Three international experts on rigid contact lens fitting came to the UK last month for the latest gathering of Ciba Vision's Specialist Club members. Alison Ewbank reports
What is a specialist contact lens fitter? A practitioner who fits the occasional gas-permeable lens, or one who regularly fits complex lens types to diseased or damaged eyes?
Ciba Vision's latest Specialist Club meeting, held near Oxford last month, catered for practitioners of all skills levels. More than 85 members heard three of the world's leading exponents of RGP lens fitting share their experiences. The combination of lectures and workshops proved a successful formula for the meeting which, like previous ones, was oversubscribed.
Opening the programme, US optometrist Ed Bennett said that the way that RGP lenses were presented by the practitioner had a profound effect on patient adaptation and acceptance of the modality. His first advice was always to describe the lenses as 'gas-permeable' rather than 'rigid' or 'hard'. Using fear-arousing terms such as 'discomfort' resulted in more patients dropping out during the adaptation period than when neutral terms like 'lens awareness' were used.
A second ingredient in successful RGP practice, though controversial, was the use of topical anaesthetic during trial fitting. For Dr Bennett, the benefits were a better initial experience for the patient and reduced chair time. New RGP wearers given topical anaesthetic had a better perception of their adaptation, greater overall satisfaction and lower drop-out rate than patients given a placebo.
The third key factor was vision, where RGPs had a major advantage over other modalities, particularly if the initial trial lenses were close to the patient's prescription. 'If they have good vision from the first pair of lenses they wear they may also perceive the comfort as better,' he said.
Dr Bennett said that the lens parameter that most influenced comfort was diameter. Large diameters in excess of 10mm were perceived as significantly more comfortable over the first four hours of wear than other lens designs. Fitting characteristics that aided centration, such as lid attachment, lenticular and ultrathin designs, could also help improve comfort.
Young people from the age of eight years were prime candidates for RGP lenses, he said. In the most recent study of eight to 11-year-olds, nearly 80 per cent successfully adapted to RGP lenses. Those continuing to wear RGPs showed less myopia progression after three years than those switched to soft lenses but there was no difference in axial length between the two groups.
Dr Bennett's view of the current status of RGP lenses was optimistic. 'When we look at gas-permeable lenses today, we're looking at a modality with new and better materials. We're getting a good handle on the comfort issue in terms of the ingredients that manage comfort. And any problems that occur are well managed with different lens designs.'
HYBRIDS AND PIGGYBACKS
The second speaker was Pat Caroline, whose subject was hybrid and piggy-back lenses. These lenses were often used almost as a last resort when the patient had suffered many months of discomfort, but were frequently very successful.
There were three main causes of irregular corneal surface: ocular injury, surgery and corneal disease. The way RGP lenses worked in these cases was to create a new surface to the front of the eye. In practice, the corneal topography could be highly asymmetric so that it was almost impossible to get an adequately fitting corneal design. For instance, in trauma cases where the cornea was lacerated and the wound gaped, a wedge of scar tissue could result in corneal flattening over a particular segment of the eye.
In many cases it was necessary to fit beyond the cornea, onto the normal sclera and vault over the distorted corneal surface. Mini-scleral designs of 13-16mm diameter were gaining popularity in the US for these patients. The lenses provided good comfort by avoiding rocking or pivoting on the eye and by distributing the weight of the lens over the sclera. High Dk scleral lenses were also very useful, for conditions such as ocular pemphygoid, Stevens-Johnson syndrome and alkali burns. The cornea was protected from the scarred lids, its hydration was maintained and symblepharon could not form.
Traditional piggy-back systems had been around for many years but high-plus silicone hydrogel lenses could now be used to create a new anterior ocular surface with altered curvature in post-refractive surgery and post-corneal transplant eyes. An RGP lens was then fitted on top of the silicone hydrogel to achieve the desired fitting relationship. Piggy-back lenses were also used to manage peripheral corneal anomalies such as 3 and 9 o'clock staining. Putting a silicone hydrogel lens under the patient's own RGP lens could resolve the problem in two to three days.
Caroline said that the availability of these new combinations had changed his fitting philosophy and he was opting for these lenses much sooner than he had before. Other options included the Flexlens piggy-back system, a soft lens with a recessed central portion on the anterior surface in which an RGP lens was fitted, which was useful in cases of uneven wound apposition. Also in prospect was a new hybrid lens with a Dk 100 RGP centre and a silicone hydrogel skirt.
Following the lectures, delegates divided into groups for workshop sessions in which Bennett and Caroline expanded on their lectures with live fittings. The third presenter, Netherlands optometrist Eef van der Worp, presented an interactive session on the art of multifocal fitting and described his five-step decision-making process for selecting the best option for any given patient. His preference was for RGP bifocals, rather than monovision, and although the first lens he tried was usually a simultaneous vision design, translating bifocals were often the most successful.