Over the past decade, the gold standard for corneal endothelial disease has been lamellar keratoplasty.

In 2018, more than 51,000 grafts were prepared for transplantation in the United States as reported by the Eye Bank Association of America. Of those grafts, more than 31,000 were lamellar grafts, and there was an increase of 41.2% with use of Descemet membrane endothelial keratoplasty (DMEK) grafts.

Thinner grafts are showing better outcomes, and DMEK is becoming the mainstay of endothelial keratoplasty. However, some surgeons are slow to adopt this technique because the transition from Descemet stripping endothelial keratoplasty (DSEK) to DMEK is difficult. In particular, the DMEK graft is technically challenging and surgical times are less predictable.

Although many surgeons are hesitant to attempt DMEK, recent data shows improved vision and decreased risk of rejection. For example, a meta-analysis reviewed 10 retrospective studies that included nearly 1,000 eyes. The outcome showed that DMEK had a better visual outcome than DSEK, with more patients obtaining 20/20 vision with DMEK and better vision across all time points.¹ Also, a report by the AAO² reviewed the published data surrounding DMEK surgery and found DMEK to be a safe and effective surgery with superior outcomes with regard to visual acuity and a decrease in graft rejection.

This article outlines some pearls for an easier transition to DMEK.

INJECTION TECHNIQUES

Several techniques can be used to inject the DMEK graft. This is an important step as the goal is to safely get the graft into the eye with minimal tissue manipulation and endothelial damage. One option is to place the DMEK graft into an IOL cartridge and then inject it into the eye (Figure 1). While some graft injection systems can cost more than $100, an IOL cartridge is an inexpensive option and can still be completed with a relatively small incision — most injectors fit in a 3.0-mm incision.

Also, a Straiko modified Jones tube (Gunther Weiss Scientific Glassblowing Co.) can be used to aspirate the free-floating graft, which is then subsequently injected into the eye. The modified Jones tubes are handmade and size can vary, but most fit in an incision less than 3.0 mm. The DMEK tissue can be requested to be delivered precut and stained in the modified Jones tube, which can save on tissue preparation time in the operating room.

The Geuder Cannula (Geuder) is another device used to inject the DMEK graft. This canula has a larger opening on one end and a smaller opening on the other. The graft can be aspirated through the larger opening, and the canula is reversed in the syringe and subsequently injected through the smaller opening on the other end. This device can fit through an incision as small as 2.4 mm.

UNFOLDING TECHNIQUE

Unfolding the DMEK graft is the most challenging part of the surgery. When the graft is injected, it has a tendency to form a scroll with the endothelium on the outside of the scroll. Several techniques can be deployed to assist in unscrolling the graft. Becoming familiar and efficient with the different techniques is important for the DMEK surgeon.

The Yoeruek technique³ utilizes digital pressure along the equator of the globe to assist in shallowing the anterior chamber. The shallow anterior chamber along with tapping on the cornea with a cannula helps the graft unfold and prevents the rescrolling of the tissue. Once unscrolled and positioned, an air bubble is placed posterior to the DMEK graft.

Dapena describes a maneuver to unscroll the DMEK graft that involves placing an air bubble between the double scroll and using the air anterior to the graft to completely unscroll the graft. Once fully unrolled, the air bubble anterior to the graft is removed and a bubble posterior to the graft is placed.⁴

A single sliding cannula maneuver is employed when the graft has a tendency to form a loose scroll. The graft can be unfolded using repetitive strokes with the cannula in the same direction as the graft folds.⁵

If the graft forms a tight scroll, the Dirisamer technique⁶ can be useful. This is performed by pinning the edge of the graft between the posterior cornea and iris and using a second cannula to unroll the rest. It is similar to unrolling carpet. This technique can be utilized if the double scroll or trifold cannot be achieved.

A newer, recently published technique utilizes relaxing incisions⁷ to prevent the graft from forming the tight scroll. The unique scrolling pattern with the relaxing incisions was also reported at ARVO.⁸ This technique helps form a trifold that can be supported and further unrolled utilizing an air bubble posterior to the graft (Figure 2).

Oftentimes, it may be necessary to utilize several techniques during one case to get a tight scroll to unfold.

AVOIDING COMPLICATIONS

The most common complication following DMEK surgery is graft detachment or separation. When this occurs, it is important to rebubble the graft during the postoperative visit.

Published reports indicate a lower rebubbling rate when sulfur hexafluoride (SF6) is used rather than air.⁹ SF6 bubbles stay in the anterior chamber longer than air, supporting the graft for a prolonged time. SF6 has not been reported to cause any endothelial cell loss, but the proper mixing of the gas is important to avoid elevated IOPs during the postoperative period (Figure 3).

RESOURCES FOR TRAINING

Many resources are available to help the beginning DMEK surgeon. Several DMEK courses are offered, and wet labs can be completed at ASCRS and AAO. This provides a chance to use DMEK tissue in a controlled environment to practice the unfolding techniques that have to be studied. Often these courses are moderated by experienced surgeons who can offer advice while beginning surgeons practice with DMEK grafts.

Local eye banks can also be a valuable resource to practice DMEK prior to direct patient care. Consider contacting a local eye bank to set up a wet lab.

Several websites can help surgeons become familiar with the different ways to unfold the grafts, the different types of scrolling and folding patterns of the grafts, as well as the easiest way to unfold and properly position the grafts. Peter Veldmen, MD, from the University of Chicago published a helpful website (patientready.org ) that documents the different types of folding patterns of the DMEK graft. There are also videos on this site on how to handle the various positions and folds of the DMEK graft.

BEYOND DMEK

Descemetorhexis without endothelial keratoplasty (DWEK) or Descemet stripping only (DSO) can be an option for patients with mostly central guttae and edema and densely populated peripheral endothelial cells.

Proper patient selection is critical. The ideal candidate for DMEK is a patient with mostly central guttae and a normal peripheral cell count.

With this technique, Descemet’s membrane is removed with a focus on peeling the central 4 mm and not scraping. Reverse Utrata forceps can be used to create a central 4-mm descemetorhexis.

There is significant cornea edema in the early postoperative period. The edema resolves over the course of three months and sometimes longer. The longer recovery time is a point of emphasis in preoperative patient discussions and managing expectations.

When compared with DMEK, DSO is of benefit due to less surgical complications, no risk of rejection and decreased cost of graft preparation. DSO may decrease the demand for DMEK tissue, potentially reduce the rate of surgical complications, eliminate the risk of rejection and hopefully lessen the demand for donor tissue.

With the discovery of Rho kinase inhibitors, there are potentially new options for treating endothelial disease. An adjuvant treatment of a Rho kinase inhibitor, ripasudil, with DSO has been found to improve recovery time,^10,11 which is the major drawback of DSO. Adding Rho kinase inhibitors may increase the number of patients that benefit from DSO.

The most exciting advancement in the treatment of endothelial dysfunction is injecting cultured endothelial cells along with Rho kinase inhibitors. Last year, Kinoshita et al in Japan published their initial data on injecting cultured cells.¹² After injecting a mixture of cultured endothelial cells and a Rho kinase inhibitor into the anterior chamber, patients were placed in a prone position for three hours. In all cases, the central corneal thickness decreased, cell count increased and vision improved.

CONCLUSION

Traditionally, the transition from DSEK to DMEK has been difficult; however, there are many resources and proven techniques to assist surgeons with this transition. The data support DMEK as the best option in lamellar keratoplasty in treating endothelial disease, and surgeons should feel more comfortable when making the switch.

There continue to be advances, and it is likely that we will continue to see more options with Rho kinase inhibitors and the use of cultured endothelial cells. OM

REFERENCES

1. Marques RE, Guerra PS, Sousa DC, et al. DMEK versus DSAEK for Fuchs’ endothelial dystrophy: a meta-analysis. Eur J Ophthalmol. 2019;29:15-22.
2. Deng SX, Lee WB, Hammersmith KM, et al. Descemet membrane endothelial keratoplasty: safety and outcomes OTA. Ophthalmology. 2018;125:295-310.
3. Yoeruek E, Bayyoud T, Hofmann J, Bartz-Schmidt KU. Novel maneuver facilitating Descemet membrane unfolding in the anterior chamber. Cornea 2013; 32:370-373
4. Dapena I, Moutsouris K, Droutsas K. Standardized “no-touch” technique for Descemet membrane endothelial keratoplasty. Arch Ophthalmol. 2011;129:88-94.
5. Liarakos VS, Dapena I, Ham L, van Dijk K, Mellers GR. Intraocular graft unfolding techniques in Descemet membrane endothelial keratoplasty. JAMA Ophthalmol. 2013;131:29-35.
6. Melles GR, Dapena I. How to get started with standardized “no-touch” Descemet Membrane Endothelial Keratoplasty (DMEK). Rotterdam: Netherlands Institute for Innovative Ocular Surgery; 2014. Chapter 4, “no-touch” DMEK surgical technique:57-72.
7. Hansen MS, Hardten DR. Small relaxing incisions may allow easier DMEK surgery. Ocular Surgery News U.S. Edition. May 10, 2019.
8. Bedard P, Justin JJ, Hansen MS, Hou JH. Descemet’s membrane endothelial keratoplasty (DMEK) scrolling patterns following paired small radial incisions (hinges). Presented at ARVO. May 2, 2019.
9. Schaub F, Enders P, Snijders K, et al. One-year outcome after Descemet membrane endothelial keratoplasty (DMEK) comparing sulfur hexafluoride (SF6) 20% versus 100% air for anterior chamber tamponade. Br J Ophthalmol. 2017;101:902-908.
10. Moloney G, Petsoglou C, Ball M, et al. Descemetorhexis without grafting for Fuchs endothelial dystrophy-supplementation with topical ripasudil. Cornea. 2017;36:642-648.
11. Macsai MS, Shiloach M. Use of topical rho kinase inhibitors in the treatment of Fuchs dystrophy after Descemet stripping only. Cornea. 2019;38:529-534.
12. Kinoshita S, Koizumi N, Ueno M, et al. Injection of cultured cells with a ROCK inhibitor for bullous keratopathy. N Engl J Med. 2018;378:995-1003.

About the Author

Mark S. Hansen, MD, is an anterior segment and refractive surgeon. He is a partner at Minnesota Eye Consultants in Minneapolis. Dr. Hansen has no relevant financial disclosures.