The Controversy of Contact Lens Convenience
By Jason J. Nichols, O.D.
Can both the patient and the practitioner agree on which mode of contact lens wear is best? See what each modality has to offer.
Patients love convenience. The more permanent and convenient the mode of visual correction, the happier patients are.
As doctors, we have an ethical obligation to promote healthy visual correction to our patients. However, we also want to make our patients happy. Two very convenient modes of contact lens wear that have become popular among both practitioners and contact lens patients are daily disposable contact lenses and extended wear contact lenses.
Daily Disposable vs. Extended Wear Contact Lenses
A daily disposable contact lens can be defined as a single-use lens worn up to one day during waking hours and discarded upon removal. Presently, extended contact lens wear can be defined as the wearing of contact lenses for 24 hours or longer, including periods of sleep. Single-use extended wear lenses are used on a weekly basis, worn for six continuous nights (seven days) and then thrown away. Disposable extended wear contact lenses were introduced to possibly avoid any ocular health complications that may be associated with lens aging. As such, there is a key feature which bridges these two modes of contact lens wear, and that is disposability.
The Food and Drug Administration (FDA) defines a disposable contact lens as a lens worn only once and then thrown away, never to be worn a second time. Thus, only these two modes of single-use contact lens wear truly fit the definition of a disposable contact lens.
Daily Disposable Benefits
Disposable contact lenses have been embraced by practitioners who continue to look to new technology to provide their patients with the most healthy and convenient mode of visual correction possible. In fact, disposable contact lenses have become the standard of soft contact lens wear today.
There has been a great deal of discussion about daily disposable lens wear since the release of the first daily disposable contact lens in 1995, the 1-Day Acuvue (Vistakon). Market growth continues to increase as other companies have since introduced daily disposable lenses, including CIBA Vision's Focus Dailies and Bausch and Lomb's SofLens One Day (Table 1). This competition has lowered costs of this once expensive mode of lens wear, allowing eye care practitioners to provide the benefits of this mode of lens wear to a wider range of patients.
Daily disposable contact lenses provide spectacle and RGP wearers the opportunity for occasional soft contact lens use without the hassles of lens care. The benefits of daily disposable lens wear include the convenience of disposability, the elimination of cleaning supplies and regimens, and improved ocular health. Table 2 highlights the advantages of daily disposable and extended-wear contact lenses.
Extended Wear Contact Lenses: Where They've Been
The extended wear of contact lenses was first described in the literature of the 1950s. Since that time, the popularity of this mode of lens wear has grown tremendously. In 1979, the FDA granted its first 30-day approval of extended wear for aphakia, and in 1981, the FDA approved the cosmetic extended wear of contact lenses for up to 30 days.
However, significant ocular health problems began to arise, and from the doctors' perspective, the growth of the extended wear of contact lenses was stunted. In 1989, the FDA repealed the 30-day approval of extended wear lenses and revised its standard to a six-night, seven-day wearing schedule.
Let's review some of the complications associated with extended contact lens wear.
Hypoxia -- The cornea has very critical oxygen demands that increase with eyelid closure. With no contact lens wear, the cornea swells on an average of four percent overnight, but returns to normal within about an hour of open-eye conditions. Even short-term contact lens wear interferes with the uptake of oxygen and the metabolic processes of the cornea.
Most currently available extended wear hydrogel contact lenses provide inadequate oxygen levels to the cornea, maintaining a Dk/L in the range of 10-40. These hydrogel lenses simply do not meet the standards set forth by Holden and Mertz to reduce or eliminate corneal swelling. Corneal swelling occurs on the magnitude of approximately 12 percent overnight and four percent during the day with these lens materials.
During extended wear, careful and precise examination of the cornea is required to detect the clinical signs related to hypoxia, including endothelial changes, limbal hyperemia, microcysts, neovascularization, striae and vacuoles.
Infection -- The major risk factor for infection with hydrogel contact lens wear is overnight use. This risk increases with each consecutive night of contact lens wear. Cases of microbial, fungal and amebic keratitis have all been documented with extended contact lens wear.
Numerous studies have been conducted which investigate the risk of microbial keratitis in patients wearing extended wear contact lenses as compared to patients wearing daily disposable contact lenses. Depending on the study, the increased risk of infectious keratitis has been found to be between five and 20 times greater with extended wear patients than with daily disposable lens wear patients.
It is thought that the induced corneal hypoxia leads to an impaired resistance of the epithelium to microbial invasion.
Inflammation -- Contact lens deposition is another significant problem associated with extended contact lens wear. A link between lens deposits and ocular inflammation has also been established with extended contact lens wear. Inflammatory ocular responses to extended wear include contact lens induced acute red eye (CLARE) and contact lens induced peripheral ulcers (CLPU). CLARE is characterized by symptoms of ocular discomfort or pain upon eyelid opening, with redness and photophobia.
Signs of CLARE include: conjunctival hyperemia, subepithelial or stromal infiltrates, corneal staining and, in severe cases, anterior chamber reactions. CLPUs are sterile corneal ulcers that are often associated with Staphylococcus aureus.
Extended Wear Benefits
Although the aforementioned complications of extended contact lens wear are serious, most patients still desire this more permanent and convenient mode of contact lens wear.
As refractive surgery continues to grow, close to one million patients are expected to undergo this procedure in the year 2000. Although successful refractive surgery is certainly a convenient mode of visual correction, much of its convenience comes from it permanency. As such, patients are seeking a convenient and permanent mode of visual correction. The ultimate contact lens might be considered by some to be a lens that is worn safely and comfortably, while providing excellent vision without having to be removed at all.
Fortunately, new-generation silicone-hydrogel contact lenses present a promising future for successful extended contact lens wear. These high-Dk extended wear lenses rely on silicone for oxygen transmissibility and have nominal Dk/L values of 110 to 175 (which are certainly above the Holden and Mertz criteria set forth to reduce or eliminate residual swelling).
Bausch and Lomb was the first manufacturer to introduce a new-generation extended wear silicone-hydrogel contact lens, the PureVision contact lens, in the United States (Table 1).
CIBA Vision will also be following suit in the United States soon. With improved oxygen transmissibility levels, the future of these new-generation extended wear contact lenses is bright.
A Forward Glance
Daily disposable and extended wear contact lenses offer many advantages for both the patient and the practitioner. While both modalities offer convenience, disposability, and lack of lens care supplies and cleaning regimens, they each offer their own specific advantages.
Daily disposable contact lenses offer improved ocular health, but extended wear contact lenses offer a more permanent, convenient mode of visual correction. As the materials that comprise extended wear contact lenses continue to improve and patients continue to seek a convenient and permanent mode of visual correction, the popularity of extended wear contact lenses will likely grow once again.
Although many practitioners consider both of these modes of lens wear to be convenient, there are currently no published studies comparing these two modes of lens wear in terms of patient preference and success. Ongoing studies at The Ohio State University College of Optometry are examining these issues, and results from these studies will be forth coming. CLS
Dr. Nichols is an advanced practice cornea and contact lens fellow at the Ohio State University College of Optometry.By Jason J. Nichols, O.D.