February 2014

 

COVER FEATURE

 

Corneal infections

DMEK experts offer pearls, pitfalls for performing procedure


by Erin L. Boyle EyeWorld Senior Staff Writer

   
Donor graft

Donor graft is being inserted into the eye. The donor is stained with trypan blue so that it can be seen. An IOL cartridge and inserter are used that provide a closed system so the back pressure from the anterior chamber does not push the donor back into the cartridge.

DMEK graft DMEK graft is inserted into the anterior chamber with small air bubble under it. The air bubble pushes the donor up against the recipient cornea, and the cannula is being used to unfold the donor.

Eye Anterior chamber Anterior chamber is completely filled with air pushing the donor firmly against recipient.

Source (all): Francis W. Price, MD

Intraop DMEK procedure Intraop DMEK procedure Source: Michael Straiko, MD

eye after DMEK Intraop DMEK procedure Source: Michael Straiko, MD

The lamellar transplant procedure is an effective corneal transplantation option, with new advances assisting treatment

DMEK (Descemet's membrane endothelial keratoplasty) continues to provide good outcomes in corneal transplantation procedures, including in Fuchs' endothelial dystrophies and pseudophakic bullous keratopathy cases, offering the possibility of 20/20 vision or better.

However, concerns remain about endothelial cell survival and the learning curve, with some surgeons still hesitant to use the procedure, preferring instead to perform Descemet's stripping automated endothelial keratoplasty (DSAEK).

"DMEK is an exciting advance but it is still a relatively new technique," said Michael Straiko, MD, Devers Eye Institute, Portland, Ore. "It has been shown to offer better vision, faster visual recovery, and lower graft rejection rates than DSAEK, but it will need to be supported with long-term endothelial cell survival rates as well."

The new era of lamellar corneal surgery—progressing from penetrating keratoplasty to endothelial keratoplasty procedures such as DSAEK and DMEK, and deep anterior lamellar keratoplasty (DALK) to target stromal disease—has provided corneal surgeons with varied individualized approaches to treat corneal disease, said Neda Shamie, MD, associate professor of ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles.

"It has made being a corneal surgeon so much more fulfilling as we offer a truly customized approach to our patients," she said. "Our patients are benefiting from this, and I think it has enriched our experience as corneal surgeons, knowing that our surgical approach is now a far more deliberate approach than the 'one size fits all' approach we had with penetrating keratoplasty."

"DMEK is part of this evolution," Dr. Shamie said. "I don't think it's going to necessarily replace DSAEK. I think it's a nice addition to the armamentarium of a lamellar corneal surgeon and one that should be offered to those patients who would benefit from it." Francis W. Price, MD, Price Vision Group, Indianapolis, and chairman of the board and founder, Corneal Research Foundation of America, Indianapolis, said that results show that DMEK is producing good outcomes for patients.

"I think as data comes out from multiple centers, what we're seeing is that the rejection rate is much lower with DMEK than any of the other transplant procedures," said Dr. Price. "Visions are better. There's less distortions in the form of higher order aberrations, and we have a smaller incision size."

Advances in instrumentation

"DMEK is ready for prime time," Dr. Straiko said. The reasons that he cited are advances including availability of pre-stripped tissue and the development of a glass, closed system injector, theStraiko DMEK injector, which he invented to simplify tissue delivery. The two biggest advancements in the procedure have been how the tissue is inserted into the eye, Dr. Price said, with closed systems offering the best results, and most importantly improvements in unfolding the grafts including using a slit lamp or OCT to determine the orientation of the endothelial side of the graft.

"Both of those have made a huge improvement in the ability to put the donor into the eye, get it to unfold, and go into place," Dr. Price said.

According to Dr. Straiko, "Our eye bank has developed a technique to apply an 'S' stamp to eliminate upside down graft placement. New graft unfolding techniques such as the tap technique, first reported by Yoeruek, have greatly simplified unfolding and positioning the graft."

In addition, 20% SF6 has helped him achieve higher success rates, with his group's rebubble rate below 6%. "All of these factors are coming together to make DMEK ready for prime time. I suspect some surgeons may be waiting for longer-term cell density data prior to proceeding," Dr. Straiko said.

Novel advancements for graft preparation include the submerged hydro-separation technique that Mohit Parekh, MD, shared at the Cornea Society/Eye Bank Association of America's 2013 Fall Educational Symposium in New Orleans, Dr. Straiko said, and the Muraine technique, which requires equipment from Moria (Antony, France).

Pearls for beginning surgeons

The first pearl for the beginner DMEK surgeon, Dr. Shamie said, is to use pre-stripped tissue from an eye bank.

"To attempt to prepare your own tissue when you're beginning is too risky," she said, unless "you can practice on the donor grafts used when performing DALK. The second pearl is, in graft adhesion, strip the recipient Descemet's larger than the size of the graft that is being inserted into the eye, she said.

"I have found … that the DMEK graft sticks better to bare stroma than it does to overlapping areas of Descemet's; Descemet's doesn't stick to Descemet's well. It's different than DSAEK. With DSAEK, you want to strip the recipient stromal bed smaller than the size of the donor graft to avoid having bare areas of the stroma without endothelium resulting in peripheral bullae. But in DMEK, if you're putting in an 8 mm graft, you want to strip at least an 8.5 mm area of the recipient stroma," she said.

The third pearl is that the ability to shallow the chamber is critical when trying to open the scrolled donor DMEK tissue. "[Being] able to shallow the chamber and to use the iris as a cushion during the step when the surgeon tries to open the scrolled graft is critical," Dr. Shamie said. "Because of that, you need to have a miotic pupil and a flat or shallow chamber. With that in mind, a patient with a deep anterior chamber or one who is post-vitrectomy, where shallowing of the chamber will be difficult will pose a lot of challenges that a beginning DMEK surgeon might not want to tackle."

In addition, the graft will scroll away from the endothelium, making it difficult to determine which side is facing up. She recommends using trypan blue to stain the graft and watching for the graft edge to scroll up "like a basket," which determines that the endothelium is facing down. Intraoperative use of a slit beam may help as would a graft stamped with an S.

Another pearl is to use topical instead of general anesthesia, Dr. Price said. This can assist when the eye is filled with air or fluid, as patients can then respond that they still see light and do not have a vascular occlusion.

Patient selection is important, too. Select eyes that are between 11.5 mm and 12 mm and that are standard with no confounding issues.

"It is critically important to select your DMEK patients carefully," Dr. Straiko said. "I recommend DMEK only in patients with a stable bicameral eye. Avoid patients with tubes, trabs, iris defects, aphakia, or post-vitrectomy eyes."

Understanding that there will be a learning curve is key for the beginner surgeon, Dr. Price said. He likened it to when surgeons made the switch from extracapsular cataract surgery to phacoemulsification.

"Like phaco, surgeons are going to have to spend a lot of time to learn the technique," he said. "Most people will not be able to get by just doing two cases a month. They're going to need to do multiple cases to get the skill set and the pattern recognition to actually do it well."

Pitfalls for beginning surgeon

The biggest pitfalls of DMEK would be the higher rebubble rate compared to DSAEK, as well as the higher risk of returning to the operating room, according to Dr. Shamie.

"I tend to watch my DMEK patients more closely," she said. "I see them several times in the first month, and if the edges are not 100% attached, there's a lot of waiting and watching and making sure that there's no extension of that separation. Taking advantage of an anterior segment OCT is helpful in monitoring the graft adhesion in the critical early postoperative period."

Dr. Straiko said it is vital that surgeons not think of DMEK as a variation of DSAEK. The two surgeries are different, with different skill sets.

"Stripping the host is the only similarity," he said. "It is important to practice your technique on donor globes prior to attempting it on your patients. It is also important to find a mentor or take a course and learn from other people's mistakes—it will shorten your own learning curve."

Both Drs. Price and Straiko advised beginner surgeons not be discouraged by early DMEK experience.

"You can't get frustrated if you have difficulties," Dr. Price said. "You have to practice. You need to use a step-by-step technique to get started. Plan to do a series of cases. Book about two hours for the first few cases so that you're not running over in the operating room. Nobody's going to complain if you get done early. Just take your time, and it should go well.

DMEK article summary

Editors' note: Drs. Price, Shamie, and Straiko have no financial interests related to this article.

Contact information

Price
: francisprice@pricevisiongroup.net
Shamie: nshamie@yahoo.com
Straiko: mike.straiko@gmail.com

DMEK experts offer pearls DMEK experts offer pearls
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