A Review of Contact Lens Modalities
From daily disposable to continuous wear, learn benefits of lenses in each modality and which patients each category best serves.
By Gregory J. Nixon, OD, FAAO
Continued advancements in the contact lens industry have produced a vast array of products that offer patients increasing opportunities to enjoy lens wear as a means of refractive correction. Additionally, practitioners enjoy an ever-expanding repertoire of contact lenses to meet the complex needs of their patients. While patients' concerns may center on cost, comfort and convenience, practitioners' main interests are fit, physiology and visual function. I attribute the growth of the contact lens market today to the advanced designs and materials that address the needs of patients and practitioners alike. I'll highlight some of the benefits of these products and the modalities in which they're used.
Daily Disposable Lenses
Daily disposable lens wear is a leading mode of correction in Europe and Asia and is a growing modality in the United States. One of the greatest benefits of this modality is that patients don't need to depend on lens care solutions because there's no need for any lens cleaning or disinfection. Consequently, patients who are prone to solution allergy or toxicity benefit greatly from this modality. Daily lens disposal also benefits patients who are heavy depositors and whose lenses don't remain clean enough for repeat wear. Other prime candidates for daily disposable lenses are allergy sufferers, for whom a clean lens every day can significantly reduce the allergy response.
Some practitioners use daily lens disposal not only as a way to decrease solution incompatibility, but also as a way to reduce solution noncompliance. Patient noncompliance can manifest as sleeping in lenses, overwear of lenses beyond the recommended replacement schedule and/or not adhering to appropriate cleaning and disinfection protocols (including the use of a clean case each night). Because practitioners often don't dispense solutions or cases with daily disposable lenses, this modality automatically removes two of the three ways patients can misuse their lenses. Assurance of compliance can especially benefit parents of child and teenage lens wearers. These parents don't have to be as concerned about complications arising from their children not following appropriate care regimens required with repeat-wear lenses.
Many patients and practitioners choose this modality simply for the convenience. Not having to clean and disinfect lenses on a daily basis can be of value to many patients including travelers, campers and people who have busy, active lifestyles. Some of the growth in this category also has arisen from the availability of specialty corrections such as a daily disposable multifocal (CIBA Vision's Focus Dailies Progressive) and a daily disposable toric lens (CIBA's Focus Dailies Toric) that allow increasing numbers of patients to benefit from this modality. CIBA's new Focus Dailies with AquaRelease may also spur further growth in this category by improving end-of-day comfort over the original Focus Dailies lenses.
Daily lenses are the modality of choice for all of the various types of occasional wearers in the contact lens market, including patients who may wear lenses as frequently as a few times each week for athletic or social reasons to once a year while on vacation, when attending a wedding or for a family portrait. I believe these lenses are dramatically underutilized for this purpose, and I make a special point of educating my patients about these options regularly. I specifically think this modality is valuable for athletic activities and for allowing an existing contact lens patient who wishes to discontinue full-time lens wear to retain occasional lens wear for certain circumstances.
The disposable (two-week replacement) lens market is the most popular in the United States. As a result, this category has the market's leading spherical lens (Acuvue 2, Vistakon), the leading toric lens (Soflens 66 Toric, Bausch & Lomb) and the leading multifocal lens (Soflens 66 Multifocal, also from B&L). This category has traditionally been dominated by hydrogel lenses that employ streamlined production and distribution that offer a combination of convenience and affordability. This compelling combination is the key aspect that makes two-week disposables the modality of choice for U.S. practitioners.
However, the continued growth of this category is attributed to the development of premium lens products with expanded parameter availability, as well as advanced lens materials and designs. These innovative products are allowing patients who have complex fits and prescriptions to take advantage of thinner, more wettable, more oxygen permeable lenses that are discarded regularly. For example, we now have at least three disposable toric lens designs that offer high cylinder powers (CooperVision's Vertex Toric at –2.25D and Vertex Toric XR at –2.75D, –3.25D and –3.75D; B&L's Soflens 66 Toric at –2.25D and –2.75D; CooperVision's Biomedics Toric at –2.25D; and Vistakon will add a –2.25D cylinder to its Acuvue Advance for Astigmatism in the coming year).
The two-week replacement category features three silicone hydrogels: CIBA's O2Optix and Vistakon's Acuvue Advance and Acuvue Oasys. Both O2Optix and Acuvue Oasys have approval for seven-day extended wear (EW). While approval of these higher-Dk lenses for EW improves the safety profile of overnight wear, these lenses are more commonly used for daily wear. Silicone hydrogels are ideal for daily wear patients who already show signs of hypoxic stress such as corneal neovascularization, microcystic keratitis, corneal edema, myopic creep or a history of microbial or hypoxic-related keratitis.
Yet, many practitioners fit silicone hydrogels for patients who simply want to enjoy a lifetime of healthy contact lens wear. With children wearing lenses at younger ages and with multifocal lenses allowing patients to wear lenses well into presbyopia, it's possible that some patients could wear contact lens correction for greater than 60 years of their life. Fitting patients in the highest Dk lens available will allow for the least disruption to corneal metabolism by minimizing cumulative hypoxic stress over a lifetime of lens wear. In addition, market research shows that up to one-third of daily wear patients admit to occasionally sleeping in their lenses. For that reason, prescribing silicone hydrogel lenses that have extended wear approval for daily wear will provide an improved safety profile (both medically and medico-legally) for this segment of patients.
Silicone hydrogels may also improve patient comfort. Lens awareness and ocular discomfort are the leading patient complaints and the leading reason for contact lens discontinuation. While this discomfort is often blamed on dryness, a multitude of factors can contribute to lens-induced discomfort including poor surface wettability, lens dehydration, lens deposition, dry eye, hypoxia, mechanical epithelial disruption and immune system responses to each of these factors. Newer silicone hydrogel lens materials that feature added hydrating and wetting agents (such as Hydraclear in Vistakon products) strive to make the lens as physiologically inert as possible to cause the least disruption to natural tear composition and cellular integrity of the ocular surface.
Two-week lenses that address patient comfort are not limited to silicone hydrogels. Many newer, nonionic hydrogel lenses have achieved improved wettability, deposit resistance and hydration. These include Extreme H2O lenses (Hydrogel Vision Corp.), SofLens 66 and SofLens 59 (B&L), Precision UV (CIBA) and the new Biomedics XC lens (CooperVision) manufactured in omafilcon A material.
Monthly Replacement Lenses
The monthly replacement modality has shown tremendous growth in recent years mostly because of silicone hydrogels that have approval for 30-day continuous wear such as Night and Day (CIBA, Dk/t = 175) and PureVision (B&L, Dk/t = 110). These materials offer the highest oxygen permeability of any soft lens, which significantly reduces the effects of hypoxic stress to the cornea. While these lenses offer an improved safety profile for overnight wear, the higher oxygen transmission hasn't eliminated corneal complications from post-lens debris entrapment, lens deposition and bacterial adherence, which remain a menace to overnight wearers of soft lenses.
Therefore, you need to consider additional factors when fitting patients for continuous wear. Patient selection is critical. Avoid overnight wear in patients who smoke; who have clinical dry eye, lid disease or evidence of hypoxic stress; or who work in a hazardous environment where dirt and debris may deposit on lenses. I also advise patients against wearing lenses continuously for 30 days. I ask patients to remove their lenses weekly and clean and disinfect them to eliminate any deposits or microbial adherence. Not wearing the lenses overnight once every week also allows for tear exchange and debris removal to lessen metabolic compromise to the cornea.
Similar to their two-week counterparts, monthly silicone hydrogels offer many benefits for daily wear patients. Silicone hydrogels may offer better wettability and less dehydration, further contributing to fewer lens-induced symptoms of discomfort. While the initial drive in developing silicone hydrogels was for continuous wear, these other benefits will actually help to further grow their future market share.
As with disposable lenses, there are monthly replacement lenses in nonionic hydrogel materials that are designed to address the all-important consumer-driven need for improved comfort. One popular lens that has shown proven success in this regard is the Proclear lens from CooperVision.
Planned Replacement Lenses
A multitude of lens options still exist with replacement cycles ranging from every two months to quarterly to biannually. Overall, these represent a small and declining portion of lenses sold in today's market place. As I've highlighted above, increasing patient demands are driving the use of premium lens materials that offer high visual and functional performance, but require shorter replacement cycles.
Annual replacement soft lenses are certainly no longer within the mainstream of the market. However, some specialty lenses for patients who have aphakia, high ametropia (hyperopia > +8.00D, myopia > –12.00D or astigmatism > 4.00D), or for patients who need a toric multifocal are available only in annual replacement. Other specialty products in this category include lenses with prism, lenses for infant/pediatric use and lenses for keratoconus.
Specialty Soft Lenses
Some soft lenses have approval for use as a therapeutic bandage contact lens. Any of the silicone hydrogels approved for EW are perfectly suited for this purpose. They impose minimal metabolic stress on an already compromised cornea while providing comfort during the wound healing phase.
A very different specialty use of soft lenses is for enhancement of sports performance. The newly introduced Maxsight lens by B&L offers two different tints that alter visual perception to facilitate better visual responses in certain sporting venues. Because they alter normal visual perception, these lenses should not be worn for other activities.
GP lenses continue to be a valuable lens wear option for a large number of patients. While their market share in the United States has remained static between 10 percent and 15 percent, they remain the lens of choice for many patients and practitioners. GP lenses have health advantages over soft lenses that attributed to their preference by many prescribers, but with the Dk improvements of newer soft lenses, this health advantage is not as discernable as it once was. The improved oxygen permeability and better initial comfort of soft lenses has resulted in fewer GP lenses used for "routine" lens wear.
However, one of the greatest benefits of GPs that remains is stellar optical quality. GPs are the lens of choice for irregular corneas, keratoconus and many post-surgical cases. Even though the availability and stability of soft toric lenses have grown dramatically, GPs still are a great lens for correcting astigmatism. When corneal toricity matches spectacle cylinder, GPs eliminate visual fluctuations that can occur from lens rotation. GP multifocals have unsurpassed visual outcomes when compared to soft lens multifocals. With the growth of the presbyopic market in the coming years, expect even more growth in the area of GP multifocals.
GPs also have an edge in the extended wear arena. As mentioned previously, a contributing factor to overnight wear complications is post-lens debris entrapment. The rigid lens surface of GPs results in greater edge lift that provides enhanced tear flow to eliminate post-lens debris. The rigid surface is also responsible for the orthokeratology effect that has become more noteworthy since the introduction of the Paragon CRT system and has continued with B&L's Vision Shaping Treatment and other orthokeratology lens designs.
Creative hybrid technology has recently entered the market as the SynergEyes A hybrid contact lens, which combines a high-oxygen GP center with a 30-percent-water soft skirt. This lens is approved to correct all major refractive conditions.
Reviewing where we currently are begs the question "What's to come?" It's clear that higher-Dk lenses that promote and preserve corneal integrity will become the norm. Therefore, we'll see continued growth of silicone hydrogels and other high-Dk materials. Also, look for lenses that use surface treatments, moisture agents or other substances to maintain comfort and cleanliness.
I believe we'll also see a continued expansion of parameters, making all prescriptions virtually readily available. Wavefront technology will further enhance the optical design of contact lenses.
Best of all, ongoing improvements in manufacturing and distribution by the leading lens companies will allow continued availability of innovative new products while keeping costs low. Yet the challenge remains up to we practitioners to invest the time and to ask the right questions of our patients to discover what lens products will best meet their needs.
Dr. Nixon is a clinical associate professor and director of the Primary Care Externship at The Ohio State University College of Optometry. He is in private practice in Westerville and Johnstown, OH and serves as a member of Vistakon's Speaker's Bureau.