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Prescribe the Best Solution for Silicone Hydrogel Lenses

These lenses require careful consideration in terms of lens-care solutions and compatibility

SUSAN J. GROMACKI, O.D., M.S., F.A.A.O., ANN ARBOR, MICH.

Silicone hydrogel contact lenses aren’t just the wave of the future; they’re the present. The transitioning of a patient from traditional soft contact lenses to silicone hydrogel lenses requires additional knowledge and understanding on the part of you and your patients. The silicone hydrogel materials are truly different from their hydroxyethyl methacrylate (HEMA) predecessors, and, as a result, require different care. This is because these materials react differently than HEMA lenses with the currently available lens-care solutions. As a result, it’s never been more important for you to understand the properties and nuances of each contact-lens solution and the potential interactions between these solutions and some silicone hydrogel materials.

MATERIAL PROPERTIES

Silicone hydrogel materials are different from their predecessors in that they have much greater Dk values than traditional hydrogels. Greater Dk decreases or eliminates the complications induced by hypoxia.

Silicone is even more permeable to oxygen than water (the opposite is true for traditional plastics). So, in general, the lower the water content of a silicone hydrogel lens, the higher its permeability. Silicone isn’t new to contact lenses — it’s been utilized in rigid gas permeable lenses and silicone elastomers for years. Only recently have scientists developed the capability to combine silicone with a hydrogel component, enabling fluid permeability and on-eye movement.¹

In addition to increased oxygen permeability, the advantages of silicone hydrogel materials when compared with traditional hydrogel lenses include better durability, less protein deposition and increased end-of-day comfort. The last of these characteristics can extend wearing time for dry-eye patients. Unlike traditional hydrogels, however, silicone hydrogel lenses are innately hydrophobic. All but one available material have to be plasma treated or contain an internal wetting agent to achieve surface wettability. The potential drawbacks to silicone hydrogel lenses include in-creased lipid deposition and stiffness of the material, reflected by higher modulus of elasticity values. Rarely, this increases the potential for mechanical changes, such as superior epithelial arcuate lesions (SEALs) or giant papillary conjunctivitis (GPC).

The individual materials within the silicone hydrogel class also vary considerably. There is great debate on when and how the Food and Drug Administration (FDA) material group classification system will be updated to include silicone hydrogels into their own new class or classes. The classification system was originally established to simplify the FDA’s lens-care approval process. The FDA reasons that since the materials within each group have similar properties, a lens-care system need only be tested with one, rather than every, material within a group to obtain approval.

SPECIFIC RECOMMENDATIONS

We are just beginning to understand the properties, nuances and on-eye performances of these materials. We are still discovering solution incompatibilities. At the present time, only four lens-care systems are FDA-indicated for use with silicone hydrogel lenses:

1. Clear Care (CIBA Vision)
2. AQuify (CIBA Vision)
3. Opti-Free RepleniSH (Alcon)
4. Opti-Free Express (Alcon)

Other solutions may very well be acceptable for use with silicone hy-drogels. The reason they aren’t FDA-indicated: The companies that manufacture these solutions haven’t yet performed and submitted to the FDA the product testing required for labeling. As a side note, with the exception Opti-Free RepleniSH, there was only one silicone hydrogel lens on the market when all the in-dicated solutions were tested. Al-though the FDA hasn’t required testing with subsequent materials, there have been no solution incompatibilities reported at this time. Un-til all lens-care products are successfully tested with silicone hydrogels, I personally instruct my patients not to make substitutions for the lens-care products I prescribe, and I educate them about the dangers of using generic products (private label). Generic products are typically older, rather than premium formulations. What’s more, the composition within a given brand of solution can even change from year-to-year. Most importantly, few of the currently available generic solutions available contain formulations indicated by the FDA for silicone hydrogel materials.

COMPLIANCE MATTERS

Although the silicone hydrogel materials represent a technological breakthrough, they still need to be cleaned and disinfected. Last year’s Fusarium keratitis outbreak was due in no small part to patient noncompliance. After Bausch & Lomb voluntarily removed ReNu with Moisture Loc from the world marketplace, the company concluded that if the formulation is allowed to evaporate, is not regularly replaced in the lens case, the bottle is kept open between uses or the case isn’t cleaned properly or replaced regularly, the concentration of the polymers included in the formula to enhance comfort may make the solution more likely to become contaminated with Fusarium in the environment. ReNu with Moisture Loc contained a high concentration of polymers. In other words, the wetting agents, during noncompliant conditions, encapsulated the Fusarium spores, allowing them to survive, then germinate.

In addition, silicone hydrogel lenses deposit lipids more readily than traditional hydrogels. For this reason, I specifically instruct my pa-tients to rub their lenses, even if the box contains the words no-rub. Following the Fusarium outbreak, the FDA and the Centers for Disease Control (CDC) also adopted the “rub and rinse” recommendation, rather than the “no-rub” cleaning method, for all contact lenses. In addition, new research has demonstrated that adding a rub step to both multipurpose- and peroxide-based cleaning systems reduces or even eliminates deposition problems on silicone hydrogel lenses, even in a deposit-prone population.² I educate patients that rubbing removes 90% of the debris and that the alternative (typically 10 seconds of rinsing prior to placing the lens in a solution-filled case) is not only less healthy in some instances, but also less economical.³

Figure 1: Corneal staining in a patient utilizing Pure Vision lenses and ReNu MultiPlus solution. Photo courtesy of Dr. Gary Andrasko, www.StainingGrid.com.

Although Fusarium keratitis af-flicted only 164 patients in the U.S. from March to June 2006, it impacted the entire nation, thanks to widespread publicity by the media, which educated patients and practitioners alike that solution composition and compliance do matter.⁴ (See “Patient Education/ Care Information,” page 64.) Each care system contains its own preservatives, buffers, salts, cleaning agents, chelating agents, demulcents and wetting agents (see “Solutions FDA-Indicated For Use With Silicone Hydro-gels,” page 62). Significant differences do exist between solutions. One important lesson the outbreak taught us: We should prescribe the solutions ourselves rather than allow a staff member to choose it. The solution needs to be tailored to the patient’s lens material, wear and replacement schedule and eye health.

I still delegate initial insertion and removal training — including contact-lens care — to my technician. But now, I personally review my chosen care system with my patient in the exam room. This includes reading the package insert with him and requesting that he review it at home.

Some O.D.s also provide a handout listing the solution name, while others present the patient a copy of the solution “prescription” on a prescription pad. Whatever the method, it’s never been more vital to reinforce good compliance and to discourage patients from deviating from your prescribed solution. (See “Quick Tips For Silicone Hydrogel Lens Care,” page 61.)

Lens/Solution COMPATIBILITY ISSUES TO CONSIDER

Although much is still to learn regarding solution interactions with silicone hydrogel lenses, here is what we do know. Listed on Bausch & Lomb’s package insert for its Pure-Vision contact lenses is the following: “Do not use the Advanced Medical Optics’ Ultracare Disinfect-ing System or any of its components (Ultracare Disinfecting Solution, Ul-tracare Neutralizing Tablets, Lens Plus Daily Cleaner and Ultrazyme Enzymatic Cleaner) to clean and disinfect the PureVision contact lens.” (Note: Lens Plus Daily Cleaner and Lens Plus Sterile Saline are now manufactured by Inyx.) Other currently used hydrogen peroxide systems haven’t demonstrated any incompatibilities with these nor any other silicone hydrogel lenses thus far. However, historically speaking, the now-discontinued SOLO-Care Plus (CIBA Vision) altered the diameter and power of Acuvue Advance contact lenses (Vistakon), though this hasn’t been found with other similarly preserved systems (polyhexamethylene biguanide, PHMB), including ReNu MultiPlus (Bausch & Lomb), Complete (Advanced Medical Optics) and AQuify MPS (CIBA Vision). The last of these was specifically formulated and is FDA-indicated for use with silicone hy-drogel materials.

Keep in mind that although not a labeled contraindication at this time, several solution/silicone hydrogel material combinations have been shown to induce corneal staining in some patients. In fact, several publications have reported this occurrence since 2002.⁵ Optometrist Gary J. Andrasko, of Ohio, recently presented the most comprehensive re-search to date. He soaked various contact lenses in known solutions — 59 different combinations in all — then applied the lenses to 30 pa-tients. Two hours later, he removed the lenses and stained the corneas with sodium fluorescein. The results: On average, 73% of the area of each patient’s cornea stained after wearing the PureVision/ReNu MultiPlus combination (see figure 1, page 63). Numbers were similar for the PureVision lens used with the Wal-Mart and Target solutions be-cause they are currently identical in composition to ReNu MultiPlus. Staining was considerably lower for other lens/solution combinations. For example, CIBA Vision’s Clear Care averaged just 1% staining with all six test lens materials, even lower than the control (unpreserved sa-line).⁶ Kathy Dumbleton, O.D., of the Centre for Contact Lens Research performed a recent study that confirmed this. In 55 patients who wore five different silicone hydrogel lenses, she found no cases of solution sensitivity staining associated with Clear Care.⁷

Although we don’t yet completely understand the mechanism of how this staining occurs, some research-ers propose that certain care products bind to lipid deposits on the silicone hydrogel lens surface, which then act as a drug delivery device.⁸ This staining is mostly asymptomatic and generally resolves at the four-to-six hour mark as the solution’s preservative has been completely released from the lens.⁹

Only time will tell whether a two-hour block of potential, mostly asymptomatic, corneal disruption can result in real health issues, such as microbial or fungal keratitis. The take-home message is that we need to evaluate the cornea with sodium flourescein and a yellow wratten filter at every visit, regardless of whether the silicone hydrogel contact lens patient is symptomatic. If corneal disruption is present, we then need to use our best professional judgment to decide if it’s relevant to that particular patient.

References

1. Jones L, Mann A, Evans K, Franklin V, Tighe B. An in vivo comparison of the kinetics of protein and lipid deposition on group II and group IV frequent-replacement contact lenses. Optom Vis Sci. 2000 Oct;77(10): 503–10.

2. Nichols JJ. Deposition rates and lens care influence on galyfilcon A silicone hydrogel lenses. Optom Vis Sci 2006 (Oct);83(10): 751–7.

3. Gromacki SJ, Doud SL. Rub vs. no-rub: a solution volume study. Optom Vis Sci 2006;83:E-abstract 065239.

4. Chang DC, Grant GB, O’Donnell K, et al. Multistate outbreak of Fusarium keratitis associated with use of a contact lens solution. JAMA. 2006 Aug;296(8):953–963.

5. 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. Optom Vis Sci. 2002 Dec;79(12):753–761.

6. Andrasko G, Ryen K. Optom Vis Sci 2006;83:E-abstract 065240.

7. Dumbleton KA, Jones W, Woods A, et al. Clinical performance of a hydrogen peroxide care regimen with silicone hydrogel lenses. Optom Vis Sci 2006;83:E-abstract 060069.

8. Jones L, Jones D, Houlford M. Clinical comparison of three polyhexanide-preserved multipurpose contact lens solutions. Cont Len Anterior Eye 1997;20:23–30.

9. Garofalo R, Dassanayake N. Corneal response of chemical agents released by hy-drogel and silicone hydrogel lenses as a function of time. Presented April 6, 2004 at the Association for Research in Vision in Oph-thalmology meeting, Ft. Lauderdale, Fla. 2004;Abstract #1538.