This article is best viewed in a PDF Format.
|
|
|
|
With practitioners constantly striving to avoid microbial keratitis (MK), it is essential in those cases where it does occur to be able to recognise and manage the condition at as early an opportunity as possible and to differentiate it from a sterile infiltrative keratitis (IK).
Recent studies by John Dart and Fiona Stapleton described in Optician (July 18, 2008) have highlighted the significant risk factors for MK and suggested that, even with daily disposable and silicone hydrogel lenses, there is still a risk of MK.
Professor Debbie Sweeney (CEO of Vision CRC) addressed the question as to whether inflammatory events (such as CLARE, CLPU and IK) act as markers for subsequent MK. Many authors have suggested that there is a spectrum of inflammatory events ranging from sterile IK at one end to infective MK at the other and that the former might, therefore, be taken as a potential step in progression to the latter.
Referring to the Stapleton paper, Sweeney argued that the risk factors for sterile infiltrates were known to include previous inflammation, older age, smoking, high ametropia and case contamination among others and that, therefore, it is likely that inflammatory events themselves are not a risk factor for MK but may be a risk factor for further inflammatory events.
Furthermore, the self-limiting nature of IK makes them unlikely to be a marker for MK. She explained how a joint Australian and Indian study showed that in only one case of MK had there been any preceding IK. In conclusion, the answer to her initial question was a resounding 'No'.
The theme was further developed by Dr Loretta Szczotka-Flynn (Ohio) who looked at the risks of inflammatory events specifically in SiH lenses. She reported that there was an increased risk of IK but a similar risk of MK when SiH lenses are used on an extended wear basis. Around 14 per cent of eyes will experience an IK event per year if SiH lenses are worn on a 30-day basis. This compares with around 7.2 per cent for daily wear low Dk lenses. She presented a study where a continuous wear SiH wearer with recurrent IK events showed no such events when moved into daily wear low Dk conventional hydrogels. Interestingly, she highlighted that the major drive for IK was microbial contamination and that infiltrates can occur even with spectacle wear.
Silicone hydrogel lens wear
Staying with SiH wear, Dr Graeme Young (Visioncare Research, UK) presented results of his recent work looking at the impact of different care systems on lens wear, an area of great interest to all regularly fitting SiH lenses and wanting to know the best solution/lens combinations.
Young followed 89 SiH wearers over two years consistently using either a PHMB system of a polyquaternium-1 system. He found there to be significantly more grittiness/scratchiness, palpebral roughness and hyperaemia, corneal and conjunctival staining, and less wettability for the PHMB group. Despite these clinical differences, Young suggested further study would be useful.
Professor Sweeney then chaired a lively roundtable (actually a large sofa) discussion between Howard Griffiths (Sauflon, UK), Christopher Kerr (private practice, UK) and Professor Roger Buckley (Anglia Ruskin University) on the supply of CLs.
She opened the debate by reminding delegates of the dangers of unregulated supply of plano lenses by the graphic display of a seriously infected cornea of a 14-year-old after MK related to wearing such lenses.
Barnes reviewed the current legality of supply of lenses. In the US, all CLs are classed as 'medical appliances' but can be bought anywhere. In Australia, rules vary from state to state but some have optometrist supply only. In the UK, regulation may occur at different stages. Products themselves may be regulated, and CLs are classed as medical devices except for plano lenses which are not (unlike condoms).
The sale of the product can be regulated though and this is where things can be tightened up. Barnes noted that the site of sale was to some extent influenced by market forces and supply of plano lenses from unregulated outlets was proving less of an appealing market proposition.
Kerr enacted what he described as the 'farcical situation' whereby a patient might order lenses over the phone and the practitioner, worried about the potential loss of business, might succumb to posting them out without having seen any prescription or having patient contact. He suggested this happens frequently and called upon Young to explain some of his findings regarding the nature of plano lenses. Many of these cosmetic plano lenses have a high modulus and greater than average thickness (and thus reduced transmissibility), meaning that the very lenses that are least regulated are, perversely, the ones that might most likely compromise eye health.
Buckley was concerned that unregulated sale may lead to a different lens being supplied to the one originally issued by a practitioner. 'Substitution is clinically wrong,' he affirmed. He too cited the recent Stapleton paper noting that internet/mail order supply of lenses increases the risk of MK by 4.76 times. He also referred to a recent study by Fogel who found that among 151 student CL wearers, those who had acquired their lenses via the internet were far less likely to follow good clinical protocols.
He questioned Kerr's proposition by suggesting that over-the-phone supply was illegal irrespective of whether it happens or not. The fact that two former BCLA presidents openly debated this point merely confirms the somewhat muddy nature of the rules.
A new BCLA pamphlet was launched that attempts to clarify the rules and is vital reading.
Posters
Space will not allow a full description of the posters at this year's events, so I have selected two, both coincidentally from Manchester. Clare O'Donnell, Miranda Marco and Hema Radhakrishnan (Manchester University) looked at aberrations of the cornea and the crystalline lens and how they change with age. It is found that there is an increase with age once inter-subject variability (for example, due to tear stability difference) were accounted for. The lens is able to compensate for corneal aberration but presbyopia restricts this ability leading to greater overall aberration expression.
Dr Martyn Russell and Dr Neil Parry (Manchester Royal Eye Hospital) fitted a dark-tinted lens and a deep red CL in the eyes of an achromatopsic patient and found that they could perceive some colours (as well as cope better with photophobia) for the first time. Rather movingly, the poster included some patient comments such as being able to spot mould on pitta bread for the first time, seeing what colour her work uniform was and noting how 'the flowers were beautiful'. Though a rare condition, this case surely holds some promise for other patients similarly compromised.
Dry eye topics
Dr Robin Chalmers delivered a thoughtful keynote address on CL-related dryness and the degree to which these symptoms go undetected by the practitioner. Nearly 80 per cent of all wearers report dryness, discomfort and intermittent blurry vision on blinking created by poor wetting. Non-CL wearers experience significantly fewer and less intense symptoms of this type.
More than one in three CL wearers believe they may have dry eye but in only one in four does the practitioner give a diagnosis of dry eye. Dissatisfied wearers were twice as likely as satisfied wearers to report wearing times under 12 hours a day, she said.
Dr Jerome Groopman, author of the book How Doctors Think, observed: 'On average, a physician will interrupt a patient describing her symptoms within 18 seconds. In that short time, many doctors decide on the likely diagnosis and best treatment.'
Almost all CL practitioners ask about dryness and comfortable hours of wear but far fewer ask about blur between blinks. Asking this simple question could help identify patients who might benefit from products to reduce dryness. Symptoms warranting treatment were: frequent to constant, intense late in the day, those that limited wearing time or shortened comfortable wearing time. One question that was hardly ever asked but probably should be was: 'Are you going to drop out?'
Carolyn Begley (Indiana University) looked at ways of measuring the effect of tear instability on optical quality and visual performance in soft lens wearers. Her group had used a customised wavefront sensor that allowed simultaneous aberrometry and contrast sensitivity measurement while viewing tear break-up within the pupil using infrared retro-illumination. Two new measures of tear quality, using light either refracted or reflected by the tear film, were identified.
German optometrist Heiko Pult (Cardiff University) and co-workers investigated the predictive value of lid wiper epitheliopathy and lid parallel conjunctival folds (Lipcof) as objective measures of discomfort. They found that CL wearers with dryness symptoms showed increased incidence of these signs, but not increased corneal staining, bulbar hyperaemia or decreased pre-lens break-up time. Summed nasal and temporal Lipcof measures seemed to be the most predictive for symptoms.
Dr Nancy Keir (University of Waterloo) described a study to determine the association between in vivo and ex vivo wettability in daily wear SiH users and whether these measures are related to comfortable wearing time and end-of-day comfort. She found no association between ex vivo wettability and in vivo wettability or comfort, but there was a weak association between pre-lens non-invasive break-up time and comfortable wearing time. Further work would look at symptomatic versuss asymptomatic wearers.
Antibacterial coatings
A session on lens coatings served up some interesting material, not least some views on future material developments.
Dr Ravi Sharma (Bausch & Lomb) described his work with antimicrobial silver and how its introduction into lens material resulted in lens efficacy against a wide spectrum of bacteria and fungi.
Professor Mark Willcox (Sydney) showed some of the successful work in animal models he has had using antimicrobial lens materials and looked forward to forthcoming human trials. Suggesting that there it would be two to three years before such materials are likely to become available, he also added that this was 'not the end of the solutions market just yet'.
Dr Alan Saks (Auckland) chaired an interesting session which he introduced with a comprehensive review of new technology in the anterior eye world, including mentions of OCT use, aberrometry and drug release contact lenses (the latter he felt might revolutionise Viagra use!).
Professor Charles McMonnies expanded his view that, as eye rubbing was a risk factor for keratoconus, measures including education about the dangers and 'de-stressing' might reduce incidence of the condition.
Luisa Simo Mannion used an in vivo technique to show that keratoconus was not redistribution of tissue but, in fact, involved tissue loss. Glenn Carp (London Vision Clinic) suggested that his results indicated that collagen cross-linking treatments now represented the first line of treatment for diagnosed keratoconus and resulted in a slowed progression of the disease.
This was heartily debated by members of the audience, including Professor Jan Bergmanson who felt that this could not yet be claimed as there may be safety implications in massive UVA dosing of the eye. Carp also noted that moves to use the technique to 'set' orthokeratology treatment were unlikely to succeed as the technique involved stromal change while ortho-k was primarily a technique of epithelial redistribution.
The lively session ended with Dr Shehzad Naroo (Aston) outlining results of a satisfaction survey which found that patients having undergone refractive surgery score much higher on a quality of life index when compared to CL or spectacle wearers.
An interesting presentation for a CL conference!