Descemet’s Stripping Automated Endothelial Keratoplasty: Different Strokes Rasik B Vajpayee, Namrata Sharma, Vishal Jhanji, Dermot Cassidy
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1Evolution, Indications, Preoperative Evaluation and Eye Banking
  1. Evolution of Endothelial Keratoplasty
  2. Indications and Contraindications of Descemet's Stripping Automated Endothelial Keratoplasty
  3. Preoperative Evaluation of Descemet's Stripping Automated Endothelial Keratoplasty
  4. Eye Banking Issues Related to Procurement of Donor Cornea
2

Evolution of Endothelial Keratoplasty1

Dermot Cassidy,
Namrata Sharma,
Rasik B Vajpayee
Endothelial keratoplasty has emerged over the last decade as a successful alternative to penetrating keratoplasty in the management of corneal endothelial disorders. This development is the most recent incarnation in a process of evolution of corneal transplantation surgery that has been underway for over a century:
‘…. Eduard Konrad Zirm produced, after decades of stellar theory but mediocre clinical results, the first truly successful graft: a small but brilliant torch to inspire his successors.’1
It was in 1905 that the Czech Eduard Zirm (Fig. 1) performed the world's first successful human corneal transplant, transplanting a donor cornea from the enucleated eye of an 11-year-old into a recipient who had sustained severe alkali burns.2 Since this first successful human corneal transplant, there have been numerous advances that have led to improved outcomes and expansion of indications for corneal transplantation (Table 1). Key among these advances includes the introduction of antibiotics in the 1940s, developments of microsurgical techniques and instruments in the 1950s, universal adoption of topical steroids in the 1970s and advances in corneal preservation and eye banking.
In the three decades following the success of Zirm's initial penetrating keratoplasty, corneal grafting was performed using donor tissue from enucleated eyes of living donors. Ground-breaking work by the Russian Vladimir Filatov in the mid-1930s ushered in the use of fresh cadaver corneas as well as highlighting the importance of direct corneal suturing and of protecting intraocular tissues during host trephination.3,4
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Fig. 1: Eduard Zirm
Table 1   Landmarks in endothelial keratoplasty
Year
Surgeon
Landmark
1905
Eduard Zirm
World's first successful human corneal transplant
1956
CW Tillett
First described selectively transplanting only posterior layers
1998
Gerrit Melles
Posterior lamellar keratoplasty (PLK)
2000
Mark Terry
Deep lamellar endothelial keratoplasty (DLEK)
2005
Francis Price
Descemet's stripping endothelial keratoplasty (DSEK)
2006
Mark Gorovoy
Descemet's stripping automated endothelial keratoplasty (DSAEK)
2006
Massimo Busin
Ultrathin Descemet's stripping automated endothelial keratoplasty (DSAEK)
2006
Gerritt Melles
Descemet's membrane endothelial keratoplasty (DMEK)
4
Today Filatov is considered the ‘grandfather’ of modern eye banking. Fresh corneal tissue was used from that period up until another break-through in corneal preservation occurred in the mid-1970s with the introduction of McCarey-Kaufman medium, allowing for tissue to be stored for up to 4 days at 4°C.5
While lamellar keratoplasty has undergone a very recent renaissance, the concept of selective replacement of diseased layers of the cornea can in fact be traced back to Arthur von Hippel in 1886, who is credited with performing the first partially successful lamellar transplant in that year.6 It was Tillett in the mid-1900s who first described selectively transplanting only the posterior layers of the cornea in a single case.7 He published an account of a procedure involving a 180-degree incision that allowed access for trephination of the posterior recipient cornea and subsequent insertion of manually dissected donor tissue. Sutures were required both to fixate the donor tissue as well to seal the corneal incision. This technique was called posterior lamellar keratoplasty (PLK).
Later, endokeratoplasty was described by Polack, who performed a technique where he first fashioned an anterior corneal flap that was retracted to trephine the recipient posterior stroma, and then positioned a posterior lamellar donor corneal button. The original anterior flap was repositioned and sutured into place.8 Jones et al further improved the technique with the description of using a microkeratome, and the surgery was named microkeratome-assisted posterior keratoplasty.9 The posterior approach to endokeratoplasty was described in a rabbit model by Ko et al. They used a scleral incision to access the endothelium and following removal they replaced it with a donor tissue.10
It was then not until 1998 that Gerritt Melles, using a similar technique, revived the concept of selective endothelial keratoplasty (Fig. 2). He described PLK using a 9.0 mm scleral tunnel incision with creation of a stromal pocket of approximately 50 percent depth across the cornea. The central posterior host cornea was trephined using a custom-made 7 to 8 mm flat trephine and a downsized donor posterior lamellar graft of 7 to 8 mm diameter was trephined and inserted using a spoon-shaped glide. The donor was then positioned against bare host stroma using air.1113 The use of a smaller donor lenticule diameter relative to the excised recipient bed helped to prevent the donor tissue from sliding out of position.
Since that time, a number of further refinements have occurred. A variation of the Melles PLK technique was described by Mark Terry (Fig. 3) and Ousley several years later and termed deep lamellar endothelial keratoplasty (DLEK).14,15
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Fig. 2: Gerrit Melles
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Fig. 3: Mark Terry
This modification undertook manual donor dissection with the aid of an artificial anterior chamber, dissected the recipient lamellar bed under viscoelastic rather than air, and advocated extending the recipient dissection beyond the area to be excised while matching the diameter of the trephined donor lenticule to the 5recipient excision diameter. This allowed for tucking the edges of the donor tissue into the lamellar pocket of the recipient to aid fixation.16 In 2002, Melles developed a small-incision PLK technique, inserting a 9.0 mm folded donor through a 5.0 mm self-sealing scleral incision.17,18 This was popularized in the United States by Mark Terry as small-incision DLEK.19 The small 5 mm incision required the donor posterior lamellar graft to be excised using intrastromal Cindy scissors in a freehand fashion, using a circular mark on the epithelial surface as a guide.
Crucially, in 2003, Melles went on to describe the technique of ‘descemetorhexis’ – involving stripping of the recipient Descemet membrane from the host cornea – thus doing away with the complicated recipient lamellar dissection that was required for the PLK/DLEK procedure.20 This made the procedure easier, safer with regards to reducing the potential for trauma to the anterior chamber and crystalline lens, and generated a superior smooth optical interface. Francis Price (Fig. 4) popularized this modification in the United States as Descemet's stripping with endothelial keratoplasty (DSEK).21 Several months later, Mark Gorovoy (Fig. 5) utilized refinements of the microkeratome to ‘automate’ the preparation of the donor tissue (consisting of corneal endothelium, Descemet's membrane and a small amount of posterior stroma), giving rise to Descemet's Stripping Automated Endothelial Keratoplasty (DSAEK).22 The acronyms DSEK and DSAEK are now largely used interchangeably in the literature, as they are in the text that follows unless otherwise indicated.
While the description of the descemetorhexis was a key development that progressed the success and uptake of DSAEK, devising a reproducible mode of insertion of the donor lenticule that minimizes trauma to donor endothelial cells has also been fundamental to the widespread adoption and success of DSAEK. As described earlier, Melles originally employed a spoon-shaped glide that carried the posterior donor lenticule on a layer of viscoelastic through a 9 mm incision. Later, he described folding the donor lenticule for insertion through a 5 mm incision with the aid of forceps.17 Other donor insertion techniques that have been and are still utilized include the use of a cartridge injection device,23 sheets glide-insertion technique,24,25 a suture pull-through technique26,27 and the increasingly widely adopted use of a purpose-built glide that allows introduction of the donor lenticule through a corneoscleral wound as small as 3.5 mm.28 This aspect of the technique remains very much in evolution and a series of subsequent chapters are dedicated to highlighting the specific techniques of a number of the leading DSAEK surgeons around the world. Once unfolded inside the anterior chamber, the donor tissue is positioned against the bare recipient stroma, positioned and fixated with the aid of an intracameral air bubble.
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Fig. 4: Francis Price
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Fig. 5: Mark Gorovoy
In utilizing a corneoscleral wound and relying on the endothelial pump function to generate adherence of the donor button without the need of sutures, the principal advantage of the technique was realized—namely the elimination of corneal surface sutures and the associated ocular morbidities, such as induced astigmatism, suture-related infections and prolonged visual rehabilitation.6
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Fig. 6: Massimo Busin
In DSAEK of course, not only are sutures eliminated in the majority of cases,29 but nor is the donor tissue held in place by the recessed edge of an excised recipient bed or tucked into a peripheral stromal pocket to aid donor fixation. This challenge of minimizing donor dislocation remains another of the most challenging areas in the evolution of DSAEK.
In order to get optimal visual results, Massimo Busin (Fig. 6) developed the concept of DSAEK is now the procedure of choice for endothelial dysfunction. Over the period 2005 to 2008, the Eye Bank Association of America reports an explosion in the number of endothelial transplants from 1429 to 17,468.30 Over the same period the number of penetrating keraoplasties has decreased from 45,821 to 32,524. While keratoconus was the leading indication for penetrating keratoplasty in the United States in 2008, when one takes bullous keratopathy and Fuchs’ endothelial dystrophy together, patients with endothelial dysfunction make up the largest indication for corneal transplantation at the current time. The DSAEK accounted for approximately 43 percent of all corneal grafts performed in the United States in 2009.31
This technique continues to evolve, and future incarnations will benefit more patients and surgeons.
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