Contact Lens Design & Materials
Materials, Designs, and Allergies
By Ronald K. Watanabe, OD, FAAO
As we head into allergy season, it's a good time to think about materials and designs. Many give up their lenses due to itching, redness, tearing, mucous discharge, and lens intolerance during this time of year. Some also experience dryness due to systemic medications taken to quell their allergies. Considering materials and/or designs may help them continue lens wear without sacrificing significant wearing time.
Daily disposable (DD) contact lenses are the obvious choice for minimizing allergy-related discomfort. Because a new, clean lens is worn each day, ocular irritants such as pollen and protein do not have a chance to accumulate, reducing the chance of inflammatory responses.
While all DD lenses are good choices for allergy sufferers, consider the materials. The silicone hydrogel material narafilcon has good Dk and protein resistance; but its modulus may be higher than other options, which may increase mechanical effects on the conjunctiva. Other DD materials are high-water-content, which tends to attract more protein, but some are non-ionic and may result in less protein deposition.
Regardless of lens choice, DD lenses are the cleanest, best option for allergy season. It is even helpful for patients wearing frequent replacement soft lenses and GPs to temporarily wear DD lenses to reduce their symptoms. With good parameter ranges available, most of your patients should be able to wear a DD lens for at least a few weeks.
Other Lens Types
If a DD lens is not appropriate, shorter replacement schedules are recommended. Also, think about the material and lens design.
Classically, high-water-content, ionic hydrogel materials tend to attract more protein deposits, while silicone hydrogels tend to collect less protein and more lipids. Though protein and lipids are not major concerns with seasonal allergic conjunctivitis, wearers may benefit from a lens that tends to deposit less.
Also consider the lens design. A loose-fitting lens with poor edge design made of a high-modulus material is more likely to irritate the conjunctiva, which may exacerbate the inflammatory process already underway. Make sure that the lens exhibits adequate but not excessive movement, and use vital dyes to stain the bulbar and palpebral conjunctivae to determine whether any lens-induced mechanical irritation exists. If so, it's time for a refit.
A good cleaning regimen also is critical for successful wear. Consider a hydrogen peroxide system, a separate daily cleaner, and an enzymatic cleaner to maintain the cleanest possible lens surface. Also consider unpreserved saline solution to rinse the lenses prior to application.
What About GPs?
For our GP wearers, disposability is not an option. Careful assessment of lens fit and surface quality are therefore even more important. Again, a lens that tends to irritate the ocular surface and palpebral conjunctiva may worsen the allergic response.
Make sure that edge lift and edge design are optimal. In addition to staining the eye, examine lens surfaces and edges for scratches, films, or other defects.
Lens care is also important, with daily and enzymatic cleaners helping to keep the surface clean. Again, using unpreserved saline or a wetting agent prior to lens application will decrease reactions to solution ingredients.
More Comfortable Lens Wear
Material and design choices alone won't always make allergy sufferers comfortable. Recommend an appropriate cleaning regimen. Use of unpreserved artificial tears and topical antihistamines, and insightful environment modification can relieve symptoms during this uncomfortable season. CLS
Dr. Watanabe is an associate professor of optometry at the New England College of Optometry. He is a Diplomate in the American Academy of Optometry's Section on Cornea and Contact Lenses and Refractive Technologies and is in private practice in Andover, Mass. You can reach him at firstname.lastname@example.org.