Eyeworld

EW FEATURE 48 All you need to know about cornea transplants • January 2018 AT A GLANCE • DMEK can be a challenging procedure. However, finding a way to conquer tissue preparation can make this approach easier. • Surgeons have different techniques they use for DMEK tissue preparation. These are especially important internationally, where there may not be access to pre-stripped DMEK tissue. • The use of pre-stripped and preloaded DMEK tissue makes DMEK easier and less costly for some corneal specialists. by Vanessa Caceres EyeWorld Contributing Writer Overcoming the challenges of tissue preparation can facilitate better use of DMEK I t can take some finesse to prepare tissue for Descemet's membrane endothelial kerato- plasty (DMEK). However, DMEK can require fewer resources to perform in the OR, so it has its ad- vantages. Here's how some surgeons from across the globe approach DMEK tissue preparation and how the use of pre-stripped DMEK tissue can make a difference. Armand Borovik, MD, Southern Ophthalmology, Sydney, Australia I use a technique where instead of scoring the tissue with a sharp instrument or trephining with a blade, I use a blunt instrument (a Rootman-Goldich modified Sloane's LASEK microhoe developed by David Rootman, MD) to find an anatomical plane of dissection beginning within the trabecular meshwork. I first stain the tissue with try- pan blue to help identify the mesh- work better. After scraping free 1 to 2 mm of the peripheral tissue for 360 degrees, I use a forceps to peel the membrane into a "taco formation" (i.e., folded over 50%). I then make a 3 mm stromal punch through which I can mark the stromal side of Descemet's membrane with an "F." This is done using gentian violet from a marking pen on the tip of the microhoe that was used for the initial peel for the "F" and the tip of a forceps for the ".". I then do a partial thickness trephination of the tissue to the desired graft size and complete the peel. After staining the tissue with 100% trypan blue for 2 minutes, I aspirate the tissue into a glass injector, and it is ready for insertion. Before injecting the graft, I always check to see where the scrolled tissue makes a "V" and ensure this is facing up while the graft is injected. It is critical to practice the technique in the wet lab prior to preparing the tissue for surgery as it is important to learn how the tissue behaves. I always work under bal- anced salt solution as this decreases tissue tension and decreases the chance of a tear. Also, make sure that you tilt the surgical microscope 30 degrees to decrease reflections. Never force the tissue; be patient and make small, slow, fine move- ments. If you do have a tear, it is useful to mark the scleral rim with a marking pen at that point so you are conscious of where it is and start again from a point away from that tear. Watching videos or attending a course with experts in DMEK tissue preparation, particularly if there is a wet lab component, are very useful when first learning this technique. Reginald Robert Tan, MD, clinical fellow, cornea, external disease and refractive surgery, University of Ottawa Eye Institute, Ottawa, Canada At our center, under the direction of Kashif Baig, MD, we perform a modified submerged cornea using backgrounds away (SCUBA) tech- nique to prepare DMEK tissue. The first step with SCUBA involves placing the corneoscleral donor tissue endothelial side up on an 8 mm Barron trephine punch block (the size will depend on the patient's white-to-white distance). After centering the cornea, we do a partial thickness punch using a 10 mm corneal trephine. This limits our initial flap edge dissection with- in this diameter. Other techniques usually start the Descemet's sepa- ration by dissecting the trabecular meshwork from its attachment with the scleral spur down to Schwal- be's line. However, we noticed that starting dissection from the 10 mm diameter edge decreased the occur- rence of tears. After staining the 10 mm borders with a few drops of trypan blue, the endothelium is completely submerged in balanced salt solution. A microfinger dissector instrument (Moria Surgical, Antony, France) is used to delineate at least 180 degrees of peripheral Descemet's membrane from the stroma. Using a curved microtying forceps, half of the Descemet's membrane is then carefully peeled off and left in a taco configuration. We then create a 2 mm full thickness window on the exposed stroma using a dermatologic punch. After placing the Descemet's mem- brane back into position, we flip the whole corneal button and place an "F" mark on the Descemet's mem- brane side of the graft through the stromal window. The cornea is flipped again endothelial side up, followed by a partial thickness punch with the 8 Best practices for DMEK tissue preparation Clinical image of a DMEK surgery with 20/20 vision 6 days after the surgery with residual gas bubble still seen Source: Mark A. Terry, MD 62-year-old male with BSCVA of 20/20 as early as 2 weeks after DMEK and phaco plus IOL for Fuchs' endothelial dystrophy Source: Mohit Parekh, PhD

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