THE SCIENCE OF COMFORT
Keeping Lenses Clean
Cleaning is the second key to unlocking the science of comfort and ensuring that your patients will be successful contact lens wearers.
Arthur Epstein, OD, FAAO: As we've already discussed, successful contact lens wear requires the synergy of several key factors. Among them: maintaining a clean lens surface, which is critical. Unfortunately, that's not as easy as it sounds. We discussed the importance of biocompatible disinfection, and in particular, staining and dual disinfection, in the first installment in this series. In this article, cleaning will be the key topic.
Modern lens care products incorporate a variety of active cleaning adjuncts, for example the cleaning agent citrate, which is found in OPTI-FREE® products. Our discussion turns to cleaning, cleaning strategies and how new lens materials and recent lens care challenges have changed the way we look at contact lens cleaning. Join us as our panel of experts explores The Science of Comfort™ — Keeping Lenses Clean.
I think we can all agree that one of the key elements in proper patient care is ensuring that lenses are clean. We accept this as a given, but there is far more to the story.
Dr. Townsend, can you tell us what constitutes a clean lens and why it's important for a lens to be clean?
William D. Townsend, OD, FAAO: Like everything else, a clean lens is a relative thing. We know that ocular proteins start coating the lens surface within minutes after insertion, so some coating is unavoidable.
Based on work by Dr. Jones and his associates in Waterloo, we know that proteins initially deposit on the surface of a hydrogel lens, but the majority eventually will penetrate into the lens matrix.1 The vast majority of these deposits are "natural," meaning they haven't been altered. In contrast, proteins deposit almost exclusively on the lens surface of a silicone hydrogel lens, but a much higher percentage of the protein is denatured.
Excessive deposits can degrade lens surface quality and stimulate an immune response. Therefore, we want to minimize deposits over the projected lifespan of a contact lens.
Dr. Epstein: How do deposits and debris on the lens surface affect the contact lens wearing experience?
Dr. Townsend: In small amounts, lens deposits and debris probably exert a very minimal effect on comfort, vision and wearing time. But larger amounts of deposition degrade comfort and can have a negative effect on vision. The problem is that the progression is gradual, so patients may not be aware of the progressive loss of acuity and comfort. That's why it's so important that we educate patients on the importance of regular lens replacement.
We're inclined to tell patients to rub their lenses after removal for two reasons. First, some studies have demonstrated that even minimal rubbing reduces the bacterial population by approximately 3 log units.2,3 Second, with the increasing popularity of silicone hydrogel lenses, we're seeing more problems with lipid deposits.
Dr. Epstein: Dr. Townsend, while we're discussing this, how important is rubbing and rinsing from a disinfection perspective? Can you share the CDC data from the Fusarium keratitis and Acanthamoeba keratitis outbreaks?
Dr. Townsend: As a general rule, we find rubbing and rinsing to be beneficial in terms of removing deposits and microorganisms, but it's not the only contributing factor to antimicrobial efficacy. This was one of the issues raised during the investigations that followed the outbreaks. When we review the findings of the FDA panel, lack of compliance was equivocal in the genesis of the outbreak. Some lens care systems are simply more efficacious for killing or inhibiting the growth of certain organisms.
METHODS FOR ENSURING CLEANLINESS
Dr. Epstein: Dr. Jones, you have a background in research. Perhaps you can share the most relevant methodologies for measuring the cleanliness of a lens. This is important when we compare cleaning efficacy of one product to another, or when manufacturers evaluate the cleaning efficacy of a new product.
Lyndon W. Jones, PhD, FCOptom, FAAO: As clinicians, we tend to record cleanliness based on the surface appearance at the slit lamp. However, visual inspection of deposits is a less reliable and accurate method to determine the level of deposition on a lens. For example, a lens may have several thousand micrograms of active protein on it and appear clean, and yet a lens with only 10-15 micrograms of denatured protein may appear very dirty. So, clinical inspection is less reliable at judging lens deposits, particularly proteins, as shown by several previous studies.4 The ideal method to assess lens deposition is to analyze it in the laboratory, using sophisticated, scientific methods.
LENS MATERIALS AND PROTEIN DEPOSITS
Dr. Epstein: Do different lens materials attract different protein deposits?
Dr. Jones: Absolutely. As a general rule, when it comes to conventional materials, Group IV materials, such as Acuvue 2* (Vistakon), which have a high water content and are negatively charged, deposit primarily positively charged proteins, such as lysozyme. In comparison, high water neutral, Group II materials, such as SofLens 66* (Bausch & Lomb), primarily deposit lipids.5-7 Silicone hydrogel lenses primarily deposit low levels of relatively denatured protein and are more prone to deposit lipids.5,8-9
Dr. Epstein: How do lipid deposits differ from other contact lens deposits?
Dr. Jones: A major problem with lipid deposits is that they're very difficult to remove from the lens surface. In contrast, protein — particularly if it's still in an active form and isn't denatured — is readily able to passively diffuse out of a contact lens material, particularly following an overnight soak in a solution that contains a sequestering agent, such as sodium citrate.10-12 Thus, Group IV lenses that contain a great deal of protein can be soaked in an appropriate solution and a significant amount of the protein deposited will be passively removed.
Dr. Epstein: That's great information. So from a practical standpoint, what systems most effectively remove lipids from silicone hydrogel lenses? Do peroxide solutions have an advantage?
PEROXIDE VS. MPS
Dr. Jones: To date, very few published studies have evaluated the ability of care systems to remove lipids from contact lenses, particularly silicone hydrogel lenses. A recent study13 reports that a POLYQUAD®/ALDOX® dual disinfection system was able to reduce deposition of the most abundant tear film lipid measured (cholesterol oleate) from Acuvue OASYS* (Vistakon) lenses by 37% compared with a peroxide-based system, when both were used in a no-rub regimen (Figure 1). Less prevalent lipid types showed no difference between the products. Other types of silicone hydrogel lenses require examination to determine if that trend is maintained with other lens materials. Nichols14 has shown that rubbing and rinsing lenses helps keep them clean. Anecdotal reports15 suggest that using dedicated surfactant cleaners, such as MiraFlow* (CIBA Vision), or rubbing and rinsing with modern surfactant-containing multipurpose systems will help remove lipid deposits. If I were prescribing a peroxide-based system, then I would opt for one that contains a surfactant.
Figure 1. A study by Heynen and colleagues, using a no-rub regimen, shows a POLYQUAD®/ALDOX® dual disinfection system reduces deposition of the most abundant tear film lipid measured (cholesterol oleate) by 37% compared with a peroxide-based system.
Dr. Epstein: Your last comment reminded me of something I heard recently. It seems some of our colleagues are combining MPS regimens like OPTI-FREE® RepleniSH® MPDS (Alcon) with occasional peroxide use for additional cleaning. I think this reflects a misunderstanding of how modern lens care products work. All modern multipurpose solutions contain components that clean lenses. For example, OPTI-FREE® RepleniSH® MPDS uses citrate and Tetronic® 1304† as cleaners. The system has been shown to be highly effective for passively removing protein. We'll get into the issue of rubbing in a bit, but it's important to realize that MPS products that achieved no-rub or rub approval had to demonstrate reasonably effective cleaning properties. Some clinicians may disagree about which is the more effective cleaner — MPS or hydrogen peroxide — but there's no evidence that their combined use is additive. So, asking a happy patient who uses OPTI-FREE® RepleniSH® to occasionally switch to ClearCare* (CIBA Vision) may confuse the patient and complicate lens wear, without making the lenses cleaner.
Dr. Lebow, what are your thoughts on this and what do you recommend for your patients?
Kenneth A. Lebow, OD, FAAO: A clean contact lens is a vital part of successful contact lens wear. We all know the best contact lens wear is achieved when patients wear clean, moist lenses on clear, moist eyes. I prefer OPTI-FREE® multipurpose contact lens care systems because they're simple to use; they contain extremely effective disinfectants, and they incorporate both active and passive mechanisms to maintain a clean and moist lens surface.
My typical approach to cleaning lenses is to monitor the patient's adaptation to contact lens wear while using a no-rub regimen. If no deposits are noted on the lens surface after the first 2 weeks of lens wear, I'll allow the patient to follow a no-rub regimen with regular lens replacement. If there are slight surface deposits, presenting a rub-and-rinse usage with the multipurpose solution typically is sufficient to clean the lens surface and maintain comfortable contact lens wear.
In the event that heavier deposits are visible on the lens surface, I add a dedicated surfactant cleaner to the patient's care regimen. However, I know that the more complex I make the care system, the less likely the patient is to follow my instructions. Miraflow*, an alcohol-based hydrogel and silicone hydrogel surfactant cleaning solution, is my cleaner of choice for deposits that require active rubbing to remove deposits. Many of my colleagues have had success with SupraClens® Daily Protein Remover (Alcon) as well.
Dr. Epstein: Dr. Lebow, that brings me to another question. Are patients aware when their lenses are dirty? Do they realize they need to clean more aggressively? I recall the old days of yearly replacement lenses when patients would come in and when you looked at the lens under the slit lamp, some were so coated with deposits that it was a wonder the patient made it to the office.
Dr. Lebow: Ah, the good old days. Patients often have no idea their lenses are dirty, and this can cause problems. I often advise patients to monitor their vision over the course of the lens-wearing cycle. Since many patients simply remove their lenses at night and drop them into their disinfecting solution without using any cleaning procedures, reductions in visual acuity usually occur several days before they need to replace their lenses. So, reminding patients to follow the instructions for more aggressive cleaning procedures may be effective in improving comfort and vision.
TACKLING HEAVY DEPOSITS
Dr. Epstein: How do you handle heavy deposits?
Dr. Lebow: Heavy deposits are certainly a major challenge to a practitioner. Patients with heavy deposits often experience poor vision, reduced wearing time and functional tissue changes, such as giant papillary conjunctivitis (GPC). Effective daily lens cleaners and multipurpose disinfecting solutions with a rub regimen may improve their lens-wearing experience. Interestingly, heavy lens deposits are more often associated with specific contact lens materials rather than solutions.
The first-generation silicone hydrogel materials incorporate various types of plasma treatment on the lens surface to improve wettability. These lenses typically accumulate slightly more protein than newer generation silicone hydrogel materials.16-17 I often find that changing lens materials does as much to reduce lens deposits as encouraging aggressive lens rubbing.
Another approach is to increase the replacement frequency of lens wear. If a patient is wearing a 2-week lens for a month or longer, the resolution is simply to increase the replacement frequency.
Dr. Lebow: Clean lenses are key to ensure successful contact lens wear. Not only do clean lens surfaces promote a healthy ocular surface and reduce the risk of GPC, clean lenses also promote clear, sharp vision.
Dr. Epstein: That has been my experience as well. In fact, more often than not, dirty lenses seem to play a role in many contact lens complications. The trick is getting the patients to keep their lenses clean. I've found the best way to improve compliance is to prescribe a solution that matches the patient's lifestyle and likely care habits. From a lens cleaning perspective what are the differences, if any, between solutions?
Dr. Lebow: As we know, contact lens care systems today are divided into multipurpose care systems and hydrogen peroxide disinfecting solutions. While some practitioners believe all multipurpose solutions are identical, specific and unique differences in cleaning efficacy exist among the products.
Among the different multipurpose care systems, surfactants typically are used as active cleaning agents to remove deposits and protein. By creating a clean surface, they also lower surface tension and improve wettability, which also improves vision. However, some multipurpose solutions incorporate passive cleaning constituents, such as citrate, which is used in OPTI-FREE® products.
Because some patients may be noncompliant, passive contact lens cleaning plays an important role in maintaining clean lenses. Citrate binds with proteins and removes them from the lens surface. In fact, when compared to other contact lens care products, OPTI-FREE® RepleniSH® was found to remove more adsorbed lysozyme than Aquify* (CIBA Vision), ReNu* (Bausch & Lomb) or Complete* Easy Rub (Abbott Medical Optics) (Figure 2).18
Figure 2. A study by Lin and colleagues shows that OPTI-FREE® RepleniSH® removes more adsorbed lysozyme than Aquify* (CIBA Vision), ReNu* (Bausch & Lomb) or Complete* Easy Rub (Abbott Medical Optics).
These differences in protein removal may represent some of the contributing factors responsible for reported19 patient satisfaction rates for OPTI-FREE® RepleniSH® MPDS (Figure 3).
Figure 3. Effective protein removal may contribute to improved patient satisfaction, according to data from a study by Potter and colleagues.
Some peroxide-based systems contain surfactants — others do not. While these peroxide systems are appropriate for some of our patients, they're not superior cleaners. Interestingly, some practitioners believe peroxide-based disinfecting solutions have cleaning capability because they produce bubbles. To my knowledge, there's no clinical evidence that peroxide systems provide more effective cleaning than modern multipurpose solutions.
Dr. Epstein: I think most, if not all of us, agree that peroxide has a role in lens care, but in my practice, it's a niche role. Given the fairly rapid neutralization of peroxide systems, disinfection efficacy may be compromised during long-term storage. Likewise, some peroxide systems may offer good cleaning. I also use MPS simply because that's what my patients want, and products like OPTI-FREE® RepleniSH® MPDS fit their lifestyles and meet their needs.
Some of us were practicing at the beginning of the soft lens revolution. The rest of us started our careers long before disposable lenses and multipurpose solutions were available. So, we've been dealing with compliance issues for most of our careers. Today, we have single-use lenses, 2-week disposable lenses and solutions that require minimal care. But the bottom line is that compliance has remained an issue. So Dr. Kading, is there any relation to compliance and lens complications?
David L. Kading, OD, FAAO: That's a great question and one with a surprising answer. Nearly all of the initial reports that came out during the Fusarium keratitis and Acanthamoeba keratitis outbreaks suggested, among other things, that compliance was a major factor in the infections. However, this was not necessarily the case. The CDC found in both outbreaks that compliance played a smaller role in causing infection. In fact, the only compliance factor was using old solution and topping off, which apparently reduced the antimicrobial effectiveness of the lens care product.
Dr. Epstein: What about hand washing? I've always been a fanatic about it, because it makes sense to never touch the eye or lens with a dirty hand.
Dr. Kading: Good point. We know that even when patients are instructed otherwise, they frequently miss vital steps like hand washing. When they do wash their hands, they often miss key areas, such as their fingertips. And even when they wash their hands properly, Stone20 reported that they reinoculate their fingers when they turn off the faucets. So even with a compliant patient, there's a significant bacterial load inoculated onto the eye. That may explain why the CDC didn't link a lack of hand washing to increased risk of infection in either outbreak. So, we've always thought that patient noncompliance was the 800-pound gorilla here, but the lesson may be as simple as this: We should select a solution that has a proven track record and a demonstrated safety profile.
Dr. Epstein: So why is passive cleaning important?
Dr. Kading: We know that the majority of patients (more than one-half) place their lenses directly in the case when they remove them. In fact, data presented at the recent FDA panel meeting showed no difference in the rate of manual cleaning before or after the introduction of no-rub solutions.20 Even the massive publicity and warnings that came out during the Fusarium keratitis outbreak didn't change patient behavior. In the end, despite what we tell them, only half of all patients rub and rinse, and the others "plunk and dunk." So, if it weren't for passive cleaning, many patients wouldn't have a clean lens at all.
Dr. Epstein: Well, that gives us some insight into the role of compliance and microbial keratitis — at least relative to the recent outbreaks, but what about less severe complications like GPC and subepithelial infiltrates? Are they more or less of a problem today?
Dr. Kading: In the classic sense, GPC is not where it was 10 or 15 years ago. Since the introduction of silicone hydrogel lenses, we haven't seen as many patients dealing with protein buildup. Instead, we think we see lipids associated with these lens materials. Mechanical GPC is still present and always will be as long as we have dirty contact lenses.
Dr. Epstein: I would agree with that except for a brief blip caused by increased extended wear during the early days of silicone hydrogel lenses. Also, I should note that the consensus these days is that GPC is mechanical — at least as a trigger.
Dr. Kading: Infiltrates are the ugly little brother. They seem to stick around no matter what we do. It was thought that new lens technology, such as silicone hydrogel lenses, would greatly reduce the number of cases we saw. We quickly learned that certain lens-solution combinations increase the risk of toxic corneal staining, and toxic corneal staining leads to a three-fold increase in the risk of corneal infiltrates as had been recognized before.21
Dr. Epstein: In a broad sense, is a clean lens less likely to cause serious complications?
Dr. Kading: Absolutely. Although there are other ways to introduce microorganisms into the ocular environment, a bacteria-laden lens poses an increased risk to the ocular environment. However, a recent article by an Australian researcher reported the risk of developing microbial keratitis from daily disposable contact lenses is slightly higher than frequent replacement lenses.21 It's important to note that a brand-new contact lens isn't necessarily a clean lens.
Dr. Epstein: We've touched on some of the hottest topics in optometry today, including rubbing and rinsing, MPS vs. hydrogen peroxide systems, and silicone hydrogel lipid removal. Hopefully, this discussion will help our fellow clinicians develop their own opinions on these subjects.
We have covered two important areas in the effort to optimize the contact lens wearing experience. In the next installment in this series, we'll discuss what could be one of the most important aspects of successful contact lens wear — wetting. CLS
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†Tetronic® is a registered trademark of BASF.