Brien Holden, Director of the Cornea and Contact Lens Research Unit (CCLRU) and the Cooperative Research Centre for Eye Research and Technology at the University of New South Wales, Australia, opened the symposium by encouraging delegates to “Get an Attitude Towards Continuous Wear”. His entertaining lecture provided an overview of patient interest in the continuous wear modality and the benefits of silicone hydrogel lenses, particularly when compared with other forms of visual correction including current refractive surgery techniques. With close to one million wearers worldwide, it would appear that the popularity of these lenses is gaining momentum despite the fact that some practitioners are still wary of continuous wear. In order to keep up with patients’ desire for the best possible form of vision correction, practitioners need to be willing to hear about their colleagues’ positive experiences with silicone hydrogels, review the research results, and try these lenses in their own practice in order to gain first hand experience of their advantages.

Lyndon Jones, from the Centre for Contact Lens Research (CCLR) at the University of Waterloo, Canada, went on to describe the unique properties of silicone hydrogel lens materials, comparing them with conventional hydrogel materials. He paid particular attention to their very high oxygen transmissibility (5-6 times greater than other hydrogel materials), superior dehydration performance and increased mechanical rigidity. Dr Jones described the unique surface modification processes of these lenses which result in low in-eye lysozyme deposition but somewhat higher lipid deposition in some patients.

Patrick Ladage presented the results of three studies of 6- and 30-night extended wear conducted at the University of Texas Southwestern Medical Centre investigating the role of the corneal epithelium in defense against infection. Patients were fitted with one of four test lens types: Focus Night & Day, PureVision, Acuvue and Menicon Z for a period of 1month daily wear, followed by 12 months extended wear. In addition to investigating Pseudomonas aeruginosa binding to exfoliated corneal epithelial cells, mechanisms of epithelial renewal (central corneal epithelial thickness, epithelial cell area and epithelial cell exfoliation) were investigated. Dr. Ladage reported that while epithelial homeostasis appeared to be suppressed by contact lens wear in general, the effects appeared to be diminished to some extent with hyper Dk/t lens materials (silicone hydrogel and RGP).

Desmond Fonn, Director of the CCLR at the University of Waterloo, reported that the long and short-term hypoxic problems seen with extended-wear of conventional hydrogel lenses appear to have been overcome with these novel materials. It was the Holden-Mertz criteria (Dk/t 87x10^-9) for the elimination of contact lens induced edema from overnight wear that laid the foundation for the development of silicone hydrogel materials. Dr. Fonn presented the results from a number of studies conducted at the CCLR with silicone hydrogel lenses. These studies clearly demonstrated that many of the clinical signs of hypoxia – corneal edema, epithelial microcycsts, limbal and bulbar vascular responses, lens induced myopia, and corneal light scatter – have been either eliminated or significantly reduced to almost undetectable levels.

Many practitioners remain reluctant to accept the safety of continuous wear with silicone hydrogel lenses due to concerns about microbial keratitis (MK). Fred Edmunds, Director of Global Professional and Clinical Affairs at Bausch & Lomb, presented the results of 27 extended wear clinical trials (5,800 patients and over 2,200 patient-years of experience) of PureVision silicone hydrogel lenses, for which there were no reports of MK. Dr. Edmunds used the results of these studies and information from market experience and post-market surveillance to extrapolate the prospective incidence of MK with these lenses to be significantly lower than that of conventional hydrogel lenses worn on an extended wear basis.

John McNally, Head of Continuous Wear Research and Development at CIBA Vision, reported on the risk factors for corneal infiltrative events. Subjects in a year long randomized clinical trial were fitted with either lotraficon A (Focus Night & Day) silicone hydrogel lenses (n=697) or etafilcon A hydrogel lenses (n=698), and the risk factors gathered at baseline were analyzed to determine their association with corneal infiltrative events. The study found that gender, prior history of extended or daily lens wear, refractive error, neovascularization, and assessment of lens fit were unrelated to corneal infiltrative events. Significant factors included subjects in the age range of 18 to 29 years, smoking, the combination of smoking and young age, prior history of corneal scarring, contact lens acute red eye and corneal infiltrates. The results from this study and current post-market approval studies investigating additional potential risk factors, will aid practitioners in selecting and counseling prospective continuous wear patients.


Complications Associated with Continuous Wear Silicone Hydrogels and their Management

Although silicone hydrogel lenses have overcome many of the hypoxia-related problems associated with traditional extended wear, some complications continue to occur. Kathy Dumbleton, from the CCLR at the University of Waterloo described the etiology and presentation of some of the non-inflammatory clinical complications resulting from mechanical disturbances or trauma when wearing these lenses. These include a form of post-lens debris (mucin balls), superior epithelial arcuate lesions (SEAL), contact lens papillary conjunctivitis (CLPC), and corneal erosions. She went on to discuss management strategies and approaches to minimize the occurrence of these clinical complications.

Deborah Sweeney, Executive Director of the CCLRU at the University of New South Wales, discussed the inflammatory complications that can occur despite the high oxygen transmissibility of silicone hydrogels. She emphasized the importance of accurate diagnosis with an impressive selection of photographic and video examples of Contact Lens-induced Peripheral Ulcer (CLPU), Contact Lens-induced Acute Red Eye (CLARE), and Infiltrative Keratitis (IK). The key to reducing and managing these events is recognizing the risk factors associated with their presentation and educating patients on when not to wear their lenses and when to consult their eye care practitioner.

One of the most important issues with continuous wear continues to be the question of the risk of Microbial Keratitis (MK), a topic presented by Brien Holden. To date 32 cases of MK have been reported worldwide in an estimated 900,000 current silicone hydrogel wearers. This rate is significantly lower than that reported with conventional low Dk extended wear lenses. Differential diagnosis between cases of MK and CLPU remains an area of confusion and yet is the most important clinical decision to be made. A number of strategies were offered to aid practitioners in their diagnoses. Holden also presented several MK case reports and examined ways of minimizing the incidence of MK by understanding the risk factors associated with its presentation, learning how to diagnose and manage the condition, and educating patients.


Continuous Wear Lenses in Practice

Jim Kerr, a practicing optometrist from Saskatchewan, Canada drew from his clinical experience in a multi doctor practice with 1300 patients currently wearing silicone hydrogels. He gave a very entertaining presentation in which he admitted to being a “HEMAholic” and offered his “Ten Point Plan” to overcoming his addiction and converting his patients to silicone hydrogel materials! He discussed routine fitting, problem cases, and clinical management, in addition to reviewing the financial impact of silicone hydrogels on a practice.

John Jantzi, Lecturer and Professional Liaison in the School of Optometry at the University of Waterloo, explored practitioner and patient reluctance to use silicone hydrogel lenses despite their superiority over conventional hydrogels. His lecture reviewed the advantages of silicone hydrogels, proposed reasons why this new material has been slow to be accepted, and offered suggestions aimed at changing the prevailing attitude.

Deborah Sweeney closed the session and the highly successful day by exploring future forms of permanent vision correction, in particular the implantable contact lens or corneal onlay. Onlay lenses are made from a synthetic, inert, oxygen permeable, highly porous, biocompatible material. The procedure would involve removing the patient’s epithelium using simple surgical techniques and placing the onlay directly on the basement membrane of the cornea, after which the recipient’s epithelium would regrow to cover the onlay lens. Coreal onlays would be offered as simple, in-office procedures and would offer advantages in being reversible, less invasive and more predictable than refractive surgery, and allowing modifications when required.