8 Techniques to Unroll the DMEK Graft in Difficult Situations Posterior lamellar keratoplasty is full of complexity from graft preparation, donor insertion, and donor graft unfolding. Unfolding of the donor graft can be particularly difficult in the case of Descemet membrane endothelial keratoplasty (DMEK) for several reasons. The first challenge is visualization of the DMEK graft tissue and orientation in the anterior chamber, second is the very fragile nature of the DMEK graft. Finally, unrolling a graft that would prefer to scroll up on itself, instead of taking a planar configuration as in DSEK surgery, is difficult as well. These are just a few of the factors that make DMEK surgically challenging in a routine case and even more so in a complex case. As a general surgical principle, any improper technique early in a case will amplify difficulty in a later step of the surgery. This rule certainly holds true with DMEK surgery. Making sure the endothelial graft can be visualized in the anterior chamber is essential. Staining the donor graft in a mixture of balanced salt solution (BSS) and trypan blue is critical to visualizing the graft in the anterior chamber. Over time the blue color will dilute out of the graft so timely unfolding is beneficial. Once the graft has lost all color it is exceedingly difficult to see it in the anterior chamber, and unfolding becomes much more difficult, though not impossible. Staining the graft in a 50/50 mixture of trypan blue and BSS for 5 minutes or so should impart enough color to the graft to allow adequate visualization. Good visualization will help with unfolding of the graft in any situation. Similar to Descemet stripping endothelial keratoplasty (DSEK), the endothelial graft in DMEK must open and be in the correct orientation, with endothelial cells posterior and membrane anterior. Visualizing the orientation of the DMEK graft can be very difficult under the operating microscope but is essential in graft survival and patient satisfaction. Several techniques can be employed to ensure proper graft orientation. Marking of the stroma has been employed in DSEK surgery for many years. Many eyebanks and surgeons are now able to put a stromal orientation mark on the membrane side of DMEK tissue. The mark is typically stamped with gentian violet ink, minimizing loss of the endothelial cells under the mark. Stromal marking can be associated with very minimal cell loss, but greatly facilitates proper graft orientation and prevents graft failure. No long-term cell loss is caused by the orientation stamp (► Fig. 8.1).1 Most surgeons agree that the stromal mark helps in graft orientation and decreases overall surgical time with no need for special instrumentation or technique needed to visualize the graft. The small amount of cell loss associated with the stromal mark is far less damaging than unfolding and attaching a graft upside down. The visualization of the DMEK graft is difficult even with adequate trypan blue staining under the operating microscope. The use of a light pipe or endoilluminator has been described to assist with visualization of the graft.2 The use of indirect lighting enhances the surgeon’s understanding of graft position and dynamics. This can be especially beneficial when the view into the anterior chamber is reduced due to corneal edema or scarring. In a similar fashion some surgeons have advocated the use of a handheld slit lamp to help with visualization of the graft.3 In these cases the slit lamp is used to help confirm graft orientation in the anterior chamber. Fig. 8.1 Photo of intraoperative optical coherence tomography being used to confirm correct orientation of the Descemet membrane endothelial keratoplasty graft. Note how the edges of the graft scroll toward the posterior stroma of the host cornea, confirming orientation. In this case a stromal S-stamp is also visible on the graft, further confirming correct graft orientation. Anterior segment optical coherence tomography (OCT) is commonly used to visualize the DMEK graft postoperatively to ensure proper attachment and orientation. Over the past few years intraoperative OCT has become available to assist with anterior segment surgery.4 The add-on to the surgical microscope allows the OCT image to be overlayed in the surgeon’s view. This allows visualization of the DMEK tissue in real time without the use of any additional instrumentation or stains. Using the OCT helps the surgeon to confirm proper graft orientation and better understand the dynamics of the endothelial graft. As the use of intraoperative OCT increases we will see if it helps novice surgeons transition to DMEK surgery and assists experienced surgeons in more difficult cases. Many surgeons do not have access to intraoperative OCT, light pipes, or portable slit lamps for use in the operating room. As long as you are able to stain the cornea with trypan blue, graft orientation can be determined using what has been called the Moutsouris sign. Using this technique, a cannula is placed over the double scroll of the graft. The cannula is then slid to the right or left. If the cannula turns blue once over the scrolled portion of the graft you can be sure the DMEK tissue is in the correct orientation. If the cannula does not turn blue the graft is upside down and needs to be rotated in the anterior chamber. Regardless of the technique used to place a DMEK tissue graft into the anterior chamber the situation will arise when the graft ends up in the incorrect orientation. This may be determined on OCT, by seeing the orientation mark upside down, or with the Moutsouris sign. Once you have confirmed that the graft is upside-down in the anterior chamber it must be flipped. Although it may seem difficult at first, the technique to flip a graft is quite easy as long as the graft can be visualized. In this situation a deep anterior chamber is needed. By deepening the anterior chamber, the DMEK graft will scroll up on itself. After making sure the main incision is closed with a suture, aggressive irrigation through a paracentesis will cause fluid waves in the anterior chamber, allowing the DMEK graft to tumble on itself. Once the graft tumbles 180 degrees the anterior chamber can be shallowed to hold the graft in place. With some luck the tissue will still be in a double scroll, which will facilitate unfolding. Using a variety of techniques, the graft can then be unfolded in the correct orientation (► Fig. 8.2). If the graft rolls up into a single scroll the jets of fluid will eventually allow a leaflet to unscroll. Once a small part of the Descemet graft begins to open, the remainder of the graft can be unscrolled using the Dirisamer technique (► Fig. 8.3). The anterior chamber over the open end of the DMEK graft is shallowed using a cannula; this holds the open portion against the iris and deepens the anterior chamber over the scroll. While one is holding the first cannula a second is used to “tap” on the cornea over the scroll to selectively open the remaining graft. Many techniques have been described to help unfold a scroll of DMEK tissue. For the most part the technique(s) used will depend on the ability to maintain a soft eye, a shallow anterior chamber, and how the graft presents itself in the anterior chamber. In many cases more than one technique will need to be employed to open and position the graft. As a general rule, tissue from older donors will open more easily as it tends to form a looser scroll, leading to shorter unfolding times.5 The more challenging the case the more important it is to be selective as to donor age. The easiest situation is the **lazy** graft (► Fig. 8.4). In this case the Descemet graft presents itself in the anterior chamber in a very loose scroll. The lazy graft is one of the easiest to open. In many cases by keeping the eye soft and the anterior chamber shallow just a few taps on the cornea directly over the DMEK graft will allow the graft to open. Once open, air of 20% sulfur hexaflouride gas (SF6) can be used to attach the graft to the overlying host stroma. Most of the time the DMEK graft is not lazy and tends to scroll endothelium outward in the anterior chamber. The graft may take the configuration of a single scroll or a double scroll. These shapes are more challenging configurations to unfold, but as long as the eye remains soft and the anterior chamber can remain shallow unfolding is relatively straightforward. The first step is to make sure the graft is in the correct orientation (endothelium down). Knowing the orientation may not be possible until the graft is partially unfolded to allow visualization of an orientation mark or evaluate for the Moutsouris sign. Before unfolding make sure to close the primary incision to ensure the graft will not be expelled from the anterior chamber. Always shallow the chamber through a peripheral paracentesis (though I have seen grafts even go through small peripheral incisions). A no-touch technique may be employed to help with initial graft unfolding. In many instances this will allow one half of the graft to unfold, leaving the other scrolled up on itself. With this configuration the open portion of the graft is held in position by shallowing the anterior chamber with a cannula. Using a second cannula with a sweeping motion the scrolled portion of the graft is opened. Once open, the graft is centered in the anterior chamber and then gas or air is used to affix the graft to the overlying host stroma. In most cases a no-touch and the Dirisamer technique are all that will be necessary to efficiently open the endothelial graft.6 As comfort with DMEK grows, more challenging cases may be attempted. Performing DMEK in eyes with glaucoma tube shunts7 or eyes that have had vitrectomy is possible but may be more challenging and have a higher complication rate.8,9 As long as the anterior chamber can be shallowed, the technique is no different than that in standard eyes. In some situations (in the author’s opinion this is especially true in postvitrectomy eyes) the anterior chamber cannot be shallowed or will not remain shallow. If the anterior chamber will not shallow, the graft will continue to curl on itself, making unfolding almost impossible. In these cases, an air bubble may be employed to assist with unfolding. The use of a bubble to assist with unfolding is named after Isabel Dapena. In the Dapena maneuver an air bubble is injected between the DMEK graft and the overlying host corneal stroma. Manipulation of the air bubble on the external cornea allows the small bubble to act as a tool to unfold the graft. Once the graft is unfolded the air bubble is removed and air is placed under the graft for final attachment. Though the technique sounds quite simple, it can be very challenging to know exactly where you are in the anterior chamber and what is the position of the cannula over the graft. Care must be taken to make sure that the air is injected in the correct place or it will make unfolding the graft even more difficult.
8.1 Introduction
8.2 Visualization of DMEK Graft
8.2.1 Stromal Marking
8.2.2 Indirect Lighting
8.2.3 Intraoperative Optical Coherence Tomography
8.2.4 Direct Visualization
8.2.5 Rotation “Flipping” of Graft Tissue
8.2.6 Unfolding DMEK Graft Tissue
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