EyeWorld Asia-Pacific September 2011 Issue

51 EW CORNEA September 2011 case, it’s a clear cornea approach, while others prefer a scleral tunnel approach. For DMEK, Dr. Price advised avoiding donors younger than 30 years old, as that tissue will curl up so tightly that it will be difficult to unfold. “The thinner Descemet’s membrane in younger donors makes the tissue nearly impossible to handle,” he said. “Thin-cut DSAEK retains the stroma and can be more readily manipulated, and we are currently evaluating thin- cut DSAEK to see how closely the visual results are to DMEK.” Preparing tissue Dr. Tan prefers to prepare his own tissue to maintain control over donor tissue thickness. He uses the ALTK unit (Moria Surgical, Antony, France), and when preparing a thin tissue, he elevates the system’s pressure “so the cornea bulges out a bit more to cut more tissue. A second way to cut thin tissue is to press down as you’re doing the microkeratome pass. As you press down, you’re actually creating a deeper cut, so you are left with a thinner lenticule. The third way is to pass it around and rotate the head across the cornea; if you do it very slowly you’ll also have a deeper cut,” Dr. Tan said. When he needs tissues thicker than 150 microns, he eliminates those additional steps. Dr. Vroman also prepares his own tissue and uses the Moria device. “The key point when you’re prepping your own is to ensure you protect the endothelial with viscoelastic so you don’t lose chamber pressure. If you lose the artificial chamber, the cornea will flatten against the metal and you’ll damage the endothelium. After removing tissue from the artificial anterior chamber, I let it sit in balanced salt solution until I use it in the case, but that’s just minutes later,” he said. Dr. Terry advised those who use eye bank tissue to warm the tissue to room temperature for at least an hour or two. “That will help the endothelium to become metabolically active, and that means it will have a better chance of sticking,” he said. Because eye bank technicians cut about 100 tissues a week (compared to the five or so cases Dr. Terry performs), they are more experienced in precise cutting. “When we harvest corneas, we don’t track the corneal curvature of the donor tissue,” Dr. Price said. There will be outliers from the standard bell curves, and when the donor tissue doesn’t match the recipient bed, “in order for the donor to conform to the back of the recipient, it has to get folds or wrinkles in it. The thicker the tissue, the more significant these folds and wrinkles are, and that degrades the optical system,” he said. In his DSAEK procedures, he said about 2 to 3% of the grafts had to be replaced because visual outcomes were not at the 20/40 level. The premise behind DMEK was to create a thinner graft that would make better vision much more likely, he said. Is DMEK the next big thing? Without question, DMEK is a more technically challenging procedure than other EKs. Early reports from England and Holland found a 30% donor loss rate, Dr. Price said. As the technique has improved, however, donor grafts lost during preparation comprise only about 1%. “We still have issues with re- bubbling the corneas quite a bit because they’re so thin and flimsy and don’t stick as easily as ones with some stromal tissue,” Dr. Price said. Some of those issues are being addressed with modified techniques, Dr. Vroman said, including DMEK with a stromal rim and DMAEK, which involve transplanting a stromal rim at the edge of the graft while retaining bare Descemet’s and endothelium centrally. Whether DMEK becomes the technique of choice for Fuchs’ “depends on what we can do to make it easier”, Dr. Vroman said. “Right now, DMEK is at the place DLEK was when we first started EK procedures—it wasn’t automated, it was a lot of work, but there were clear advantages to doing it. DMEK has a clear advantage—we get better vision out of DMEK, but the procedure is more difficult, we lose more tissue, and we don’t know about the long-term cell counts,” he said. Dr. Tan said average cell loss with DMEK at 1 year is about 30%, which is similar to the average cell loss rates currently reported with DSAEK. Dr. Van Meter said the biggest issue is how pliable DMEK tissue is and how easily damaged it is while being prepared and inserted. “We’re missing some piece of information that’s going to make DMEK work well,” he said. “The problem with DMEK is that the tissue coils up and becomes very difficult to manipulate in the anterior chamber without damaging the endothelium,” agreed Dr. Tan. “We’ve been using a fibrin protectant and spraying the cornea with fibrin glue—it’s like putting plastic wrap over the cornea—and you can hold the donor cornea and then insert it without damaging the endothelium. We’re still doing the trials and trying to get that right, but if it works, it’ll make DMEK a lot easier.” In his hands, Dr. Price said about 75% of the patients who have received DMEK are at 20/25 (6/7.5) or better at 6 months. Because the technique requires a 2.8-mm incision (compared to 5 mm for DSAEK), the ability to correct astigmatism is much more predictable, he added. When DMEK is successful, “it’s wonderful and we are delighted with the outcomes,” Dr. Terry said, but he thinks DMEK will only gain market acceptance when eye banks can provide quality precut tissue. “The biggest problem is the lack of uniformly precut tissue. The technical difficulty of the surgery will improve as others develop better techniques,” he said. In his hands, the graft dislocation rate for patients with Fuchs’ is 1.5%, and “we have essentially a zero failure rate” with the DSAEK procedure. “Until DMEK comes close to that number, it won’t be at the forefront of EK surgery.” Dr. Vroman said his “very first DMEK patient” was someone with a multifocal IOL and persistent corneal edema from cataract surgery. “If you do a DSAEK and limit his vision to 20/30 because of the stromal interface and cause the typical hyperopic shift of DSEK, that patient is not going to be a happy multifocal patient,” he said. “DMEK gave him 20/20 and J1+ by 1 month, and that has persisted for over 18 months now with excellent cell counts.” Bottom line? “DMEK still needs to evolve. It needs to be at a stage where the average surgeon can do it well most of the time,” Prof. Tan said. Dr. Price said the international collaboration will help overcome these obstacles sooner rather than later. “The excitement of routinely obtaining 20/20 or 20/25 postoperative acuity in a cornea transplant will drive further modifications until it becomes an easily reproducible surgery,” Dr. Vroman said. EW Editors’ note: Dr. Price has a financial interest with Moria. Dr. Tan has a financial interest with the Tan EndoGlide. Drs. Terry, Van Meter, and Vroman have no financial interests related to their comments. Contact information Price: 800-317-3937, wendymickler@pricevisiongroup.net Tan: +65 9818 1962, snecdt@pacific.net.sg Terry: 503-413-6223, mterry@deverseye.org Van Meter: 859-555-1212, wsvanmeter@aol.com Vroman: 843-797-3676, drvroman@carolinacataract.com