Article Date: 9/1/2011

Topic: Impact of Solution on Comfort

Topic: Impact of Solution on Comfort

Point: The Role of Contact Lens Solution on Comfort is Overstated

By Brian Chou, OD, FAAO

Contact lens solutions do matter. They're engineered to disinfect, clean, and condition, ideally with minimal toxicity to the eye. It's no simple feat. When any single step in the disinfection process goes awry, complications such as microbial keratitis (MK) can arise.

But do lens care solutions affect comfort in a significant way? Solution manufacturers want us—and our patients—to think so. It's relevant because discomfort is the principal reason for contact lens drop outs (Young, 2002). What's more, a practitioner in an average practice hears complaints about comfort every day but sees contact lens-related MK only rarely.

Consider solution-induced corneal staining (SICS). An initial report (Jones et al, 2002) found that one silicone hydrogel produced asymptomatic corneal staining with PHMB-preserved disinfection. Subsequent studies have characterized SICS with various lens materials and solution systems. Nichols and Sinnott (2011) found that corneal staining generally was not related to the care solution, whether by brand or preservative. Evidence indicates SICS does not increase the risk of MK. Still, SICS may be associated with other side effects, such as inflammation, although this is still open to debate (Carnt et al, 2007). Other studies have shown SICS is associated with decreased comfort (Garofalo et al, 2005; Andrasko and Ryan, 2008).

If SICS negatively impacts comfort, might wide-scale use of daily disposables and peroxide-based systems banish lens discomfort? Some evidence supports the belief that a peroxide-based system used with silicone hydrogel lenses can extend comfortable wearing time more than a multipurpose solution (Keir, 2010). But not even a peroxide system can restore comfort for a patient with florid blepharitis who's wearing a torn hydrogel lens that was soaked in an unknown solution, and has jelly bumps to boot.

Contact lens discomfort is multifactorial, affected by lens thickness profile and edge design, the physical fitting relationship to the eye, tear exchange, and material properties such as wettability, modulus, lubricity, oxygen permeability and deposit resistance. There are also patient-inherent factors: ocular sensitivity, tear composition and existence of ocular surface disease (dry eye, allergy, blepharitis). I hypothesize that care systems contribute little toward comfort versus the sum of the other factors. Support exists in a large-scale study, which found that care systems, even when grouped by preservative, were not predictive of patient-reported dry eye during contact lens wear (Ramamoorthy et al, 2008). Another study found that the lens care system was not significantly related to contact lens dryness (Young et al, 2011).

Suppose a low myope wearing methafilcon A and using a PHMB-preserved solution complains of dryness and discomfort. You can 1) refit her into a silicone hydrogel without changing solution, which may lead to SICS, or 2) switch her lens care system without any refit. If you could only choose one—admittedly an uncomfortable decision—which choice would you make? My clinical experience is that silicone hydrogel lenses play a greater role in comfort than avoiding SICS, which is why I would take the first approach. High oxygen permeability is a suggested factor for improved comfort of silicone hydrogels as are other material characteristics associated with these materials (Dillehay, 2007, Ramamoorthy et al, 2008).

There are encouraging efforts to improve contact lens comfort. One paper has favorably compared the first daily disposable silicone hydrogel to wearing no lens at all (Walline et al, 2010). Recently, the noticeable difference in wearing comfort was determined (Papas et al, 2011), which sets up the groundwork for identifying the relative importance of each factor in overall comfort. Now we're barking up the right tree, especially with a continued focus on lens materials and designs as opposed to care solutions. CLS

For references, please visit www.clspectrum.com/references.asp and click on document SE2011.


Dr. Chou is in private practice in San Diego. He is co-developer of EyeDock.com, the contact lens reference for eyecare professionals.

Counterpoint: Improved Contact Lens Comfort—The Solution Is in the Bottle

By Arthur B. Epstein, OD, FAAO

When it comes to contact lenses, clinicians typically focus on fit and vision—elements they can easily control. However, from a patient's perspective, successful lens wear hinges largely on comfort. If you doubt this, consider how often patients complain of discomfort—especially end-of-day dryness. Additionally, discomfort is recognized as the primary reason for contact lens dropout.

The quest for sustained comfort has become a key focus for clinicians and the industry. Indeed, one of the primary rationales for the first hydrogel lenses was improved comfort. Put simply, a consistently wet lens surface is associated with decreased friction, sharper vision and enhanced comfort.

Improvements in lens design and manufacturing techniques and the incorporation of lens wetting agents within materials and packaging solutions have improved comfort. However, the relative lack of success of this approach is clearly evidenced by continued patient complaints and dropout rates that remain unacceptably high.

Manufacturers of contact lens care products have also targeted discomfort, by utilizing a variety of agents to keep contact lenses more comfortable for longer periods of time, achieving significant success in some cases.

My opponent believes that the contact lens itself is the key to solving the comfort equation. To the contrary, I will explore the underlying science of why lenses become dry and uncomfortable during wear, and I will explain how modern lens care solutions can halt and even reverse drying, yielding improved all-day comfort.

Hydrogel (especially silicone hydrogel) materials epitomize molecular ambivalence. Mixing plastic and silicone with water creates a polymer possessing both hydrophobic and hydrophilic qualities.

One result is that in vivo stability is not the strong suit of hydrogel or silicone hydrogel materials, especially at their interface with air or water. Hydrophilic and hydrophobic elements seek their match and the one finding the strongest attraction and the lowest energy state dominates. The material's molecular structure will actually reorient until this is achieved.

When a lens is immersed in solution, maximal hydrophilicity is achieved as hydrophilic moieties align at the surface. This is reflected by subjective patient reports of greatest comfort upon insertion. It also explains why some patients re-soak lenses to reduce discomfort toward the end of the wearing day.

When a lens is placed in the eye, tear film break up time becomes more rapid, and the lens surface is exposed to the hydrophobic atmosphere for greater periods of time. This drives reorientation of hydrophobic moieties which align with the surface and results in drying of the lens surface. It should be noted that this still occurs in the presence of various coatings and eluting agents incorporated into the lens.

A number of agents, including cellulose-based agents and hyaluronic acid, have been used but they tend to lubricate rather than lead to a more wettable lens surface.

In contrast, block copolymers used in multipurpose care solutions mirror the hydrophilic-hydrophobic duality of hydrogel materials, which results in prolonged effectiveness.

The recent introduction of oxyethylene/oxybutylene block copolymers may further enhance surface wetting, stability and substantivity. Maintaining a wet surface halts molecular re-orientation and breaks the cycle of dryness and discomfort.

This new development alone should lay this debate to rest in favor of the care solution being the key to comfort—at least until new lens materials shift the balance back to my opponent's side. CLS

For references, please visit www.clspectrum.com/references.asp and click on document SE2011.


Dr. Epstein is a well known speaker, author and advocate for optometry. He resides in Phoenix, Ariz., where he focuses on clinical research. He has received honoraria, research grants or served as a consultant for Alcon Labs, Ciba Vision, CooperVision, and Vistakon.

Contact Lens Spectrum, Issue: September 2011