Descemets Stripping Endothelial Keratoplasty:  DMEK – corneal transplantation of the future

SNEC surgeons introduced Descemets Membrane Endothelial Keratoplasty (DMEK).  DMEK is a complex minimally invasive corneal transplantation technique, in which only a delicate sheet of corneal cells on a membrane 1/00 mm thick is transplanted, in patients whose corneas are cloudy from ageing processes or diseases.

SNEC’s Endothelial Keratoplasty Program

DMEK is a complex technique  of minimally-invasive, sutureless, keyhole surgery known as Endothelial Keratoplasty (EK).

Prior to this, DSAEK (Descemets Stripping Automated Endothelial Keratoplasty) was the major form of EK, which now constitutes 44% of all transplants performed in SNEC.  SNEC and SERI’s team of scientist introduced a surgical device, the Tan EndoGlide, in 2009, to perform DSAEK, in which the donor cornea is split into 2 layers, and only the inner layer, about a 10th of a millimeter thick, is transplanted onto the patient’s own cornea, which now does not need to be totally exchanged, unlike the older procedure of full thickness transplantation.

Licensed to a UK surgical company, the EndoGlide is a FDA approved device for EK to implant this donor tissue through a keyhole incision at the side of the cornea. It now has a safety record compared to other devices, and over 3,000 corneal transplants using this device have been performed around the world to date.

DMEK is however, a more complex form of EK, recently invented in Europe.  Instead of implanting a 10th mm thick donor, this new complex procedure now just replaces the actual damaged corneal endothelial cells which are on a membrane just 1/100th mm thick.

The major advance over current DSAEK is that patients now have the possibility of attaining 100% vision within a few weeks of surgery, i.e 6/6 vision, unlike DSAEK in which patients may often attain only 90-95% perfect vision.

DMEK surgery results in an eye in which it is almost impossible to tell that any transplant has been performed.  Early studies also suggest that while DSAEK surgery has much less risk of rejection than conventional full transplants, DMEK now appears to have even less risk of rejection than DSAEK.

The current downside of DMEK is that it is an extremely difficult form of surgery, and only 3 main centres in the US and Europe regularly performing this operation.  The ultra- thin membrane containing the corneal cells to be transplanted is highly delicate:  holding or touching the membrane, which naturally wrinkles and scrolls up into a tight roll, damages the corneal cells, and surgeons may have to spend over an hour trying to unscroll and unwrinkled the membrane and attach it into position onto the inner surface of the patient’s own cornea. 

In Asia, Prof Tan introduced and performed the DMEK procedure in SNEC 12 months ago, with success.Recognizing that the surgical technique was highly complicated and just too difficult for most surgeons, he and his team at SERI worked in the laboratory to develop a new surgical technique which was safer, and easier to perform.

After extensive laboratory studies under SERI’s Eye Flagship TCR (Translational Clinical Research) grant from the National Research Foundation (NRF), Prof Tan and A/Prof Jodhbir Mehta developed a new DMEK technique and Prof Tan recently performed DMEK on a patient using this method, resulting in 6/6 vision within days.  The risk of transplant rejection has also been greatly reduced to near zero.   This method, which includes a new DMEK surgical insertion device is now being patented.

SNEC – An Asian Centre for Development of Corneal Transplantation

SNEC has been introducing new forms of corneal transplantation in Asia, with well over 200 scientific publications in the corneal field over the last 2 decades.   In 2007, Professor Tan formed the Asia Cornea Society (ACS), a professional society of corneal specialists with representation from India, China, Taiwan, Korea, Thailand and the Philippines on its ACS Council, with Professor Tan as its President.  Headquartered in Singapore, ACS also formed the Association of Eye Banks of Asia (AEBA) which spearheads eye banking development in Asia.

ACS has formal affiliations with the 2 other major international corneal societies, the US-based Cornea Society, and the European-based EuCornea. In 2010, Professor Tan was elected as the President-Elect of the US-based Cornea Society.

SNEC’s corneal surgeons perform 85% of all the 350 transplants a year here in Singapore.
Of these, slightly less than half are foreign patients from Asia and the Middle East, who come for the latest forms of corneal transplantation and keratoprosthesis surgery. Thanks to the Singapore Eye Bank’s success in procuring corneas from local donors, waiting list for corneas for surgery is only a couple of weeks, while any immediate shortfall in corneas is made up by the recent setting up of the National Eye Bank of Sri Lanka by SEB, which also provides corneas for our foreign patients who come to Singapore for the new forms of corneal surgery.

Singapore corneal and refractive surgeons making an impact at European Corneal and Refractive Meeting

SNEC’s team of corneal and refractive surgeons have just returned from the Joint EuCornea Meeting and European Society of Cataract and Refractive Surgery (ESCRS) Meeting in Vienna, Austria, where our 6 surgeons presented 12 papers and 2 courses on various corneal and refractive surgery topics, and the team also won a video prize for innovative corneal and refractive surgery.  Professor Tan was invited to deliver a EuCornea Keynote Lecture on changing trends in corneal transplantation and artificial cornea (keratoprosthesis) surgery in Asia, which focused on Singapore leading the field in developing new advances in corneal transplantation and keratoprosthesis surgery.

Improvements in corneal graft survival and outcomes with the new forms of corneal transplantation
SNEC and SEB have monitored transplant results and success in the last 2 decades, with the ongoing Singapore Corneal Transplant Study (SCTS), which now has over 3,300 transplants in its database dating back to 1991, and yearly audits of transplants in SNEC. The most recent transplant statistics show that DSAEK now has a 99% 1 year survival rate, surpassing all other results internationally. This is largely due to the use of the Tan EndoGlide, which has been shown to reduce corneal endothelial cell loss by as much as 50% compared to other forms of DSAEK surgery.  In contrast, conventional penetrating keratoplasty (PK), which now makes up a much smaller percentage of cases (reserved now only for the most severe cases of corneal disease in which EK is not possible), has a success rate of 82.4%.  The other major form of transplant performed, Deep Anterior Lamellar Keratoplasty (DALK), also has a highly improved success rate of 92.7%, far surpassing PK success.    Most of these improvements in success rates in DSAEK and DALK are because of the significant reduction in transplant rejection, which is now zero risk in DALK and only about 1% in DSAEK. 

SNEC is also a centre for artificial cornea (keratoprosthesis) surgery in Asia.

In 2004, SNEC embarked on its “tooth-in-eye” keratoprosthesis program, by introducing the highly complex Osteo-Odonto Keratoprosthesis (OOKP) surgery to SE Asia.  Since then, SNEC has been one of the leading centres for OOKP surgery worldwide, and its multidisciplinary team of nearly 20 eye surgeons, dental surgeons and radiologists have performed OOKP surgery in 40 patients from 13 countries from Asia, Australia, the Middle East, and also from the US.  The Singapore OOKP Study (SOS) is pleased to report a 100% success rate in device retention to date, which is unsurpassed by the other few groups performing OOKP surgery in Europe and Asia.

In addition to the OOKP procedure, SNEC has also been performing and studying other forms of artificial corneas.  One of these is the Boston Type 1 Keratoprosthesis, of which 4 cases have been performed in SNEC, by both Professor Donald Tan and Dr Leonard Ang.   SNEC has been quite cautious to adopt the Boston KPro, because of controversies regarding the long-term success of this device and the potentially high rate of complications.   Of our 4 cases, 2 of which have only recently been performed, and hence have very short follow-ups, we have had one failure due to retinal complications resulting in total visual loss.  Our other 3 cases are doing well, however. 
The Boston KPro is best used only in cases of multiple previous corneal graft failures due to transplant rejection, and is contraindicated in the more severe cases of corneal blindness, for which the OOKP is the gold standard device.  This indication is also shrinking, as many surgeons are now turning to using DSAEK to treat previous failed grafts, as there is much less rejection with DSAEK surgery compared to performing another PK.  Although in recent years, there has been a reduction of complications with the Boston device, due to minor changes in the device, and the life-time use of antibiotics and a contact lens over the device, there are still concerns about the relatively high rate of complications.

A most recent paper published this year, detailing the longer term success of the Boston KPro from University of California, Davies, involving 40 cases which has surgery in the last 6 years, showed that 55% of cases developed inflammatory scarring behind the implant, affecting vision, 27.5% developed sight-threatening glaucoma due to the surgery, 15% developed serious melting of the cornea around the device, 17.5% had to have the device removed or replaced, 12.5% developed serious eye infection (endophthalmitis), and 57% required major surgery to treat postoperative complications, and as a result a significant number of patient lost vision overall.

Other recent studies have shown that although new changes in medical treatment after Boston KPro surgery, which include the lifelong use of antibiotic eye drops and contact lenses, while certainly reducing the risk of bacterial infections, may make the patient more prone to developing antibiotic resistance and especially fungal infections which has now been reported in Boston cases.  Fungal infections are far more common in Asia than in the US (where the Boston KPro has been used most), and the current consensus of Asian surgeons has been to exercise major caution in using the Boston KPro in tropical climates, as Indian surgeons have already reported higher rates of infection.

Finally, the Boston KPro remains highly controversial for use in cases of dry eye and inflammatory corneal diseases, such as chemical burns or Stevens Johnson syndrome, and published studies show that these conditions carry the highest risk of failure with the Boston KPro.  For these cases, most surgeons today feel that OOKP remains the ideal treatment, and while some surgeons feel that the Boston KPro may be used in milder cases, many more feel that this higher risk group should not have Boston KPro surgery.

These results clearly show that Boston KPro surgery does have significant risks, and at SNEC we reserve this form of device only for a very small handful of cases who have failed at least several transplants, or are not suitable for OOKP surgery, which appears to carry less postoperative risks in the long term, and we will continue to very carefully select these few patients who would require lifelong medication and follow-up to prevent visual loss.

Press Release by Singapore National Eye Centre
For more information, please contact:
Ravi Chandran
Corporate Communications
Singapore National Eye Centre
Email: ravi.chandran@snec.com.sg