Eyeworld

EW FEATURE 44 put on a tapering steroid dose from four times daily immediately after surgery to about once a day by 9 months. Most patients will need to remain on daily steroids, as Dr. Terry said a few studies have shown rejec- tion rates increase once steroids are removed. Surgical pearls Although there are some similarities between DSAEK and cataract sur- gery, "you can't fold a cornea or coil it up with impunity like you can an IOL; you'll do damage. I say that be- cause surgeons are trying to go through much smaller wounds now, like cataract surgery. They try to be astigmatically neutral, they try to use 3-mm incisions," Dr. Tan said. Dr. Terry's group has shown that smaller incisions will cause more en- dothelial damage than incisions around 5 mm. "Another aspect is that surgeons don't like to operate on the sclera because you've got to open up the conjunctiva; they like clear corneal incisions like IOL surgery. But that's more challenging because on the clear cornea there's more astigma- tism so they try to go smaller. Most surgeons today feel a scleral incision is safer in terms of the endothe- lium," Dr. Tan said. He believes using a scleral tun- nel incision, coupled with sutures and a larger incision, is safer for the endothelium. Successful DSAEK surgery is aided "by starting with good quality tissue," Dr. Van Meter said. With eye banks being paid more for EK tissue preparation, PK tissue may be a lesser grade, he said. Graft dislocation can be a con- cern, he added, "and that comes from not getting the bubble big enough and eliminating the inter- face fluid." A secondary concern is pupillary block, which can be man- aged by ensuring no air is left be- hind the iris. Dr. Vroman suggests surgeons should use a technique "that makes sense for your skill set." In his case, it's a clear cornea approach, while others prefer a scleral tunnel ap- proach. 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 han- dle," he said. "Thin-cut DSAEK re- tains the stroma and can be more readily manipulated, and we are cur- rently 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 pres- sure "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 microker- atome pass. As you press down, you're actually creating a deeper cut, so you are left with a thinner lentic- ule. 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 elimi- nates those additional steps. Dr. Vroman also prepares his own tissue and uses the Moria de- vice. "The key point when you're prepping your own is to ensure you protect the endothelial with vis- coelastic 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 tis- sue from the artificial anterior cham- ber, 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 en- dothelium 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 per- forms), 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 stan- dard bell curves, and when the donor tissue doesn't match the re- cipient bed, "in order for the donor to conform to the back of the recipi- ent, 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 pro- cedures, he said about 2-3% of the grafts had to be replaced because vi- sual 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 be- cause 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 stro- mal rim at the edge of the graft while retaining bare Descemet's and endothelium centrally. Whether DMEK becomes the technique of choice for Fuchs' "de- pends 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 proce- dures—it wasn't automated, it was a lot of work, but there were clear ad- vantages to doing it. DMEK has a clear advantage—we get better vi- sion 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 in- formation 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 protec- tant 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 in- sert it without damaging the en- dothelium. 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 or better at 6 months. Because the technique requires a 2.8-mm incision (com- pared to 5 mm for DSAEK), the abil- ity 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 pro- vide quality precut tissue. "The biggest problem is the lack of uni- formly precut tissue. The technical difficulty of the surgery will improve as others develop better techniques," he said. In his hands, the graft dislo- cation 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 vi- sion to 20/30 because of the stromal interface and cause the typical hy- peropic 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 post-oper- ative 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 February 2011 CORNEA May 2011 Endothelial continued from page 43

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