Q: What are the major advantages of DMEK vs. other deep lamellar procedures?
A: “The true strength of Descemet’s membrane endothelial keratoplasty appears to be the speed and extent of visual recovery,” says Aaron Bronner, O.D., of Boise, Idaho. “In other forms of EK, vision seems to be limited to some degree. With Descemet’s stripping automated endothelial keratoplasty (DSAEK), for example, though 20/30 outcomes are common, 20/20 vision is much less frequent. This has been speculated to result from optical degradations at the host-graft interface.” In DMEK, on the other hand, 30% of patients achieve 20/20 final acuity, while 70% achieve at least 20/25.1
DMEK is the latest incarnation in the evolution of EK. An earlier technique, deep lamellar endothelial keratoplasty (DLEK), gave way to Descemet’s stripping endothelial keratoplasty (DSEK) and DSAEK, which, in turn, may be supplanted by DMEK.
• DLEK. This is the immediate precursor to DSEK/DSAEK. “The key difference between DSEK and DLEK is that a more technical dissection of the host is required in DLEK. This entails the creation of a recession of the host stroma,” allowing the graft to sit firmly in place, Dr. Bronner says. But, “this difficult step proved unnecessary with the advent of air tamponading,” he explains.
• DSEK. “DSEK and DSAEK are currently the most widely used incarnations of EK. Both of these surgeries, like DLEK, use a posterior donor button. This graft button includes some posterior stroma as well as Descemet’s membrane and endothelial cells,” Dr. Bronner says. “The difference between the two is that a microkeratome is used to dissect the donor button with DSAEK, while DSEK requires a careful manual dissection. After stripping of host endothelium and Descemet’s membrane, the donor button is placed and secured by an air tamponade.”
What makes DMEK so different from DSAEK or DSEK? “Previous EK transplants used not just the endothelium and Descemet’s membrane, but a posterior stromal component as well,” says Dr. Bronner. “The stromal carrier allows for easier transportation and insertion via the traditional forceps technique. The endothelium is fragile, and trauma during implantation is a frequent source of graft failure.”
In DMEK, however, no stroma is included in the graft. “The surgeon is dealing with endothelium and Descemet’s membrane alone, which increases the risk of significant trauma to the endothelium and resultant graft failure.” The first prospective study of DMEK in the U.S., led by Francis Price, M.D., and Marianne Price, Ph.D., found that DMEK provided higher rates of 20/20 or 20/25 vision, but donor graft preparation and attachment were significantly more challenging.1
A few issues may hinder the widespread adoption of DMEK, notes Dr. Bronner. “The role of the stromal carrier is not optical—it’s protective. Elimination of this layer requires adjustment in surgical technique. In Dr. Price’s group, the challenge was met with intraocular lens or implantable contact lens injectors to facilitate donor sheet insertion. Still, determination of the most atraumatic insertion technique is pending.”1
As was also noted in the study, graft preparation for DMEK differs from that for other techniques.1 “Currently, EK grafts can be taken as intact corneas/scleral rims and prepared at the surgical site, or pre-cut grafts are available in some eye banks. With DMEK, the donor button is different, so the protocol for preparation in eye banks and at surgical sites needs to be developed.”
The risks of DMEK are similar to those of other EK procedures—i.e., primary graft failure, early dislocation and immunologic rejection.
Bottom line: “All EK procedures are ‘game changers’ and represent a paradigm shift in treatment of endothelial decompensation,” says Dr. Bronner. “But, if a patient is suffering from an endothelial breakdown, don’t wait for DMEK to become available; refer for DSAEK. Your patient will thank you for it.”
1. Price MO, Giebel AW, Fairchild KM, Price FW Jr. Descemet’s membrane endothelial keratoplasty: prospective multicenter study of visual and refractive outcomes and endothelial survival. Ophthalmology. 2009 Dec;116(12):2361-8.