How DMEK is changing corneal surgery

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Descemet’s membrane endothelial keratoplasty may provide absolute visual rehabilitation and precise anatomic restoration of the diseased cornea.

By Cheryl Guttman Krader; Reviewed by Gerrit R.J. Melles, MD, PhD

Rotterdam, Netherlands-As endothelial keratoplasty (EK) evolves, myriad reasons support why corneal surgeons should also be performing Descemet’s membrane endothelial keratoplasty (DMEK).

Currently, Descemet’s stripping (automated) endothelial keratoplasty [DS(A)EK] is the most widely performed EK technique.

Gerrit R.J. Melles, MD, PhD, reviewed some of the leading features of the partial-thickness transplant technique that uses a graft comprised only of donor endothelium and Descemet’s membrane. He is director of the Netherlands Institute for Innovative Ocular Surgery, Rotterdam, and pioneered EK and the DMEK technique.

First, Dr. Melles pointed out that the DMEK procedure is safe; techniques for graft preparation and no-touch DMEK surgery have been standardized; and DMEK can be performed easily also in phakic eyes.

In addition, patients are happy with results because the procedure allows for maximum visual rehabilitation of the eye in a shorter period compared with DS(A)EK.

“The rule of thumb is that 80% of eyes achieve best-corrected visual acuity of 20/40 within 1 month after DMEK, 80% reach 20/25 or better by 6 months, and quite often, visual acuity is even 20/20 or better,” Dr. Melles said.

“The outcomes are even better in phakic eyes, and so we are becoming more and more conservative regarding extraction of the crystalline lens,” he said. “If there is no cataract, our feeling is that the surgeon should just leave the lens in place and perform DMEK.”

Low risk of complications

From a safety perspective, changes in endothelial cell density after DMEK are comparable to the losses reported after DS(A)EK. In addition, there is a relatively low risk of complications with DMEK. One of the most common is early partial detachment of the graft that can be resolved with a re-bubbling procedure or even by simply waiting.

“Re-bubbling is not always effective and local partial graft detachment may occur in up to 30% of eyes after 1 week in response to resolution of swelling of the host cornea,” Dr. Melles said.

“However, in following these eyes for 6 or 12 months, we realize that many of these detachments reattach spontaneously.”

Secondary glaucoma is one of the most important complications that can occur after DMEK and has been reported in 4% to 7% of eyes. The mechanism for glaucoma is thought to be migration of a portion of the inserted air bubble behind the iris, inducing lens tilting and acute mechanical angle closure. This problem arises in the first 24 hours and could be easily solved with pupil dilation or aspiration of the air bubble.

Moreover, small modifications in the technique-such as performing a peripheral laser iridotomy preoperatively and leaving a smaller air bubble of about 30% in phakic eyes or taking into account the anatomy of the anterior chamber in general-have resulted in considerable reduction of the incidence of acute postoperative glaucoma.

In addition, when DMEK is performed in phakic eyes, there is a 4% to 7% chance of inducing a cataract. However, cataract extraction in post-DMEK eyes is easily done without endangering the survival of the DMEK graft.

“We were a little afraid that the transplanted Descemet’s membrane would detach from the host cornea during phacoemulsification,” Dr. Melles said. “However, for some reason that we don’t understand, the DMEK graft seems to attach more strongly to the host posterior cornea than does [treatment-naïve] Descemet.”

As documented in series from multiple surgeons, the rate of allograft rejection after DMEK is <1% and, unlike DS(A)EK, DMEK does not appear to be plagued by the problem of interface haze or irregularity that can limit visual acuity.

“In eyes with haze after DS(A)EK, we have performed an exchange with a DMEK, and we saw that visual acuity improves,” Dr. Melles said.

The low rate of complications after DMEK and the need for relatively limited aftercare are appealing to surgeons. The procedure should also be appealing to surgeons because it seems to be feasible in most clinical settings and requires no major investment for new equipment. Surgeons can also either obtain the donor graft from an eye bank or prepare it themselves.

EK evolution

Looking ahead, Dr. Melles noted that DMEK may not be the final step in the evolution of EK, because there is some evidence that corneal clearance can be achieved in eyes with Fuchs’ dystrophy after removing host Descemet’s membrane and placing a free-floating Descemet-endothelial graft partly in contact with the recipient posterior cornea. The latter technique has been termed Descemet’s membrane endothelial transfer (DMET).

“DMET would be a minimally invasive procedure that dramatically simplifies surgery and would revolutionize the whole concept of corneal transplantation,” Dr. Melles said.

fyi

Gerrit R.J. Melles, MD, PhD

E: melles@niios.nl

Dr. Melles is a consultant for D.O.R.C. International BV/Dutch Ophthalmic USA. This article is adapted from Dr. Melles’ presentation during Cornea 2012 at the annual meeting of the American Academy of Ophthalmology.

**sidebar**

Reasons to learn no-touch DMEK

• Standardized and safe procedure (phakic)

• BCVA ~maximum visual potential

• ECD >/= PK

• Low risk of complications (detachment, rejection)

• Happy patients: good results

• Happy doctor: smooth aftercare

• No major investments required

• Feasible in virtually every clinical setting

• Gateway to next step in EK evolution

-Gerrit R.J. Melles, MD, PhD