lenses in a clinical setting. That guidance closely follows the recommendations in the ISO 19979:2018 standard, which discusses hygienic management of multiuse contact lenses (Sindt et al, 2020; ISO, 2018).

Importantly, they recommend that any contact lens that has been in contact with a patient who presents with or is diagnosed with an infectious disease—including hepatitis, HIV, Prion disease, ocular herpes infection, adenovirus, and Acanthamoeba—should immediately be discarded rather than attempting to disinfect or sterlize it (Sindt et al, 2020). This also applies to patients who may be carriers of infectious diseases of concern; contact lenses used in patients or potential patients who have herpes simplex, HIV, adenovirus, or Creutzfeldt-Jakob disease also need to be discarded rather than disinfected for reuse.

For contact lenses that can be disinfected, 3% hydrogen peroxide is the recommended solution; those lenses need to be in hydrogen peroxide for at least three hours prior to being transferred to the neutralizing case (Sindt et al, 2020).

IN SUMMARY

For the contact lens practitioner, knowledge of the effectiveness of solutions and procedures associated with safe contact lens practice is reassuring, particularly in a period of heightened awareness of disease transmission. While there continues to be a need to remain vigilant in reducing the risk of disease transmission, the standard procedures associated with the processing and disinfecting multiuse contact lenses appear to continue to be effective and are supported by research in their reduction in infectious microorganisms when used correctly. CLS

The author would like to thank Dr. Christiane Lourenco Nogueira for her helpful comments and editing of this article.

REFERENCES

1. International Organization for Standardization (ISO). ISO 14729:2001: Ophthalmic optics — Contact lens care products — Microbiological requirements and test methods for products and regimens for hygienic management of contact lenses. 2017. Available at iso.org/standard/25382.html . Accessed Nov. 22, 2022.
2. Gabriel MM, McAnally C, Bartell J. Antimicrobial Efficacy of Multipurpose Disinfecting Solutions in the Presence of Contact Lenses and Lens Cases. Eye Contact Lens. 2018 Mar;44:125-131.
3. ISO. ISO 18259:2001/2014. Ophthalmic Optics–Contact Lens Care Products–Method to Assess Contact Lens Care Products with Contact Lenses in a Lens Case, Challenged with Bacterial and Fungal Organisms. 2019. Available at iso.org/standard/61901.html . Accessed Nov. 22, 2022.
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