Hybrid DMEK technique shows promise

New approach opens horizon for more challenging cases. 

Dermot McGrath

Posted: Tuesday, October 2, 2018

Donald Tan FRCS

The promising early results of a modified Descemet’s membrane endothelial keratoplasty (DMEK) technique may pave the way for the procedure being used in more challenging cases where DMEK would normally be contraindicated, Donald Tan FRCS told delegates attending the World Ophthalmology Congress in Barcelona.

“DMEK remains challenging surgery and it is clear that we need to continue to innovate and modify techniques to make the surgery easier and more predictable. The pull-through hybrid DMEK (H-DMEK) technique, which I have been using over the past few years, is one such promising approach. It provides good control of donor tissue and relatively good anterior chamber control, allowing one to perform DMEK in more challenging scenarios,” Dr Tan said.

The H-DMEK approach draws on the standard Descemet’s stripping automated endothelial keratoplasty (DSAEK) technique, Dr Tan said, but uses the DSAEK stromal tissue only as a carrier. After stripping Descemet’s membrane from the pre-cut tissue, it is replaced loosely on to the stroma and the graft is coiled into an EndoGlide (Network Medical Products) inserter. Dr Tan then pulls only the donor tissue into the anterior chamber, leaving the DSAEK stromal tissue behind in the EndoGlide chamber.

This approach enables better control of the donor tissue and results in reduced endothelial cell loss, enabling more complex cases to be treated using DMEK, said Dr Tan.

“Patient selection for conventional DMEK typically meant an intact cornea, iris and anterior chamber. This new approach means that we can now extend DMEK to more complex situations such as aphakia, blebs and valves, anterior chamber IOLS, prior vitrectomy, peripheral anterior synechiae, aniridia and prior failed grafts,” he said.

Dr Tan has now performed H-DMEK in more than 40 challenging cases and the results have been encouraging.

“The main goal is not 20/20 vision, as most of these eyes will never attain such visual acuity. I think that the main aim is the very low rejection rates. A lot of these are previous failed grafts, either penetrating keratoplasty (PK), or DSAEK. The advantage of DMEK over DSAEK in these cases is not having that thick DSAEK donor in the anterior chamber which encounters the iris, the IOL and other structural abnormalities. We are essentially isolating the endothelium from the rest of the anterior chamber structures, and the pull-through technique allows for better control of the donor during these more challenging procedures,” he said.

Dr Tan said that the benefits of using DMEK are evident in the graft survival rates for the Singapore Corneal Transplant Study, one of the largest such databases in the world. For Fuchs’ Dystrophy, the five- and 10-year survival rates for both DSAEK and DMEK are significantly better than PK. However, for pseudophakic bullous keratopathy, DMEK is clearly superior to both DSAEK and PK with three or four years’ follow-up, added Dr Tan.

While H-DMEK works well in challenging cases, there is nevertheless scope to further improve the procedure, said Dr Tan.

“There were two main problems with it: firstly, it still goes through a 4.5mm scleral tunnel wound, which is much larger than conventional DMEK incisions. There is also the additional cost of using pre-cut DSAEK stromal tissue, which is then discarded,” he said. The solution has been to use a new EndoGlide inserter, which works with a 2.65mm clear corneal tunnel incision and no longer requires pre-cut tissue.

“This works like standard DMEK, we insert the DMEK donor in a tri-folded configuration into the new DMEK EndoGlide chamber, which is narrower than the conventional EndoGlide DSAEK inserter, and which is now able to enter the eye a much smaller 2.65mm clear corneal incision. The anterior chamber maintainer is positioned nasally and the rest of the procedure is very similar – as the donor is pulled in, the cartridge is removed and we tap gently to close the wound. We just wait for the AC to slowly reform, and usually what happens is that the graft will automatically unfold in the right position. It works very smoothly,” he said.

Preliminary endothelial cell studies after about six cases performed with the latest method shows about 10% endothelial cell loss, concluded Dr Tan.