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A New Generation of Contact Lens Care
How several factors play a part in choosing the best lens care regimen for silicone hydrogel contact lenses.
BY JENNIFER L. SMYTHE, O.D., M.S., F.A.A.O., PORTLAND, ORE.

There's no doubt that silicone hydrogel contact lenses are here to stay. With the introduction of two new materials into the market place in the last year and the promise of toric and bifocal options in the not-so-distant future, it's clear that high-Dk contact lenses are the future for successful contact lens practices. Although the manufacturers developed the first two marketed silicone hydrogel lenses for continuous wear, many practitioners prescribe them for daily wear.

The success of Johnson & Johnson's daily wear product, Acuvue Advance Brand Contact Lenses with Hydraclear, and CIBA Vision's O₂Optix, which has approval for both daily and overnight wear, has demonstrated that eyecare professionals recognize the benefits of providing oxygen permeability for any contact lens wear schedule. Successful daily, flexible or continuous wear requires pairing an appropriate lens care regimen with the appropriate lens material. Along with high oxygen permeability comes other features characteristic to silicone hydrogel materials that can result in some solution-based nuances. CIBA Vision recently introduced a new generation of lens care, AQuify 5 Minute Multi-Purpose Solution (MPS), which the company specifically formulated for use with silicone hydrogel contact lenses. Let's look at the critical roles that lens material, lens modality, lens care and other factors play in determining overall success with the new-generation materials.

MATERIAL NUANCES

Silicone hydrogel contact lenses are a combination of silicone rubber and conventional hydrogel monomers. The siloxane component of the material provides the oxygen permeability and the hydrogel component allows fluid permeability and on-eye movement.¹ Silicone itself is hydrophobic and earlier silicone elastomer lenses had limited success because of poor wettability and a subsequent affinity for surface deposition and lens tightening on eye. Technological advances in manufacturing and material chemistry have addressed the issues related to the hydrophobic nature of these polymers.

Current contact lenses achieve surface wettability with either a plasma coating or the incorporation of an internal wetting agent. CIBA's Night & Day and O₂Optix lenses have a uniform plasma surface coating on the anterior and posterior sides of the lens. This is an extension of the lens polymer and therefore, cannot be removed or scratched off with normal wear and handling. A plasma oxidation process is used on PureVision (Bausch & Lomb), which leads to glassy silicate islands that allow the wettability to bridge over the small areas of exposed balafilcon material. Acuvue Advance contact lenses aren't surface-treated, but rather contain the internal wetting agent Hydraclear, which provides a hydrophilic layer that "shields" the hydrophobic silicone.²

Most of the silicone hydrogel contact lenses fall into the category of FDA Group I materials (low water, non-ionic); however, they have unique surface characteristics that may warrant reclassification as an entirely new category.³ One benefit of the FDA Group classification system is simplification of the lens care approval process. The groups sort materials that have similar properties together, thus allowing manufacturers to test new solutions with representatives from each material group rather than the laborious process of comparing products with every lens on the market.

Most currently marketed lens care products were tested with HEMA-based conventional materials, not silicone hydrogels, as is the case with AQuify 5 Minute MPS. The similarities that exist within this sub-group of materials are different from the traditional, low-H₂O ionic or non-ionic polymers. Balafilcon (PureVision) is a Group III material, but the surface deposition appears more like the other Group I silicone hydrogels. We must base appropriate lens care regimen selection, patient education and problem solving on an understanding of the common nuances observed with these new materials, not with what we typically see with a Group I, III or even the lens previously worn by a given patient such as a Group IV.

And a topic that goes hand in hand with materials is protein deposition, so let's explore that subject.

SURFACE DEPOSITION

Several studies have shown that the amount of protein deposition on a silicone hydrogel is significantly lower than HEMA-based, low-Dk conventional hydrogel contact lenses.^4,5 On the other hand, lipid deposition is greater.⁴ These greasy, oily deposits can lead to decreased wettability, comfort and visual acuity (Fig. 1). Lipids are easily removed with digital rubbing of a surfactant cleaner, a step often left out with the "No-Rub" multipurpose disinfection systems and, they are also readily dissolved in solvent (alcohol) based cleaners such as MiraFlow (CIBA Vision).

Biocompatibility could also present an issue in some patients. Researchers at the University of Waterloo's Centre for Contact Lens Research (CCLR)⁴ have shown that although the amount of lysozyme deposition is considerably lower on some high-Dk lenses, the degree to which the protein was denatured was significantly greater with the silicone hydrogels tested. The concern is that this could lead to the diffuse presentation of immunologic contact lens papillary conjunctivitis (CLPC), which occurs in response to prolonged exposure to denatured protein on the surface of a lens. This adverse response is more common with continuous wear and may warrant more frequent lens removal and active cleaning such as digital rubbing with an MPS or the bubbling action of a peroxide system.

MODALITY NUANCES

One of the biggest differences between the daily wear of a reusable contact lens and the continuous wear of a lens is the necessity for a contact lens care regimen. In reality, although many patients aspire to achieve 30 days of continuous wear with their lenses, not all of them can successfully keep a contact lens on the eye for one month at a time. Therefore, a contact lens care regimen truly is a necessity for all modalities. With continuous wear especially, one key to avoiding an adverse response is to ensure that only a clean and disinfected lens is inserted into his eye. A multitude of reasons exist for why a patient may need to remove a lens during the day, including to remove foreign matter, illness or to participate in water activities.

To prevent an inflammatory adverse event, many practitioners encourage their patients to only wear their contact lenses on a daily wear basis when they're ill and to return to overnight wear of their lenses when they're completely well and their immune system is functioning normally. It's also good practice to instruct patients who participate in water sports or who use hot tubs to remove their contact lenses and to fully clean and disinfect them before sleeping in them again. Selecting a contact lens care regimen that's quick and easy to use can aid in patient compliance, but the developers of modern contact lens care products have been challenged by the need to balance microbial efficacy with patient convenience.

SOLUTION NUANCES

When we review the list of factors that a single-bottle contact lens solution needs to accomplish, it's easy to appreciate the complexity of today's multi-purpose lens care products. The solution needs to:

• have a high microbial efficacy with a wide range of microorganisms
• be compatible with the ocular tissues
• be compatible with all of the currently available lens polymers
• be easy to use and economical for the patient
• disinfect the lenses quickly.

Shortly after the introduction of silicone hydrogel contact lenses, anecdotal reports of corneal staining with them and certain solutions began to surface.³ This may have led to a great deal of confusion, uncertainty and misinformation regarding the compatibility of specific silicone hydrogel materials with various lens care regimens. Fortunately, several well-controlled, randomized, independent studies have now examined these relationships and enable us to see specific patterns.

	Fig. 1: Lipid deposits on the surface of a silicone hydrogel lens.
	Fig. 2: Solution-related corneal staining.

In 2002, researchers at the CCLR⁶ compared the amount of corneal staining observed in a group of 50 subjects wearing PureVision contact lenses on a daily wear basis. In this cross-over study, subjects used Alcon's Polyquad-based regimen Opti-Free Express and the PHMB-preserved regimen ReNu MultiPlus for one month each. The researchers observed atypical staining in 37% of the eyes using ReNu MultiPlus and only 2% of the eyes using Opti-Free Express. They assumed that the staining was solution-induced because it involved at least three of the five regions of the cornea. This reasoning led to another assumption that maybe the culprit in solution-related corneal staining or, what has also been referred to as solution-related keratitis, is the preservative PHMB. Further work with silicone hydrogel contact lenses has shown that this is an oversimplification and the greatest incidence of this adverse response occurs with the combination of ReNu MultiPlus and PureVision contact lenses.³

A NEW GENERATION SOLUTION

The recently introduced AQuify MPS is the first lens care regimen specifically formulated for silicone hydrogels. AQuify MPS contains the "HydroLock" lubricating system that patients can also use for other contact lens materials. This sophisticated lubricity agent is a combination of dexpanthenol (ProVitamin B5), a moisturizer and Sorbitol, a humectant. Sorbitol is a substance that draws moisture to the lens and the dexpanthenol creates a barrier effect that retards evaporation or helps maintain wettability (Fig. 2). Together, they shift the equilibrium of evaporative loss to maintain moisture on the lens through hydrogen-bonding mechanisms.

Another advantage of using AQuify MPS with silicone hydrogel contact lenses is convenience. Patients who want quick disinfecting and moisturizing can perform a fast, convenient 10-second rub followed by a five-minute soak or, if they prefer not to rub their lenses, they can perform a four-hour soak. So the question is, "How does AQuify stack up against the other lens care products?"

Recently, Amos⁷ reported on a study comparing the incidence of corneal staining with ReNu MultiPlus and AQuify MPS, when used with Night & Day on a daily wear basis. (Both solutions are preserved with 0.0001% PHMB; however, the buffers, surfactants and lubricating agents differ.) At the end of one month, 24% of the eyes exposed to ReNu MultiPlus exhibited atypical staining; however, no accentuated staining was observed with AQuify MPS. The exact culprit that causes this staining pattern is unknown; however, it seems to be a lens material/solution combination, not strictly related to the presence of a particular preservative.

SIMPLICITY FACTOR

There's no underestimating the importance of ease of use and the overall simplicity of a contact lens care regimen. Every practitioner has encountered the patient who can't remember the name of the lens care solution he's using but identifies it as "the all-in-one-no-rub bottle." Data on file from CIBA Vision⁸ specifically comparing AQuify MPS to the habitual lens care regimens that participants used reveals an 83% preference for the new solution. Of those who tried AQuify, 97% agreed that it was convenient and 100% liked a product that cleans and moisturizes in just five minutes. These data validate what we've known all along: Convenience matters!

MORE OPTIONS

The FDA has approved two other contact lens care regimens for use with silicone hydrogel lenses. CIBA Vision's Clear Care is a one-bottle peroxide-based contact lens solution that has some distinct advantages. The natural bubbling activity helps loosen debris attached to the surface of the lens. Peroxide does not bind to the lens surface and once neutralized it's considered a preservative-free solution that is non-irritating.

Alcon's Opti-Free Express Multi-Purpose Disinfecting Solution (MPDS) was the first product to receive FDA approval for use with silicone hydrogels. Opti-Free Express contains the patented surfactant Tetronic 1304, which aids in lipid removal and attracts water to the surface of the contact lens. Both solutions have been put to the "staining-challenge."

The Waterloo study, which used the PureVision contact lens, compared ReNu MultiPlus and Opti-Free Express. The amount of staining observed with Opti-Free was minimal. Amos⁹ recently compared the clinical performance of Clear Care with that of Opti-Free Express in conjunction with Night & Day lenses worn on a daily wear basis. After one-month, no (0%) eyes using Clear Care showed atypical staining and only two (8%) of the 25 Opti-Free Express eyes exhibited what was suspected to be solution-related atypical staining.

KEYS TO SUCCESS

With new silicone hydrogel contact lens designs on the horizon, we'll be able to provide healthy contact lens wear for the majority of our patients, regardless of refractive error. The ultimate key to success with these novel contact lens materials is to make specific lens care recommendations to every patient based on the surface characteristics of the material, the patient's lifestyle and wear schedule. This is especially critical when switching a patient from a conventional contact lens because previously used lens care solutions may no longer be appropriate. Also recognize that even though many of the contact lens care products are being reformulated, earlier versions may still sit on store shelves or bear a generic label.

The presence of corneal staining can serve as a clue to incompatibility issues and compliance with contact lens care. You should suspect solution-related staining if epithelial disruption is evident in at least three of the five regions of the cornea. Typically, the staining begins in the inferior region of the cornea (the area closest to the tear meniscus), and then works its way around the periphery with the central cornea being the last region affected (Fig. 3). Not all patients are symptomatic at first, so evaluate the cornea with NaFl and a yellow Wratten filter at every visit, regardless of subjective complaint.

When the need for problem solving becomes apparent, practitioners may lose confidence in the lens material when really the solution is simple: Consider the lens care an integral part of success with silicone hydrogel contact lenses. Not all lens care solutions are created alike and not all contact lens materials behave the same.

Dr. Smythe practices at Murrayhill EyeCare and is an associate professor at The Pacific University College of Optometry. She's also a Fellow of the American Academy of Optometry and is a Diplomate in the Academy's Section on Cornea & Contact Lenses.

REFERENCES

1. Jones L. Modern Contact Lens Materials: A Clinical Performance Update. CLSpectrum 2002:9.

2. Jones L, Tighe B. Silicone Hydrogel Materials Update - Part 2. www.siliconehydrogels.org 2004:8.

3. Jones L. Understanding Solution Incompatibilities. CLSpectrum 2004:7.

4. Senchyna M, Jones L, Louie D, et. al. Quantitative and Conformational Characterization of Lysosyme Deposited on Balafilcon and Etafilcon Contact Lens Materials. Curr Eye Res. 2004;28:25-36.

5. Jones L, Senchyna M, Glasier MA, et al. Lysozyme and Lipid Deposition on Silicone Hydrogel Contact Lens Materials. Eye Contact Lens. 2003;29:S75-S79.

6. Dumbleton K, Jones L, Chalmers R, et al. Clinical Characterization of Spherical Post-Lens Debris Associated with Lotrafilcon High-Dk Silicone Lenses. CLAOJ. 2000 Oct;26(4):186-92.

7. Jones L, Macdougall N, Sorbara L. Aysmptomatic Corneal Staining Associated with the Use of Balafilcon Silicone-Hydrogel Contact Lenses Disinfected with a Polyaminopropyl Biguanid-Preserved Care Regimen. Optom Vis Sci. 2002;79:753-761.

8. Amos C. Performance of a New Multipurpose Solution Used with Silicone Hydrogels. Optician. 2004;227:18-22.

9. CIBA Vision Data on File, 2004.