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Endothelial keratoplasty: where are we?

The first successful human corneal transplant was performed more than a hundred years ago in 1905 by Austrian born Eduard Zirm, and the first successful lamellar keratoplasty (LK) for visual improvement was performed by Arthur von Hippel in the last quarter of the nineteenth century. Penetrating keratoplasty (PK) has long been the standard procedure for treating corneal diseases and has changed from the initial square grafts of Castroviejo to the current circular ones. Although PK allows tissue transfer with the maintenance of good endothelial function, the procedure can suffer from unpredictable surface topography, suture-related complications and poor wound strength. Recent advances in corneal surgery permit component surgery of the cornea, with selective replacement of diseased tissue. Such surgery has been made possible by recent improvements in surgical technique and advances in instrumentation, including the artificial anterior chamber and microkeratome. The last decade has seen a resurgence of interest in the field of LK, and in particular, posterior lamellar graft for endothelial dysfunction – endothelial keratoplasty (EK). Medline search on ‘EK’ alone in mid 2008 yielded more than 50 articles. Endothelial keratoplasty in its modern form was pioneered by Gerrit Melles from the Netherlands. He was the first surgeon to perform a scleral-limbal procedure termed posterior lamellar keratoplasty (PLK) in humans. The procedure was innovative and promising, but technically demanding and required the apposition of two manually dissected surfaces, thereby increasing the potential for interface opacity and glare. Terry et al. later modified the instrumentation and surgical technique and popularized this procedure in the USA. This procedure, via a 9.0 mm incision was renamed as deep lamellar endothelial keratoplasty (DLEK). In 2002, Melles reduced the incision size to 5 mm and advocated that the tissue be folded in half during insertion. However, the resultant loss of endothelial cell density was noted to be greater than his large incision series. In 2005, Terry similarly introduced a small-incision DLEK technique with a 5 mm scleral incision. Shortand intermediate-term follow up of these patients revealed encouraging results for induced astigmatism, alteration in corneal contour and stability of refraction, visual acuity and endothelial cell count. These results were comparable with standard full-thickness penetrating keratoplasty procedures. In an attempt to eliminate the need to perform demanding stromal dissection and to improve the smoothness of the recipient corneal surface, Melles described Descemetorhexis, – stripping only the Descemet’s membrane from the recipient and apposing the donor tissue directly onto the posterior surface. This resulted in a simpler procedure in comparison to PLK and DLEK and Descemet stripping endothelial keratoplasty (DSEK – manual/DSAEK – automated form) is currently the most popular EK procedure and has been developed based on the above concept. As with any evolving technique, a few controversies exist with this procedure – including its applicability, the optimal width of the scleral incision, how the donor tissue should be folded (if at all) and preference of ‘push’ or ‘pull’ insertion techniques. First, in localities where graft donation rates are low, not infrequently, by the time a graft is available to patients with bullous keratopathy, the ocular surface is already scarred, secondary to the chronic repeated rupture of bullae. In such cases, in addition to the potential postoperative interface haze that is common to all DSEK/ DSAEK procedures, the residual superficial opacification will limit the visual potential. In addition to graft scarcity, cost may be another issue in localities without access to quality pre-cut tissue from eye banks. The artificial chamber is much cheaper than the automated lamellar microkeratome unit or femtosecond laser, but still expensive for the corneal surgeon with budget constraints who is not in institutional practice. Eye banks in affluent societies may apply the femtosecond laser to dissect a thin, uniform thickness posterior lamellar disk of pre-cut donor tissue. However, the potential improved disc adherence and long-term visual benefits will need to be studied. The indications and, more importantly, the relative or absolute contradictions are not yet well-defined scientifically. In any small eye with a shallow anterior chamber (such as Chinese or oriental eyes), it is technically more difficult to insert and unfold the donor in the anterior chamber, especially if an 8.5 mm donor is used. In cases with significant peripheral anterior synechiae, it is probably best to opt for a large incision technique obviating the need to fold and unfold the donor so as to minimize trauma to the endothelium. A smaller donor size may also be considered, but this will be at the expense of total number of endothelial cells transplanted to the recipient. The optimal size of the scleral incision is another area of contention. Smaller incisions preserve the recipient corneal contour better and result in less induced astigmatism. However, one inherent problem associated with small incision EK, regardless of how the donor is prepared, is the unavoidable endothelial trauma associated with grasping, folding and squeezing the donor tissue into the anterior chamber. The small incision DLEK technique results in a significantly higher endothelial cell loss at 1 and 2 years than that after large incision DLEK surgery (mean of 43% vs. 27% loss at 2 years after DLEK). EK insertion forceps resulted in a reproducible pattern of endothelial damage in an in vitro study. Thus patients should be informed of the pros and cons of a large versus small incision EK procedure. In order to circumvent this inherent endothelial trauma, nonfolding techniques devised for pulling the donor through the small incision include the use of cartridge devices, modified sheet glide or custom-made devices such as Busin Glide Spatula (Moria SA, France). In situations where it may be difficult to maintain a reasonable anterior chamber depth during placement of donor into the eye or unfolding of the donor ‘taco’, an anterior chamber maintainer may also be considered. Whether pulling the graft into the eye with sutures or forceps produces less long-term endothelial loss remains to be determined. Clinical and Experimental Ophthalmology 2008; 36: 707–708 doi: 10.1111/j.1442-9071.2008.01883.x