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    Cutting Edge: One Corneal Layer at a Time

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    Fig. 4. DMEK scroll.

    More than a century has passed since the first successful corneal transplant. Today, corneal transplantation remains an important tool for visual rehabilitation. Here’s a review of the most common techniques used for mod­ern keratoplasty.

    The major indications for keratoplasty include Fuchs’ dystrophy, pseudophakic bullous keratopathy, repeat transplants and keratoconus.

    Evolving Techniques

    A little over a decade ago, 95 percent of harvested cor­neal grafts were used for penetrating keratoplasty (PK), the surgical replacement of a full-thickness host cornea. The long-recognized limitations of PK include pro­longed visual rehabilitation, unpredictable refractive outcomes and vulnerability to trauma.

    With advances in surgical instruments and techniques, three lamellar keratoplasty methods have gained popu­larity. Each of these selectively removes diseased cor­neal tissue while preserving healthy tissue: deep anterior lamellar keratoplasty (DALK), Descemet strip­ping endothelial keratoplasty (DSEK) and Descemet membrane endothelial keratoplasty (DMEK).

    These lamellar techniques have several advantages over PK, such as less surgically induced astigmatism (especially for DSEK and DMEK), expedited visual reha­bilitation and reduced risk of rejection. Consequently, these techniques have largely replaced PK.

    Deep Anterior Lamellar Keratoplasty

    You can use DALK to treat keratoconus, corneal dys­trophies and partial-thickness corneal scarring. The goal of DALK is to remove the corneal stroma down to the Descemet membrane in order to create a smooth graft-host interface. You can achieve this by using tech­niques like the Anwar big-bubble technique and the Melles technique and the use of the femtosecond laser (Fig. 1, see slideshow). However, DALK has only accounted for about 2 percent of total corneal transplants since 2005 — likely because it is more technically demanding and time con­suming than PK.

    Endothelial Keratoplasty

    This method involves selectively replacing the diseased corneal endothelium. EK is the preferred technique in patients with corneal endothelial dysfunction. Since 2012, it has rapidly overtaken the number of PK proce­dures in the United States as it provides faster and more reliable visual rehabilitation while maintaining the eye’s structural integrity.

    You have two possible ways to perform EK:

    Descemet stripping endothelial keratoplasty

    The most widely used technique, DSEK involves strip­ping the host Descemet membrane and endothelium (descemetorhexis) and inserting a posterior lamellar donor button, which you position against the host with an air bubble to promote adherence. The button is com­prised of Descemet membrane, endothelium and a small portion of posterior stroma. A variation of DSEK using thinner donor grafts is called ultra-thin DSEK. (Fig. 3, see slideshow).

    Descemet membrane endothelial keratoplasty

    DMEK eliminates the donor stromal layer found in DSEK by only using donor Descemet membrane and endothelium. Compared to DSEK, the donor prepara­tion for DMEK is more technically challenging given the graft’s thinness and chance of tearing as you peel it off the underlying stroma.

    The technique used to insert and unscroll the DMEK donor tissue requires a “no-touch” technique or a series of maneu­vers such as tap­ping and pressing along wounds to help unfold the donor in the correct orientation (Fig. 4, see slideshow).

    For many surgeons, the increased surgical times of DMEK compared to DSEK has made DSEK the procedure of choice for routine EK. In eyes with more significant struc­tural abnormalities, such as aniridia and aphakia, DSEK is generally preferable to DMEK. A DMEK graft can more easily escape into the posterior chamber or be damaged by contact with plastic IOLs or artificial irises. While the use of sulfur hexafluoride (SF6) gas in DMEK has reduced the incidence of postoperative complications, DMEK still has increased rates of graft detachments and rebubbling compared to DSEK (Fig. 6, see slideshow).

    Despite the surgical challenges associated with DMEK, its use has grown. In fact, the number of DSEK procedures peaked in the United States in 2013 as surgeons began to adopt DMEK. Notably, DMEK can provide even quicker visual rehabilitation, better final visual acuity and reduced risk of immunologic rejection compared to DSEK.

    Hopefully, this gives you a quick primer on the newer keratoplasty techniques, so you can start to familiarize yourself with the indications and limitations of the vari­ous types of lamellar keratoplasty.

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    Victoria H. Yom, MD, MSCIAbout the author: Victoria H. Yom, MD, MSCI, is a cornea spe­cialist at UCLA and has been a member of the YO Info editorial board since 2018.