• Cornea/External Disease

    Speaking at the 2012 World Ophthalmology Congress, Dr. Friedrich E. Kruse made the case that it's time to switch from DSAEK (Descemet stripping automated endothelial keratoplasty) to DMEK (Descemet membrane endothelial keratoplasty).

    There's no question that DMEK delivers significantly better visual acuity, as it allows for transplantation of the endothelium-Descemet membrane (EDM) layer practically without alteration of the posterior stroma. Dr. Kruse presented data on 300 procedures showing that 60 percent of patient can see 20/25 or better after DMEK; and 90 percent, 20/40 or better.  But surgeons haven't switched in droves because of problems with donor preparation and the difficulty involved in unfolding the EDM graft in the anterior chamber.

    Dr. Kruse, a professor at the University of Erlangen-Nuremberg, Erlangen, Germany, described two recent modifications that address these issues, making DMEK more reproducible, predictable and successful. 

    For donor prep, accessing the margin of the EDM is a crucial step in separating the EDM from the attached corneal stroma. Dr. Kruse uses a razor blade to scratch or peel rather than cut the tissue outside the marked 8-mm zone, which prevents the EDM from tearing inside the marked zone.

    Then he uses two forceps for the stripping procedure instead of one. Using one forceps can easily cause ruptures of the EDM. But the two forceps approach allows the surgeon to lift the EDM like a tablecloth practically without folds, and distributes the force required to separate Descemet membrane from the underlying stroma over a larger portion of the grafts' circumference. This minimizes stress on the endothelial cells.  Dr. Kruse says this graft technique has resulted in a successful harvest 99 percent of the time.

    For reliable orientation of the EDM during surgery the donor disc is marked. Before completion of stripping, three circular marks are set in an identifiable order at the edge of the disc. The donor graft is then inserted into the anterior chamber, unfolded, and attached to the posterior corneal stroma with an air bubble. Correct anterior-posterior orientation of the graft is identified by the clockwise order of the three marks.

    Unfolding the EDM is the most difficult of the whole procedure. Dr. Kruse has helped develop a step-wise technique that uses water jets and air bubbles for an easier unfolding of the graft. He injects a small air bubble into the lumen of the EDM roll. Gentle movements of this bubble and subsequent injection of more air allowed for spreading out the membrane in the anterior chamber.

    When he first switched to DMEK, Dr. Kruse said his dislocation rate was 50 percent. With these modifications, the rate had dropped to 5 percent. Even more impressive, he said, are more recent results reported by the Cornea Research Foundation of America.

    Marianne Price, PhD, reported in October that the Cornea Research Foundation looked at 150 prospectively collected, consecutive DMEK eyes and compared them with 598 DSEK eyes and 30 penetrating keratoplasty (PK) eyes. All eyes used the same rejection criteria and corticosteroid regimen. The rate of rejection episodes was less than 1 percent at two years with DMEK, 12 percent with DSEK and 18 percent with PK, she said.

    "It's time to change technique. It is worth it," Dr Kruse said. "It really is the technique which is superior."