DMEK is a partial-thickness cornea transplant procedure that involves selective removal of the patient’s Descemet membrane and endothelium, followed by transplantation of donor corneal endothelium and Descemet membrane without additional stromal tissue from the donor. The graft tissue is just 10-15 microns thick. Almost like DSAEK, direct contact with the DMEK graft tissue should be avoided to stop endothelial cell damage and graft failure.
A clear corneal incision is formed, the recipient endothelium and Descemet membrane are removed, and therefore the graft is loaded into an inserter. After injecting the tissue into the anterior chamber, the surgeon orients and unscrolls the graft, and a bubble of 20% sulfur hexafluoride (SF6) is placed within the anterior chamber to support graft adherence. The indications for DMEK are almost like those for DSAEK, including endothelial dystrophies (such as Fuchs corneal dystrophy and posterior polymorphous corneal dystrophy), pseudophakic bullous keratopathy, ICE syndrome, and other causes of corneal endothelial dysfunction.
DMEK offers a rapid visual rehabilitation of any keratoplasty technique so far . Final visual acuity will be outstanding because of minimal optical interface effects.
After the procedure, the patient should lie supine as much as possible with periodic breaks for meals or using the restroom. The amount of time spent supine should gradually decrease over the course of the first week.
One sample medication regimen: Prednisolone acetate 1% should be used every two hours while awake for the first week, 4 times daily over the next 3 months, then slowly tapered and stopped at year 1. A recent study showed that loteprednol etabonate 0.5% gel was as effective as prednisolone acetate 1% solution in preventing immunologic graft rejection episodes after DMEK and was significantly less likely to cause IOP elevation. Antibiotic drops should be used for 1 week after surgery.
Patients should initially be seen on post-operative Day 1, week 1, week 2, month 1, month 3, month 6 and month 12. Some advocate an OCT before surgery and on post-operative day 1, post-operative week 1, and post-operative month 1 to look at the stroma and edge position of the graft. The graft should be attached and the stroma should be less edematous than after DSAEK. A significantly edematous stroma may indicate the graft is not functioning well or is upside down.
Advantages of DMEK over DSAEK
DMEK has been shown to possess superior visual outcomes in comparison to DSAEK. In multiple studies where patients had DSAEK in one eye and DMEK within the fellow eye, significantly better visual acuity and preference were reported within the DMEK eye. 85% reported a far better quality of vision within the DMEK eye.
However, some studies suggest that DSAEK visual outcomes are often improved by ultra-thin tissue. Though recovery is slower with ultra-thin DMEK versus DMEK, final visual outcomes at 1 year are comparable. DMEK also features a lower immunologic rejection rate and has the advantage of employing a smaller incision (2.8 mm) than DSAEK (5 mm).