Dealing with Deposits
A primer on how to best manage (or even prevent) protein deposition on contact lenses.
By William J. Lapple, OD
We're all aware of the fact that low-carb eating is all the rage in nutrition and lifestyle circles; I'd like to see a similar awareness created around the need for low-protein deposits within the contact lens fitting community. This article will attempt to stimulate some of the same "excitement" and interest that the low-carb trend enjoys.
Protein Denaturation Cascade
Proteins are complex organic compounds comprised of amino acid chains that can contain a variety of elements (carbon, nitrogen, hydrogen, phosphorous, iron, etc.) that peptide bonds connect. Oxidation, heat, ultraviolet (UV) light exposure and drying can denature or alter naturally occurring proteins (such as lysozyme). Lysozyme is the main protein within the tear film, and one of its primary functions is to combat microbial activities on the surface of the eye.
Denaturation is a chemical and physical transformation that causes a change in the configuration of the protein. This change in configuration alters the function of the protein and may inactivate it entirely. You can observe this inactivation microscopically as an unfolding of the tertiary structure of the protein. In addition to deactivation, the unfolding exposes previously hidden portions of the protein, causing the denatured protein to bind or attach to other substances.
Within the tear film, as lysozyme denatures, it can build up on the surface of contact lenses, forming what we all refer to as protein deposits. Not only do these deposits impact the transparency of the lens and the integrity of the lens surface, but they may also challenge the body's immune system. The ocular system may perceive denatured protein deposits as a foreign body invasion and produce antibodies in response. These antibodies can cause inflammation and ocular side effects such as irritation, redness and itching.
The denaturation cascade can also lead to the increased potential for more serious ocular reactions such as giant papillary conjunctivitis (GPC) and superior limbic keratoconjunctivitis (SPK), while keratitis is another immune response that experts have linked to denatured protein deposits. In addition, because lysozyme is no longer in its native state, it's no longer capable of effectively fulfilling its anti-microbial function, which can result in further complications. The bottom line is that denatured protein can contribute to a variety of adverse effects in and around the eye, all of which may diminish the patient's contact lens-wearing experience, leading even to drop out.
Figure 1. ReNu with MoistureLoc prevents irritating protein deposits.
|Figure 2. Patients consistently rated ReNu with MoistureLoc higher than their previous lens care system.|
Managing Protein Deposits
While a lot of protein may be good for your Atkins diet and for your waistline, a large amount of denatured protein on your contact lenses isn't a good thing. Studies indicate that protein deposition on lenses begins the minute you apply a lens to the eye. As this protein denatures, the deposits become more opaque, which contributes to lens discoloration and decreased visual quality.
Protein deposits that are visible to the naked eye are most often a result of denaturation. While even a visibly clean lens may still have protein deposits, only denatured deposits increase the possibility of clinical symptoms associated with contact lens deposits. As such, denatured protein on the contact lens surface can result in negative changes in optical properties as well as increased potential for ocular reactions. It stands to reason that the physiological reactions resulting from denatured protein can have a negative impact on lens wearer success and can drive patients to drop out of contact lens wear.
Within my practice, I strive to give my patients the greatest chance of success with contact lenses any way that I can. I manage protein deposits in a variety of ways, including using lens materials that have a proven low-protein uptake profile; effectively training my opticians and optometric technicians to ensure proper patient education as well as recommending superior multipurpose solutions to patients to facilitate proper cleaning and disinfection regimens.
The goal of effective protein management isn't only the improved eye health of patients, but it's also an improved comfort factor for them and a reduction in contact lens dropouts. And for eyecare professionals who take protein management seriously, those aforementioned patient benefits can ultimately translate into benefits for your practice.
Preventing Protein from Denaturing
When it comes to multipurpose solutions, there hasn't been a significant innovation regarding ways to specifically combat denatured protein deposits on contact lenses. Indeed, no system specifically addresses denatured protein -- they simply aim to remove protein.
Up until recently, the primary method of dealing with protein deposits was to use a surface-active ingredient to adhere to the protein and to remove it from a lens or to use a calcium-sequestering agent to bind calcium and thereby remove a necessary protein-binding factor. All the leading multipurpose solutions use some variation of these approaches to remove protein from the lens surface. However, once a patient has cleaned his contact lens and applied it back onto his eye, the protein deposition cascade and denaturation begins within minutes.
I believe that a better approach to managing protein deposition is to prevent proteins (such as lysozyme) from denaturing in the first place. That way, we keep the protein in its naturally occurring native state, which enables the helpful lysozyme to carry out its beneficial anti-microbial functions while preventing the negative outcomes associated with the denaturation cascade.
Preventing Protein Deposition
According to an in-vitro study submitted to the FDA, researchers used a lysozyme activity assay to compare the percent of native lysozyme deposition on contact lenses as an indicator of protein stabilization. They combined ReNu with MoistureLoc Multi-Purpose Solution (Bausch & Lomb), Opti-Free Express (Alcon) or Complete MoisturePlus (Advanced Medical Optics) each with lysozyme and exposed them to an 80°C water bath for 20 minutes. The researchers then assessed lysozyme activity using a spectrophotometer. The results show that ReNu with MoistureLoc prevented significantly more denatured lysozyme deposition compared to other marketed multipurpose solutions. Specifically, the newly re-engineered ReNu prevented 98 percent of potentially irritating protein deposits; the next closest multipurpose solution allowed twice the amount of protein deposits on the study lenses as ReNu with MoistureLoc (Figure 1).
Patient Preference: Clinical Results
I recently participated in a multi-site clinical study involving an innovative multi-purpose solution that has been proven to keep more protein within its native state than any other available solution, thereby reducing the overall amount of denatured protein within the eye. The product used in my patient satisfaction clinical was ReNu with MoistureLoc, a new multi-purpose solution that contains a proprietary combination of non-ionic surfactants and moisture-retaining polysaccharides.
Figure 2 shows the aggregate results for the controlled clinical evaluation that was the basis of the FDA submission. Within that evaluation, 99 patients used ReNu with MoistureLoc Multi-Purpose Solution for three months without lens replacement. At the completion of the study, the researchers asked the patients to complete a forced-choice questionnaire that quantified preferences in performance for ReNu with MoistureLoc Multi-Purpose Solution vs. the patients' previous lens care system. Previous systems included ReNu MultiPlus (B&L, 36.4 percent), Opti-Free Express (18.2 percent), Complete MPS (10.1 percent) or other (35.4 percent).
My own clinical results, which involved 20 participants, mirror the findings of the study submitted to the FDA. You'll note that one-third more of the participants preferred ReNu with MoistureLoc over their previous solution regarding perceived lens comfort and cleanliness throughout the day with 50 percent more respondents stating that ReNu with MoistureLoc made their contact lenses more comfortable upon application compared to their previous solution.
Comfort and Protein
I believe that one of the reasons for this higher patient preference for ReNu with MoistureLoc is its inherent ability to keep more lysozyme in its native state than the leading multi-purpose solutions that are currently available. Denatured protein that adheres to the surface of the lens creates an unhealthy ocular environment that can lead to inflammatory reactions, reduced visual acuity, discomfort and, ultimately, contact lens drop out.
We know that comfort is a key criterion for lens wearers and whether or not they ultimately remain in contact lenses. In fact, lack of comfort or discomfort, is the number-one reason why individuals stop wearing contact lenses, according to a 2003 Gallup survey. Your patients rely on you to make the best choice for them at every decision point. Your recommendation of multipurpose solution can help prevent excessive and unnecessary protein buildup from occurring on your patients' contact lenses.
Ultimately, contact lenses are medical devices, and medical devices require professional recommendations to ensure the safest and most effective lens-wearing experience. Your professional recommendation regarding multipurpose solutions should be more than just an afterthought, because it may help give your patients a positive, event-free lens-wearing experience. Given the fact that many of the new lens wearers in my practice, and probably in yours as well, are teenagers, they may not be accustomed to proper lens care and may not follow a proper care regimen or replacement schedule. If we combine that reality with the typical physiological conditions that impact all lens wearers' success, it's easy to see just how important a role the issue of protein management plays as part of a comprehensive lens selection process.
Dr. Lapple received his optometric degree from The Ohio State University College of Optometry. His primary eyecare facility in LeRoy, NY, provides a full range of services. Dr. Lapple has performed many contact lens research projects and has lectured extensively on the microbiologic efficacy of contact lens solutions. He has no affiliation with Bausch & Lomb other than as an independent clinical investigator.