Hunter Valley, NSW, Australia
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The 11th International Contact Lens Congress presented by the Contact Lens Society of Australia and the New Zealand Society of Contact Lens Practitioners was held recently at the fabulous Hunter Valley, in New South Wales Australia. Every 3 years the congress gives an in-depth overview of the status of vision correction and this year topics covered: myopia; children and contact lenses; continuous wear; microbial keratitis; disease, tear film and dry eye; gas permeable lenses and orthokeratology; a contact lens industry update; refractive surgery; contact lenses for presbyopia; specialty contact lenses and a practice management workshop to increase business. It was a stimulating meeting with a host of distinguished national and international presenters giving the audience an update on the Future of Vision Correction. Here we present a summary of some of the presentations covering clinical experience with silicone hydrogels and continuous wear as well as an update on microbial keratitis study group and sensations of dryness with silicone hydrogels.
Clinical Experience
Philip Morgan from UMIST in the UK provided a snapshot of the factors contributing to the relative success of silicone hydrogels from his most recent prospective survey of contact lens practitioners. Results from his 2003 survey indicate that practitioners are choosing silicone hydrogels for soft lens extended wear, with this lens type accounting for practically all extended wear fits in Australia, and the UK (Table 1).
Table 1 |
| Country |
Si-H for DW |
Si-H for EW |
| Australia |
34% |
99% |
| Netherlands |
48% |
44% |
| United Kingdom |
10% |
99% |
| United States |
59% |
52% |
Although released only relatively recently compared to Europe, Australia and New Zealand, silicone hydrogels are well accepted in the United States, but are considered to be a problem solving lens, rather than a lens of first choice. Overall his data indicate that a large number of practitioners fit silicone hydrogels and they are confident in prescribing these lenses to existing wearers.
In silicone hydrogels – where are we and what’s next? Deborah Sweeney gave an overview of results from a 3 year clinical trial with silicone hydrogels showing the low physiological response to extended wear with these lenses, and little difference between 6 or 30 nights of wear. The majority of the clinical trial patients could wear their lenses for > 21 consecutive nights of wear, and 39% indicated they would like to wear their lenses for more than 30 consecutive nights. During the trial, more than 80% of patients remained in silicone hydrogels for more than 3 years with the main lens-related discontinuations being caused by mechanical events. Of these, superior epithelial arcuate lesions (SEALs) and contact lens induced papillary conjunctivitis (CLPC), both local and general, were the major events. Newer generation silicone hydrogel lens designs appear to prevent the lenses interacting with the cornea and events of SEALs are likely to be almost eliminated in the near future. In practice, practitioners report very low rates of adverse events (1 to 4%) in patients wearing silicone hydrogels and a very small percentage of patients will experience discomfort, dryness and vision-related difficulties. The majority of corneal infiltrative events are detected at unscheduled visits and the percentage of mechanical events such as CLPC are detected fairly evenly between routine and unscheduled events. The flexible approach that silicone hydrogels allow is paving the way for their use with children, presbyopes and in therapeutic cases. Children aged 7 to 12 are very accepting of silicone hydrogels with the majority achieving a good fit and 77% of monovision patients prefer silicone hydrogels over conventional lenses. As a therapeutic lens, silicone hydrogels are being used as a piggy-back lens for keratoconus ( put in link to last month’s poster) and as bandage lenses. The future for silicone hydrogels will be the developments designed to improve biocompatibility and hopefully new designs for both astigmats and presbyopes.
Ray Fortescue, a practitioner with more than 20 years private practice in Sydney, continued the theme of clinical experience with silicone hydrogels by further emphasizing the low physiological response of these lenses. He described his clinical experience and showed how these lenses make his practice professionally and financially rewarding. Since the release of silicone hydrogels he has doubled his business. He finds that a commitment to inventory, good education of staff and patients and a confidence in managing adverse events leads to happy patients, a low drop-out rate and increased patient loyalty. Ray Fortescue also reported that approximately 12% of his hypermetropic patients experience up to a +2.00D shift with silicone hydrogel lenses. He associated these effects with corneal flattening and found that if patients are changed to a daily wear schedule, or are refit with a lower modulus lens material, then the effects can be reduced.
Microbial keratitis
Dwight Cavanagh from the University of Texas Southwestern Medical Center at Dallas gave a thorough overview of the clinical trials and laboratory studies that he has conducted to investigate whether increased oxygen supply regulates binding of Pseudomonas aeruginosa to the cornea. His studies using an exfoliated epithelial cell assay clearly show that lens-induced hypoxia causes increased binding of bacteria to the cornea. He also showed high Dk silicone hydrogels either for extended or daily wear induce less bacterial binding compared to conventional hydrogel lenses. These results suggest that the incidence of microbial keratitis should be lower with silicone hydrogels compared to conventional soft lenses. Fiona Stapleton, Lisa Keay and Katie Edwards from the Australian Microbial Keratitis Study group gave the congress an update on their surveillance study of all cases of microbial keratitis secondary to contact lens wear in Australia and New Zealand for one year, commencing October 2003. They have now reached the half way mark and so far the response rate has been excellent. Almost half the responses have been received via internet reporting which has greatly facilitated rapid feed back. Analysis of the referral pathways for patients diagnosed with microbial keratitis in Australia and New Zealand is illuminating and involves optometrists, ophthalmologists and general practitioners. Once this study in Australia and NZ is complete, the Microbial Keratitis Study group will be able to estimate the penetrance of contact lens wear in Australia and New Zealand and provide an estimate of the incidence of microbial keratitis with silicone hydrogels.
Dryness
Arthur Back from Ocular Sciences examined the characteristics that may contribute to the reduction in frequency of symptoms of dryness with wear of silicone hydrogels. He reported results from 6 hour non-dispensing trials with experienced lens wearers that used the degree of inferior corneal staining as a marker for an unstable tear film and dehydration. Results indicated that ocular signs of dryness after 6 hours with currently marketed and an experimental silicone hydrogel varied with each lens type. He surmised that the key to overcoming dryness is in improving the lens surface and manufacturing process. OSI have designed a new high Dk silicone hydrogel that does not require surface treatment, is naturally wettable and therefore should have less interaction with the cornea. This lens is not currently marketed and preliminary results indicate that inferior staining is minimal and are very encouraging.
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Serina Stretton, BSc, PhD