Compromises’ End? The introduction of a silicone hydrogel daily disposable lens

Lyndon Jones, PhD FCOptom DipCLP DipOrth FAAO (DipCL) FIACLE Lyndon Jones is currently Professor at the School of Optometry, and the Departments of Physics, Biology, Chemistry & Chemical Engineering (cross-appointed), and Associate Director of the Centre for Contact Lens Research at the University of Waterloo in Ontario, Canada. He graduated in Optometry from the University of Wales, UK in 1985 and gained his PhD from the Biomaterials Research Unit at Aston University, UK in 1998. He is a Fellow and Diplomate of the American Academy of Optometry, has authored over 200 papers and conference abstracts, one text-book and given over 300 invited lectures at conferences worldwide.

Craig Woods PhD, FAAO Research Manager, Centre for Contact Lens Research Craig is currently the CCLR's Research Manager. He graduated from The City University and after a period of working in private practice in London, joined the staff at the Institute of Optometry, in London as Assistant Clinical Director. He then moved to Manchester, where he obtained his PhD whilst Clinic Manager for the Department of Optometry and Vision Science, UMIST. In 1999 he moved to Melbourne to become the Deputy Clinic Director at the Victorian College of Optometry. Craig is a therapeutically accredited optometrist, a Fellow of the Victorian College of Optometry, the American Academy of Optometry and a member of the College of Optometry (UK).

As we rapidly approach the tenth anniversary of the introduction of silicone hydrogel lens materials, it is apparent from both clinical experience and information obtained from many controlled scientific studies that such materials provide huge benefits to our patients. Hypoxic issues such as epithelial microcysts, stromal striae, endothelial polymegethism, limbal hyperemia, neovascularisation and myopic creep are all markedly reduced or reversed  with these materials, [1-7]  as they provide many times more oxygen to the corneal surface than that seen with conventional polyHEMA-based hydrogel materials. [8] As a result, clinicians have rapidly adopted their use, and in many countries they now constitute a significant number of both new fits and refits from other lens materials. [9-11]
           
Despite their obvious advantages, these materials are not yet the “perfect panacea” in contact lenses that clinicians continue to seek, with a variety of complications still being observed. The incorporation of siloxane monomers results in the majority of materials exhibiting a higher modulus than that seen with hydrogel materials, [8, 12-14] resulting in reduced comfort for some patients when they are refitted from the lower modulus hydrogel materials, and also a variety of mechanical complications have been reported, including the development of superior epithelial splits, papillary conjunctivitis and corneal erosions. [3, 5, 7, 15, 16] Silicone hydrogels are also more hydrophobic, resulting in an increased accumulation of hydrophobic deposits from the tear film, notably lipid. [17-19] In addition, the past 5-6 years has seen an increasing number of reports of “incompatibilities” between various combinations of silicone hydrogel lens materials and preserved care systems, resulting in increased degrees of unanticipated corneal staining. [20-24] Finally, the expected reduction in risk for microbial keratitis during overnight wear did not materialise with the introduction of these highly oxygen permeable lenses [25-28] and patients continue to exhibit a variety of inflammatory, infiltrative conditions, at rates similar to that seen with reusable hydrogel materials. [29, 30]

Thus far, the shortest replacement frequency available for silicone hydrogel materials is two weeks, with many patients using these materials for four weeks. In Japan, Scandinavia and the UK over one-third of all soft lens fits are daily disposable lenses. [11, 31-33] With hydrogel materials this modality has shown significant advantages, with fewer overall complications, fewer unscheduled visits and greater patient satisfaction, [34-39] particularly amongst those with pre-existing allergic eye disease. [40, 41] Adoption of such a modality with silicone hydrogel lenses would potentially overcome several of their aforementioned problems, namely deposition and care system incompatibilities. [22] Additionally, such an option would result in enhanced convenience, a reduction in potential inflammatory complications and the removal of the physiological compromise that exists with current hydrogel-based daily disposable lenses, particularly when patients wear such lenses for long periods of time or “take a nap”. [42] However, to-date this has not been an option with silicone hydrogels, with manufacturing issues relating to the production of a cost-viable single-use daily disposable being a significant impediment.

However, in May of 2008 at the British Contact Lens Association’s Annual Clinical Conference, Johnson and Johnson announced the release of the first daily disposable silicone hydrogel contact lens, to be called 1-DAY ACUVUE® TruEye™ (Table 1 and Figure 1). This lens will first be made available in the UK in Autumn 2008. The lens is made from a new material (narafilcon A) and utilises a new version of the proprietary Hydraclear™ technology that J&J uses in all their silicone hydrogel lenses, which incorporates polyvinyl pyrrolidone (PVP) throughout the lens matrix as a moisturising and wetting agent. It has a modulus of 0.66 MPa, which is similar to ACUVUE OASYS, and a water content of 46%, which is similar to ACUVUE Advance and Biofinity. It has an inside-out indicator and Class 1 UV protection and will initially be available as a one-fit lens in minus powers only.

So, after much waiting the contact lens world will see the imminent introduction of a silicone hydrogel in a daily disposable format, which no doubt will be followed closely by other manufacturers introducing their lenses on such a platform. This will be a very valuable addition to clinicians and enable them to end the physiological compromise that exists when they opt to fit daily disposable lenses. However, they still need to be cogniscent of the fact that even daily disposables can result in severe complications, [43-48] particularly if their use is abused, and patients still need to be constantly reminded that lenses are medical devices and that hygiene practices, particularly on lens insertion, remain paramount to their safe use.

Table 1: 1-DAY ACUVUE® TruEye™

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