CONTACT LENS MANAGEMENT TRENDS 2010
Comparing Lens Care Systems
An expert considers the effects of comfort, disinfection efficacy and wettability
By Mile Brujic, OD
Comfort and safety are critically important to contact lens wearers throughout the world. Effective cleaning, disinfection and wetting are key components of an optimal lens care system. Here, I'll consider the science of lens care and its central role in optimizing our patients' lens-wearing experiences.
AN EVOLVING SYSTEM
Contact lens systems have evolved significantly since they were first introduced. Cleaning is an important but often overlooked function of contact lens care. There are a variety of approaches to keeping lenses clean. Among them is the use of citrate. We know citrate dissolves deposits on the surface of the contact lens. Cleaning agents (surfactants) may also increase patient comfort by removing deposits, such as proteins, away from the surface of the lens (Figure 1).1
Results of an independent study looking at intrinsic lens cleaning ability reported that Opti-Free* Replenish MPDS was twice as effective at removing protein as the next best brand.1
Just as important as a clean surface, is a biocompatible disinfecting agent that reduces microbial contamination. We can't control the virulence of pathogens but we have the power to influence two key factors related to ocular surface health in terms of care solution prescribing for our patients. These factors include ocular surface integrity and barrier function, and the size of the microbial load surviving the disinfection cycle.
To kill the broadest range of organisms, we should recommend a lens care solution system that has a wide range of activity against pathogens. This can be achieved by utilizing Polyquad* and Aldox*, highly effective disinfectants, creating a complementary disinfecting system. Polyquad has high levels of activity against bacteria and fungi, while Aldox works effectively against Acanthamoeba. Combining these agents in one care system produces a synergistic effect greater than the sum of its parts.2-4
MEASURING CONTACT LENS SYSTEMS
The disinfection efficacy of contact lens care systems is measured with criteria developed by the FDA and the International Standards Organization (ISO) and the American National Standards Institute (ANSI). Obviously, currently marketed care solutions produce adequate FDA/ISO testing results based on tests that involve laboratory isolates of organisms. However, we know that clinical isolates tend to be much more virulent than laboratory strains. So, how can we better reflect the impact of real-world challenges on the efficacy of care solutions, including factors such as noncompliance and clinical isolates amongst other things?
To help find out, Ruth A. Rosenthal, MS, conducted a study to assess the impact of preservative uptake into a contact lesns.6 She soaked the contact lenses, then measured the effectiveness of the remaining solutions against Staphylococcus and Pseudomonas.
The Polyquad* and Aldox* system remained efficacious under these study conditions. The other three solutions were PHMB-preserved, and the disinfection efficacy was significantly reduced. This may have occurred because much of the disinfectant in the solutions appeared to have been absorbed by the contact lens and thus removed from the solution.7
Preservative uptake was demonstrated in another study8 in which a silicone hydrogel contact lens was soaked for 8 hours in either a Polyquad* and Aldox* dual disinfection system or a PHMB-based system. The lenses were removed from the respective care systems and inserted into a fresh saline solution for 24 hours. The lenses were removed from the saline, and the respective levels of disinfecting agents were then measured in the saline.
One potential explanation for finding less disinfectant in the saline is that less disinfectant was removed from the initial care system (and was made available for antimicrobial activity). The Polyquad* and Aldox* system was not found in significant levels in the saline, suggesting it may not be taken up by the contact lens polymer. This is part of the reason why such a high level of disinfection is achieved, even after the contact lens has been soaked in the solution for a number of days. These findings should encourage practitioners to be very comfortable offering patients a sustained level of disinfection despite possible non-compliance by patients.
The ocular surface may be adversely affected when the disinfectant of a contact lens care system is absorbed by the contact lens and then released. In 2002, Arthur Epstein, OD, FAAO, was the first to observe a relationship between PHMB systems and silicone hydrogel contact lenses, reporting excessive, clinically relevant corneal staining.9 Since then, a number of studies have supported his initial findings.10–19
In 2006, Gary Andrasko, OD, presented research on interactions that contact lenses and care solutions had on the cornea.20,21 His results were published in Optometry in 2008.22 Dr. Andrasko has evaluated 11 contact lens care systems and nine contact lens solutions to date. Evaluated patients wore lenses that had been pre-soaked in the different care systems. After removing the lenses after 2 hours of wear, Dr. Andrasko used fluorescein to quantify the corneal area that showed micro-punctate staining (Figure 2).
Contact lenses, when fit correctly and worn as instructed, are associated with corneal staining that is typically minimal but can vary. When looking at care systems that are preserved with Polyquad and Aldox disinfectants in Dr. Andrasko's research, you can see there is minimal staining. The same is true for hydrogen peroxide-based products. However, for the PHMB-based products, higher levels of (moderate to excessive) corneal staining are observed with the use of certain contact lens materials. This suggests the contact lenses in these combinations may be taking up disinfecting agents from the care solution and releasing them onto the ocular surface.
The third concept related to this discussion is wettability—and, specifically, how contact lens systems interact with the lens surface. Wettability can be evaluated in-vitro and ex-vivo by measuring wetting angles through the use of tests such as the sessile drop technique. The more a drop of water “beads” on the surface of a lens, the higher the angle that forms between the wall of the drop and the contact lens surface. The flatter the water droplet, the lower the angle, the higher the wettability of the system. Put another way, higher angles reflect hydrophobic surfaces and lower angles reflect hydrophillic surfaces (Figure 3).
Some care solutions show poor wettability after 8 hours of wear.23-24 Yet, Opti-Free* Replenish* MPDS demonstrates a wetting angle of less than 10°, even after 14 hours of wear.23-24
BASIS FOR WETTABILITY DIFFERENCES
The reason for the differences among wetting angles lies in the properties of the wetting agents in these contact lens care solutions. Tetronic 1304* combined with C9-ED3A form TearGlyde*, which contributes to the significant wetting capability of the Opti-Free Replenish solution.
The original studies on Replenish evaluated this TearGlyde* molecule (Figure 4).25 In a doubled-masked study, lens wearers who reported being uncomfortable were given Opti-Free Replenish MPDS or Renu† MultiPlus. After 28 days, patients using Opti-Free Replenish MPDS rated their level of agreement with the statement “this solution enhances my lens comfort” at statistically significantly higher levels than those randomized to Renu* MultiPlus. What was most interesting was that patients using Opti-Free Replenish MPDS care solution with an advanced wetting system for 28 days responded at the same level as patients who maintained normal, asymptomatic, comfortable contact lens wear.
The chemical structure of the TearGlyde* Reconditioning System (a combination of Tetronic 1304** and C9ED3A) used in Opti-Free* Replenish* MPDS to clean and wet hydrogel contact lenses.
PUTTING PERSPECTIVES INTO PRACTICE
We need to think about the three factors I've just discussed to strengthen our contact lens practices and satisfy our patients. Remember the importance of the cleaning capability, the effectiveness of disinfecting agents, and the wettability of the lenses. These are the keys to enhancing our patients' contact lens-wearing experiences. CLS
*Registered trademark of Alcon
†Trademarks are the property of their respective owners.
**TETRONIC is a registered trademark of BASF.
|1. Lin MC, Tatyana TF. Differences in protein-removal efficiency among multi-purpose solutions. Presented at Association for Research in Vision and Ophthalmology (ARVO) meeting; April 2008; Ft. Lauderdale, Fla.|
2. Rosenthal RA, McAnally CL, McNamee LS, Buck SL, Schlitzer RL, Stone RP. Broad spectrum antimicrobial activity of a new multi-purpose disinfecting solution. CLAO J. 2000;26(3):120-126.
3. Rosenthal RA, Bell WM, Henry CL, Schlech BA. Antimicrobial spectrum of a new contact lens disinfectant. Poster presented during the annual meeting of the American Academy of Optomery, San Diego, Calif. December 2005.
4. Codling CE, Maillard JY, Russell AD. Aspects of the antimicrobial mechanisms of action of a polyquaternium and an amidoamine. J Antimicrob Chemother. 2003;51(5):1153-1158.
5. Chang DC, Grant GB, O'Donnell K, et al. Fusarium Keratitis Investigation Team. Multistate outbreak of Fusarium keratitis associated with use of a contact lens solution. JAMA. 2006;296(8):953-963.
6. Rosenthal RA, Henry CL, Buck SL, Bell WM, Stone RP, Schlech BA. Extreme testing of contact lens disinfecting products. Contact Lens Spectrum, July 2002.
7. Rosenthal RA, McAnally CL, et al. High capacity disinfection of contact lenses. Poster presented at the 2001 meeting of the British Contact Lens Association.
8. Data on file, Alcon.
9. Epstein AB. SPK with daily wear of silicone hydrogel lenses and MPS. Contact Lens Spectrum, November 2002.
10. Jones L, Jones D, Houlford M. Clinical comparison of three polyhexanide-preserved disinfecting solutions. Cont Lens Anterior Eye. 1997;20(1):23-30.
11. Caroline P, Campbell R. Multipurpose Non-Keratitis. Contact Lens Spectrum, March 1997.
12. Jones L, MacDougall N, Sorbara LG. Asymptomatic corneal staining associated with the use of balafilcon silicone-hydrogel contact lenses disinfected with a polyaminopropyl biguanide-preserved care regimen. Optcom Vis Sci. 2002;79(12):753-761.
13. Pritchard N, Young G, Coleman S, Hunt C. Subjective and objective measures of corneal staining related to multipurpose care systems. Cont Lens Anterior Eye. 2003;26(1):3-9.
14. Lebow KA, Schachet JL. Evaluation of corneal staining and patient preference with use of three multi-purpose solutions and two brands of soft contact lenses. Eye Contact Lens. 2003;29(4):213-220.
15. Garofalo R,J Dassanayake N, Carey C, Stein J, Stone R, David R. Corneal staining and subjective symptoms with multipurpose solutions as a function of time. Eye Contact Lens. 2005;31(4):166-174.
16. Dassanayake N, Garofalo R, et al. Correlating biocide uptake and release profiles with corneal staining and subjective symptoms. Poster presented at the annual ARVO meeting; 2005, Fort Lauderdale, Fla.
17. Jones J, Keir N, Situ P, Fonn D. Centre For Contact Lens Research, University of Waterloo, Ontario, Canada. The impact of post insertion time on corneal staining and comfort with group II hydrogel materials disinfected with various lens care regimens. ARVO 2005.
18. Townsend W, Katims S, Rosen J. Investigating a new-generation multi-purpose solution. Contact Lens Spectrum, December 2005.
19. Lebow K, Schachet JL. Differences in clinical performance of multi-purpose solutions with a silicone hydrogel lens. ARVO 2006.
20. Andrasko GJ, Ryen, KA, Garofalo, RJ, Lemp JM. Ocular response observed with silicone hydrogel lenses and multi-purpose solution combinations. Presented during the American Optometric Association meeting, Las Vegas, June 2006.
21. Andrasko G, Ryen KA. Evaluation of Ocular Response and Comfort with Solution and Lens Combinations—An Update. American Optometric Association meeting, Boston, Mass. June 2007.
22. Andrasko GJ, Ryen K. Corneal staining and comfort observed with traditional and silicone hydrogel lenses and multipurpose solution combinations. Optometry. 2008;79:444-454.
23. Ketelson HA, Meadows DL, McQueen N, Stone RP. Enhancing Wettability with Multi-purpose solutions. Review of Cornea ' Contact Lenses. January/February 2005:44-47.
23. Ketelson H, Meadows D, McQueen N, Stone R. Wettability of Silicone Hydrogel Lenses in the Presence of Tear Components. Review of Cornea ' Contact Lenses. April 2005; 24-28.
24. Wooldridge RP, Schenker HI, Rigel LE, Hamada K, Eiden SB. A comparison of two lens care formulations. Contact Lens Spectrum. November 2006.