SUCCESSFUL LENS WEAR
Healthy Materials, Modalities and Lens Care
With so many options available, you should have no problem adjusting patient's lenses and regimens to fit their needs and allow for successful wear.
By Jennifer Smythe OD, MS, FAAO and Pamela Wong OD
Open any popular magazine, tune into a hit radio station or network TV show during "sweeps" week and the message resonates loud and clear: "Finally," contact lenses are breathable, so comfortable that they "cannot be felt while wearing them" and that lens care can be a "spa for the eyes." Manufacturer direct-to-consumer advertising is bound to reach the majority of our patients and it's critical to stay abreast of current lens materials, modalities and care regimens.
The themes of consumer advertising are oxygen, comfort and convenience. To the savvy patient and practitioner, that translates to better ocular health and physiology during contact lens wear.
The figures above depict a reduction in limbal hyperemia after fitting a patient with a silicone hydrogel
Healthiest Materials Available
Silicone hydrogels and hyper-Dk gas permeable (GP) lenses are at the top of the healthy materials category. Advancements in these contemporary lens materials provide greater oxygen permeability, resistance to surface deposition, less on-eye dehydration and longer wearing schedules. The advantages extend both to daily wear and to overnight wear. It's clear from the extensive published literature and worldwide experience that complications related to hypoxia are virtually nonexistent with high-Dk materials. With high-Dk materials, the epithelium is healthier and better able to resist adherence by microorganisms.
Overnight wear, and in some cases even daily wear, of low-Dk materials can lead to physiological changes such as epithelial microcysts, bulbar and limbal hyperemia, neovascularization, corneal swelling and endothelial polymegathism. Physiological changes weaken ocular immunity and sick corneal epithelium is at greater risk for infection. Ren et al (2002) have shown that high-Dk lens wear produces significantly less binding of Pseudomonas aeruginosa to the corneal epithelium than occurs with wear of conventional low-Dk materials.
A Look at Silicone Hydrogels
Focus Night & Day (CIBA Vision) is a low-water (24%), nonionic silicone hydrogel that is approved for up to 30 nights of continuous wear. It has the highest Dk/t (175) in the silicone hydrogel category and has FDA approval for therapeutic use. The material has a uniform plasma surface coating on both the anterior and posterior sides of the lens. This surface coating is an extension of the lens polymer itself; it can't be destroyed with lens wear or with handling. Both the surface coating and the addition of fluorine in the Night & Day lens provides wettability and resistance to protein deposition. In some patients, this "teflon-like" coating can have an affinity for lipid deposition, which patients can easily manage with regular use of a surfactant cleaner. Particularly effective are solvents such as Miraflow or Quick Care (both CIBA Vision products).
PureVision (Bausch & Lomb) is a low-water (36%), ionic silicone hydrogel that is available worldwide, with the exception of the United States. This lens also has 30-day continuous wear approval and a Dk/t value of 110. PureVision's surface treatment is through a plasma oxidation process. It too is an extension of the lens polymer and therefore, remains intact with both handling and wear.
Acuvue Advance (Vistakon) is the newest high-Dk lens in the marketplace. This two-week replacement daily wear lens is low water (47%), nonionic and has a Dk/t listed as 60. This material isn't, however, surface treated. By adding the patented Hydraclear, described as a wetting agent, the hydrogel material stays moist on the eye throughout the day.
02Optix (CIBA Vision) is the newest silicone hydrogel lens with national distribution set for September. The 02Optix is a one- to two-week replacement lens approved for daily wear. CIBA Vision has applied for FDA approval for overnight wear of up to six nights. The 33% water, non-ionic material with a Dk/t @-3.00D of 138 utilizes the same biocompatible plasma polymerization surface treatment employed with the Focus Night & Day lens.
What's New for GPs
Menicon-Z (Menicon), with a Dk of 163-250, is the only GP lens material approved by the FDA for up-to 30 days of continuous wear. The advantages of this GP lens are stable optics, virtually unlimited parameter availability (including torics and a multifocal), essentially no evaporation or preservative uptake and superior oxygen permeability.
Additionally, two other high-DK materials Boston XO (Polymer Technology) and Paragon HDS 100 (Paragon Vision Sciences). Boston XO is approved for daily wear in conventional and ortho-K designs. Paragon HDS 100 is available for daily wear or conventional extended wear.
Other Unique Materials
Ocular dryness and discomfort are still contact lens wearers' most common complaints. Patients who have dryness symptoms tend to have greater dehydration of their lenses than do asymptomatic patients. Lens materials that dehydrate significantly less than conventional materials perform well in clinical practice.
Proclear Compatibles (CooperVision) has the only FDA-approved claim that its lenses "may provide improved comfort for contact lens wearers who experience mild discomfort or symptoms relating to dryness during lens wear." The lens material is high-water (62%), nonionic with a Dk of 34 and has surface technology using phosphorylcholine (PC). PC is a substance found in human cell membranes, with hydrophilic properties that retain the pre-lens tear film structure and decreases its dehydration rate. CooperVision now offers the Proclear Toric and Tailor Made Toric in the same material.
Extreme H2O (Hydrogel Vision Corporation) is a high water (59%), nonionic material with a listed Dk value of 21. The manufacturer claims that the material "retains its saturated water content on the eye, even in extreme conditions," and the lens will retain its dimensions and oxygen permeability throughout the day. The Extreme H2O X-tra (double the center thickness) is also available and claims to offer even less on-eye dehydration.
Another consideration for healthy contact lens wear is the selection of materials with UV blocking properties. This is an excellent option especially when fitting children, as they often don't wear sunglasses when playing outdoors.
Both replacement frequency and wear schedule can define lens modality. Current marketplace trends show a decrease in conventional and planned replacement lens sales, countered with an expected significant rise in daily disposables and silicone hydrogels over the next three years. This indicates that the profession is slowly embracing high-Dk lenses as the future and that the physiological advantages are important. At the same time, the continual increase of daily disposable lens sales indicates that practitioners are recognizing the advantages of single-use lenses and that patients are willing to pay for a clean lens every day and freedom from lens care.
There's no doubt that continuous wear of high-Dk lenses is safer for the ocular surface than previous low-Dk overnight wear. Trial any patient who presents to the practice with either a history of overnight wear or the desire to wear contact lenses while sleeping with a high-Dk lens -- either a silicone hydrogel or hyper-Dk GP lens design.
Lens modality is critical for managing the patient who has allergies. Daily disposable lenses are the optimum choice during acute allergy season because surface deposition isn't an issue and it eliminates the potential of exacerbating signs and symptoms from exposure to lens care ingredients. Practitioners should consider continuous wear contraindicated during acute ocular allergies because of the potential of further inflammation and the likelihood of concurrent medication use.
Finally, lens material and design advancements have made overnight corneal reshaping safer and more predictable. The FDA approval of Corneal Refractive Therapy (CRT) has given practitioners another contact lens modality for the treatment and management of refractive error.
Lens Care Challenges
Both patients and practitioners can find lens care confusing. Studies reporting efficacy against microorganisms, particularly strains of Acanthoemeba and cytotoxicity are contradictory depending on study protocol, study sponsors and the age of the microorganisms tested. Probably the healthiest solution to lens care is to eliminate the need for solutions altogether. Unfortunately, single use isn't an option for all patients or all refractive errors.Therefore, it's important to recognize the role that lens care can play in the overall success of lens wear.
Patients and practitioners should consider solutions "guilty until proven innocent." Sometimes solutions can cause dryness symptoms which may be revealed by causing a punctate keratitis, dry spots on the cornea or tarsal plate changes. Include fluorescein staining and simple lid eversion in all contact lens follow-up exams to properly ascertain the ocular response to both contact lens wear and the lens care solutions.
The developers of modern lens care products are challenged to balance microbial efficacy with patient convenience. When reviewing what a single-bottle solution needs to accomplish, it's easy to appreciate the complexity of today's multipurpose 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 the currently available lens polymers
- be easy to use and economical for the patient
- disinfect the lenses quickly
It may be unrealistic to think that we could continually use a solution containing chemicals such as a surfactant (soap for cleaning), a preservative for disinfection and an ingredient to solubolize protein and not compromise the delicate balance between the ocular surface and the tear film in certain patients.
Even in the absence of corneal staining or palpebral hyperemia, consider multipurpose solutions suspect when patients complain of chronic dryness while wearing their contact lenses. Many patients find symptomatic relief when their practitioner changes their lens care products to a preservativefree disinfection system such as peroxide, UV-C or eliminates them altogether.
Presenting the Options
Have a conversation with every patient detailing the best new materials, modalities and lens care options. Modern consumers are aware that new options are continually being made available. It's up to the practitioner to let the patients know what is best for each individual patient.
Dr. Smythe is an associate professor of optometry at Pacific University and is in private group practice in Beaverton, Oregon.
Dr. Wong is the current cornea and contact lens resident at the Pacific University College of Optometry.