20131010 Nov Eurotimes third spread advert Advance.pdf 1 10/10/2013 17:09:29
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Special Focus
PAEDIATRIC OPHTHALMOLOGY
ARTIFICIAL CORNEA
Device gives clinicians treatment option for corneal disease not amenable to standard penetrating keratoplasty or corneal transplant by Dermot McGrath in Copenhagen
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Boston KPro keratoprosthesis device has shown considerable promise as a safe and viable alternative to penetrating keratoplasty in selected paediatric patients, Kathryn Colby MD, PhD, told delegates attending the 2013 Congress of the Society of European Ophthalmology. “The Boston KPro is a wonderful device which has successfully restored vision to thousands of patients throughout the world. While paediatric patients are particularly challenging and require extremely rigorous follow-up, we have already achieved very positive outcomes using the implant in children with minimal complications,” said Dr Colby, associate professor of ophthalmology at Harvard Medical School, Boston, MA, US. She explained that the Boston KPro gives clinicians a treatment option for corneal disease not amenable to standard penetrating keratoplasty or corneal transplant. “We know that penetrating keratoplasty outcomes in children are very variable and unfortunately not optimal. Although graft survival can range from 44 per cent to 67 per cent several years after surgery, it is nevertheless very difficult to get good vision in paediatric patients and especially in younger children after keratoplasty. The most common reason for this is high astigmatism after keratoplasty, which limits amblyopia management in these patients,” she said. Dr Colby noted that the concept of an artificial cornea is not a new one and dates back to the time of the French revolution when Guillaume Pellier de Quengsy first suggested the idea for keratoprostheses in 1789. The need for an artificial cornea, said Dr Colby, stems from situations where the traditional tissue transplant does very poorly, and includes indications such as repetitive graft failure. “After the first regraft the rate of success to achieve corneal clarity several years after surgery is approximately 30 per cent, but for subsequent regrafts this falls to virtually zero fairly quickly,” she said. Discussing the characteristics of the device, Dr Colby said that the Boston KPro comes in two models: type I, the most commonly used version, utilises a donor cornea and leaves the eyelids intact, and type II which is reserved for severe end-stage ocular surface disease desiccation. The device is made up of three components: a front plate with optical stem, a back plate and a titanium locking c-ring. The type I Boston KPro is available in either a single standard pseudophakic plano power or customised aphakic powers with 8.5mm diameter back plates for adults and 7.0mm for children. There are several advantages to using the implant in adult populations, said Dr Colby. “First of all the surgery for the Boston KPro is relatively straightforward and well within the skills set of a trained corneal surgeon. Furthermore, the retention is generally excellent in non-autoimmune diseases and the visual
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EUROTIMES | Volume 18 | Issue 11
recovery is rapid to the point that we are now using this device as primary corneal surgery before failed transplantation for those situations where traditional keratoplasty has a poor success rate, including for anaesthetic and vascularised hosts and those with stem cell deficiency,” she said. Dr Colby stressed, however, that the benefits of the implant can only be achieved in the presence of comprehensive ongoing postoperative care. “Postoperative care is really where the art of keratoprosthesis comes into play as these patients require very close follow-up by someone trained to understand and manage the complications following Boston KPro implantation. Patients need to wear a soft contact lens for life which helps reduce the chance of cornea melting, and they use not only topical steroids but also topical antibiotics to prevent subsequent endophthalmitis,” she said. For paediatric patients, the device provides rapid visual recovery in days to weeks rather than months, which aids in amblyopia management, said Dr Colby. “The lack of corneal astigmatism also helps in this respect. Another advantage is that the device allows us to have a reduced number of examinations under anaesthesia since we are not counting on the corneal tissue itself to stay free of vascularisation. Retinoscopy is also easy through the device and it is very straightforward to correct residual refractive error through the bandage contact lens, so this can be helpful as the child grows,” she added. Dr Colby said that the incidence of retroprosthetic membranes, which was one of the principal complications associated with implantation of the Boston KPro and typically occurred in two-thirds of all patients, seems to have been resolved thanks to design modifications of the back plates. “Histopathologic studies of the explanted implants with retroprosthetic membranes showed that the membranes came from activated keratocytes from the host cornea that migrated through gaps in the posterior graft host junction. To address the issue, we introduced a larger titanium back plate which results in a decreased graft-host junction thickness. None of the patients implanted with this new back plate have developed retroprosthetic membranes so we are hopeful that the problem is now resolved,” she said. She added that there is a lot of help available to surgeons interested in using the Boston KPro device, including training packs, newsletters, users’ meetings and on-site training in Boston. Further information can be obtained from the Boston KPro coordinator Larisa Gelfand (Larisa_gelfand@meei.harvard.edu).
contact Kathryn Colby – kacolby@meei.harvard.edu