Brien Holden, Director of the Cornea and Contact Lens ResearchUnit (CCLRU) and the Cooperative Research Centre for Eye Researchand Technology at the University of New South Wales, Australia,opened the symposium by encouraging delegates to “Get anAttitude Towards Continuous Wear”. His entertaining lectureprovided an overview of patient interest in the continuous wearmodality and the benefits of silicone hydrogel lenses, particularlywhen compared with other forms of visual correction includingcurrent refractive surgery techniques. With close to one millionwearers worldwide, it would appear that the popularity of theselenses is gaining momentum despite the fact that some practitionersare still wary of continuous wear. In order to keep up with patients’ desirefor the best possible form of vision correction, practitionersneed to be willing to hear about their colleagues’ positiveexperiences with silicone hydrogels, review the research results,and try these lenses in their own practice in order to gain firsthand experience of their advantages.

Lyndon Jones, from the Centre for Contact Lens Research (CCLR)at the University of Waterloo, Canada, went on to describe theunique properties of silicone hydrogel lens materials, comparingthem with conventional hydrogel materials. He paid particularattention to their very high oxygen transmissibility (5-6 timesgreater than other hydrogel materials), superior dehydrationperformance and increased mechanical rigidity. Dr Jones describedthe unique surface modification processes of these lenses whichresult in low in-eye lysozyme deposition but somewhat higherlipid deposition in some patients.

Patrick Ladage presented the results of three studies of 6-and 30-night extended wear conducted at the University of TexasSouthwestern Medical Centre investigating the role of the cornealepithelium in defense against infection. Patients were fittedwith one of four test lens types: Focus Night & Day, PureVision,Acuvue and Menicon Z for a period of 1month daily wear, followedby 12 months extended wear. In addition to investigating Pseudomonasaeruginosa binding to exfoliated corneal epithelial cells, mechanismsof epithelial renewal (central corneal epithelial thickness,epithelial cell area and epithelial cell exfoliation) were investigated.Dr. Ladage reported that while epithelial homeostasis appearedto be suppressed by contact lens wear in general, the effectsappeared to be diminished to some extent with hyper Dk/t lensmaterials (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 withextended-wear of conventional hydrogel lenses appear to havebeen overcome with these novel materials. It was the Holden-Mertzcriteria (Dk/t 87x10^-9) for the elimination of contact lens inducededema from overnight wear that laid the foundation for the developmentof silicone hydrogel materials. Dr. Fonn presented the resultsfrom a number of studies conducted at the CCLR with siliconehydrogel lenses. These studies clearly demonstrated that manyof the clinical signs of hypoxia – corneal edema, epithelialmicrocycsts, limbal and bulbar vascular responses, lens inducedmyopia, and corneal light scatter – have been either eliminatedor significantly reduced to almost undetectable levels.

Many practitioners remain reluctant to accept the safety ofcontinuous wear with silicone hydrogel lenses due to concernsabout microbial keratitis (MK). Fred Edmunds, Director of GlobalProfessional and Clinical Affairs at Bausch & Lomb, presentedthe results of 27 extended wear clinical trials (5,800 patientsand over 2,200 patient-years of experience) of PureVision siliconehydrogel lenses, for which there were no reports of MK. Dr. Edmundsused the results of these studies and information from marketexperience and post-market surveillance to extrapolate the prospectiveincidence of MK with these lenses to be significantly lower thanthat of conventional hydrogel lenses worn on an extended wearbasis.

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


Complications Associated with Continuous Wear Silicone Hydrogelsand their Management

Although silicone hydrogel lenses have overcome many of thehypoxia-related problems associated with traditional extendedwear, some complications continue to occur. Kathy Dumbleton,from the CCLR at the University of Waterloo described the etiologyand presentation of some of the non-inflammatory clinical complicationsresulting from mechanical disturbances or trauma when wearingthese lenses. These include a form of post-lens debris (mucinballs), superior epithelial arcuate lesions (SEAL), contact lenspapillary conjunctivitis (CLPC), and corneal erosions. She wenton to discuss management strategies and approaches to minimizethe occurrence of these clinical complications.

Deborah Sweeney, Executive Director of the CCLRU at the Universityof New South Wales, discussed the inflammatory complicationsthat can occur despite the high oxygen transmissibility of siliconehydrogels. She emphasized the importance of accurate diagnosiswith an impressive selection of photographic and video examplesof Contact Lens-induced Peripheral Ulcer (CLPU), Contact Lens-inducedAcute Red Eye (CLARE), and Infiltrative Keratitis (IK). The keyto reducing and managing these events is recognizing the riskfactors associated with their presentation and educating patientson when not to wear their lenses and when to consult their eyecare practitioner.

One of the most important issues with continuous wear continuesto be the question of the risk of Microbial Keratitis (MK), atopic presented by Brien Holden. To date 32 cases of MK havebeen reported worldwide in an estimated 900,000 current siliconehydrogel wearers. This rate is significantly lower than thatreported with conventional low Dk extended wear lenses. Differentialdiagnosis between cases of MK and CLPU remains an area of confusionand yet is the most important clinical decision to be made. Anumber of strategies were offered to aid practitioners in theirdiagnoses. Holden also presented several MK case reports andexamined ways of minimizing the incidence of MK by understandingthe risk factors associated with its presentation, learning howto diagnose and manage the condition, and educating patients.


Continuous Wear Lenses in Practice

Jim Kerr, apracticing optometrist from Saskatchewan, Canada drew from hisclinical experience in a multi doctor practicewith 1300 patients currently wearing silicone hydrogels. He gavea very entertaining presentation in which he admitted to beinga “HEMAholic” and offered his “Ten Point Plan” toovercoming his addiction and converting his patients to siliconehydrogel materials! He discussed routine fitting, problem cases,and clinical management, in addition to reviewing the financialimpact of silicone hydrogels on a practice.

John Jantzi, Lecturer and Professional Liaison in the Schoolof Optometry at the University of Waterloo, explored practitionerand patient reluctance to use silicone hydrogel lenses despitetheir superiority over conventional hydrogels. His lecture reviewedthe advantages of silicone hydrogels, proposed reasons why thisnew material has been slow to be accepted, and offered suggestionsaimed at changing the prevailing attitude.

Deborah Sweeney closed the session and the highly successfulday 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 involveremoving the patient’s epithelium using simple surgicaltechniques and placing the onlay directly on the basement membraneof the cornea, after which the recipient’s epithelium wouldregrow to cover the onlay lens. Coreal onlays would be offeredas simple, in-office procedures and would offer advantages inbeing reversible, less invasive and more predictable than refractivesurgery, and allowing modifications when required.