A Beginner’s Guide to DMEK

Acquiring the right tissue and technique for your patients

By Sumit (Sam) Garg, MD

As we work to improve corneal transplantation procedures, our goals are clearer vision and easier recovery. Descemet’s membrane endothelial keratoplasty (DMEK), a recent addition to our surgical options, has the potential to fulfill both of these goals for patients who will benefit from endothelial transplantation.

If you have been reading about DMEK and are interested in trying it, you might begin by thinking about your options for tissue preparation, outlets for learning and practice, as well as considerations for your first procedure.

Advantages of Pre-prepared Tissue

Although I have prepared my own tissue for DMEK procedures in the lab, I now use only pre-prepared tissue. Donor preparation can be difficult and time-consuming, and if you do not have a reproducible method to dissect Descemet’s membrane from the stroma, it is easy to damage the tissue. This is an expensive error with respect to both cost and potential loss of a donated cornea.

Surgeons who perform DMEK regularly typically choose pre-prepared tissue. It saves costs by reducing tissue loss and cuts OR time, which is good for surgeons as well as patients who appreciate an “on-time” start. Surgeons also value the following advantages:

• Predictable quality. For DMEK, we need tissue that is reliably stripped and free from the underlying stroma. I use SightLife Surgical pre-prepared tissue, which offers older donors (typically older than 50 years), which makes the tissue easier to unscroll.

• Ease of use. The level of anxiety associated with stripping the tissue yourself is not trivial — if you can take that out of the equation, you make DMEK that much easier. If you have not performed DMEK but are thinking about it, it may help you to know that pre-prepared tissue increases the likelihood of successful DMEK and shortens the learning curve. SightLife Surgical also offers backup Descemet’s Stripping Automated Endothelial Keratoplasty (DSAEK) tissue for the first few cases, if surgeons want it. I asked for the backup tissue when I started, and, although I never used it, it was reassuring to have it on hand.

• Flexible sizes. Most tissue from an eye bank is around 8 mm in diameter; however, surgeons need the flexibility to get a larger graft for a larger transplant, if needed.

SightLife Surgical can provide grafts up to 9.5 mm in size, making larger transplants possible.

• Clear orientation. Prepared tissue is marked with an “S” stamp to help the surgeon orient the graft in the anterior chamber. The mark can be placed on the graft in a few ways. Some eye banks make a hole in the stroma to allow for placement of the stamp, but this can become dislodged or torn.

SightLife Surgical places the stamp directly on the stromal aspect of Descemet’s membrane without a stromal hole. The graft also has a hinge indicator mark and an epicenter dot on the anterior stromal surface for trephination.

• Customized products. SightLife Surgical customizes tissue according to my needs. I can get tissue pre-peeled with a stromal hinge. The company is also considering ways to deliver the tissue in a preloaded cartridge or via another step-saving route.

Choosing an Eye Bank

When choosing an eye bank, I followed several criteria. First, the eye bank had to provide good-quality tissue that I felt comfortable transplanting into my patients’ eyes, and they had to be amenable to any special requirements I might need.

Second, the company had to visit customers’ facilities to learn how they work, following the processes and procedures at a hospital to set up an effective work arrangement. For example, SightLife Surgical helps with the logistics of drop-off and the bureaucracy of getting their product into the OR.

Finally, troubleshooting and communication are important skills for eye bank staff. The SightLife Surgical staff is great at communicating with me about the tissue they are preparing for my cases.

Preparing for DMEK

The best way to begin performing DMEK is to learn from the challenges and triumphs of others, rather than trying to reinvent the wheel. Attend a meeting, take a course, watch videos, and talk to colleagues or experts about the procedure.

DMEK has a unique learning curve from DSAEK. When I began performing DMEK about 18 months ago, I found that the real challenge was becoming comfortable with unscrolling the graft. The rest of the procedure is similar to DSAEK.

To practice, you need the right tools, several of which are different from the ones used for DSAEK. For example, I use a modified Jones tube to inject the graft. SightLife Surgical has always been amenable to giving me practice tissue to get a feel for the process, including punching and loading with my preferred injection method.

When selecting a first case, I recommend starting with a patient who has mild to moderate edema, which will enable you to view the anterior chamber and see the graft unscroll. This may not be possible if you select a case where the cornea is too hazy. Fuchs’ endothelial dystrophy patients are a good choice over pseudophakic bullous keratopathy patients because the endothelium tends to strip easier in Fuchs’ patients.

Performing the First Procedure

The DMEK procedure proceeds similarly to other endothelial transplants — the only major difference being the injection and unscrolling process. In my corneal transplant procedures, I prepare the graft before touching the patient to ensure that the graft is suitable for transplantation.

To begin, I remove the prepared tissue from its packaging. I place it under the microscope, stain it, punch it, remove the peripheral skirt, and lift the graft from the underlying stroma, leaving the tissue on the side table soaking in dextran sulfate sodium or in a corneal storage media.

Next, I perform an inferior peripheral iridotomy on the patient, stripping Descemet’s membrane with descemetorhexis 0.5 mm larger than the graft size. The DMEK graft is considerably thinner than a DSAEK graft. This makes the DMEK graft more challenging to insert and position in the anterior chamber.

The key is to see how the graft is curling, twist the tube so it is in the correct orientation, and finally inject it into the eye. I find that the shallower you make the chamber, the easier it is to unfold. I verify the correct orientation by visualizing the “S” stamp. Next, I utilize 20% sulfur hexafluoride gas under the graft to tamponade the graft into place. Finally, I suture all of the corneal incisions.

Great Results, Happier Patients

Once you are used to performing DMEK, the procedure is neither difficult nor comparatively time-consuming. What’s more, since transitioning to DMEK, I have noted faster visual recovery, improved vision, and happier patients overall.

Dr. Garg is associate professor of ophthalmology, vice chair of clinical ophthalmology, and medical director of the Gavin Herbert Eye Institute at University of California, Irvine School of Medicine.