Donald Tan FRCS
Descemet’s membrane endothelial keratoplasty (DMEK) appears to offer the best option today for long-term graft survival for the management of endothelial dysfunction, but remains a challenging procedure, Donald Tan FRCS told delegates in his EuCornea Medal Lecture delivered at the 11th EuCornea Congress.
In a wide-ranging lecture, Dr Tan spoke about the paradigm shift in corneal transplantation techniques in recent years away from penetrating keratoplasty (PK) towards lamellar and endothelial keratoplasty approaches.
“Over the last 10-to-15 years we have seen a trend away from PK towards selective lamellar transplantation, where we do not replace the whole cornea in one stage, using techniques such as deep anterior lamellar keratoplasty (DALK), Descemet stripping automated endothelial keratoplasty (DSAEK) and DMEK. The main reason why we are transplanting less tissue is that physiologically there are less complications and reduced rejection rates with these lamellar approaches compared to PK,” he said.
National and international corneal transplant registries are useful in determining the real-world success rates of different techniques, said Dr Tan. For instance, data from the Australian Corneal Graft Registry showed that DMEK fared worse compared to PK in terms of graft survival.
“This might have something to do with the learning curve. The data showed that surgeons who performed more than 100 transplants got better results in terms of graft survival,” he said. Similar findings were also reported by studies based on the United Kingdom Transplant Registry.
“I think these unexpected results from the major registries show that selective lamellar keratoplasty results vary a lot. In the best-case scenario of a single-case series with an experienced surgeon who has mastered the technique, EK has major advantages over PK. However, in the real world the results may not be as good and there are many possible reasons for this including the learning curve with lamellar keratoplasty, variable surgical techniques and patient selection, among others,” he said.
The Singapore Corneal Transplant Registry (SCTR) provides prospective tracking on more than 5,000 transplants performed since 1991 and covers about 85% of all transplants in Singapore, said Dr Tan. Unlike other registries, the SCTR unified surgical protocols for each lamellar keratoplasty procedure with ongoing training of corneal surgeons to adopt new techniques and protocols and included a constant review of surgical results and long-term registry data.
“The upshot is that similar PK, DALK and DSEK, clinical protocols have evolved over time for our Asian phenotype. When we look at the graft survival rate out to 10 years both endothelial keratoplasty and anterior lamellar keratoplasty have significantly better graft survival compared to PK,” said Dr Tan.
Based on the SCTR, a recent study of patients who underwent DMEK, DSAEK and PK for Fuchs' endothelial corneal dystrophy (FECD) and bullous keratopathy (BK), showed that for both conditions, PK showed poorer five-year graft survival compared to EK. Interestingly, while DSAEK and DMEK showed very similar good five-year outcomes for FECD, for BK cases, DMEK was found to be superior to DSAEK.
The complications profile was also better in DMEK compared to DSAEK and PK, with less graft rejection and less risk of elevated IOP, said Dr Tan.
“The rate of secondary glaucoma was around 23% for both PK and DSAEK compared to 11% for DMEK. With less rejection for DMEK we were able to halve the amount of topical steroids being administered,” he said.
However, despite its advantages DMEK remains challenging surgery and not all cases of endothelial dysfunction are created equally, said Dr Tan.
“For instance, pseudophakic bullous keratopathy with co-morbidities such as peripheral anterior synechiae, dilated or distorted pupils, unstable IOLs, glaucoma blebs or tubes, open capsules or vitreous and abnormal anterior chambers make DMEK a much more challenging procedure,” he said.
To overcome some of these issues, Dr Tan said he has modified his DMEK technique over time to enhance surgical control and improve outcomes.
One such adaptation is the ‘pull-through endo-in’ DMEK technique, which involves the use of specialised forceps to hold on to a donor graft that has been precoiled endothelium-in, and pulling it into the anterior chamber for enhanced control and less risk of tissue eversion. The evolution of this technique involves redevelopment of the EndoGlide inserter device (Network Medical Products) originally designed for DSAEK, into a new model for DMEK, the DMEK EndoGlide device – in this approach, the DMEK graft is trifolded endothelium-in, into a narrower cartridge that enters a 2.6mm incision, and is pulled into the AC using EndoGlide forceps.
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, he said.
The latest innovation is to restore and reconstruct the anterior chamber, by performing synechiolysis of abnormal iris and scar tissue, and replacing the abnormal iris with the Humanoptics CustomFlex Artificial Iris.
“This all helps to restore a stable anterior chamber environment, essentially clearing the decks for DMEK to be performed more easily. With better surgical control, we can now perform more complex cases where anterior segment and chamber abnormalities may make conventional DMEK a real challenge,” he concluded.
Donald Tan: donald.tan.t.h@singhealth.com.sg
