CORNEA CLINICAL UPDATE EK Evolves: Are PDEK and Hybrid DMEK on the Horizon? dvances in endothelial kerato- 1 2 plasty are giving patients with Acorneal endothelial dysfunction ever-more novel treatment options even though Descemet stripping auto mated endothelial keratoplasty (DSAEK) and Descemet membrane endothelial ker- atoplasty (DMEK) are the mainstays. “The field of endothelial keratoplasty is a dynamic one; it has been revolu- 3 4A 4B tionized in the last 20 years, and we are continuing to refine our surgical ap- proaches,” said Kathryn A. Colby, MD, PhD, at the University of Chicago. Some might say that this trend of innovation is attributable in part to the fact that DSAEK and DMEK have their drawbacks. Amar Agarwal, MS, FRCS, FRCOphth, at Dr. Agarwal’s Eye STEPS. Stills from the PDEK video mentioned on page 29 show (1) creation of the Hospital and Eye Research Centre in Type 1 Big Bubble to harvest the donor graft, (2) graft injection into recipient Chennai, India, noted, “In DSAEK, the eye, (3) the eye on postop day 1, and (4A,4B) the preop eye compared with the donor tissue is about 80 to 150 mi- eye at 3 months postop. crons. So, effectively, a 500-µm cornea will become a 600- to 650-µm cornea keratoplasty (PDEK), an emerging pro- and described the technique in March [after surgery], and the endothelium cedure intended to address both chal- 2014 in the British Journal of Ophthal- has to pump more. lenges. In another corner of the field, mology.1 Candidates include patients “In DMEK, the donor tissue is only Donald T.H. Tan, MD, at the Singapore with endothelial decompensation such 15 µm, which is good,” he said. How- National Eye Centre, is developing as Fuchs dystrophy and pseudophakic ever, for this procedure, he noted that hybrid DMEK (H-DMEK, see sidebar), or aphakic bullous keratopathy, he said. only grafts from older donors can be another technique designed to combine The procedure involves transplanting used. This is because in donors younger the best of both DSAEK and DMEK. only 25 µm of tissue: the pre-Descemet than age 40-50, the endothelium layer, the Descemet membrane, and adheres so strongly to the stroma that PDEK the endothelium. “The pre-Descemet they cannot be separated. Dr. Agarwal performed the first PDEK layer gives a splinting effect to the graft Enter pre-Descemet endothelial procedure in India in September 2013 and makes it easy to manipulate,” said Dr. Agarwal. Several benefits of PDEK are directly attributable to the graft’s BY LORI BAKER-SCHENA, MBA, EDD, CONTRIBUTING WRITER, INTERVIEW- relative stiffness, he said. ING AMAR AGARWAL, MS, FRCS, FRCOPHTH, ALAN N. CARLSON, MD, Bigger donor pool. Unlike DMEK, KATHRYN A. COLBY, MD, PHD, AHAD MAHOOTCHI, MD, AND DONALD T.H. which relies on grafts from donors Amar Agarwal, MD, FRCS, FRCOphth MD, Amar Agarwal, TAN, MD, FRCS, FRCOPHTH. aged 40 years and older, PDEK has no EYENET MAGAZINE • 27 donor age restriction, said Dr. Agar- get the DMEK graft to unscroll, sur- tissue may be at risk of falling through wal. “The youngest we have used is a geons intentionally shallow the anterior to the posterior segment. 9-month-old donor.2 This gives us the chamber. But in complicated situations, Lower detachment risk? Based big advantage of healthier grafts with a such as in patients with vitrectomized on what he’s seen in his practice, better endothelial cell count.” eyes or those with prior Nd:YAG poste- Dr. Agarwal said that the 10-µm pre- Easier manipulation. As with DSAEK, rior capsulotomy in whom the anterior Descemet layer lowers the risk of PDEK grafts can be manipulated more chamber can be difficult or impossible detachment compared to DMEK. easily than DMEK grafts, Dr. Agarwal to shallow, it may be a challenge to And in correspondence to the Journal said. Alan N. Carlson, MD, at Duke Eye un roll the DMEK graft. PDEK grafts of Cataract and Refractive Surgery, Institute, in Durham, North Carolina, are ideal for these complex patients,” Dr. Agarwal and colleagues reported agreed, noting that DMEK can be un- he said. outcomes in 12 PDEK patients. Eight predictable. “You could have the perfect Dr. Colby added that in some patients, grafts adhered successfully, and there procedure, and the graft tissue itself you may not want to do a DSAEK, but were 4 detachments, 3 of which did not would end up scrolling or detaching. you can’t do a DMEK. She said that she require intervention. None detached With PDEK, I feel I have better control sees a case for PDEK or H-DMEK in completely.3 of the tissue because of the added Dua patients with aphakia, iris defect, or a Good visual outcomes. Of the cases (pre-Descemet) layer.” vitrectomized eye—situations in which he has done so far, Dr. Agarwal said that Advantage for complex patients. the anterior chamber might not suffi- postoperative edema improves, and Ahad Mahootchi, MD, in private prac- ciently shallow for successful unscroll- vision stabilizes in PDEK patients as tice in Zephyrhills, Florida, noted, “To ing of a DMEK graft, or where DMEK rapidly as it does in DMEK patients. Hybrid DMEK The basic idea behind hybrid DMEK clinical series of about 90 H-DMEK EndoGlide (coupled with an anterior (H-DMEK) is to make it more like cases in both standard and more chamber maintainer). This allows for DSAEK, said Donald Tan, MD, FRCS, challenging cases, which he plans to a closed chamber procedure, which FRCOphth, in Singapore. “This is be- submit for publication. Of the cases, minimizes fluctuation of anterior cause there is greater reproducibility over 40 were in eyes that ordinarily chamber depth. Both are important with DSAEK and surgeons are more would be unsuitable for DMEK. These to a successful procedure and allow comfortable with it, whereas DMEK were performed in the latter half of surgeons to tackle these more chal- requires much skill and can be more the series, once the technique had lenging cases, he noted. stressful for the surgeon.” been refined. These complex cases He added that because the tissue What is hybrid DMEK? H-DMEK included aphakia, aniridia, vitrecto- is always held right-side up with the uses a standard DSAEK approach mized eyes, eyes with tube shunts, forceps, it is generally not possible to with a few differences. During donor and previous failed penetrating kera- have an inadvertent “upside-down” graft preparation, the Descemet toplasties or DSAEK. graft. Further, this means that addi- membrane and endothelium is sepa- Despite the difficulty of these tional donor preparation steps such rated from the pre-cut DSAEK tissue, cases, the series had a relatively low as the placement of an “S” stamp the DMEK graft is laid back loose- primary graft failure rate of 2.2% and mark, to signify the exact orientation ly over the stroma, and the whole a rebubbling rate of 8.8%. There were of the tissue, is not required. complex is coiled into an EndoGlide 2 documented cases of endothelial Considerations. Because H-DMEK Ultrathin DSAEK inserter (Network rejection, which were subsequently utilizes the EndoGlide DSAEK surgi- Medical Products). Once the Endo- reversed with topical steroids. cal approach, Dr. Tan recommended Glide is inserted inside the anterior He reports that in his own prac- that surgeons have sufficient expe- chamber, the surgeon uses intraoc- tice, his H-DMEK endothelial cell loss rience with this form of inserter and ular forceps to pull only the DMEK rates are about 24% now that he with using this “pull-through” forceps tissue from the inserter, leaving the has become very proficient with the technique before attempting or stroma in the cartridge, which is procedure. When he first started, his adapting the H-DMEK technique then removed. The DMEK tissue is cell loss rates were 37%, and he has to their practice. always right-side up, and the forceps brought these rates down steadily Of note, Dr Tan has developed provides enhanced surgeon control with practice. a new DMEK EndoGlide inserter over the DMEK tissue, which tends to Benefits.Dr. Tan said that H-DMEK specifically for DMEK surgery, which naturally uncoil of its own accord in gives enhanced surgical control of may further simplify the H-DMEK the anterior chamber. the graft tissue and also control procedure. It is currently undergoing Results. Dr. Tan just completed a of the anterior chamber with the clinical trials. 28 • AUGUST 2018 In the same 12-patient study, corrected Type 1 BB. In this approach, injec- Carolina, to determine how the eye distance visual acuity (CDVA) at 90 tion of air separates the pre-Descemet bank could prepare PDEK grafts days was between 20/35 and 2/90 for all layer (Dua layer)/Descemet membrane/ effectively and predictably in order to but 2 patients whose CDVA was 20/200, endo thelium complex from the residual minimize waste of corneal donor tissue and at 1 month, 1 eye had minimal stromal bed. The graft is approximately and endothelial cell loss. The result, interface haze.3 25 µm thick and 7.5 to 8 mm in diam- said Dr. Carlson, is that “Miracles in Dr. Agarwal added that PDEK may eter. Research has shown that the Dua Sight Eye Bank has done a tremendous have a role for badly scarred corneas. In layer confers additional strength to the job preparing tissue that is preloaded a prospective, interventional study, Dr. recipient cornea.5 and prestamped.” Agarwal’s group reported on 4 patients Type 2 BB. This contrasts with the In Florida. Dr. Mahootchi adopted with chronic pseudophakic bullous Type 2 BB in which the Descemet DMEK, due in large part to the avail- kera topathy who underwent PDEK or membrane is separated from the pos- ability of preloaded and prestamped coupled with epithelial debridement.