Ensuring Wettability and Comfort
The Science of Comfort
Ensuring Wettability and Comfort
Wetting is the third key to unlocking the science of comfort and ensuring that your patients will be successful contact lens wearers.
Arthur Epstein, OD, FAAO: We all know contact lenses are medical devices, which require special skills and knowledge to fit properly and safely. However, to our patients, a contact lens is more about the experience than about the device. My old friend and legendary contact lens expert, Stan Yamane, OD, had a simple way to evaluate his patients' success. He would ask them if they looked well (no red eyes), felt well (sustained comfort) and if they could see well (no change in prescription). These three pillars are critical to contact lens success.
As we come to the end of our three-part series, we'll cast a critical eye on comfort. Patients look to you for good vision, and they expect that you'll keep them safe. However, dryness is the most common cause of contact lens dropout, because discomfort usually becomes an issue over time and often is outside of our sphere of interaction. Patients often contribute to their own misery by switching to less expensive private label lens care products that may not be biocompatible with their lenses and may not contain advanced comfort agents. Ask a contact lens dropout why they discontinued lens wear and more often than not they'll cite dryness and discomfort, especially with prolonged wearing times.
Advances in our understanding of the surface chemistry of contact lenses and improvements in lens care products provide answers to many of our patient's comfort problems. In this final installment in the Science of Comfort series, an expert panel discusses scientific advances and offers their clinical perspectives.
DISCUSSING THE DYNAMICS OF THE EYE
Dr. Epstein: Let's turn to something that we don't talk about as much as we should, as it really is the basis of comfort. An eye is a dynamic organ. The lid sweeps over the ocular surface about 15 times a minute. When a patient wears a lens under ideal conditions, the inherent wettability and lubricity of the surface allow the patient to be relatively unaware of the presence of the lens.
We know that a lens tends to lose surface moisture over the course of the day. The lens surface becomes hydrophobic and, as a result, the patient becomes uncomfortable. This can spiral and eventually lead to dissatisfaction and even contact lens drop out. Recently, new lens care products and lens material advances have addressed this issue. Let's start with the tear film.
When the tear film breaks down, … the contact lens and the corneal surface become quite dry. This leads to blurring, hazy vision and a feeling of dryness that can lead to decreased wearing times and unhappy patients.
John L. Schachet, OD
EXAMINING THE TEAR FILM
Dr. Epstein: Dr. Schachet, what role does the tear film play in the comfortable lens wearing experience?
Dr. Schachet: Having a normal, consistently wettable contact lens surface is critical to the wearing success of any contact lens patient. When the tear film breaks down during contact lens wear, the contact lens and the corneal surface become quite dry. This leads to blurring, hazy vision and a feeling of dryness that can lead to decreased wearing times and unhappy patients.
Those of us who wear contact lenses have all experienced this feeling, but when it happens on a regular basis, our patients complain and stop wearing their lenses. It's up to us as their doctors to address these issues when they arise, and pursue them until we have a correct diagnosis of the problem at hand.
Figure 1. Wettability studies have shown that OPTI-FREE® RepleniSH® MPDS, helps tested lenses become more wettable and maintain wettability over time.1–3
Dr. Epstein: How do you measure the interaction between tear film and lens over time? Specifically, can you explain wetting angle measurements with soft lenses?
Dr. Schachet: Clinically, this is difficult to measure, but from laboratory studies on worn lenses, we know any surface that has lower wetting angles is a wetter surface. Therefore, we can apply this knowledge to the wetting angles associated with the lens care products and lenses we recommend and prescribe.
When a patient is having a problem in this area, we must consider the research that's been done to determine if there might be a positive interaction between the solution and the lens that would render it more wettable. For example, when we look at the wettability studies that have been conducted on OPTI-FREE® RepleniSH® MPDS, we see that this product helps tested lenses become more wettable and maintain wettability over time (Figure 1).1–3
While this may not solve the problem 100% of the time, it's a good idea to change the care solution first. In many cases, this change solves the problem and nothing more has to be done. Other times, however, it may be necessary to prescribe a lens made of a different material or treat an underlying dry eye issue. This is where our clinical experience comes into play.
ADDRESSING DRY EYE
Dr. Epstein: Dr. Townsend, you have great expertise in dry eye and CL wear. Does a more wettable surface improve wearability for the dry eye patient?
Dr. Townsend: I'm very interested in this area because symptoms of dryness — perhaps disguised as "my eyes feel tired" or "my vision blurs with my contacts at the end of the day" — constitute the majority of contact lens complaints. I've learned a great deal about surface chemistry from other physicians, such as Ralph Stone, PhD, David Meadows, PhD, and Lyndon Jones, PhD. There are actually physical changes in the surface molecules of a contact lens after it's exposed to air (Figure 2).4–7
We know that subtle alterations in the polymer structure of lens materials can enhance wettability. … We also know the formulation of a contact lens solution can positively impact lens comfort throughout the day.
William D. Townsend, OD, FAAO
We know that subtle alterations in the polymer structure of lens materials can enhance wettability. Two lenses that come to mind are OASYS* (Vistakon) and BIOFINITY* (CooperVision). We also know the formulation of a contact lens solution can positively impact lens comfort throughout the day.2 Dr. Jones' wetting angle studies made this abundantly clear.8 I personally experienced this myself when OPTI-FREE® RepleniSH® MPDS was introduced. So a more wettable surface, whether it's because of lens material design or solution formulation, plays a very important role in how comfortably and how long a dry eye patient can wear contact lenses.
Dr. Epstein: Dr. Townsend, you're from the arid area of Canyon, Texas — and I've been there so I know how dry it can be — you must have dry eye figured out. So what's the secret of your success? What do you recommend for your dry eye contact lens patients?
Dr. Townsend: We start by recommending simple things, such as increasing water intake and switching to a solution specifically designed for the "wettability factor." My first choice is OPTI-FREE® RepleniSH® MPDS.
Many of our dry eye patients have meibomian gland issues, and we find that aggressively treating this condition is very helpful to this patient group. We also find that a specific subset of dry eye contact lens patients benefit from topical cyclosporine therapy.
Finally, Stephen Cohen, OD, published a study9 on extended comfortable wearing time in dry eye contact lens patients who used SYSTANE® lubricant eye drops before and after wearing contact lenses (Figure 3). I was initially skeptical of this idea, but in fact I've found that it's a very simple and practical way to help dry eye patients wear their lenses longer.
Dr. Epstein: I've also had great success with SYSTANE® lubricant eye drops in my lens-wearing population. All of our GP lens wearers get SYSTANE® drops to use before inserting their contact lenses. We're starting to recommend SYSTANE® ULTRA eye drops more with our soft lens wearers as well. It's important to keep in mind that it's not indicated for use with lenses, but I've found it may help if used before and after lens wear.
So getting back to the topic at hand, can you share with us some of the different strategies that have been used to make lenses more wettable and how successful they've been?
Increasing Lens Surface Wettability
Dr. Townsend: This subject could be an extended article all on its own. I've already mentioned that contact lens solutions can be formulated to optimize wetting quality and duration. Hydrogel lenses in their hydrated state are fairly wettable, but the inherent nature of silicone hydrogel materials is hydrophobic.
Several strategies have been used in an attempt to make these materials more hydrophilic. One strategy is the use of a plasma treatment that alters the surface structure to render it more hydrophilic. I've inquired as to the precise manner in which this is accomplished, but I've yet to uncover the method.
Some lens manufacturers have begun including wet ting agents in the lens polymer matrix itself. These procedures may be effective in enhancing comfort. One issue in formulating silicone hydrogels has been trying to find the "perfect mix" of silicone and hydrogel (which contains water) materials.
Figure 2. Studies have shown that air exposure can cause physical changes in the surface molecules of contact lenses.
The issue of hydrophobicity involves more than just comfort. There's evidence that increased hydrophilic surface characteristics discourage bacterial adhesion to contact lens surfaces. In a recently published article, Santos and colleagues showed that simply wearing a silicone hydrogel lens reduces hydrophobicity and, therefore, bacterial adherence to the lens surface.10
||Most lenses on the market have employed different mechanisms in an attempt to hide the silicone portions of the lens from the ocular and tear surfaces. These mechanisms aren't always successful and, for some, they create significant comfort issues.
David L. Kading, OD, FAAO
In summary, modification of lens materials and solutions enhances lens surface wettability. The degree of success is variable, but we are seeing increasing improvement in this area.
Figure 3. A study by Stephen Cohen, OD, showed that comfortable wearing times could be extended in dry eye contact lens patients if they used SYSTANE® lubricant eye drops before and after wearing their lenses.
DOES INCREASED WETTABILITY EQUAL BETTER COMFORT?
Dr. Epstein: I think you covered that topic in greater depth than I've heard before. So, Dr. Kading, what does this mean from the patient's perspective? Do you agree that a more wettable lens surface translates into a more comfortable patient?
Dr. Kading: It typically does. When we start talking about a wettable contact lens, most of us think back to the days of difficult-to-wet rigid gas permeable lenses (eg, silicone acrylates). We know from those days that contact lenses that don't wet create a very uncomfortable surface.
Dr. Epstein: Do you think this has had any effect on patient dropout in your office?
Dr. Kading: I do, especially with certain silicone hydrogel lenses. When I see patients for follow-up and they complain of irritation and discomfort, I frequently find their lenses are covered in debris and not wetting properly. Had I not checked these patients and addressed their problems, they undoubtedly would have dropped out.
Dr. Epstein: Do you think there's a correlation between sustained wettability and patient comfort?
Dr. Kading: Absolutely, why do you think patients get uncomfortable at the end of the day? I've found that lens-solution combinations that don't create a long-lasting, wet surface may cause subjective comfort issues, and with time, ocular surface dryness.
IMPROVING WETTABILITY IN YOUR PATIENTS' EYES
Dr. Epstein: Great point! So tell me, what strategies have you used to improve wettability of contact lenses?
Dr. Kading: Obviously, contact lens and solution manufacturers have been working on this for years. Silicone as a plastic is very hydrophobic and can cause significant wettability issues. For this reason, most lenses on the market have employed different mechanisms in an attempt to hide the silicone portions of the lens from the ocular and tear surfaces. These mechanisms aren't always successful and, for some, they create significant comfort issues. Additionally, several solution manufacturers have attempted to formulate solutions that maintain a wettable lens longer in order to increase comfort.
Because the average lens wearing time is 13 hours, it's key to maintain a wettable state beyond the traditional 8 hours and ideally closer to 14 hours. Some manufacturers added moisturizing agents or polymers that may have contributed to recent solution recalls. In addition, many practitioners give their patients rewetting drops that aid in comfort issues. These rewetting drops create a more wettable surface, but the comfort is very short lived.
SEARCHING FOR SYNERGY
I find it interesting to see how much of our focus has shifted from basic aspects of lens care and design to our current approach of improving lenses, making them more comfortable.
Wettability is a particularly interesting issue. There appear to be two different angles of attack. One looks to modify the lens material to increase innate wettability. The other is to develop lens care products to create a longer-lasting, more wettable surface. Some of the attempts have been quite successful, most notably OPTI-FREE® RepleniSH® MPDS. The future is bright for increased synergies between new lens materials and more effective lens care products.
As we come to the end of this series, I'd like to thank my colleagues for their insight and willingness to share their knowledge and experience.
Sincere thanks as well to Alcon Laboratories for supporting this educational series. I hope you find this information helpful for successfully managing your patients and better understanding the latest scientific developments in lens care. CLS
- Data on file. Alcon Laboratories, Inc.
- Schachet J, Zigler L, Wakabayashi D, Cohen S. Clinical assessment of a new multi-purpose disinfecting solution in asymptomatic and symptomatic patients. Poster presented at the 2006 annual meeting of the American Academy of Optometry in Denver, Colo.
- Meadows D, Ketelson H, Napier L, Christensen M, Mathis J. Clinical ex vivo wettability of traditional and silicone hydrogel soft contact lenses. Poster presented at the 2006 annual meeting of the British Contact Lens Association in Birmingham, UK.
- Holly FJ and Refojo MF. Wettability of hydrogels. J Biomed Mater Res. 1975;9:315-326.
- Valint PJ et al. In situ surface modification of contact lens polymers. In Ratner BD, Castner DG, eds. Surface Modification of Polymeric Biomaterials. New York: Plenum Press. 1997;21-26.
- SH Kim, Opdahl A, Marmo C, Somorjai GA. AFM and SFG studies of pHEMA-based hydrogel contact lens surfaces in saline solution: adhesion, friction, and the presence of non-crosslinked polymer chains at the surface. Biomaterials. 2002;23:1657-1666.
- Ko YC, Ratner BD, Hoffman AS. J Colloid Interfac Sci. 1981;82:25-37.
- Rogers R, Jones L, Srinivasan S, Varikooty J, Simpson T, Fonn D. The influence of care regimen composition and wear time on ex vivo wettability of etafilcon contact lenses. Poster presented during the 2006 annual meeting of the British Contact Lens Association in Birmingham, England, UK.
- Cohen SM, Potter WB, Christensen M, Kern J. Prospective case history study using Systane® lubricant eye drops to help reduce symptoms of dry eye associated with contact lens wear. Poster presented during the 2004 annual meeting of the American Optometric Association.
- Santos L, Rodrigues D, Lira M, et al. Bacterial adhesion to worn silicone hydrogel contact lenses. Optom Vis Sci. 2008;85:520-525.
Contact Lens Spectrum, Issue: July 2009