Is the Key to Successful Lens Wear in the Lens or in the Bottle?
Product innovations are aimed at keeping patients happily wearing their lenses all day every day. Here’s a look at how we’re faring in our efforts to meet this goal.
|Dr. Gleason, founder of Foresight Regulatory Strategies Inc., has greater than 35 years of experience in basic research and management of clinical trials for medical devices. He has extensive experience in design control, product development requirements and regulatory submissions for both the U.S. and international markets. He is a consultant to Vistakon, Menicon, Sauflon, Allergan, Semprus BioSciences, and CooperVision.|
By William J. Gleason, OD
Since the introduction of the first hydrogel contact lens material in the early 1970s, our expectation has been that each new material, design, and care solution would answer the needs of another segment of the population. Spherical lenses were followed by toric and multifocal lenses, and handling tints made way for longterm protection with ultraviolet-absorbing materials. Cosmetic lenses could change iris color or improve cosmesis for those with congenital or traumatic defects. Improvements in the physical properties of materials allowed a select population to wear their contact lenses overnight, not only eliminating the hassle of daily care for some average wearers but also providing comfort and relief to people needing the protection provided by therapeutic lenses.
Soft Lens Evolution
In the early years, cost was a major factor influencing contact lens replacement—practitioners paid an average of $35 per lens—and replacement was considered only when discomfort or poor vision became unbearable. Filmy hydrogel lenses were still more comfortable compared to the rigid lenses at that time.
Nonpreserved, normal saline, the original care solution for hydrogel lenses, kept the material hydrated and flexible, while a modified baby bottle warmer was used for disinfection. Lenses became coated with deposits after only a few weeks but were worn for months or even years before they were replaced.
Cleaners in the form of enzymes to dissolve the denatured proteins as well as surfactants to remove lipids and environmental debris became too numerous to count. These did extend the life of the lenses, but in the end, the heat-generated denatured deposits would necessitate replacement. Chemical disinfection systems that reduced the denatured deposits had irritating chemicals and toxic breakdown products. Peroxide systems, similar to those in use today, cleaned lenses effectively without the irritation and toxicity of the chemical systems—as long as patients followed their instructions for use.
Modifications to the preservatives in contact lens care products and the addition of surfactants and viscosity agents took us from a three-bottle system of cleaning, disinfecting, and rinsing to a two-bottle system and eventually to single-bottle multipurpose solutions. The simplicity of using one product for cleaning, rinsing, storing, and disinfecting contact lenses at the end of the wearing period, plus rinsing and rewetting before lens application, has become the preferred approach to contact lens care.
Despite improvements in surface properties, designs, and manufacturing processes for materials and a paradigm shift in care systems, a significant number of contact lens wearers drop out every year, offsetting the number of new wearers. Researchers and clinicians have studied this phenomenon and continue to look for ways to prevent it.
Increased Oxygen and Wettability
Pritchard et al (1999) found that 34 percent of patients who had worn contact lenses for five to six years stopped wearing them at least once, mainly because of discomfort, dryness, and red eyes. Some scientists theorized that increasing contact lens oxygen permeability to nearly atmospheric conditions would solve many of these problems. Others believed reducing friction between the front surface of the lens and the upper lid margin or palpebral conjunctiva would result in less fatigue and discomfort at the end of the day.
|How Fashion and Function Influence Dropout|
Contact lenses were once considered necessary to avoid unattractive or annoying eyeglasses. People who wore rigid lenses tolerated the edema, the spectacle blur, and the edge discomfort as long as they believed that they looked better wearing contact lenses than they did wearing eyeglasses. Sports enthusiasts considered contact lenses a functional necessity because eyeglass lenses fog up and the frames can limit the field of vision.
Today, however, frame designs are so stylish that contact lens wearers are less inclined to endure discomfort when they can still be fashionable wearing eyeglasses, and vented, wraparound sports glasses or refractive surgery obviate the need for contact lenses for sports.
New material polymer structures frequently work against these intended endpoints. The addition of silicone to increase oxygen permeability generally decreases surface wetting, creating drag on the upper lid and decreasing comfort. Manufacturers have introduced surface modifications to help offset these effects. Some silicone hydrogel lenses are plasma-treated in a neutral environment to remove hydrophobic material from the surface to increase wetting. Others are plasma-treated in an active environment to improve wettability through chemical interaction with the surface. Both methods deliver a significant amount of energy to the lens surface, which can produce surface defects (Teichroeb et al, 2008). Another approach is the addition of wetting agents to “hide” the hydrophobic surface and improve the hydrophilic surface by trapping the agent within the polymer matrix or adding the agent to the repeating chains.
Fresh Lenses Every Day
If most people stop wearing contact lenses because of discomfort or irritation from deposited lenses and incompatible care solutions, why haven’t daily disposable lenses become the lens of first choice everywhere? U.S. practitioners tend to use them mostly as problem-solvers for patients who have excessive deposits or upper lid abnormalities, for those who wear their lenses only occasionally, and, more recently, for patients under the age of 18.
The use of a fresh lens every day without repeated exposure to the environment, contaminated storage cases, or potentially irritating care solutions intuitively predicts lower rates of inflammation and infection. If this is true, then it should follow that discomfort and dropout rates should be lower for patients wearing daily disposables than for those wearing frequent-replacement hydrogel lenses. Some reports from retrospective record examinations and case-controlled studies support the assumption that daily disposable lenses used according to the labeling have the lowest risk for severe disease (Stapleton etal, 2008; Dart et al, 2008). It has been difficult to thoroughly analyze the associated complications, however, because the subjects may not have been using the lenses as labeled. Various post-approval registry studies are underway to find out whether this modality, when used as labeled, can reduce complications and maintain higher wearer retention rates.
We can improve success by careful patient selection.
With the introduction of ocular-compatible surfactants into formulations already approved for rinsing and disinfecting, the first multipurpose lens care solutions became available in the late 1980s. The acceptance of one-bottle care systems led to reformulations that included preservatives to increase disinfection efficacy, surfactants for better cleaning, and viscosity agents to ease lens application and to buffer the ocular tissue from the surfactants and the preservatives. Although these products meet all of the standards established by various regulatory agencies, they are no match for the poor lens care practices of some contact lens wearers. Furthermore, eliminating the rub-and-rinse step prior to overnight storage has resulted in a higher organic load on the lenses and inside the case. This shortcut combined with contaminated cases and the practice of topping off used solution rather than replacing it has resulted in tragic outcomes for some patients.
Another important step in contact lens care is the rinse between the lens case and the eye. If we truly are killing a significant number of organisms, then the care solution on the surface of the lens as it comes out of the case contains remnants of bacterial and fungal organisms that can trigger an inflammatory response when the lens is applied. Although this may be a low-grade inflammation, I believe it could contribute to decreased wearing time and could eventually result in sufficient irritation to cause discontinuation of lens wear.
What’s the Answer?
According to a recent survey (Rumpakis, 2010), 15.9 percent of U.S. contact lens wearers stop wearing their lenses. The top three reasons for discontinuation are discomfort (50 percent), vision not as good as with eyeglasses (15.9 percent), and the cost of contact lens wear (12.3 percent). Internationally, comfort was by far the leading reason why patients stopped wearing their lenses, with percentages varying by only a few points.
Lack of comfort can be associated with ocular dryness, burning, stinging, itching, or a combination of these factors, but regardless of the cause, the outcomes are often the same. Patients will try to continue wearing their lenses, depending on their needs and self-image, but most will revert to eyeglasses or explore the possibility of refractive surgery when their symptoms persist.
Although the dropout statistics are discouraging, by no means are contact lenses a failure. Indeed, 84.1 percent of patients are successfully wearing contact lenses (Rumpakis, 2010). In the meantime, researchers continue to search for a truly biocompatible lens material, exploring multiple paths to trick the eye into believing that a contact lens is not a foreign object. One possible option is to coat the current materials with a biocompatible substance to hide the lens from the body’s defenses.
We are fortunate that many problems related to vision, physiology, manufacturing consistency, and costs have been addressed. In my opinion, we can improve our success rates and minimize the potential for dropouts by carefully selecting the patients we fit. For example, those who have lid margin disease, allergies, and low tear meniscus may not be the best candidates for contact lens wear.
So, is the key to successful lens wear in the lens or in the bottle? I believe for some patients the answer is neither. It is in our hands. CLS
To obtain references for this article, please visit http://www.clspectrum.com/references.asp and click on document #205.
|The Role of Packaging Solutions in Contact Lens Comfort|
The first soft contact lenses were packaged in nonpreserved normal saline. Viscosity agents and surfactants were added to prevent the lens edges from adhering to one another or to the blister package.
In recent years, manufacturers have introduced new and, in some cases, patented packaging solutions to promote initial comfort, with the goal of extending comfort to later in the day. In general, the effects of these solutions are short-lived, and their value on day 2 and beyond is difficult to establish.