Brighton, England

CONTINUOUS WEAR

Much of the research presented throughout the conference, and the main focus of the first day's proceedings, concerned continuous wear.

Opening the Continuous Wear Symposium on Friday morning, Mr Graeme Young spoke of a renaissance in contact lenses, with wearers at record levels in the UK. Chairman Professor Debbie Sweeney (CCLRU Sydney) reported a rapid increase in myopia worldwide, especially in Asia, suggesting that refractive correction would continue to be a significant challenge.

Professor Brian Tighe (Aston University) gave an interesting account of the differences between the currently available silicone hydrogel lenses, PureVision and Night & Day, including some of the background to the recent legal wrangles between CIBA Vision and Bausch & Lomb. The CIBA material (lotrafilcon A) was described as biphasic, and this allowed it to transport water and ions at approximately twice the rate of pHEMA, without the need for a high water content. Water transport was an important influence upon lens movement on the eye. The PureVision material (balafilcon A) was essentially homogenous, and so had a lower water and ion transmission, yet its water content was still 10 per cent above that of pHEMA, suggesting that it was at least partly biphasic in nature.

Professor Tighe discussed the different surface treatments of the two lenses and the implications for wettability, and the 'stiffness' of the material, which influenced how the lens behaved during the blink cycle. Various chemical markers released by corneal and conjunctival cells were being used to analyse the interaction between eyelid and lens, and lens and cornea.

Dr Philip Morgan (Eurolens Research) reported on a year-long comparative study of 30-day continuous wear of a silicone hydrogel (Focus Night & Day) and a 'hyper-Dk' RGP lens (Menicon Z). Most patients were successful with either lens. The silicone hydrogels were associated with more adverse events overall, but these were manageable by the practitioner. The RGP lens created more issues with comfort, but this was more marked in neophytes than in experienced wearers.

Ophthalmologist Andrena McElvanney (Epsom & St Helier NHS Trust) discussed the therapeutic use of extended wear lenses, mostly high water content hydrogels, although there was a move towards silicone hydrogels in those cases where monthly visits were possible. The use of silicone hydrogels might improve the performance of bandage lenses in cases of dry eye and recurrent erosion.

The distinguished US ophthalmologist and humorist Professor Dwight Cavanagh (University of Texas, Dallas) described the effects of lens wear on the life cycle of the corneal epithelial cells. All types of contact lens wear slowed down cell apoptosis (the predetermined self-destruction or 'programmed cell death' that is an essential part of growth, metabolism and ageing) and surface shedding of epithelial cells, and decreased basal cell division and differentiation also occurred. In other words, the turnover of epithelial cells slowed, perhaps because the surface was shielded from shear forces induced by blinking. There was an adaptive recovery over time, but not to previous levels. Professor Cavanagh said that these effects were more marked in higher Dk lenses and greater in hyper-Dk RGPs than in silicone hydrogels. Nevertheless, Pseudomonas did not bind to these geriatric cells in significant numbers unless there was hypoxia as well. The possibility that cell stagnation could adversely affect stem cells was mentioned, as was the question as to whether orthokeratology, by interfering with cell migration, could also have long-term effects.

Microbiologist Mark Willcox (CCLRU, Sydney) reported on a study of bacterial contamination in continuous wear of silicone hydrogel and high water hydrogel lenses. The types of bacteria that colonise the eye appeared to be independent of both lens type and whether lenses were worn for six nights or 30, although there might be a slight tendency towards increasing frequency of bacterial contamination during extended wear.

Half an hour on mucin balls might not sound too enticing, but Eric Papas (CCLRU, Sydney) talked with an appealing, self-deprecating humour, and pulled some interesting rabbits from the hat. Although mucin balls were usually dismissed as of no significance, it had been found that keratocytes in the corneal stroma, which were normally dormant, proliferated under them. They indented the epithelium to a surprising level, yet no evidence of squashed cells was found, supporting the view that the epithelial cells moved aside. There also appeared to be an increased incidence of contact lens-related peripheral ulceration in patients with mucin balls.

GLOBAL MK RATES

Professor Brien Holden (CCLRU, Sydney) revisited a favourite topic, goading the host nation on Australian triumphs in cricket, rugby league and football. He has been doing this for many years, which may explain why the result of the latest England versus Australia rugby union match had slipped from his memory. Global surveillance of rates of microbial keratitis (MK) with silicone hydrogel use suggested much lower levels than those associated with lower Dk lenses, even though the true levels of MK with either were probably significantly higher than those reported. Professor Holden gave an overview of the incidence, diagnosis and management of adverse events. The next generation of silicone hydrogels could have surfaces which repelled bacterial adhesion, and eventually surfaces that wetted as well as the cornea itself might become the norm.

Dr John McNally (Ciba Vision) discussed risk factors for infiltrates in continuous wear. Significant factors included age below 30, and prior history of a corneal scar, contact lens-associated red eye or infiltrates. Smoking in the over-30s was found to be insignificant, yet it was a factor in the younger patient. Male gender, prior lens wear, refractive error and neovascularisation were all found to be insignificant.

Jacinto Santodomingo-Rubido (Aston University) described a study in which new wearers were observed for 18 months wearing daily wear or continuous wear silicone hydrogels. Digital image analysis was used to monitor hyperaemia with greater sensitivity than would be possible by subjective assessment. By using both colour detection and edge detection, the researcher could differentiate between increases in the number of vessels and dilation of existing ones. All groups studied showed an increase in hyperaemia over time, which is certainly at odds with claims for silicone hydrogels based on subjective observations or anecdotal evidence. The number of vessels remained steady. There was a decrease in non-invasive tear break-up time with duration of wear in continuous wear subjects. Differences between the materials were slight.

Professor Desmond Fonn (University of Waterloo, Canada) gave an entertaining presentation on dry eye and discomfort. Dry-eye symptoms occurred in twice as many contact lens wearers as non-wearers and were a major reason for dropping out of lens wear. Silicone hydrogels did not appear to have improved matters significantly. In cases where silicone hydrogels were less comfortable than hydrogels, the cause was likely to be mechanical and related to lens fit, but the patient might adapt. Dryness became worse with time. It was known that tear break-up time reduced with contact lens wear, but this might not be the cause of the symptoms.

EDUCATION AND RESEARCH

Saturday morning's dual-track sessions provided a useful mix of education and research presentations.

For John Meyler (Johnson & Johnson), proper definition, accurate diagnosis and correct management were key to dealing with adverse events in contact lens wear. Many complications had 'disappeared from the radar screen' with the predominance of disposable and single-use lenses. But with the move towards continuous wear, practitioners needed to be comfortable with managing conditions such as CLPC and SEALs. He reminded delegates of the acronym 'pedal' - Pain, Epithelial defect, Discharge, AC reaction and Location - to help practitioners identify features distinguishing MK from contact lens peripheral ulcers. In the discussion that followed, the differentiation of such adverse reactions was described as one of the most important areas of current contact lens practice.

In her keynote address, "Continuous wear - how far have we come?" Professor Debbie Sweeney said that increased confidence in silicone hydrogel continuous wear had doubled their use in the past year and there were now almost one million wearers worldwide. At the same time, the number of laser eye surgery procedures was in decline. When patients were asked which vision correction option, if it were perfect, they would prefer, six out of 10 opted for 30-night continuous wear and only four in 10 for laser surgery. Once patients had experienced wearing contact lenses for 30 consecutive nights they wanted to be able to wear the lenses for even longer periods.

First-generation silicone hydrogels would be superseded by second and third generation products with new designs and materials. Work was under way on anti-bacterials such as furanones, extracted from algae, that could reduce colonisation and adhesion to lens surfaces. An aspheric Focus Night & Day lens had been shown to reduce peripheral bearing and minimise pressure on the cornea, and aberration-corrected designs provided significant improvement in visual performance over spherical designs.

Increased tear exchange might be effected by incorporating fenestrations or channels in the lens or by smaller lens diameters. If silicone hydrogels were to be used for hyperopic, astigmatic and presbyopic correction, Dks as high as 250 could be needed. Lower modulus, improved biocompatibility and reduced cost were other desirable features.

Presentations during Saturday's research session reported some interesting findings with silicone hydrogels.

Christine Purslow (Aston University) had used dynamic ocular thermography to measure the temperature of the anterior eye in silicone hydrogel lens wear. Temperature decreased when the lenses were inserted but increased to above baseline levels when they were removed. Further work would determine whether this effect was unique to silicone hydrogels and investigate the mechanism behind the temperature change.

Although soft lens dehydration has been well covered in the literature, as yet there have been no reports on in vivo dehydration of silicone hydrogels. Philip Morgan had used a gravimetric technique to compare the water content of the PureVision lens with that of Acuvue 2 worn over four weeks of extended wear. Acuvue 2 underwent a greater degree of dehydration after two weeks (6 per cent versus 3 per cent) and its Dk decreased by 3.6 barrer. Paradoxically, the loss of water from PureVision was associated with a 6 barrer increase in oxygen permeability at four weeks.

Lyndon Jones (University of Waterloo, Canada), reported on differences in practitioner attitudes to prescribing daily disposable, seven-day extended wear and 30-day continuous wear in four countries: Australia, Canada, the UK and US. The UK fitted the highest percentage of daily disposables, with 34 per cent of practitioners fitting more than 40 per cent of patients with this modality, compared to 14 per cent of practitioners in other countries. The UK was also the least conservative towards continuous wear, with 45 per cent of practitioners recommending 30-nights wear. But practitioners here were more likely to review their patients frequently, two out of three seeing patients at intervals of six months or less.