Use of DMEK Will Expand

Excellent results can be achieved using this posterior lamellar keratoplasty procedure.

BY THOMAS JOHN, MD

PENETRATING KERATOPLASTY (PKP) is still the most frequently performed corneal transplant procedure in the United States.¹ However, lamellar keratoplasty (LKP), pioneered by Tillett and Barraquer and further advanced by Melles, is gaining ground. LKP procedures are more selective than PKP. They enable us to remove only the diseased layers of the patient’s cornea and preserve the healthy parts, which has several potential advantages — not the least of which is better biomechanics.

Descemet’s-stripping endothelial keratoplasty (DSEK) is the current procedure of choice for the majority of surgeons who perform posterior LKP for endothelial dysfunction. In this procedure, Descemet’s membrane, the endothelium and a small amount of stroma are replaced with a donor tissue graft. DSEK is a very good procedure, but Descemet’s membrane endothelial keratoplasty (DMEK) offers some enhanced benefits. In DMEK, Descemet’s membrane and the endothelium, but no stroma, are replaced with donor tissue. Because so little tissue is transplanted, the corneal anatomy remains closer to normal thickness. More patients achieve 20/20 vision postoperatively, and they tend to achieve it more quickly than with DSEK. In one study, for example, 15 patients underwent DSEK in one eye and DMEK in the fellow eye. At 1 year, mean best spectacle-corrected visual acuity was 20/24 in the DMEK eyes and 20/32 in the DSEK eyes. The majority of the patients (85%) perceived better visual quality in the DMEK eye, and 62% preferred or would recommend DMEK to a friend or relative, while only 15% preferred DSEK.² Also with DMEK, the rate of graft rejection is lower. In a study reported by Anshu, Price and Price,³ the rates at 1 year were PKP 14%, DSEK 8%, and DMEK 1%. At 2 years, the rates were PKP 18%, DSEK 12%, and DMEK 1%.

Once I began performing DMEK, I did not go back to DSEK even though DMEK is more challenging to perform. The primary hurdle is that the ultrathin tissue involved is more difficult to control than the thicker tissue used in DSEK (Figure 1).

FIGURE 1. The ultrathin graft used in DMEK can be difficult to control.

DMEK Learning Curve Tips

It’s important to use the proper tools when performing DMEK. I find the DMEK Dexatome I developed as part of the new DMEK instrument set with B+L/Storz to be very useful. Because of its curvature, the surgeon is able to easily touch every point on the inner concave surface of the patient’s cornea as the 12-15 µm thick tissue is being removed. This reduces trauma to that surface, and the Dexatome tip is used to touch the folded Descemet’s membrane of the recipient cornea, avoiding the corneal stroma which results in a clearer interface and better postoperative vision. I also developed a DMEK Smoother with B+L/Storz, which allows the donor Descemet’s membrane to be unfolded in the patient’s eye without use of an air bubble. The instrument’s highly polished ball tip facilitates moving the donor membrane to any desired position within the patient’s anterior chamber. This is a significant step toward simplification of DMEK surgery.

Along with the tools, DMEK technique is evolving. For example, the graft can be removed from the concave surface of the donor cornea under fluid, or a “flip” technique can be used whereby the cornea is made convex and the surgeon works under air to separate the donor tissue. In another development, many surgeons now make their peripheral iridotomy inferiorly, after considering that the air bubble that will hold the graft in place might go superiorly. Also, some surgeons remove the patient’s epithelium to improve visualization, and I use a surgical microscope mounted slit lamp intraoperatively to ascertain that the graft is properly placed, uniformly attached without wrinkles, and no interface debris or pockets of air or fluid collection exist. Finally, an important consideration for surgeons who are new to DMEK is the depth of the patient’s anterior chamber. Because tissue is being placed in such a confined space and needs to be unfolded with a no-touch technique, it is best not to choose eyes with either very shallow or very deep anterior chambers for one’s initial series of cases.

Expect a Paradigm Shift

I have no doubt that new techniques and instrumentation designed for DMEK will continue to simplify the procedure. When that happens, given the excellent results that can be achieved, we will likely see a paradigm shift away from other posterior LKP procedures and toward DMEK. The future of DMEK looks bright!

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