Alison Ewbank, Anna Sulley and Nick Atkins report on some of the highlights of this year's BCLA conference and exhibition.
Conventional wisdom has it that the large numbers of practitioners flocking to CET events are there simply to get much-needed points. But the increasing success of one CET event would seem to challenge that perception.
Approaching its 30th year, the British Contact Lens Association conference has been growing steadily over several years. This year's meeting saw more than 1,200 participants gather in Brighton for the three-day conference and exhibition, with delegate numbers up 16 per cent on 2004's record levels. The event is also becoming a major date on the international contact lens calendar, around a third of visitors coming from overseas.So what attracted delegates along in such large numbers this year? For UK practitioners, the introduction of compulsory CET and additional burden for conta
Professor Brien Holden |
Fears about the likely impact of changes to contact lens supply, which have seen the likes of Tesco already entering the market, may also have been a factor the BCLA added two special sessions discussing the new regulations to its conference programme (see panel 'New rules on supply' on page 32).
But the consensus at this meeting was that the current surge in interest in contact lenses reflected a phase of rapid development for the industry and the emergence of novel materials that would improve the wearer's experience.
New and future generations of silicone hydrogel lenses and comfort-enhanced daily disposables were the major advances in lens technology, and there were new solutions designed to 'condition' the lens and offer greater compatibility with modern materials. Within the next 2-3 years, there was also the prospect of lenses with antimicrobial surfaces - clinical trials of lenses coated with furanones, compounds derived from marine algae, are to begin this year.
NEW FINDINGS ON INFECTION
Two sessions in particular summarised current thinking on recent material developments and the properties that future materials will need to be more successful.
Setting the scene was a session in which researchers from the UK and Australia reported conflicting findings on the incidence of complications with current hydrogels. Dr Philip Morgan (University of Manchester) described an ongoing hospital-based study that looked at all patients wearing contact lenses attending an acute referral centre. A clinical severity matrix was used to record signs and symptoms of 118 'corneal infiltrative events' (CIEs) and differentiate between severe and non-severe cases. The wearing modalities and lens types used by all contact lens wearers in the hospital's catchment area were calculated from market and demographic data.
The key finding of the study was that the use of traditional extended wear hydrogels was associated with a five times greater risk of a severe CIE compared with extended wear silicone hydrogel lenses. The risk with extended wear silicone hydrogels was probably greater than with daily wear traditional hydrogels although this difference was not statistically significant.
Lens modality was the important risk factor for the development of a CIE; patients using extended wear hydrogels were seven times more likely to develop any form of hospital-presenting CIE and 15 times more likely to develop a severe CIE compared with those using the same lens type on a daily wear basis.
There were also differences in the location of infiltrates. Patients using traditional hydrogels for daily wear showed significantly more infiltrates in the peripheral cornea, although with daily disposable lenses infiltrates were more likely to be central. With extended wear silicone hydrogels, infiltrates were found in the superior cornea, although with the softer materials now emerging the mechanical effects might be different.
Those at greatest risk for CIE were males, smokers and those with no other eye or health problems, and incidence was greatest from January to March.
Dr Morgan said that apparent differences in the reported incidence rates for severe keratitis between centres might be due to the number of investigational sites involved and the clinical criteria used.
A group led by Associate Professor Fiona Stapleton (Vision CRC, Sydney) had looked at 307 new cases of presumed microbial keratitis (MK) presenting to ophthalmic practitioners throughout Australia between October 2003 and September 2004. A clinical definition of MK was used and cases were stratified by severity according to the size and location of the lesion. A telephone survey of randomly selected households determined the number of contact lens wearers, of various types, in the community.
This group found no statistically significant difference in incidence of moderate or severe MK between silicone hydrogels and traditional hydrogels when used for extended wear. At one per 10,000 wearers per year, the lowest incidence was with daily disposable lenses. With daily wear silicone hydrogels the incidence was 4.5 per 10,000 wearers per year, although these patients were much more likely to wear their lenses on an occasional overnight basis than conventional daily wear users, among whom the incidence was 3 per 10,000 wearers per year.
In this study, the severity of infection was not significantly affected by high or low Dk or by wearing modality. More severe disease was, however, associated with a delay in receiving appropriate treatment. Daily wear users at increased risk were smokers and those who occasionally used their lenses overnight or failed to wash their hands prior to lens handling. More worrying in the current UK context was that daily wear users who bought their lenses over the internet had a significantly greater risk of having a severe corneal infection, 5.5 times that of patients who did not purchase via this route.
For extended wear users, lack of hand washing was a high risk factor and those who had used their current lens-wearing modality for less than six months were more at risk than those with longer wearing experience.
Dr Stapleton suggested that the results of studies into infection rates in contact lens wearers were very sensitive to small changes in the denominator. In particular, they depended on how extended wear was defined in terms of number of nights' wear per week or per month. More relevant to the practitioner was that the Vision CRC group was developing clinical guidelines on MK that would help avoid this most serious complication of contact lens wear.
Dr Robin Chalmers (Atlanta) described a US post-market evaluation of Focus Night & Day lenses used for 30-day continuous wear. Wearers were contacted three months and 12 months after registration and asked, among other questions, whether they had experienced an episode of painful, red eyes which caused them to seek advice. Such events were also reported directly by participating practices. All events were reviewed for the presence of a corneal infiltrate and forwarded to an adjudication committee.
Nearly 5,000 of the wearers registered completed one year's wear and 14 per cent discontinued, mainly in the first three months. At 12 months, 79 per cent of wearers reported overnight wear of more than 21 consecutive nights. Of the reported events, 180 (2.9 per cent) corneal infiltrates of varying severity were confirmed in 164 wearers (2.6 per cent), a similar rate to other studies. Risk factors were youth, male gender and higher prescriptions.
Ian Cameron (University of Manchester) pointed out the shortcomings of Dk/t as a predictor of oxygen performance and described a new graphical representation of oxygen flux for soft contact lenses. The difference in Dk/t between Proclear and Focus Night & Day, which has the highest value of current silicone hydrogels, was a 500 per cent increase. But the difference in actual oxygen reaching the eye was only 10 per cent, he said.
Cameron calculated oxygen flux at 36 points across the diameter of a range of lens types, using the method proposed by Brennan, and produced colour-coded maps to illustrate flux across the entire lens for both open-eye and closed-eye conditions. All silicone hydrogel lenses provided over 95 per cent flux for daily wear and about 90 per cent or greater for extended wear, and there were few differences between lens types.
He argued that Dk/t was of 'no use' with modern lenses and should be replaced by oxygen flux as the standard measure of oxygen performance.
Practitioner Ken Gellatly (Alberta, Canada) described a patient satisfaction study conducted in 10 sites in Canada, comparing the new Acuvue Oasys lens with Focus Night & Day for extended wear. Acuvue Oasys showed no significant change in comfort between the initial visit and after seven days of continuous wear. For a majority of comfort and overall performance attributes, subjects graded Acuvue Oasys as significantly better than Focus Night & Day, particularly for moisture-related benefits.
Professor Brian Tighe (Aston University) explained how comfort with soft lenses could be enhanced by soluble polymer release. Some currently available lenses benefited from the presence of hydrophilic polymers in the lens matrix that shared two features while otherwise being dissimilar: they were not formally part of the cross-linked ploymer matrix and had a beneficial influence on the lens-tear interface.
Acuvue Advance and Acuvue Oasys contained polyvinyl pyrrolidone (PVP) which contributed to surface enhancement by remaining anchored into the lens surface. With Focus Dailies and the new Focus Dailies with AquaRelease, it was the release of polyvinyl alcohol from the lens matrix that maintained and enhanced comfort.
Elsewhere on the programme, delegates heard news of Johnson & Johnson's new daily disposable - 1-Day Acuvue Moist - designed to provide 'day-long comfort'.
UP FOR DISCUSSION
It was the final session of the conference, a round-table discussion led by Professor Brien Holden, that brought together the themes of this year's event, provided more information for delegates on the differences between current materials and allowed some much-needed debate.
Opening the session, Professor Holden said that the jury was still out on the rate of microbial keratitis with silicone hydrogels. The incidence was probably lower than with conventional hydrogels and the severity might be reduced but recent findings were still disappointing. The next stage was to develop lenses with anti-bacterial and other properties that might keep the epithelium free from microbial contamination.
For Professor Holden, the 'big leap forward' had been the idea that material coming out from the lens into the tear film could make a difference to comfort, at least in the short term. On the other hand there were surface-treated materials that showed consistent longer term performance with improved comfort over time.
Solution manufacturers were also developing products that would enhance wettability before the lens was placed on the eye. The first trials of anti-bacterial lenses were now under way and anti-bacterial cases were already available. It was, he said, a very exciting time for the industry which had recently seen a period of major growth and soaring share prices.
Professor Brian Tighe examined in detail the properties of the five silicone hydrogels now available. For Tighe, the most important property of any soft lens material was water content, which ranged from 24 per cent for lotrafilcon A (Night & Day) to 47 per cent for galyfilcon A (Acuvue Advance). The Dk of the current materials varied from 140 to 60 as a consequence and the modulus or stiffness was also reduced, broadly in line with increasing water content. As expected, relative dehydration rate was higher with the higher water materials; lotrafilcon A had a much lower dehydration rate than conventional hydrogels.
For wettability, there were subtle differences in surface properties between lotrafilcon A and B (O2Optix). The new Acuvue materials had appreciably lower advancing contact angles when fully hydrated and very low coefficients of friction in comparison with the other silicone hydrogels.
However, the in-eye properties of all these materials were influenced by environmental factors and were not easy to predict from ex vivo measurements. The answer lay in achieving a balance of properties and the extent to which similarities between the lens material and the cornea could be sacrificed in order to provide high levels of oxygen. A combination of approaches would be needed to render lenses more wettable and resistant to lipid deposition.
Professor Tighe concluded that this was a very interesting time for contact lens development because there was such a variety of products available. Recent advances had been mainly in manufacturing technology and there had been no equivalent leap forward in materials since the 1970s.
Presenting on behalf of Professor Joe Barr (Ohio State University), Keith Edwards looked at the demise of HEMA since the introduction of high Dk lenses. In the US, silicone hydrogels now represented 12 per cent of total soft lens fittings, up from 8 per cent in 2004. Continuous wear was also increasing in popularity.
The reasons why HEMA was still fitted were not all good, nor were they in the patient's best interest. HEMA lenses were cheaper to produce and there was a perception that their oxygen performance was adequate and surfaces better. Practitioners often failed to look for problems with these lenses if the patient was asymptomatic although the effects of hypoxia were clear to see.
Among the factors influencing comfort and dryness with hydrogels were the lens surface, deposits and lens edge design. Some materials such as omafilcon A (Proclear) - the only lens with an FDA dry-eye indication - maintained hydration, although dehydration did not necessarily correlate with comfort. Where the lens edge turned inwards on dehydration, discomfort might be caused by a mechanical effect at the corneo-scleral junction.
Professor Barr had found the frequency and severity of dryness symptoms were lower with lotrafilcon A lenses than with conventional hydrogels both during the day and at the end of the day. He predicted that the rate of demise of HEMA would depend on the surface qualities and drying effects of current and future silicone hydrogels. Companies would move towards making all their lenses, including speciality lenses, in high Dk materials. However, it was worth remembering that some novel HEMA-based materials were equal in terms of Dk/t to silicone hydrogels.
Elsewhere at the conference there was more support for such materials. The first prize in the poster competition went to researchers from CooperVision led by Dr Nikki Iravani, who found that omafilcon A (Proclear) lenses showed similar comfort and comfortable wearing time to galyfilcon A (Acuvue Advance) lenses and were preferred by patients for overall comfort.
Intriguingly, CooperVision's senior director of R&D Arthur Back showed a slide in his platinum sponsor's presentation listing 'Proclear silicone hydrogel' among the company's product portfolio. He said that in order of priority, the important characteristics of future silicone hydrogels would be wettability/surface chemistry, modulus, design and water content. The comfilcon A material was described as having 'natural wettability' without surface treatment or wetting agents, with lower modulus and higher water content than current silicone hydrogels. So when would it be available? The answer was 'soon'.
SURFACING CONCERNS
'It's all in the surface' was the title of a presentation from Professor Lyndon Jones (University of Waterloo, Canada) reviewing the surface properties of silicone hydrogels. For Professor Jones, the future lay in the development and continued use of silicone hydrogel materials which, to date, had been extraordinarily successful but could still be improved. To be truly successful, they had to combat symptoms of dryness and discomfort which were still a major cause of patient dissatisfaction.
Manufacturers were using three different approaches to overcoming the hydrophobic nature of the silicon component. Night & Day and O2Optix were surface treated with a 25nm layer to 'hide' silicon from the tear film and make the lens as wettable as possible. PureVision had a silicate surface, created using a different plasma technique and with a very different appearance. Acuvue Advance and Acuvue Oasys were not surface modified but incorporated PVP within the lens itself; linear PVP groups came to the surface to make the surface more hydrophilic.
There were also major differences in wettability between these products. When taken directly out of the packaging solution, the Ciba lenses had lower contact angles and PureVision had a very high contact angle. Acuvue Advance had an extremely low contact angle because its packaging solution contained methyl cellulose, but when the solution was rinsed off the surface the contact angle increased to a much higher value.
When a conventional hydrogel lens was put on the eye, comfort was initially good but dropped off towards the end of the day as wettability decreased. With silicone hydrogels, contact angles were initially high but decreased over the day's wear. After eight hours' wear and two weeks of daily MPS use, when Acuvue Oasys was removed from the eye it was 'infinitely wettable', he said. It seemed that the tear film was able to modify these lens surfaces over a period of time.
Silicone hydrogel lenses also showed very low levels of protein deposition compared with conventional hydrogels, although it was more likely to be denatured. Lipid deposition was more of a problem. Some patients developed significant lipid spots within 3-4 days of lens wear, although the Ciba lenses tended to show a filmy deposit.
Better care products were needed to address lipid deposition with silicone hydrogels and a rub regime was recommended. Lens 'conditioning' might play a vital role in initial and longer-term comfort with these lenses and choosing the right lens/care product combination would become increasingly important.
In this concluding session, Professor Holden took the opportunity to point out what he considered to be some misconceptions about current materials. These were the perception that extended wear was not important (it was), that daily wear resulted in fewer cases of microbial keratitis (in absolute numbers it didn't), that oxygen was everything (not true), that all silicone hydrogels delivered the same amount of oxygen to the cornea (definitely not true) and that flux was a more useful measure of oxygen performance than Dk/t or Dk (it wasn't).
With that, delegates emerged blinking into the cold light of a dreary Sussex day after three very full days of lectures, workshops, discussion and partying. But not before they'd had the final stamp put on their CET sheets.