Optimal Instruments for DMEK

Challenges encountered by early adopters prompted the creation of surgeon-friendly instruments to help improve outcomes

By Thomas “TJ” John, MD

Although Descemet’s membrane endothelial keratoplasty (DMEK) is an excellent procedure in terms of visual outcomes and recovery time, it made a less-than-ideal debut because the available tissue and instrumentation posed significant challenges for surgeons.

Today those challenges have been overcome. Tissue banks now offer prepared tissue, which takes half the burden off of surgeons. New instruments designed specifically for DMEK make it much easier to perform this exciting procedure. I developed a set of instruments for DMEK in response to common challenges encountered by surgeons, and that problem-solving approach has proven very rewarding.

CHALLENGE #1: Accessing the Cornea’s Inner Surface

When performing DMEK, we work on the cornea’s concave inner surface. This is the first time in ophthalmic surgery (with the patient in the supine position) that we have changed the surgical direction of work from working toward the floor (instruments directed toward the posterior pole and optic nerve) to working on the eye’s roof (instruments directed to the inner corneal surface). This was difficult in the early days of DMEK, when we used straight instruments designed for other procedures. For example, the straight shape of a reverse Sinskey hook made it very difficult to touch points in the cornea’s inner dome via a single entry point.

SOLUTION #1: To address this challenge, I developed the John DMEK Dexatome. This dexatome has a multi-curve design, allowing the tip to touch points within the inner concave corneal surface via a single pivotal point of entry into the anterior chamber (AC). By sliding the dexatome farther in, or retracting it outward, this surgeon-friendly instrument is able to access almost all regions of the inner cornea.

Furthermore, the curvature is specially designed to limit the likelihood of mechanical damage to the anterior iris or the lens capsular surface when the pupil is dilated, as in a triple procedure combining DMEK with phacoemulsification and a posterior chamber IOL. Additionally, in challenging surgical cases where there is a space-occupying AC IOL that compromises the available working space within the AC, the dexatome can be used to perform descemetorhexis and Descemet’s membrane detachment and removal as a single disc. By sliding the instrument into the AC and pivoting it through a single-entry pivotal point, surgeons can remove not only Descemet’s membrane, but also the corneal disc from previous Descemet’s stripping endothelial keratoplasty (DSEK) or DMEK that has failed.

When removing Descemet’s membrane, the instrument makes it easy to touch the folded regions of the detached Descemet’s membrane and avoid touching the inner corneal stroma. This is important to avoid damage to the inner stromal surface during Descemet’s membrane removal. Keeping the donor-recipient interface pristine is optimal for postoperative vision.

In addition, the smooth tip of the John DMEK Dexatome is designed to tear Descemet’s membrane in a single, 360-degree movement while gliding along the corneal surface — first clockwise 180 degrees, followed by counter-clockwise for the remaining 180 degrees.

CHALLENGE #2: Unfolding the Donor Membrane

In the DMEK procedure, the surgeon introduces the donor Descemet’s membrane by inserting the scrolled graft into the AC. The next task is to unfold the graft in the proper orientation and attach it to the inner corneal surface of the recipient’s cornea. Early adopters of DMEK identified this unfolding process as being a challenge. Because the donor Descemet’s membrane has no stroma attached, it is very flimsy and can move very fast, quickly going to the periphery, out through an unsutured corneal wound, or through a mid-dilated or fully dilated pupil.

SOLUTION #2: In my experience, the John DMEK Smoother simplifies the steps of unfolding and positioning the donor Descemet’s membrane, significantly improving the ease and outcomes of DMEK. It provides better control, requires fewer manipulations than using a cannula, and offers better fluid displacement within the AC, which aids in unfolding and positioning the donor Descemet’s disc within the AC.

The instrument has a highly polished steel sphere at its tip, which allows the surgeon to unfold the donor membrane easily and position the tissue centrally without damaging or losing control of it. The surgeon taps the spherical ball first on the corneal, exterior dome, which results in larger-volume fluid displacement within the AC than a straight cannula. This helps in accelerated unfolding of the donor Descemet’s membrane scroll, simplifying the DMEK procedure for the surgeon.

Next, the spherical ball is used to tap on the peripheral downslope of the corneal dome, resulting in horizontal aqueous displacement and an almost immediate movement of the donor Descemet’s disc toward the center to park in the central cornea, where the disc margins exactly coincide with the circular mark on the external corneal surface. This easy positioning at the center, unfolding, and subsequent attachment clear the hurdle of difficulty that existed previously with DMEK. Finally, surgeons use the instrument to smooth the donor-recipient interface.

Sometimes, difficult circumstances, such as a shallow AC, a very deep AC, the presence of a seton tube, a trabeculectomy opening, AC IOL,or a circular wound of a penetrating keratoplasty with interior stromal protrusion, can make unfolding of the donor Descemet’s membrane surgically challenging. The smoother can help in all of these difficult cases. If the membrane does not unfold for any reason, the John DMEK Manipulator can be used to gently unfold it in the AC. Again, these specialized instruments may help to simplify the DMEK procedure.

CHALLENGE #3: Cutting and Handling Delicate Donor Tissue

The purpose of DMEK is to remove and replace Descemet’s membrane alone, without any stroma, and this donor tissue is very delicate. For optimal outcomes, early adopters of DMEK recognized the need for specially designed instruments to cut and handle the donor tissue.

SOLUTION #3: The John DMEK Base, Cutting Block, Scroller, Separator, and Lifting Forceps are designed to make it easy to cut and harvest the delicate donor Descemet’s membrane as a single disc without damaging it.

The base has two vertical pins that lock the cutting block in place and prevent any sliding, and the cutting block has two wells with different diameters and central colored discs. The surgeon places the donor tissue in the cutting block’s smaller well, removes the donor Descemet’s membrane under fluid, and then places the membrane in the larger well containing trypan blue stain that is subsequently diluted with sterile balanced salt solution (BSS) prior to insertion into the recipient’s AC. An extra ledge within the larger well keeps the membrane centered while BSS is added, preventing damage from contact with the Weck-Cel sponge (Beaver Visitec) that is simultaneously used to aspirate the excess fluid. The surgeon creates a 360-degree score in the donor membrane with the Scroller, and then uses the Separator to separate the peripheral membrane.

Transfer of the donor tissue is performed with the John DMEK Lifting Forceps, whose paddle tips are designed to help surgeons pick up delicate tissue easily. The Lifting Forceps reduce the risk for tears in donor Descemet’s membrane, distributing their force while holding the membrane firmly.

No Longer a “Challenging” Procedure

New instrumentation has facilitated a major step forward in performance of the DMEK procedure. Instead of focusing on its challenges, we can perform DMEK with ease and a focus on achieving excellent visual outcomes and a comfortable recovery. The new instruments have a very fine and unique finish for easy manipulation and a comfortable, surgeon-friendly feel in the hands. Learning DMEK with these advanced instruments, many more surgeons will bring the advantages of DMEK to their patients.

Dr. John is clinical associate professor at Loyola University at Chicago and visiting professor at the Military University Military Medical Academy in Belgrade, Serbia. He is the editor of five surgical lamellar keratoplasty books as well as The Chicago Eye and Emergency Manual.