Eyeworld

OCT 2014

EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.

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EW CORNEA 60 October 2014 Current issues and solutions with the Boston keratoprosthesis by Lauren Lipuma EyeWorld Staff Writer can be done concurrently with a glaucoma surgical procedure. Less common yet potential- ly serious complications include infectious endophthalmitis, corneal melting, and sterile vitritis. Advanc- es in design and postoperative care have drastically reduced incidences of these complications, but active re- search efforts are dedicated to better understanding and treating them. "Generally now the only people who get endophthalmitis in our population are people who aren't compliant with their antibiotic drops," Dr. Colby said. "So one avenue of investigation is to see if a contact lens can be impregnated with an antibiotic because patients wear bandage lenses after their KPro surgery." Other options in development include exploring whether the keratoprosthesis itself can be modified to reduce the risk of infection—potentially to include surface modifications that have antibacterial properties. Incidences of corneal melting have largely disappeared due to the introduction of holes in the back plate and the use of bandage contact they've had multiple failed trans- plants, which is a risk for glaucoma, because the more surgery you do on the cornea, the more you change the anatomy of the drainage angle. But the actual etiology of the glaucoma is multifactorial and it's not very well understood." With the exact etiology un- known, glaucoma progression in KPro patients remains a major un- solved problem, Dr. Colby said. As a result, many current research efforts are dedicated to understanding the pathophysiology of glaucoma in KPro patients as well as to create better surgical techniques for glaucoma treatment. The glaucoma issue is further complicated by the fact that sur- geons cannot reliably measure the IOP once a KPro is implanted. Glaucoma should be well managed prior to inserting the device. "If our glaucoma specialist is able to implant a glaucoma drain- age valve or do a cyclodestructive procedure prior to the KPro, that is generally our preference," she said. In cases where the glaucoma cannot be well managed before KPro implantation, however, insertion KPro surgeon population that it's harder to get the oversized back plate in," she said. "It requires a little bit of manipulation to get those in the eye. But I think it's a reasonable strategy, and there's no downside to it. In the last 2 years in almost all the cases I've done, the back plate has been larger than the opening." As a surgeon at Mass Eye and Ear where KPros are made, Dr. Colby has access to different sized back plates, but for surgeons outside of the center who want to employ this method, Dr. Colby suggests making a smaller host opening and using a regular-sized back plate. She recom- mends sewing in the first suture of the KPro and ovalizing the wound to maneuver the back plate in. "You can put viscoelastic on the exposed edges of the back plate to lubricate it and facilitate it getting into the opening," she added. Retroprosthetic membranes may be the most common complication, but the biggest threat to vision in KPro patients is glaucoma. "It's a population with a high incidence of glaucoma to begin with," Dr. Colby said. "Typically C ontinued advances in the design of the Boston KPro (also called the Dohlman-Doane, de- veloped at Massachusetts Eye and Ear Infirma y, Boston) have led to dramatic improvements in patient outcomes and an exponen- tial increase in the use of the device. Surgeons using the KPro continue to create innovative solutions to common complications and expand their knowledge of the mechanisms behind them. In an interview with EyeWorld, Kathryn Colby, MD, PhD, Massachusetts Eye and Ear Infirma y, discussed current complications associated with the KPro, new solutions to those complications, and active areas of research in the field. Current issues The most common complication with the Boston KPro is the forma- tion of retroprosthetic membranes, Dr. Colby said. Forming behind the keratoprosthesis, they can develop in up to two-thirds of KPro patients, blocking the visual axis to vary- ing degrees. While retroprosthetic membranes are successfully treated by YAG membranotomy in most cases, they can occasionally lead to more serious complications such as corneal melting. To better understand the mechanism behind membrane formation, Dr. Colby and the team at Mass Eye and Ear studied the his- topathology of a group of explanted keratoprostheses with retroprosthet- ic membranes. They discovered that keratocytes in the host cornea were becoming activated and forming the membranes through a gap in the graft-host junction. "That led us to the idea of using oversized back plates to better appose the posterior aspect of the graft-host junction and eliminate physically that discontinuity where the membrane could grow through," Dr. Colby said. So far, she has performed about 20 surgeries using a back plate 1.5 mm larger than the host opening —a 9.5 mm back plate for an 8 mm opening. She has successfully reduced the incidence of retropros- thetic membranes to about 15%, and she has not seen any wound healing issues with the procedure. "There is concern in the general Innovations in the use of the Boston K-Pro have reduced the once-high complication rate with the keratoprosthesis. Source: Kathryn Colby, MD

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