Eyeworld

EW CORNEA 18 August 2011 Weighing whether it's time to move to DMEK W hen patients these days need a corneal transplant, often the popular choice is DSEK (Descemet's stripping endothelial keratoplasty). But recently a new, more technically challenging procedure, DMEK (Descemet's membrane endothelial keratoplasty), which promises better acuity, has been making strides. EyeWorld asked a couple of leading practitioners to offer their insights on whether corneal surgeons today need to adopt the DMEK procedure or if DSEK is giving good enough re- sults. Clara C. Chan, M.D., Univer- sity of Toronto, sees DSEK, in which some stroma is removed along with the endothelium and Descemet's membrane, as the procedure of choice. "In the United States DSEK has gained widespread use and is now the most frequently performed corneal transplant," she said. Mean- while, DMEK, in which just the very thin sliver of Descemet's membrane is used, is in the early stages. Dr. Chan stressed that both pro- cedures are extremely safe ones. "We're going through a small inci- sion compared to our traditional penetrating keratoplasty—there's a much lower risk of intraoperative suprachoroidal hemorrhage since we're not using an open sky tech- nique," she said. "DSEK is very safe but so is DMEK, which is also done through a small incision." In DSEK's corner However, in terms of other factors, at this point in time DSEK is much more efficient for surgeons because of the difficulty in preparing the tis- sue for DMEK. Dr. Chan pointed out that prepared tissue from eye banks has made surgeon productivity very high with the process. "There's a learning curve and the DSEK tech- nique is certainly more predictable, reliable, and repeatable," she said. When eye banks first started cutting tissue for DSEK, wastage rates were in the 1.5 to 3% range. With experi- ence, however, this went down to a rate of about .5%, according to Dr. Chan. "We also have to look at those factors because tissue supply in the U.S. might not be an issue, but in many other places in the world there is a huge shortage of tis- sue," she said. "What is an accept- able tissue wastage rate?" While this question remains unanswered, what is clear, Dr. Chan pointed out, is that with DSEK this rate is very low. Another issue is how long the graft will last. "With DMEK we still don't know because it's in its early stages. With DSEK we know that with current 5-year survival rates being reported that at 5 years it's 95% for Fuch's dystrophy, which has the best tolerances for DSEK, and up to 76% for patients with pseudopha- kic or aphakic corneal edema," Dr. Chan said. There's also the difficulty factor. Dr. Chan pointed out that, for DMEK, the preparation involved in removing a 10-micron layer is very demanding. "It can tear and you have to convert, or you may not get a perfect piece at the same time," Dr. Chan said. There can also be damage to the tissue while it's being peeled and then it can take a long time. "Also, there's the fact that most sur- geons get their supply from an eye bank and do not prepare tissue on their own. That's probably a major limiting factor," Dr. Chan said. While there are currently a couple of eye banks that are able to prepare DMEK tissue, they are still in the midst of refining the technique to lower the tissue wastage rate to an acceptable degree. One of the other knocks against DMEK is that there are issues of tis- sue dislocation. "During the proce- dure it's difficult to get that very thin piece of DMEK tissue to stick, whereas in DSEK there's no trouble at all to get the tissue into position," Dr. Chan said. "Even after the sur- gery, tissue dislocation rates seem to be higher with DMEK." When it comes to results, Dr. Chan finds that thin DSEK, where tissue of less than 130-microns is used, provides excellent outcomes. With the thin technique approxi- mately 70% of eyes achieve best cor- rected vision of 20/20. A group in Italy recently adopted an ultrathin technique with a graft thickness of less than 100 microns. "They are re- porting 20/25 acuity or better in over 80% of their eyes," Dr. Chan said. "I think with visual outcomes there's a trend now of believing that thinner is better." In addition, new insertion de- vices that can go through sutureless wounds as small as 3.75 mm are making the DSEK procedure even more atraumatic to the tissue. "We've been trialing one called the EndoSerter (Ocular Systems Inc., Winston-Salem, N.C.), and we found that within 1 week patients were al- ready hitting the 20/40 mark," Dr. Chan said. "That's very similar to what DMEK papers are claiming." DMEK's knockout acuity advantage However, David T. Vroman, M.D., co-founder, Carolina Cataract and Laser Center, Ladson, S.C., likes the crisp acuity that DMEK can offer. "The advantage is simply that vision is better with DMEK—the average vi- sual acuities for my series are be- tween 20/20 and 20/25," he said. "In eyes that are otherwise healthy I have no patient that can't see 20/25 or better." For patients with high vi- sual demands, being able to achieve this type of vision consistently is very appealing. DSEK, meanwhile, does not al- ways offer the best acuity. "We all have patients who have had routine uneventful DSEK surgery and have 20/40 best corrected vision," Dr. Vroman said. "We think that it's a problem with the interface and the stromal-to-stromal interaction." While not everyone needs per- fectly crisp vision, Dr. Vroman finds the technique to be a real boon for those with very high visual demands by Maxine Lipner Senior EyeWorld Contributing Editor Corneal contenders: DMEK and DSEK square off Corneal lamellar surgery continues to pro- vide our patients tremendous outcomes when compared to penetrating kerato- plasty. For patients with endothelial dis- ease, Descemet's stripping endothelial keratoplasty (DSEK) is now the procedure of choice in almost all cases. Just when corneal surgeons were seeming to get comfortable with the DSEK procedure, a new twist in this operation is being touted. Descemet's membrane endothelial kerato- plasty (DMEK) is technically more chal- lenging but may result in better vision. I have asked two talented corneal surgeons, Clara Chan, M.D., and David Vroman, M.D., to put these two techniques into per- spective for us. Edward J. Holland, M.D., cornea editor Cornea editor's corner of the world continued on page 20 EyeWorld Factoid Approximately 6,000-8,000 corneal transplant patients reject their donor corneas each year Source: Massachusetts Eye and Ear Infirmary 18-21 Cornea_EW August 2011-FINAL_Layout 1 4/2/14 3:32 PM Page 18

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