REVOLUTIONARY FUTURE USES OF CONTACT LENSES.

It is estimated that there are approximately 39 million contact lens wearers in the United States and the global value of the contact lens market may be as high as $7.6 billion annually. Currently, contact lenses are almost exclusively used to correct ametropia and provide clear vision. However, the recent availability of new materials and new technologies has resulted in some revolutionary proposals for contact lenses.

This OVS Feature Issue highlights the potential future opportunities for the prescribing of contact lenses that extend far beyond their traditional uses. In our opening manuscript, Lyndon Jones sits down with four world renowned experts to highlight recent developments in the use of contacts to deliver topical ocular and systemic drugs, assist with ocular surface disease management, and limit the progression of myopia. Particular attention is paid to the barriers to the commercialization of such innovative products, and the article provides a fascinating insight for the clinician into the likelihood of such revolutionary contact lenses being available in a clinical setting.

The progression of myopia and its impact on disease in the long term has been a topic of much debate and concern recently, with the prevalence of myopia in some Asian countries being over 90%. In light of the known association between ocular disease and high myopia, attempts to slow the progression of myopia have grown in importance and contact lens options for this purpose are of growing interest to eye care practitioners. Paul and Kate Gifford provide a timely overview of the current state of knowledge regarding the use of contact lenses to slow myopia progression. This review is followed by two prospective clinical studies describing the use of soft lenses for this very purpose. In a 12-month study,

Aller and colleagues enrolled 86 myopic subjects and fitted them with a commercially available center distance soft multifocal lens or single vision soft lens in the same material. The multifocal lens resulted in reduced myopia progression and reduced axial elongation in comparison, and opens up the discussion around whether clinicians can consider using commercially available products off-label before the launch of a product with a specific indication for reduction in myopia progression.

Cheng and co-workers investigated the impact of a novel soft lens design incorporating positive spherical aberration on myopia progression and were also able to show a reduction in axial progression. Interestingly, upon cessation of wear of the test lens, no rebound effect was noted, unlike that previously noted upon cessation of atropine treatment for myopia control.

Taken together, these three manuscripts suggest a bright future for contact lenses in the management of myopia control, especially as new designs, with the appropriate approvals, come onto the market.

Contact lenses have been discussed as potential reservoirs to deliver drugs to the eye since the publication of the first soft contact lens patent in the 1960s. Hui and Willcox eloquently summarize the data thus far from in vivo animal and human studies that have investigated novel materials and approaches to delivering topical pharmaceutical agents to the eye.

They conclude that while currently available lenses provide limited benefits, materials that are modified specifically for this purpose may prove to be attractive in terms of dosing kinetics. However, the number of in-eye studies remains small at this point in time and more work is required to confirm if the promised benefits are tangible. Many methods exist to modify materials to control the delivery of drugs, and among these, molecular imprinting has received considerable attention, particularly for contact lens delivery. In an in vitro study, Byrne and colleagues developed silicone hydrogel materials and used the concept of molecular imprinting to release a cocktail of agents that may assist in mediating contact lens comfort.

The results demonstrated that with careful design, a high level of control can occur and that multiple molecules of interest can be released over time periods from days to weeks in physiologically relevant conditions. Many in vitro studies use small volumes to look at drug release, in which the materials of interest release their drugs into a 2 to 10 mL volume of fluid in a static, immobile system. These systems, although simple, do not mimic the in vivo system, in which there is a small volume of tear fluid that is constantly being replenished and in which blinking and air exposure occurs.

This marked difference in test environments may help to explain the apparent mismatch that often occurs between in vitro and in vivo results with drug delivery systems. As an illustration of this phenomenon, Phan et al. describe the release of an antifungal agent (fluconazole) from commercially available daily disposable soft lenses into both a traditional vial-based environment and a system that mimics air exposure, blinking, and physiological tear flow.

The markedly extended release kinetics shown in the latter setup indicate how important it is to make physiologically relevant measurements in this field. Some drugs that are of interest to treat ocular disease are photounstable, and extending their release profile is of little value unless they can be protected from light during storage or wear. One method of addressing this issue involves incorporating vitamin E into the hydrogel polymer matrix, and Hsu and Chauhan investigate the impact of both vitamin E and UV-blocking contact lens materials on the photodegradation of dexamethasone.