JAN 2014

EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.

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46 EW CORNEA January 2014 Tools & techniques Pre Descemet's endothelial keratoplasty (PDEK): A novel method of by Amar Agarwal, MS, FRCS, FRCOphth Introduction E ndothelial keratoplasty is evolving at an incredibly rapid pace. For most of the 20th century, endothelial dysfunction was treated with a full thickness procedure that changed very little from the time of its original inception. However, in the last decade alone, replacement of diseased corneal endothelium has evolved into a paradigm utilizing less and less of the recipient's tissue, toward a technique wherein only Descemet's membrane and endothelial cells are transplanted. The ultimate conclusion of this evolution is a method whereby only endothelial cells would be transplanted. We aren't there yet, however, the current state of the art in DMEK is yielding excellent results with quick visual rehabilitation and extremely low immune rejection rates. As with most new procedures, DMEK requires a learning curve, and is more challenging than its DSAEK predecessor. In this month's column, Amar Agarwal, MS, FRCS, FRCOphth, discusses a variation of the DMEK procedure (pre Descemet's endothelial keratoplasty), which appears to incorporate the newly discovered Dua's layer of the cornea into the donor graft. This variation may allow for a wider range of ages as donors for endothelial keratoplasty and perhaps improve the ability to handle, unfold, and secure the tissue to the recipient. Richard Hoffman, MD, Tools & techniques editor clinical.ewreplay.org/ ?v=2955144492001 Watch this video on your smartphone or tablet using your QR code reader. (Scanner available for free at your app store.) The problems with the existing procedure of endothelial transplantation are difficult graft handling, intraoperative unrolling of the graft roll, and tissue loss during surgical manipulation. This has been overcome by our recent innovative technique in which a thicker graft than the conventional Descemet's membrane endothelial keratoplasty (DMEK) is used. We call it pre Descemet's endothelial keratoplasty (PDEK). Recently, Harmindar Dua, MD, University of Nottingham, U.K., identified the presence of the pre Descemet's collagen layer, which differed in several properties from the overlying posterior stroma. After learning the nature of the pre Descemet's layer (Dua's layer), this concept of transplanting the pre Descemet's layer along with Descemet's membrane (DM) has begun in collaboration with Dr. Dua. Pre Descemet's endothelial keratoplasty (PDEK) involves the transplantation of the DM with endothelium along with the pre Descemet's (Dua's) layer. Donor graft preparation A corneoscleral disc with an approximately 2-mm scleral rim is dissected from the whole globe or obtained from an eye bank. A 30-gauge needle attached to a syringe is inserted from the limbus into the mid-peripheral stroma. Air is slowly injected into the donor stroma until a type 1 big bubble is formed; this is a well-circumscribed, central domeshaped elevation measuring 7.5 mm to 8.5 mm in diameter. It always starts in the center and enlarges centrifugally, retaining a circular configuration. Trephination of the donor graft is done along the margin of the big bubble. The bubble wall is penetrated at the extreme periphery, and trypan blue is injected into the bubble to stain the graft, which is then cut all around the trephine mark with a pair of corneoscleral scissors and covered with the tissue culture medium. The graft is loaded into an injector when ready for insertion. Recipient bed preparation After administering peribulbar anesthesia, the recipient corneal epithelium is debrided, if grossly edematous, for better visualization. A trephine mark is made on the recipient cornea respective to the diameter of the Descemet's membrane to be scored on the endothelial side. A 2.8-mm tunnel incision is made at 10 o'clock near the limbus. The anterior chamber is formed and maintained with saline injection or infusion. The margin of the Descemet's membrane to be removed is scored initially from the endothelial side with a reverse Sinskey hook. Once an adequate edge is lifted, non-toothed forceps are used to gently grab the Descemet's membrane at its edge, and the graft is separated from the underlying stroma in a capsulorhexis-like circumferential manner. The peeled Descemet's membrane is then removed from the eye. 1 2 Donor lenticule implantation The donor lenticule roll (endothelium-Descemet's membrane-PDL) is inserted in the custom-made injector and slowly pushed up the lumen of the nozzle. The injector is improvised from an IOL implant injector by removing the sponge tire and spring and reattaching the sponge tire, to prevent any back suction and inadvertent damage to the donor graft. Using the injector, the graft roll is injected in a controlled fashion into the anterior chamber. The donor graft is oriented endothelial side down and positioned on to the recipient posterior stroma by careful, indirect manipulation of the tissue with air and fluid. Once the lenticule is unrolled, an air bubble is injected underneath the donor graft lenticule to lift it toward the recipient posterior stroma. The anterior chamber is completely filled with air for the next 30 minutes, followed by an air-liquid exchange to pressurize the eye. The eye speculum is finally removed, and the anterior chamber is examined for air position. The patient is advised to lie in a strictly supine position for the next three hours. Results so far The spectral domain optical coherence tomography evaluation of the grafts shows no interface changes like opacification at one month follow up. PDEK graft harvesting is 3 4 5 6 Recipient bed preparation and graft insertion. From the top: 1. Preop image of the eye with endothelial decompensation. Epithelium debridement being done. 2. Trephine marking done on the cornea. 3. Descemet's membrane scored and stripped with reverse Sinskey hook. 4. Graft lenticule is loaded into an injector. 5. Intraoperative manipulation of the graft for proper positioning. 6. Air injected underneath the donor graft lenticule to lift it toward the recipient posterior stroma. Anterior chamber filled with air. Source: Amar Agarwal, FRCOphth

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