Dr Jacqueline Beltz
Corneal specialist and senior lecturer, Centre For Eye Research Australia, Royal Victorian Eye and Ear Hospital, and Eye Surgery Associates, Melbourne
Over the past decade, endothelial keratoplasty (EK) has replaced penetrating keratoplasty (PK) as the treatment of choice for the surgical management of corneal endothelial failure.1 In 2012, 42.6 per cent of all corneal transplants performed in Victoria were EKs. That number has been steadily increasing since 2008, when it represented only 10.3 per cent of treatments.2
Of the several advantages EK has over PK, perhaps the most important is the increased amount of intra- and post-operative safety it affords. In addition, visual results for EK patients are faster and better than for those undergoing PK. There is an absence of induced astigmatism, which is often seen after PK, and an absence of other suture-related complications.1 Significantly, the incidence of rejection is reduced with EK3 and this may have a positive impact on the long-term survival.
The concept of targeted replacement of the corneal endothelium was first published in 1956 by Charles Tillett,4 but it was not until Gerrit Melles published in 1998 that this concept began to take hold.5 Melles developed a technique called posterior lamellar keratoplasty (PLK) that was later refined by Mark Terry to be termed deep lamellar endothelial keratoplasty (DLEK).6 DLEK was a promising procedure but the technique was somewhat difficult as it involved an intraocular trephination and an inlay of donor tissue.
In 2002, Melles again refined the technique to be an onlay procedure, in which additional tissue was added to the inner surface of the cornea.7 This procedure was later named Descemet's stripping endothelial keratoplasty (DSEK), by Francis Price.8 Corneal surgeons around the world adopted this technique rapidly, as early results were extremely promising.9
DSEK involved a manual preparation of donor tissue, such that just the endothelium, Descemet's membrane (DM) and posterior stroma could be transplanted. Mark Gorovoy in 200410 described the automated preparation of donor tissue, using a microkeratome, similar to the microkeratomes previously used during corneal refractive surgery. As a consequence, DSAEK was developed and it is this technique that forms the gold standard of EK today.
The most common indications for EK are Fuchs' corneal endothelial dystrophy, pseudophakic bullous keratopathy, and failed PK, although the surgery is appropriate for any form of endothelial failure. For DSAEK, donor tissue is prepared by removing the anterior portion with the microkeratome, leaving a smooth surface that will later form the interface between the donor and the host.
Tissue may be `precut' in the eyebank and provided to the surgeon, or may be prepared in the operating room by the surgeon just prior to the procedure. The surgery is most commonly performed under local anaesthesia, and involves removal of the diseased endothelium and DM from the host prior to insertion of the donor tissue. The eye is then filled with air, to provide tamponade and allow the smooth surfaces of the donor and host cornea to stick together without sutures. (Figure 1)
Figure 1. Surgical steps of DSAEK. A: Descemet membrane (DM) is
scored under air. B: DM is ‘stripped’ or removed. C: Inferior iridotomy
is created to avoid pupil block glaucoma. D: Prepared donor tissue
is loaded onto a Busin Glide. E: Donor tissue is pulled into the eye.
F: Air is injected underneath the donor tissue and surgical
wounds are sutured.
Results of DSAEK have consistently been reported as excellent (Figure 2); 75 per cent of eyes without comorbidities have achieved spectacle-corrected acuity of 6/9 or better at one year, increasing to 90.7 per cent by three years.11
In a quest to further improve visual outcomes, Gerrit Melles again developed a new technique. Descemet's membrane endothelial keratoplasty (DMEK) was described in 200612 and involves the insertion of just DM and endothelium of the host cornea.
Figure 2. (Left) Preoperative appearance of an eye with marked endothelial failure secondary to Fuchs’ endothelial dystrophy.
(Right) Three months postoperatively, the patient already has 6/9 visual acuity.
Visual results of DMEK were found to be even better than DSAEK, with 98 per cent reported to achieve 6/9 or better at one year.13 However, DMEK is challenging surgery and the complication rate may be unacceptably high.14 Tissue may be lost during the preparation phase, and unfolding the tissue inside the eye is perilous. The incidence of detachment requiring repeat air injection is much higher than for DSAEK, and tissue loss and primary failure occur more commonly.14
In attempt to achieve the visual results of DMEK, with the surgical ease of DSAEK, Massimo Busin developed ultrathin (UT) DSAEK.15 UT DSAEK involves the use of a very thin donor tissue, prepared by a double pass with the microkeratome (Figure 3). Results of UT-DSAEK were published this year,15 with 95 per cent of patients without comorbidities achieving 6/9 vision by 12 months and 100 per cent by two years. The complication rate was much lower in the 280 cases reported, with a detachment rate of less than four per cent, compared to as much as 68 per cent reported for DMEK.15
Figure 3. (Left) Postoperative appearance of an eye three months post ultrathin DSAEK. The relative thickness of the donor compared to the host cornea can
be seen in the slit. (Right) Anterior segment ocular coherence tomography may be used to ensure attachment of the donor and measure the central
thickness, in this case just 52 µm.
It has been reported that the incidence of endothelial rejection is much less in DSAEK than PK,3 occurring in about 12 per cent of cases by year two. The incidence of rejection after DMEK is just one per cent at two years,3 and UT-DSAEK, perhaps as expected, falls between at three per cent.15 While it is too early in the development of these new techniques to comment on the comparative survival, the initial endothelial cell loss is similar across all three groups15 and is likely to be the most important predictor.
As we await the long-term data on all of these forms of EK, new techniques are in development. Stem cell culture of endothelial cells and medical treatments for endothelial failure may well be a reality in the future. Hopefully, there will be many more exciting developments to come in this field but the one consistent message is that PK is no longer indicated for the treatment of corneal endothelial failure.
References available on request. Email firstname.lastname@example.org, Subject: Beltz Endothelial keratoplasty