Article Date: 8/1/2009

The Science of Contact Lens Care

The Science of Contact Lens Care

Contact lens care is a complex topic. Noncompliance is a significant issue that likely will cause comfort issues. Additionally, it's important to select suitable contact lens care systems for our patients. First, we'll discuss the science behind contact lens care. Then, we'll discuss ways to improve patient behavior and compliance.

CONTACT LENS CARE

Addressing the disinfection capabilities of contact lens solutions is intricate and complex. We learned this in 2006 with the recall of a major contact lens solution, which used a monomeric biguanide, Alexidine, as its preservative and Polyquaternium-10 and poloxamer 407 as its wetting agent. ReNu* with MoistureLoc* (Bausch & Lomb) was associated with an increased risk of Fusarium keratitis.1,2 About 1 year later, Complete MoisturePlus* (Abbott Medical Optics), a PHMB-preserved product that used propylene glycol and hydroxypropyl methylcellulose as its wetting agent, was recalled. This solution was associated with an increased risk of Acanthamoeba keratitis.3-5

The recalls were unfortunate, but they served as a much needed wake-up call for many practitioners who realized the influence that care systems could have on corneal health. Keeping patients healthy in their contact lenses is our first priority and plays the biggest role in providing an optimal wearing experience for all patients.

DISINFECTION

Research has assessed the efficacy of contact lens care systems using a variety of approaches. In two different studies testing efficacy against various organisms, research groups found that contact lens multipurpose solutions have variable disinfecting capabilities after being soaked for a week in the presence of a group IV soft, hydrophilic contact lens.6 All PHMB multipurpose solutions tested showed decreased activity against various organisms in this study.6 Only the multipurpose solutions containing POLYQUAD® and ALDOX® preservatives retained similar activity after a 7-day soak with this type of lens.6,7

One reason for reduced clinical activity of care solutions is that certain disinfecting molecules more readily uptake into contact lenses.7-8 With these preservatives in the contact lens and not in the solution in the case, the solution is believed to be less effective against microbes over time. This is of greatest significance for patients who top off their solution. Additionally, preservatives in the contact lens can be released onto the ocular surface when the lens is placed on the eye. This is the likely mechanism that causes transient corneal staining with certain contact lens´┐Żmultipurpose solution combinations.8-12

CORNEAL STAINING

The most extensive study on staining responses with various lens-solution combinations was performed by Andrasko and Ryen.12,13 They tested the staining response from various contact lenses soaked overnight in different multipurpose solutions, then worn by patients for 2 and 4 hours. After the contact lenses were removed, a masked examiner graded the corneal staining response. A summary of the staining responses from the 2-hour timepoint appears in Figure 1.

Figure 1. A summary of the staining responses seen with various contact lens-solution combinations.

Although this transient staining response has been well documented, there's still significant debate as to the clinical consequences.13-15 In an attempt to gain further insight, corneal permeability studies were undertaken using fluorophotometry. Corneal permeability was measured in patients wearing contact lenses that were soaked overnight in various multipurpose solutions. Results showed that higher staining contact lens and lens care solution combinations were more likely to demonstrate higher levels of fluorescein permeability.16-17 Additionally, there's evidence to show that corneal inflammatory events are more likely to occur when corneal staining is present in contact lens wearers.15

Although an increase in infection hasn't been correlated with solution-induced staining, we believe that it's incumbent upon the eyecare practitioner to maintain the structural integrity of the cornea. As such, we should recommend contact lens care systems that deliver a high level of disinfection and minimal corneal staining. We should use the staining grid as an educational tool for our patients and as a guide when making care system recommendations.

WETTING

Disinfection is only part of the equation. Surface wetting is also important when discussing comfort and contact lens care systems. Research into the understanding of how a contact lens interacts with its environment has brought much attention to this topic.

Contact lenses that are highly wettable will have the hydrophilic portion of their molecular polymers oriented toward the surface of the lens. The process of converting this very hydrophilic surface into a hydrophobic one may occur readily upon repeated exposure to air. Unfortunately, we also know those areas that become hydrophobic are very difficult to convert back to hydrophilic without the aid of a wetting agent.

We should consider ways to maximize the hydrophilicity of contact lens surfaces. Many novel wetting agents have been introduced to contact lens formulations. Polyquaternium-10 with poloxamer 407 found in ReNu® with MoistureLoc* (recalled), propylene glycol with hydroxypropyl methylcellulose found in Complete MoisturePlus* (recalled), and TETRONIC 1304* combined with C9ED3A to form TEARGLYDE® found in OPTI-FREE® RepleniSH® MPDS are examples of the most contemporary wetting and lubricating agents included in the newest generation of multipurpose solutions.

Interesting research using the Shack-Hartmann sensor may have the ability to indirectly detect tear film stability over a contact lens. Using a novel study design, researchers at Manhattan Vision Associates had patients wear either a group IV hydrogel lens or a silicone hydrogel lens. These lenses were soaked overnight in either ReNu MultiPlus* (wetting agent TETRONIC® 1107) or OPTI-FREE® RepleniSH® MPDS (TEARGLYDE® wetting agent). After 8 to 10 hours of wear, the Shack-Hartmann sensor was used to take wavefront measurements. The results were quite dramatic, favoring the OPTI-FREE® RepleniSH® MPDS in the silicone hydrogel group and showing no difference in the hydrogel group.18 This may suggest that hydrophilicity, and thus wettability, of a lens would be better at promoting an improved wavefront, which might be associated with a more stable prelens tear film.

Interestingly, prelens tear thinning time (PLTTT) was measured19,20 in symptomatic and asymptomatic contact lens wearers by specular reflection. Seventy-five percent of symptomatic contact lens wearers had an average PLTTT of less than 3 seconds. Both the prelens tear stability and PLTTT suggest the prelens tear film plays a key role in contact lens comfort.

HYDROGEN PEROXIDE

Hydrogen peroxide provides a unique option for patients who are hypersensitive to any multipurpose solution components. The highest level of disinfection efficacy occurs when lenses are soaked in a 3% peroxide solution for 4-6 hours.

In a recent study,21 symptomatic contact lens wearers wore senofilcon A contact lenses and used either OPTI-FREE® RepleniSH® MPDS or Clear Care* in a crossover, double-masked randomized study design. Extracted lipids were quantitatively measured, revealing that 36% more lipids were found on lenses cleaned with hydrogen peroxide.

COMPLIANCE

Care of contact lenses begins with clean hands, yet 35% of patients don't wash their hands before handling their lenses, and 42% leave their hands wet with tap water after washing and while handling their lenses.22 It's been documented that 71,000 colony forming units (CFUs) were recovered from contact lenses handled with unwashed hands, 9,200 CFUs with washed but not dried hands and 3,600 CFUs with washed and dried hands.22 This indicates that our patients can significantly reduce the microbial load delivered to a contact lens by washing and drying their hands before handling their lenses.

Many patients don't wash their hands correctly. They often miss key areas (Figure 2). To wash hands correctly, patients should remove hand jewelry, wet their hands with warm, running water, apply soap and lather well, rub hands together for 10-15 seconds, while scrubbing all surfaces (back of hands, under fingernails, nail beds, wrists and between fingers), rinse well and dry with a clean or disposable towel.23 When selecting a soap product to clean the hands, it's best to avoid perfumes and moisturizing agents and products that are lanolin based. These products tend to stay on the hands after rinsing and can contaminate the lens surface by causing deposits.23

Figure 2. This image shows the areas most frequently missed when hand washing.

When washing with a source other than soap and water, it's important for patients to use an alcohol-based product. They should apply a sufficient amount of sanitizer to cover all of the hand and wrist surfaces, and they should wait until their hands are completely dry before handling contact lenses to avoid contamination. Additionally, hand sanitizers shouldn't be used if the hands are visibly dirty, because they sanitize rather than clean.24

Patients seek convenience more than ever. Up to 90% of patients aren't compliant with their recommended lens care regimens.22 The contact lens council reports that more than 44% of lens wearers always or occasionally top-off the solution.25 Contact lens solution recalls have made us realize the danger of this practice. Topping off can reduce the effectiveness of solutions, allowing microbial growth and encouraging biofilm growth.

Additionally, topping off may indicate that patients aren't cleaning their lens cases as often as they should. All products contain specific instructions for lens case care. Furthermore, 71% of eyecare providers instruct patients to clean their lens cases, but only 46% of patients actually do this after each use.25 Gromacki26 reports that nearly 70% of all contact lens cases are contaminated with bacteria, fungus, yeasts or amoeba. For these reasons, we tell patients to clean their lens cases each day by rinsing them with fresh solution before allowing them to air dry. We suggest that patients replace their cases according to product directions. There are also novel contact lens cases, such as PRO-GUARD* Lens Case (CIBA Vision), that contain antimicrobial properties that may reduce case contamination in addition to potentially disinfecting the lens.

Significant hurdles also exist in getting patients to comply with our care solution recommendations. In a recent study of over 250 eyecare practitioners, none said they recommend store brand or generic contact lens solutions.27 But market analyses of care systems show that more than 30% of all solutions sold are private label or store brand.27 Consider that it may be difficult for some patients to differentiate between solutions, especially since some carry labeling that's very similar to branded care systems.

In addition, many of our patients don't replace their lenses as often as they should. The Contact Lens Council reports that about half (49%) of contact lens wearers will wear their lenses longer than prescribed or recommended,25 which can cause surface deposits, lid anomalies and ultimately comfort issues.

We're fortunate that poor compliance doesn't often result in corneal morbidity. But the unfortunate reality is that over long periods of time, noncompliant patients will risk uncomfortable contact lens wear and increase their likelihood of dropping out of contact lenses completely. If your patients understand why compliance is important, they'll be more likely to comply with your recommended care regimen. Here's a sample of what we tell our patients: "I never want the comfort of your contact lenses to be an issue for you. In my experience, the best way to keep you comfortable in contact lenses is for you to replace your contact lenses the way we discussed and use the solution that I recommended in exactly the way we discussed. This will maximize your chances of always being able to wear contact lenses comfortably."

When patients decide they want to wear contact lenses, most of them have the intention of staying a contact lens wearer for a very long time. Compliance will help minimize microbial build-up, decrease lens deposits and help keep their lenses comfortable. By explaining these issues to our patients, we'll help them realize the benefits of proper hand washing, lens care and replacement in their long-term healthy contact lens plan.

UNDERSTANDING SCIENCE, PROMOTING COMPLIANCE

Understanding the science behind the care systems we recommend will help us maintain a healthy contact lens practice by helping to keep patients comfortable in their contact lenses. Proper disinfection, retaining moisture on the lens and keeping the surface of the lens clean are all key components in creating an ideal lens-wearing experience. With the right balance of the three, we offer patients their best chance to remain healthy and comfortable in contact lenses. CLS

TETRONIC® is a registered trademark of BASF
*Trademarks are the property of their respective owners

REFERENCES

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  2. Saw SM, Ooi PL, Tan DT, et al. Risk factors for contact lens-related fusarium keratitis: a case-control study in Singapore. Arch Ophthalmol. 2007;125:611-617.
  3. Joslin CE, Tu EY, Shoff ME, et al. The association of contact lens solution use and Acanthamoeba keratitis. Am J Ophthalmol. 2007;144:169-180.
  4. Thebpatiphat N, Hammersmith KM, Rocha FN, et al. Acanthamoeba keratitis: a parasite on the rise. Cornea. 2007;26:701-706.
  5. McAllum P, et al. Acanthamoeba Keratitis: a New Epidemic. Presented at the 2007 Canadian Ophthalmology Society Meeting. Montreal, Canada.
  6. Rosenthal RA, et al. High capacity disinfection of contact lenses. Poster presented during the 2001 annual meeting of the British Contact Lens Association.
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  8. Carey, et al. Correlating biocide uptake and release with corneal staining and subjective symptoms. Poster presented during the 2005 annual meeting of the American Optometric Association.
  9. Epstein AB. SPK with daily wear of silicone hydrogel lenses and MPS. Contact Lens Spectrum. November 2002.
  10. Jones L, MacDougall N, Sorbara LG. Asymptomatic corneal staining with the use of balafilcon silicone-hydrogel contact lenses disinfected with polyaminopropyl biguanide-preserved care regimen. Optom Vis Sci. 2002;79:753-761.
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  14. Geffen D. Multipurpose solution compatibility in clinical experiences. Review of Optometry. May 2008.
  15. Carnt N, Jalbert I, Stretton S, Naduvilath T, Papas E. Solution toxicity in soft contact lens daily wear is associated with corneal inflammation. Optom Vis Sci. 2007;84:309-315.
  16. Hall JQ, Paugh JR, Peinovich M, et al. A pilot study of the effect of silicone hydrogel lenses and marketed multipurpose solutions on human epithelial barrier function. Poster presented during the 2007 annual meeting of the Association for Research in Vision and Ophthalmology.
  17. Webb JF, Paugh JR, Ramsey AC, et al. Clinical and epithelial barrier function evidence of lens material and care solution bio-incompatibilities. Poster presented during the 2008 annual meeting of the Association for Research in Vision and Ophthalmology.
  18. Zikos GA, Kang SS, Nason RJ, et al. Objective in vivo contact lens wettability testing with different MPS using the Shack-Hartmann sensor. Poster presented during the 2008 annual meeting of the Association for Research in Vision and Ophthalmology.
  19. Hom MM, Bruce AS. Prelens tear stability: relationship to symptoms of dryness. Optometry. 2009;80:181-184.
  20. Potter B, Stiegemeier M, Movic W, Larsen S, Friederichs G. A clinical evaluation of solutions. Review of Cornea and Contact Lens. November 2005.
  21. Heynen M, Lorentz H, Dumbleton K, Varikooty J, Woods C, Jones L. Lipid deposition on senofilcon A silicone hydrogel contact lenses disinfected with 1-step hydrogen peroxide and Polyquad®/Aldox® preserved care regimens. Poster presented during the 2008 annual meeting of the Association for Research in Vision and Ophthalmology — ARVO abstracts 2009; E-abstract 5660.
  22. Stone R. The importance of compliance: focusing on the key steps. Poster presented during the 2007 annual meeting of the British Contact Lens Association.
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  25. Contact Lens Council. New survey finds more education on contact lenses and lens care will help consumers see 20/20. Study published August 2007.
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  27. Alcon; data on file.


Contact Lens Spectrum, Issue: August 2009