Alvin L. Young, FCOphth, FRCOphth
Tae-Im Kim, MD
In the January 2013 issue of EyeWorld, cornea surgeons came together to compare thin Descemet's stripping automated endothelial keratoplasty and Descemet's membrane endothelial keratoplasty as options for endothelial keratoplasty procedures. "DSEK involves a transplant of the back layers of a donor cornea into a patient's eye. This technique offers a certain ease because it has been the procedure of choice for many years. DSAEK is the automated version of this procedure, which uses a machine to cut tissue," the
"DMEK, on the other hand, uses extremely thin donor tissue, with a better chance of restoring good vision to the patient. However, surgeons using this technique often experience obstacles with handling the donor tissue because of how fragile the grafts can be. Recently, thin DSAEK has offered an alternative to the other two techniques,
utilizing the ease of DSAEK with thinner grafts."
In our sister publication,
EyeWorld Asia-Pacific, Alvin L. Young, FCOphth, FRCOphth, of Hong Kong, and Tae-Im Kim, MD, of Korea, shared their thoughts on the techniques.
Dr. Young: There has been a major paradigm shift in the field of corneal transplantation since the advent of modern endothelial keratoplasty. The popularity of the technique has been widespread. One of the main reasons for the immense positive
response toward this surgery is the relative ease of performing the whole procedure. In the earlier days, DLEK (deep lamellar endothelial
keratoplasty) surgery was technically more demanding and difficult, hence subsequently replaced by DSEK. Most corneal surgeons are now using DSEK or DSAEK depending upon the availability of an automated microkeratome or precut tissue in their setup. More recently, the focus of discussion has shifted to the use of thin donor lenticules, consequently bringing ultra-thin DSAEK and DMEK to the forefront. However, there are certain pertinent issues that need to be considered before these relatively new surgeries can be adopted. Obtaining a thin cut donor lenticule or only the Descemet's membrane (in DMEK) can be a difficult proposition resulting in inadvertent wastage of human tissue, which certainly is not affordable in countries where there is an obvious dearth of donor corneas. In addition, using two
microkeratome heads for ultra-thin DSAEK lenticules would impose extra financial burden in less affluent economies and especially when these heads are disposable. Furthermore, Asian eyes are commonly found to have shallow anterior chambers, limiting the freedom of movement inside the eye when the surgeon is trying to "center" or orientate a very thin donor lenticule. The situation becomes worse if another intervention, such as refloating the graft, is required.
At the moment, there is still a relative scarcity of reports on excellent visual outcomes after thin lenticule DSAEK or DMEK. In the absence of any long-term comparative clinical trials, one needs to weigh the benefits and risks that are local in terms of graft availability, preparation, wastage rate, patient factors, and surgeons' expertise in deciding whether or not to adopt thin lenticule DSAEK, DMEK, or to "settle" with a fairly confidently attainable visual acuity of 20/30 with conventional DSEK/DSAEK.
As mentioned earlier, the ease of performing a conventional DSEK/ DSAEK is one of the highlights of this surgery. Further research and refinement in innovation of better technology and techniques aimed at the better and safer preparation of donor material (perhaps best served by an eye bank), surgical handling of donor and its insertion are warranted.
Dr. Kim: Over the years, keratoplasty has been developed and has recently diversified from penetrating keratoplasty (PK) to refined lamellar keratoplasty. Anterior stromal corneal abnormality was corrected by lamellar keratoplasty or deep lamellar keratoplasty using various techniques. The posterior part of the cornea abnormality, mainly related to endothelial dysfunction, was treated by selective replacement of diseased recipient endothelium via Descemet's stripping endothelial keratoplasty (DSEK) or Descemet's membrane endothelial keratoplasty (DMEK).
In Descemet's stripping automated endothelial keratoplasty (DSAEK), the outer layers of the cornea are skimmed off using a mechanical microkeratome, leaving a very thin layer of stromal fibers supporting the inner Descemet's membrane and the endothelial cells. The bottom 20% of divided cornea is used for DSAEK and the top 80% can be used as donor tissue for anterior lamellar transplants. Automated cutting improves the donor preparation procedure with smooth cut surfaces and predictable thickness. The
quality of the visual recovery after DSAEK is generally better than that achieved by a penetrating graft. The stability of the refraction and rapid visual rehabilitation are major advantages of all endothelial keratoplasty techniques. However, because of the remaining stromal tissue and the interface, DSAEK still shows suboptimal visual acuity and relatively slow visual rehabilitation.
Also, expensive equipment and a drop in donor endothelial cell density in the early postoperative period remain drawbacks. In an attempt to overcome these limitations, pioneering corneal surgeons have invented the donor preparation surgical
procedure to minimize the remaining stromal tissue. The donor
Descemet's membrane is scored and trephined from the endothelial side without any donor corneal stroma. Also, there is no need for an artificial anterior chamber or a microkeratome in the donor tissue preparation. This DMEK procedure can accelerate the recovery and increase the chance of obtaining 20/20 vision postoperatively. Moreover, the rate of rejection with DSAEK may be successfully reduced by minimizing antigen exposure. However, DMEK is a more challenging procedure than established DSAEK surgery. DMEK has the potential of inflicting damage to the donor endothelium and Descemet's membrane during the surgical preparation and introduction into the anterior chamber. Moreover, unfolding procedure and re-attachment techniques are more challenging.
The pros and cons of each advanced posterior lamellar replacement procedure have been proven. However, apart from the results of each procedure, an important factor in selecting particular surgical technique is the experience of the operating surgeon.
Even though the surgical outcome of DMEK is superior in many aspects, the surgeon with lack of surgical experience and limited skills may elect not to choose DMEK.
Too aggressive trial of a difficult procedure may induce significant added cost to this surgery.
In the near future, better surgical techniques and instruments will be introduced to facilitate DMEK procedure without jeopardizing the surgical outcome. Until then, DSAEK will account for a great part of posterior lamellar procedures.
Editors' note: Dr. Young acknowledged the assistance of Dr. Vishal Jhanji in writing his comments. Dr. Young has no financial interests related to this article. Dr. Kim has no financial
interests related to this article.