Intraoperative and Postoperative Complications of Descemet Membrane Endothelial Keratoplasty

Donor Tissue Damage During Graft Preparation

Unlike DSAEK, the donor endothelium and Descemet membrane must be isolated from the adjacent stroma in DMEK. This can be accomplished using several different techniques, with the two most commonly used being the “submerged cornea using backgrounds away” or “SCUBA” technique, in which forceps are used to manually peel the Descemet membrane from the stromal bed or less commonly by pneumatic dissection to create a “big bubble” similar to the technique used in deep anterior lamellar keratoplasty (DALK). Safety is high for both techniques, but long-term clinical outcomes have been described only with manual peeling, a technique that has a reported success rate of up to 98%−99% in the hands of experienced surgeons or eye bank technicians.

Damage to delicate tissue during graft preparation can be more easily avoided using proper harvesting strategies ( Video 136.1 ). In particular, it is critical to maneuver in ways that minimize stress along the edges of the graft to reduce tissue tension and the likelihood of tearing the Descemet membrane, a number of which have been described. ^, In performing forceps stripping of Descemet membrane, the donor cornea should be submerged in media while the Descemet membrane is carefully peeled towards the center one quadrant at a time to decrease overall surface tension. Two forceps instead of one can be used to distribute the stress more evenly. Depending on the extent of the tears, certain torn grafts can still be transplanted successfully. Grafts can be prepared immediately prior to surgery or stored in a refrigerator in advance (at 4°C), as the time of tissue preparation has been shown to have minimal effect on primary graft failure, endothelial cell loss, and graft adherence. An increasing number of eye banks are preparing DMEK grafts for surgeons, offering prestripped, prepunched, and preloaded grafts, and have demonstrated comparable success rates with those prepared by individual surgeons just prior to surgery. The donor is now also stamped with an orientation mark to help the surgeon in determining correct orientation upon implantation. This orientation mark can be in the form of a trypan blue stamped letter on the stromal side of the graft or sequential marks at the edge of the graft.

Video 136.1 Torn Donor Graft During Descemet Membrane Endothelial Keratoplasty Graft Preparation Using Scuba Technique. Dagny Zhu, Neda Shamie.

The ease with which a single donor graft can be harvested appears to be influenced by specific donor characteristics. Gorovoy et al. found the incidence of developing a tear in one eye to be significantly higher in cases where tears had also occurred in the contralateral eye of the same patient, suggesting intrinsic patient characteristics that influence the ease of peeling. Because the posterior nonbanded layer of Descemet membrane continues to thicken with age, older age donor grafts (>50–55 years old) are more resistant to tears during graft preparation and are thus easier to peel than their younger counterparts. ^, Donor preparation has also been shown to be more challenging with corneas harvested from patients with diabetes and hyperlipidemia due to higher mechanical adhesion between host Descemet membrane and stroma. Fortunately, the overall rate of graft failure due to unsuccessful mechanical separation of Descemet membrane from stroma is low, ranging from 2% to 6%. ^, Additional studies identifying other important donor characteristics that may facilitate DMEK preparation and influence the selection of specific patient populations used for DMEK are currently underway.

Poor Visualization of Donor Tissue

The thin Descemet membrane graft must be stained with trypan blue prior to anterior chamber insertion to facilitate visualization. Prolonged surgical manipulation of the scrolled graft during positioning and unfolding can result in loss of the stain and poor visualization. With preloaded DMEK grafts, especially one prepared more than 24 hours prior to implantation, the staining of the graft may also dissipate, and the surgeon may want to consider restaining the graft before implantation. A sufficiently stained graft is especially important in eyes with dark irides, as visualization of the DMEK graft is more difficult with the darker background. It is extremely difficult to transplant a poorly stained DMEK graft successfully, especially in the setting of a cloudy cornea. Although poor corneal clarity is usually inherent to the diseased corneas that require endothelial keratoplasty, it may be wise to plan for DSEK instead of DMEK in patients with very scarred or edematous corneas, as manipulating a DSEK graft can more easily be done even if visualization is limited. Intracameral restaining of the graft is possible by injecting trypan blue into the anterior chamber and gently irrigating with balanced salt solution after less than 1 minute. Debriding epithelium and/or using topical anhydrous glycerin can help improve visualization. An intraoperative handheld slit beam or optical coherence tomography are more involved approaches that can also be helpful in evaluating the donor tissue during surgery.