Eyeworld

EW FEATURE 44 Corneal lamellar surgical procedures April 2015 The anterior part of the cornea can be used for a deep anterior lamellar keratoplasty (DALK) and the posteri- or layers can be used for DMEK. Dr. Dapena said the main differ- ence between DMEK and DSAEK is graft thickness. In DMEK, an isolat- ed Descemet's membrane devoid of stroma is transplanted, so the graft is much thinner than in DSAEK, she said. "This means that in DMEK, exactly the same layers that are removed are substituted by donor tissue (Descemet's membrane and endothelium), whereas in DSAEK a layer of stroma is transplanted also," Dr. Dapena said. This extra (irregular) layer of stroma presumably decreases the visual quality and/or outcomes of the procedure, she said. Insertion techniques There are a number of techniques for insertion of the tissue in DMEK. Dr. Price is using an IOL injector. Dr. Terry uses an injector that his partner, Michael D. Straiko, MD, designed, based on an already Food and Drug Administration-approved product. "One of the problems in the development of DMEK is that in the U.S., we do not have access to many of the instruments that they are using in Europe," he said. The injectors specifically are not FDA ap- proved, so surgeons in the U.S. can't import and use them. This leaves U.S. surgeons using FDA-approved IOL insertion devices on an off-label basis, Dr. Terry said. "There were a lot of problems because they're designed to push an IOL forward but not designed to push fragile tissue forward." Dr. Terry has been performing DMEK since 2010 and teaching DMEK since 2012. He said that in 2012, Dr. Straiko began to look at using a glass injector, and instead of developing one from scratch, he took an FDA-approved device, the Jones tube, and used it off-label as an injector. "When we did that, any prob- lems that we had with donor tissue injection went away," Dr. Terry said. This method makes no-touch load- ing easy and tissue injection simple. He added that a dry ink "S" stamp on the tissue from the eye bank is making the procedure even easier because the marking allows Evolution continued from page 43 " It's been exciting to see these huge advancements in corneal transplant surgery." … As patients are finding out about DMEK, it is increasing the demand for the procedure. " –Francis Price, MD the surgeon to know the orienta- tion of the tissue at each step of the surgery. This makes it impossible to put a tissue in and have it upside down at the end of surgery, Dr. Terry said, which helps reduce the risk of primary graft failure. Different devices have been designed for the insertion of the DMEK graft inside the eye, Dr. Dapena said. "In our opinion, injectors made of glass rather than plastic are presumably bet- ter because they have a smoother surface, probably decreasing endo- thelial cell damage," she said. "Fur- thermore, we would rather not use viscoelastics, which could interfere with graft unfolding or graft adher- ence to the posterior corneal surface of the patient." When to use DMEK or DSAEK Dr. Terry is using DMEK for 100% of routine cases of Fuchs' dystrophy, pseudophakic bullous keratopa- thy, and failed prior PK. However, there are some cases where he does not use DMEK, including patients with altered anterior segments, anterior chamber IOLs, tubes or trabs, or those who have had a previous extensive vitrectomy. He has previously done DMEK in all of these scenarios (except with anterior chamber lenses), but he said it may not be the best option. The reason for not doing DMEK on these eyes is because the tissue manipulation required and the risk of problems postoperatively do not warrant the improvement of vision that you get going from DSAEK to DMEK, he said. DMEK is for a certain type of eye that needs an endothelial transplant, Dr. Gorovoy said, "and DSAEK is still the required surgery for eyes that aren't going to be DMEK candidates." DMEK eyes are those that have almost perfect anterior segments, he said, with normal pupils that can be constricted to 1 to 2 mm, and a well-positioned posterior chamber lens. Dr. Price thinks that if a surgeon is doing a high volume of corneal transplant surgeries, DMEK is the best way to go. It gives better vision with a reduced rejection rate, he said. The problem, however, is that corneal transplants are often done by surgeons who do not do a lot of transplants, so it may be hard to get consistently good results with DMEK. Dr. Price said there were a num- ber of cases he did not do initially with DMEK, including filtering tubes, trabeculectomies, or previous pars plana vitrectomies. Addition- ally, he said that someone who is aphakic is not recommended for DMEK. "It's been exciting to see these huge advancements in corneal transplant surgery," Dr. Price said. Published data that has come out of his site as well as others around the world is starting to show the overwhelming advantages of DMEK compared to DSAEK. As patients are finding out about DMEK, it is increasing the demand for the pro- cedure, Dr. Price said. EW Editors' note: Drs. Dapena, Gorovoy, Price, and Terry have no financial interests related to their comments. Contact information Dapena: Dapena@niios.com Gorovoy: mgorovoy@gorovoyeye.com Price: francisprice@pricevisiongroup.net Terry: MTerry@DeversEye.org In the news Wisdom teeth stem cells may become corneal cells S tem cells from the dental pulp of wisdom teeth can be coaxed to turn into cells of the eye's cornea and could potentially be used to repair corneal scarring from infection or injury, according to researchers at the University of Pittsburgh School of Medicine. These cells could also become a new source of corneal transplant tissue made from the patient's own cells, the university said in a news release. Senior investigator James Funderburgh, PhD, professor of ophthalmology at the University of Pittsburgh and associate director of the Louis J. Fox Center for Vision Restoration of University of Pittsburgh Medical Center (UPMC) and the University of Pittsburgh, said that this research could assist in providing solutions to issues posed by corneal transplantation procedures. "Shortages of donor corneas and rejection of donor tissue do occur, which can result in permanent vision loss," Dr. Funderburgh said in a release from UPMC. "Our work is promising because using the patient's own cells for treatment could help us avoid these problems." Lead author Fatima Syed-Picard, PhD, and colleagues showed that stem cells of the dental pulp, obtained from routine human third molar extractions at the university's dental school, could be turned into corneal stromal cells (keratocytes). The researchers then injected the engineered keratocytes into the corneas of healthy mice, where they integrated without signs of rejection. In addition, they used the cells to develop constructs of corneal stroma akin to natural tissue. EW

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