Surgeons transition to DMEK in clinical practice

Despite the risk of postoperative graft detachment, DMEK is gaining favor with surgeons and patients alike due to its enhanced visual outcomes.

As Descemet’s membrane endothelial keratoplasty, or DMEK, continues to demonstrate superior visual outcomes for patients with corneal endothelial dysfunction, many surgeons are incorporating the procedure as a primary treatment option.

“DMEK is what I recommend to people who want to get the absolutely sharpest, clearest vision, the best visual recovery possible, because currently it is going to induce the least amount of distortion of any technique,” Francis W. Price Jr., MD, told Ocular Surgery News.

While the DMEK corneal graft is known to detach more frequently than that of its predecessor, Descemet’s stripping endothelial keratoplasty, it is also more likely to achieve visual outcomes of 20/25 or better.

According to a study, 75% of clinical cases treated with DMEK result in 20/25 or better within the first 1 to 3 months postoperatively, and it is not uncommon for patient vision to reach 20/40 the first day after surgery. The technique’s selective replacement of only the diseased corneal layers is believed to be responsible for this visual enhancement.

“Apparently, near normal anatomical restoration of a cornea with isolated transplantation of Descemet membrane often results in full recovery of the eye’s visual potential, whereas the presence of even a thin donor posterior stroma layer in DSEK/DSAEK may somehow limit the optical performance of the transplanted cornea to a visual acuity of about 20/40,” the study authors wrote.

The long-term benefits of DMEK over DSEK are limited to visual recovery, but because surgeons are more likely to avoid a hyperopic shift and get their targeted refractive result with DMEK, they may offer patients the option of correcting astigmatism, Dr. Francis Price said.

The procedure requires postoperative air injections about 50% of the time, Dr. Francis Price said, and he has a discussion with patients before surgery, explaining the pluses and minuses of both DSEK and DMEK. Patients are informed that the DMEK graft does not seal as well around the edges, requiring more postop care.

Yet despite this complication, Dr. Price’s patients are gradually opting for DMEK; in November, more of his patients chose DMEK than DSEK for the first time ever.

This shift may decrease the strain on eye banks because DMEK is more efficient in its use of corneal donor tissue. According to a study, tissue considered unsuitable for penetrating keratoplasty or DSEK may be used for this procedure. Moreover, because the removal of Descemet’s membrane does not cause significant endothelial cell damage, donor corneas used for DMEK can be recycled for deep anterior lamellar keratoplasty procedures, the study authors said.

Surgical distinctions

While DMEK does not require the equipment that DSEK calls for, the technique is currently more time-consuming preoperatively, perioperatively and postoperatively.

Surgeons do not need to purchase a microkeratome or the blade that goes into the microkeratome, but they do require trypan blue to stain the donor cornea so that it will be visible when injected into the eye, Dr. Francis Price said. Harvesting the donor cornea takes more time, as does preparing the tissue that must be carefully dissected off the back, he said.

Additionally, unfolding the scrolled-up Descemet’s membrane after injection and discerning which side is endothelium and which is Descemet’s membrane may also be difficult, particularly for those surgeons who are new to performing the procedure.

“There is typically a learning curve with DMEK. … When DSEK was new and people were first learning how to do it, there was more of a tendency to lose the donor tissue, to maybe have to redo the graft, and so with DMEK, there is similarly a new learning curve,” Marianne O. Price, PhD, said.

Perioperatively, an air bubble pushes the corneal transplant into the correct position; however, some patients must return for a second or third injection to adhere the graft. While this postoperative complication remains difficult to avoid, Dr. Francis Price has cut substantial time off his donor preparations and surgery simply with experience.

“The other thing that helps with DMEK is to use older donors, donors who are over 40 years of age. If you do that, the tissue does not curl up as tight and it is much easier to handle inside of the eye,” he said.

DMEK’s improved visual outcomes may be modestly affected by the small diameter of the surgical incision. Dr. Francis Price performs a 2.8-mm incision for DMEK, the same size used for cataract surgery, as opposed to the 5-mm sutureless scleral tunnel used in DSEK.

When not recommended

Dr. Francis Price advises surgeons to avoid performing DMEK when a patient has a glaucoma tube shunt, a substantial iris defect or missing iris, or any sort of opening to the posterior chamber, because the thin DMEK graft may go through the tube or get lost posteriorly.

He also deters patients with a tube shunt from undergoing DMEK, because the donor graft may tumble around the anterior chamber during irrigation, possibly damaging the endothelium.

Patients with a deep anterior chamber, either due to a previous pars plana vitrectomy or genetics, pose a unique struggle; surgeons may have difficulty unrolling the DMEK implant and maintaining its flattened shape during air injection, Dr. Francis Price said. By contrast, a shallower anterior chamber leaves less space for the graft to fold back up again.

Transitioning, future plans

The Drs. Price conduct a CME course on DMEK that incorporates wet lab and surgical observation, providing participants with an instructional DVD and encouraging them to practice on research corneas as well as scheduling more time for surgery.

“The tissue behaves differently than people are accustomed to seeing and dealing with, so it takes a little time to recognize how to manipulate it efficiently,” Dr. Marianne Price said.

They make it a point to encourage collaborative dialogue during their CME courses and urge participants to also speak with a local eye bank.

“With DMEK, it is really important to have a discussion with your eye bank when you are first getting started, because there is a higher risk of losing the tissue during donor preparation,” Dr. Marianne Price said.

In the future, Dr. Francis Price foresees surgeons using a newer hybrid procedure called Descemet’s membrane automated endothelial keratoplasty (DMAEK), which incorporates aspects of both DMEK and DSEK. Only the central 6 mm of Descemet’s membrane is detached and then the overlying stroma is removed, leaving just an outer rim of stroma.

In DMAEK, the center of the corneal graft consists solely of Descemet’s membrane and endothelium, providing for the visual outcomes of DMEK, while the outer ring of stroma makes the graft easier to manipulate, resembling the handling of DSEK, Dr. Francis Price said. He cautioned that the donor preparation is more complex but said that eye bank technicians may be trained to prepare the tissue for the surgeon. The Indiana Lions Eye and Tissue Transplant Bank currently prepares DMAEK donor tissue.

In the meantime, however, DMEK remains the form of endothelial keratoplasty shown to most reliably achieve superior visual acuity.

“What we’re trying to do with DMEK is just help ensure people get the best vision possible,” Dr. Marianne Price said. – by Michelle Pagnani

References:

• Dapena I, Ham L, and Melles GR. Endothelial keratoplasty: DSEK/DSAEK or DMEK – the thinner the better? Curr Opin Ophthalmol. 2009;20(4):299-307.
• McCauley MB, Price MO, Fairchild KM, Price DA, Price FW. Prospective study of visual outcomes and endothelial survival with Descemet membrane automated endothelial keratoplasty. Cornea. 2011;30(3):315-319.
• Price MO, Giebel AW, Fairchild KM, Price FW. Descemet membrane endothelial keratoplasty: prospective multicenter study of visual and refractive outcomes and endothelial survival. Ophthalmology. 2009;116(12):2361-2368.

• Francis W. Price, MD, and Marianne O. Price, PhD, can be reached at the Cornea Research Foundation of America, 9002 N. Meridian St., Suite 212, Indianapolis, IN 46260; 317-814-2990; email: mprice@cornea.org.
• Disclosures: Dr. Francis Price and Dr. Marianne Price receive travel grants from Moria.