Eyeworld

EW CORNEA 66 February 2016 by Matt Young and Gloria D. Gamat EyeWorld Contributing Writers thinly cut, better visual outcomes follow. This has led to the development of a modified DSAEK called "ultra- thin DSAEK," where the donor tissue is cut thinner than the usual 100- to 150-um thickness, with the idea that visual outcomes are improved with thinner grafts, while maintaining the ease of performing DSAEK. This procedure is gaining pop- ularity among many surgeons, as it provides a good balance of excellent visual outcomes with low complica- tion rates, Dr. Ang noted. "Various studies have shown that visual outcomes in ultra-thin DSAEK, where donor grafts may be as thin as 50 to 70 μm, are superior to standard DSAEK using thicker grafts," he added. Meanwhile the learning curve in DMEK is one of the reasons for the slow adaptation of DMEK by surgeons. For example, Dr. Ang said, donor tissue stripping must be per- formed as skillfully as the procedure itself. In current clinical practice, do- nor tissue harvesting for DMEK is es- sentially performed by the surgeon. According to Dr. Ang, the donor tissue is extremely thin and fragile, so it may easily tear during harvest- ing. Essentially, tissue preparation remains a barrier. On the other hand, "if improve- ments in technique or new devices could help in the harvesting of Descemet's membrane so that it can be done very predictably with little endothelial cell loss or damage to the tissue, this may encourage more surgeons to perform DMEK," Dr. Ang said. "Eye banks could also help in harvesting DMEK tissue in the fu- ture, so that the transition to DMEK is less tedious for surgeons," he said. "As Descemet's membrane is very delicate and may easily be torn during stripping by a machine or de- vice, it may be some time before an automated method of DMEK tissue harvesting is possible," he conclud- ed. EW Editors' note: Dr. Ang has no financial interest related to this article. Contact information Ang: leopk12@gmail.com However, posterior lamellar ker- atoplasty, Dr. Ang noted, does not suit eyes with manifest corneal scar- ring in the stroma and pronounced corneal neovascularization—in these cases, penetrating keratoplasty would still be required. DSAEK vs. DMEK Compared to DSAEK, patients have a faster visual recovery in DMEK, the visual acuity may be better, refrac- tive outcomes are more predictable, and there is a lower incidence of immune rejection because there is much less donor tissue transplanted. Numerous studies have shown that less than 30% of DSAEK pa- tients may achieve 20/20 BSCVA compared to 40–50% of DMEK patients. "The comparatively lower best corrected visual acuity in DSAEK eyes is believed to be related to the stroma-to-stroma interface; by elim- inating the stromal carrier in DMEK, the visual outcome would therefore be superior," Dr. Ang said. Because of this potential for better vision quality, DMEK is grad- ually becoming more popular for straightforward cases of endothelial dysfunction. However, Dr. Ang not- ed, the DMEK procedure is still slow to be adopted, as it is has a steeper learning curve and a higher rate of complications. "The Descemet's membrane is extremely thin and delicate, mak- ing it more difficult to handle the donor membrane after it is inject- ed into the anterior chamber," he said. Hence, in this case, there is an increased rate of early endothelial cell loss, more graft detachments, and loss of donor tissue in the preparation of the graft. Besides, not all patients are ideal candidates for DMEK, Dr. Ang said. "DSAEK will still be the pre- ferred technique in eyes with aphakia prior to vitrectomy, tube implants, large iris defects, and hypotony," he said. "In view of the difficulty in handling the extremely thin and fragile tissue in DMEK, DSAEK is still the preferred option for many surgeons." Procedure modifications in DSAEK and DMEK Some studies have demonstrated that if the donor tissue in DSAEK is sutures. "This avoids ocular surface and suture-related problems, and reduces postoperative irregularity and astigmatism," he said. In addition, because only a thin posterior lamellar surface is replaced and secured without the need for sutures, this has a minimal effect on the anterior corneal curvature. "This means that the visual recovery after DSAEK is much faster and the visual acuity is significantly better than conventional PKP; the residual refractive error and astigma- tism following DSAEK is also much lower," Dr. Ang said. There is also a lower risk of immune rejection in DSAEK, allowing patients to enjoy better long-term vision. Since only a small incision is required, there is greater wound strength and the likelihood of wound rupture is much lower, according to Dr. Ang, all making this procedure widely used and popular in clinical practice. "The complication rates for DSAEK are very low; only occasion- ally, the graft may not adhere and dislocate, and rebubbling may be required to reattach the graft," he said. Impact of automation in patient outcomes The availability of new insertion devices in the ophthalmic market today has certainly improved the way surgeons handle and insert the graft. "While these procedures can be performed manually, the use of automated microkeratomes have further enhanced our ability to cre- ate a smoother dissection plane for the donor cornea, thereby reducing interface irregularity and improving the visual outcome," Dr. Ang said. Improvements in surgical tech- nique, the use of automated prepa- ration of the donor cornea, and the use of new graft insertion devices have enabled ophthalmic surgeons like Dr. Ang to perform the proce- dure more effectively and predict- ably and through smaller incisions. "All of these contribute to an even safer surgery, faster recovery and better vision; because of the greater safety and improved out- comes, surgery can now be recom- mended at an earlier stage of the cornea disease," he said. I n the past decade, the field of endothelial keratoplasty has progressed in leaps and bounds, in a way that it has largely replaced penetrating keratoplas- ty (PKP) as the standard treatment for endothelial dysfunction without significant stromal scarring. Most importantly, advances in surgical techniques and devices have significantly improved the surgical outcomes and reduced complication rates of procedures such as Descemet's stripping au- tomated endothelial keratoplasty (DSAEK) and Descemet's membrane endothelial keratoplasty (DMEK). Today, even newer methods such as ultra-thin DSAEK and DMEK have enabled patients to achieve excellent visual results with low complication rates. "With these advances, the threshold to offer surgery in patients with endothelial dysfunction and cornea decompensation is much lower than it was in the past, so that patients can have their visual acuity restored at a much earlier stage," said Leonard Ang Pek Kiang, MD, medical director and senior con- sultant ophthalmologist, Lang Eye Centre, Mount Elizabeth Novena Specialist Centre, Singapore. Key factors in the success of DSAEK Modern partial-thickness (lamel- lar) cornea transplant techniques, according to Dr. Ang, have provid- ed ophthalmologists with better options for treating endothelial diseases such as Fuchs' dystrophy. "During Descemet's stripping endothelial keratoplasty (DSEK) or Descemet's stripping automated en- dothelial keratoplasty, the diseased Descemet's membrane and endothe- lium is removed and replaced with a posterior lamella comprising of approximately 100- to 150-μm thick donor stroma with Descemet's mem- brane and healthy endothelium," Dr. Ang explained. "The graft is then maneuvered into position and secured onto the recipient posterior stroma using an air bubble." Ophthalmic surgeons today have recognized the numerous im- portant advantages that made them adapt to DSAEK more than PKP. First of all, Dr. Ang emphasized, the graft is attached onto the recipient pos- terior stroma without the need for Why DSAEK may be the preferred technique for corneal endothelial diseases

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