Nearly two decades ago, the field of corneal transplantation changed dramatically with the introduction of DSEK. The procedure boasted several advantages over traditional corneal transplantation, PK (penetrating keratoplasty); and DSEK’s predecessors (PLK, DLEK, etc.), but the landscape has shifted again with the introduction of DMEK. While benefits and drawbacks exist for each of these, this article will explore the two approaches in turn.
DSEK/DSAEK (Descemet’s Stripping [Automated] Endothelial Keratoplasty) is a partial-thickness corneal transplant. The procedure involves replacing a patient’s own Descemet’s membrane and diseased endothelial cells (the two bottom-most layers of the cornea) with a thin graft of posterior corneal stroma, Descemet’s membrane, and healthy endothelium from a donor. This means that the rest of the patient’s cornea is left intact as opposed to the entire tissue being replaced as with a traditional Penetrating Keratoplasty (PK/PKP), or full-thickness corneal transplant.
DSEK is indicated in patients with diseased or damaged endothelia as with Fuchs Dystrophy, pseudophakic corneal edema, or iridicorneal endothelial syndrome. In cases where only the back-most part of the cornea is diseased or damage, it isn’t always necessary to perform a full-thickness transplant. Partial-thickness transplants by and large have a quicker visual recovery time and are more comfortable for the patient. Because less of the tissue is transplanted, there is also a greatly reduced risk of rejection.
To perform a DS[A]EK, the corneal tissue is retrieved from the donor the same way it might be for a patient undergoing a full-thickness transplant, but the section of tissue to be used (the endothelial layer, Descemet’s membrane, and part of the stroma) are separated from the rest of the tissue sample in a graft that is about 70-120 microns thick. This preparation is either done by hand by a certified eye bank lab technician for the most part, or with an automated microkeratome. That tissue is later inserted (after being position in a “taco” shape for DSEKs or scrolled for a DSEK) through a small incision near the limbus or via a sclera tunnel and placed behind the patient’s own cornea where it is held in place by an air bubble. The patient must then remain on their back as much as possible for approximately 24 hours so that gravity forces the air bubble to rise up and hold the graft against the backside of the cornea to adhere properly.
A DMEK (Descemet’s Membrane Endothelial Keratoplasty) is performed in much the same way as the DS[A]EK, with the chief difference being that the graft used is only 5-10 microns thick. This makes the tissue much more delicate and even more difficult to handle. Surgeons have to take extra precautions and find unique ways to manipulate it in order to move it into position. Because the DMEK tissue does not contain stromal tissue, the grafts are typically able to mold to the host tissue with less unevenness at the juncture where the edge of the graft tissue and the host tissue meet. This leads to quicker visual recovery and less induced refractive error post operatively.
While the DMEK procedure and its techniques are still evolving, DS[A]EK has been performed successfully since 2004. It is a tested and true method of corneal transplantation that still yields great results, but there are some contributing factors that may indicate why DS[A]EK may trail behind DMEK when it comes to visual results. Some of these include residual higher-order aberrations because of a rippling effect of the tissue that occurs in DMEK as well, but is typically greater in DS[A]EK given the procedure calls for a greater amount of tissue. While in some cases a hyperopic shift can occur when a tissue that is cut more thickly at its center and more thinly at its periphery induces more minus lens, this issue has been mostly resolved with the introduction of the automated microkeratome to prepare the tissue as it does so with uniformity across the diameter of the tissue in a way that cannot be achieved by hand.
Although DS[A]EK has been the gold standard for partial thickness transplants, patients will often defer to the ease of comfort and rapidity of visual recovery in DMEK despite its newness. Because the rejection rate in DMEK is lower, surgeons will often opt to taper a patient off steroids more quickly. Some debate still exists, however, about whether long-term steroids are necessary post-DMEK and studies are ongoing. Additionally, there is no index of refraction in the tissue that is transplanted in a DMEK because only the tissue that has been removed is replaced. The diseased endothelium and Descemet’s Membrane is replaced by healthy donor tissue without the added stromal tissue that is used in DS[A]EK. Because this tissue is so thin, it has no index of refraction, is therefore optically neutral, and yields a more speedy visual recovery with less refractive error post-operatively.
Deciding between DS[A]EK and DMEK is a decision that should be made with your surgeon and should be done in full understanding of the pros and cons of each. As with any surgical procedure, there are associated risks involved and it is important to only move forward with surgery if the possible benefits outweigh the potential risks. Weighing your options with your surgeon, your surgical counselor, and your family is crucial step in the pre-operative process.
Our physicians perform both of these procedures and have been extremely impressed with the visual outcome for our patients. They feel that they are widely successful on the right candidate and part of the evaluation with one of our surgeons is determining your candidacy. At Cornea Associates we are proud to offer both of these options for a patient considering corneal transplantation and look forward to staying on the cutting edge of these expanding technologies to be able to provide the best possible care for our patients.