EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
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122 EW CORNEA March 2013 Pearls for using AMT by Michelle Dalton EyeWorld Contributing Writer Amniotic membrane tissue at its simplest can be either a bandage or a permanent graft W hen it was first introduced, amniotic membrane was attached to a defect area and sutured, and it was used to treat everything from corneal defects to scar tissue removal. "When we talk about amniotic membrane for severe chemical burns or acute Stevens-Johnson syndrome (SJS), we're talking about its use as a bandage, not as a surgical graft," said Scheffer C.G. Tseng, M.D., director, Ocular Surface Center, Miami; medical director, Ocular Surface Research & Education Foundation, Miami; and director, research and development, Tissue Tech, Miami. "Most of the time, we can handle the insult to the eye and it resolves with minimal issue, but with some diseases, any inflammation can be detrimental," Dr. Tseng said. Controlling scarring or cicatricial complications before vision loss occurs is paramount. To avoid introducing additional inflammation, avoid dissolvable sutures, said Darren Gregory, M.D., associate professor, University of Colorado School of Medicine, Aurora, Colo. "Nylon sutures are much more inert and won't incite an inflammatory process," he said. "The downside, of course, is that you have to remove them." Dr. Gregory also uses fibrin glue to fasten the membrane down. "If I have a conjunctival tumor, rather than leave the surface bare (which is painful), I'll glue the amniotic membrane, which provides a kind of scaffolding for the epithelium to grow over. Inflammation is also decreased while the epithelium is growing over it," he said. "But glue only works in an area that's missing epithelium—fibrin glue crosslinks to itself and to exposed collagen. If there's an intact epithelium, there's no exposed collagen for the glue to stick to," he said. Esen K. Akpek, M.D., associate professor of ophthalmology, and director, Ocular Surface Diseases and Dry Eye Clinic, Wilmer Eye Institute, Johns Hopkins University, Baltimore, advises surgeons to use amniotic membrane in lieu of a bandage contact lens in cases of non-healing neurotrophic corneas or infectious corneal ulcers. "Bandage contact lenses form a biofilm around and germs stick to it," she said. "That, in turn, causes infection. I would be very worried about infection in a neurotrophic eye. Amniotic membrane works better, and there's no risk for infection." The downside, however, is that surgery needs to be scheduled, and surgeon time and effort is increased. "But in those cases, it's worth it because the results are much better with amniotic membrane," she said. In general, Dr. Akpek prefers to use glue in lieu of sutures, but acknowledges sutures are often necessary. "Stitches can cause neovascularization, so remove the sutures as soon as possible once the problem has resolved," she said. For non-healing epithelial defects, she advises surgeons to "really scrape the cornea well to get all the calcium buildup out. The membrane has to be nicely stuck on top of the cornea. Dry up the cornea, place the membrane, ensure there's no air, no bleeding, no saline, nothing underneath. The membrane should be snug against the cornea. Otherwise it's not going to integrate, it's just going to come up." Limitations still remain There are several types of amniotic membrane on the market, each with a different thickness and use. ProKera (Bio-Tissue, Doral, Fla.), which is amniotic membrane attached to a ring that can be placed like a bandage contact lens without the need for sutures and glue, "is very useful if there are epithelial defects of the cornea. It will cover the cornea and the area right next to the limbus," said Kimberly C. Sippel, M.D., assistant attending ophthalmologist, New York-Presbyterian Hospital, and associate professor of ophthalmology, Weill Cornell Medical College, New York. But in acute cases of SJS, where there's widespread conjunctival involvement, sheets of amniotic membrane (attached with either glue or sutures) can be used to cover a larger surface area of the conjunctiva and may be more useful, she said. Similarly, in cases of pterygium removal or conjunctival tumors, surgeons need to use a sheet of amniotic membrane in order to provide coverage of the involved area, she said. Some patients may complain of a foreign body sensation due to ProKera wear, but Dr. Tseng has recommended placing a temporary tarsorrhaphy on the eyelid "to help cover the eyelid a bit more to enhance healing and make it more comfortable for the patient," Dr. Sippel said. Any disease that warrants the use of amniotic membrane is challenging, but "there are no alternatives, no better treatment," Dr. Sippel said. There is also a potential for blood-borne illness when using amniotic membrane, she said. In the U.S. the safeguards against that occurrence are exemplary; freeze-dried amniotic membrane is dried and sterilized. The cryopreserved formulations are not released for use until the mother has been tested and retested for illness. Synthetic membrane While amniotic membrane can be incredibly useful, it degrades anywhere from three days to a couple of weeks after placement, Dr. Gregory said. He believes patients will have better outcomes when their own tissue can be used, but when that is not a viable option—in cancerous tumors, for instance—amniotic membrane is a good substitute. "In some of the eyes, a badly inflamed eye, membranes don't last too long; I've seen them dissolve in a couple of days," Dr. Akpek said. Ideally, a synthetic, "thin membrane that would last until inflammation subsided, that could have integrated into it antibiotics for infectious cases, that could be crystal clear, would be even better because it wouldn't impair patients' vision." Dr. Gregory said synthetic membrane "holds some promise; if you could potentially impregnate it with various growth factors that could have a timed release onto the area you're trying to heal, there might be some use." Cost may be prohibitive, however. Some of Dr. Sippel's colleagues are developing a synthetic membrane, "but it's not beyond the reach of the lab just yet." EW Editors' note: Dr. Tseng has a proprietary interest in his comments. The other physicians have no financial interests related to this article. Contact information Using Ambio5 amniotic membrane as a bandage contact lens, secured with vicryl sutures and fibrin glue The same patient, on postop day one; the ocular surface was maintained. Source (all): Jai G. Parekh, M.D. Akpek: 410-955-5494, esakpek@jhmi.edu Gregory: 720-848-2500, darren.gregory@ucdenver.edu Sippel: 646-962-3126, kcs2002@med.cornell.edu Tseng: 305-274-1299, stseng@ocularsurface.com