Endothelial keratoplasty: historical perspectives, current techniques, future directions Linda Rose,* MD, PhD; Clare Kelliher,† MB, MSc; Albert S. Jun,† MD, PhD ABSTRACT • RÉSUMÉ Endothelial keratoplasty (EK) has recently emerged as an alternative to penetrating keratoplasty (PK) for patients with endothelial diseases, including Fuchs’ endothelial dystrophy, pseudophakic bullous keratopathy, and corneal graft failure. EK provides distinct advantages over PK, in that it is a less invasive procedure and leads to more rapid recovery of vision. Additionally, this procedure does not require long-term corneal sutures, eliminating problems with suture breakage, suture abscesses, astigmatism, and wound dehiscence. Disadvantages of EK include the need for specially prepared donor tissue and additional surgeon training or experience. In this review we discuss the history of EK, recent advances that have led to its widespread use, limits and complications of the procedure, and areas for future improvement. La kératoplastie endothéliale (KE) offre depuis peu une solution de rechange pour la kéroplastie pénétrante (KP) aux patients qui ont une maladie endothéliale, y compris la dystrophie endothéliale de Fuchs, la kératopathie bulleuse pseudophakique et l’échec de la greffe cornéenne. La KE offre nettement des avantages sur la KP en tant que procédure moins invasive menant à un recouvrement plus rapide de la vision. En outre, elle ne requiert pas de sutures cornéennes à long terme, ce qui élimine les problèmes de bris de suture, d’abcès de suture, d’astigmatisme et de désunion des sutures de plaie. Les inconvénients de la KE comprennent le besoin de préparation particulière du tissu du donateur ainsi que de formation ou d’expérience additionnelle du chirurgien. La présente étude porte aussi sur l’historique de la KE, les progrès récents qui en ont répandu l’usage, les limites et complications de la procédure et les secteurs d’améliorations futures.
he current interest in endothelial keratoplasty (EK) began with the report of a “partial cornea transplant” in 1998, in which Melles et al.1 described an experimental model for posterior lamellar keratoplasty (PLK). The following year Melles et al.2 accomplished their first patient surgery. In 2001, Terry and Ousley3 reported successful results in patients using a similar procedure, which they named deep lamellar endothelial keratoplasty (DLEK). To perform these surgeries, a deep stromal pocket was created in the host cornea, and a specialized intrastromal trephine was inserted. The trephine was used to remove a thin disc of posterior stroma and endothelium. Ideally, the stromal pocket was deep in the host cornea, so that only 100 mm of posterior stroma was removed. The donor tissue was prepared by lamellar dissection and trephination of a donor corneo-scleral rim and consisted of a thin layer of posterior stroma, Descemet’s membrane, and healthy endothelium. This donor disc was inserted to replace what had been removed from the patient. In the early form of EK, the incisions were large enough to accommodate an unfolded 8–9 mm donor disc. In 2002, Melles’ group reported that the donor disc could be folded in half, thus allowing its insertion through a smaller (5 mm) incision.4,5
T
In 2004, Melles et al.6 advanced the technique by developing the “descemetorhexis,” in which only the diseased Descemet’s membrane and endothelium were stripped off the host, eliminating the need for host stromal dissection. The donor disc was apposed without prior removal of host stroma, resulting in a 100–200 mm increase in corneal thickness. Price and Price7 later reported the visual outcomes after surgery, and no detrimental effect from the additional posterior stroma was suggested. This technique gained wide acceptance, and it became known as Descemet’s stripping endothelial keratoplasty (DSEK). Another major shift in EK surgery came with a transition in donor preparation from a manual to an automated method employing a microkeratome.8 This development gave rise to the term Descemet’s stripping with automated endothelial keratoplasty (DSAEK), the “A” designating that donor preparation was automated. DLEK has essentially been replaced by DSEK/DSAEK.9 DLEK was a more complicated procedure to perform, and the alternative techniques produced similar outcomes10 with additional benefits, including less induced hyperopic shift and fewer higher-order aberrations. Lastly, patients who have had both procedures perceive better vision in the DSEK/DSAEK eye.11
From *Cornea and External Diseases, University of New Mexico, Albuquerque, N.M., and †the Wilmer Eye Institute, Baltimore, Md.
Correspondence to Albert S. Jun, MD, Wilmer Eye Institute, Wilmer/ Woods 474, 600 N. Wolfe St., Baltimore, MD 21287;
[email protected]
Originally received Oct. 12, 2008. Revised Feb. 22, 2009 Accepted for publication Mar. 2, 2009 Published online July 13, 2009
This article has been peer-reviewed. Cet article a été évalué par les pairs. Can J Ophthalmol 2009;44:401–5 doi:10.3129/i09-090 CAN J OPHTHALMOL—VOL. 44, NO. 4, 2009
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Endothelial keratoplasty—Rose et al. Current techniques
Manual preparation of the donor tissue requires considerable skill and extra instruments, and it carries a risk of inadvertent perforation of Descemet’s membrane. This approach also adds considerably to the overall surgical time. Thus, most surgeons elect to use an automated microkeratome to section the donor tissue. As in manual preparation, the donor tissue is mounted on an artificial anterior chamber. The microkeratome cutting depth is adjustable to a depth of 350 mm, which generally prepares a donor tissue of 150–200 mm in thickness. The procedure resembles the preparation of a LASIK flap, except that a “free cap” is made, and the posterior donor tissue is then trephined to the required diameter. The tissue may also be prepared in advance by an eye bank. Initially, there were concerns about donor tissue being handled extensively by nonsurgeons and then stored before use. Rose et al.12 addressed these concerns and showed that with an experienced technician, automated microkeratome presectioned tissue had stable endothelial cell (EC) counts and viability for up to 48 hours. Clinical outcomes also support the use of eye-bank-prepared tissue. Price et al.13 found no difference in EC loss at 1 year in donor tissue prepared by an eye bank versus a surgeon. This study also reported similar visual outcomes and donor detachment rates. Eye-bank-prepared tissue is an increasingly common component of EK. The surgeon places a request for a “precut” cornea for DSAEK, and an eye bank technician uses an automated microkeratome to section the donor tissue before shipment to the surgery location. The clinical outcomes and rate of EC loss have repeatedly been shown to be comparable to those for tissue cut by the surgeon intraoperatively.14
interface prevents graft–host adherence. The host anterior chamber is filled with balanced salt solution (BSS). An anterior chamber maintainer may be used for this purpose. A popular technique for introducing the graft into the host anterior chamber uses an asymmetric 60/40 fold of the tissue. A very small amount of viscoelastic is placed on the endothelium before folding to protect the endothelium. The folded donor tissue is then inserted through the main incision with specialized graft insertion forceps that appose only at the tips, thus minimizing the area of endothelial compression. Once the folded donor tissue has been inserted and the forceps have been gently removed, BSS is used to deepen the anterior chamber. The epithelial side of the cornea can be tapped with a cannula to direct the graft into position. If this approach is not sufficient, the folded graft is engaged at the edges using a reverse Sinskey hook and pulled into a satisfactory position. Once the graft has been centred, BSS is added slowly until the graft is partially unfolded, and then air is introduced through a paracentesis incision in such a direction as to complete unfolding of the donor tissue. Occasionally, the reverse Sinskey hook is used to engage the stromal surface of the reflected portion of the donor tissue and manually unfold it. Once the graft has been centred and unfolded, a large air bubble is placed posterior to it. The anterior surface of the cornea is then stroked from centre to periphery with a fine spatula or sweeping instrument to remove residual fluid from the host–graft interface. The air bubble is left in place for approximately 10 minutes. During this time, the main wound is secured with sutures. At the end of the surgery, the air is reduced to 60%–70% of the anterior chamber diameter. Patients are instructed to maintain a face-up position for the next 12–18 hours so that the air bubble continues to support the graft.
Descemet’s membrane stripping and graft insertion
Additional variations on technique
A scleral tunnel or clear corneal wound that can be enlarged to 4.5–5.0 mm is constructed with 2 paracentesis wounds each oriented 90° to either side of the primary wound. Using the same size trephine blade used to prepare the donor tissue, the host corneal surface is marked to create a circular guide for Descemet’s membrane incision. The anterior chamber is maintained with viscoelastic or saline infusion while a specialized instrument, known as a reverse Sinskey hook, is inserted through paracentesis incisions and used to create a circular descemetorhexis. Once the circular incision has been completed, the reverse Sinskey hook is used to reflect the central cut edges, strip the disc of Descemet’s membrane and diseased endothelium from the overlying corneal stroma, and remove it from the anterior chamber. Before the graft is inserted, steps are taken to encourage adherence of the graft to the host. First, the peripheral 2 mm of host stroma (outside the visual axis) is scraped with a specialized instrument to roughen its surface. Next, any remaining viscoelastic is removed completely from the anterior chamber. Residual viscoelastic in the tissue
A number of technical variations on this technique have been reported in the literature. Lee et al.15observed that presoaking the donor disc at room temperature in BSS (BSS, Alcon, Inc., Fort Worth, Tex.) before insertion resulted in a decrease in graft dislocation rates. Srinivasan and Rootman16 advocate use of full-thickness corneal slits placed in the recipient cornea to facilitate draining of fluid from the graft–host interface, either intraoperatively or at the slit lamp on the first postoperative day. Bahar et al.17 showed improved endothelial survival with the use of a Busin glide to aid insertion. This instrument consists of a hollow tube in which the donor tissue is placed unfolded, endothelial side down. The glide is then inserted into the wound. Using small grasping forceps introduced into the anterior chamber across from the main wound, the donor tissue is pulled into position. This instrument eliminates trauma caused by forceps compression and endothelium-to-endothelium contact. Even with use of this instrument, however, these authors reported an EC loss of 25% at 6 months.
Donor preparation
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Endothelial keratoplasty—Rose et al. Outcomes
Extensive reviews of EK results show that minimal astigmatism is induced,18 although some studies have reported a hyperopic shift up to 1 D.13,19 Average best spectaclecorrected visual acuity (BSCVA) after EK is reported to be 20/40.20 Initial suggestions that this effect was due to increased corneal thickness after DSEK have been largely discounted, as no correlation has been found between post operative corneal thickness and BSCVA.20 Additionally, Bahar et al.11 found similar BSCVA outcomes in DSAEK and DLEK, a procedure that does not generally increase corneal thickness. The postoperative BSCVA of 20/40 for EK procedures is more likely to be due to subclinical stromal interface disturbances. Hindman et al.21 showed increased light scattering and decreased wavefront aberrations in postoperative DLEK patients, suggesting that subclinical stromal haze may persist, even in an optically clear graft. Reducing interface haze would likely lead to improved visual acuity outcomes for EK surgery.
1 year for very experienced surgeons24 and may be as high as 45% after 2 years.25 Pupillary block due to the air bubble left in the anterior chamber is a risk of the procedure. Terry et al.9 reported no occurrence of pupillary block in a series of 200 DSAEK cases using his technique. He recommended using a freely mobile 8 mm air bubble that clears the midpupil position when the patient intermittently becomes upright in the early postoperative period. For additional assurance, some surgeons instill mydriatic agents at the end of the surgery. Other surgeons advocate complete removal of the air bubble at the conclusion of the surgery. Prophylactic peripheral iridotomies are generally not performed. In a recent series of 118 patients, Suh et al.26 reported 2 cases of pupillary block for a rate of 1.7%. Not all patients are ideal candidates for DSAEK. The procedure is difficult in aphakic and vitrectomized eyes because of migration of the supporting air bubble into the posterior segment. Although some surgeons perform EK in phakic patients, tissue manipulation within the anterior chamber creates a risk of cataract formation.
Complications
The most common complication of EK is graft dislocation, with a reported rate of 6% for experienced surgeons.7 Any fluid or viscoelastic present in the graft–host interface can promote dislocation. This complication generally presents within the first week postoperatively. A recent development in technique that may reduce dehiscence involves creating ports in the recipient cornea through which interface fluid can be removed.16 Surgeons who perform this additional step place 4 peripheral slits in the host cornea (within the expected margins of the graft) before the donor graft is inserted. Postoperatively, if fluid is present in the interface, the anterior chamber can be refilled with air, and forceps can be inserted into the slits to allow fluid egress. Another potential complication of DSAEK is graft rejection. Allan et al.22 found rejection episodes were lower with EK (7.5%) than PK (13%) at 2 years, but they also noted a tendency for continued use of topical steroids after EK that may explain this difference. At 2 years, 80% of EK patients were still taking topical corticosteroids, whereas topical corticosteroids had been discontinued after 1 year in nearly all PK patients. Rates of EC loss are higher among EK (35% at 1 year) than PK patients (24% at 1 year).23 This observation is thought to be due to the extra manipulation of EK graft tissue. Folding the graft in half offers the advantage of small incision surgery. However, folding also causes trauma to the endothelium, and this is more marked when the incision size is reduced from 5 mm to 3 mm.19 When using long Kelman-McPherson forceps to insert the graft, there is a higher rate of cell death (38% at 6 months) than when using single-point fixation forceps (33% at 6 months), which localize crushing trauma to a smaller area.23 Overall, reported rates of EC loss after EK are as low as 34% at
The triple DSAEK procedure (phaco/IOL/DSAEK)
EK does not alter anterior corneal topography, and thus performing phacoemulsification and intraocular lens (IOL) implantation followed by DSAEK, as a combined procedure, results in rapid visual recovery and a more predictable refractive outcome than a PK triple procedure.27 This technique also avoids the risks associated with an open-sky PK procedure. A hyperopic shift of approximately 1 D observed with EK alone has also been reported to affect refractive outcomes in DSAEK triple procedures. Covert and Koenig,27 in a series of 21 eyes in which a DSAEK triple was performed, found the difference between target and actual postoperative refraction averaged +1.1 D. EC survival is reportedly higher when DSAEK is performed in combination with clear corneal phacoemulsification. The 6-month rate of cell loss in combined phaco/IOL/DSAEK using a clear cornea wound was 27% (n = 43) compared with DSAEK alone at 36% (n = 218)24. When performed through a scleral wound, the rate of EC loss is the same in both procedures.24 One disadvantage of the phaco/IOL/DSAEK combined procedure is that the cataract extraction must be performed through a cloudy cornea. However, trypan blue staining of the capsule, glycerin, and epithelial scraping can be used to improve the view during the phaco/IOL portion of the surgery. Future directions
The increased availability of precut tissue has contributed to the widespread acceptance of DSAEK. In 2005, 4.5% of requested corneal tissue was for EK, and this increased to approximately 50% in 2007 (Tissue Banks International, Baltimore, Md., unpublished data). CAN J OPHTHALMOL—VOL. 44, NO. 4, 2009
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Endothelial keratoplasty—Rose et al. Although DSAEK offers significant advantages over PK, several areas of improvement can be identified. Refinements in graft insertion techniques may improve post-EK EC counts. Proposed techniques include using a glide to assist with graft insertion,28 or using a suture29 or instrument30 to pull the graft through the wound from a paracentesis made 180° away. It is also likely that BSCVA outcomes would improve with reduction of stromal interface haze. This may be achieved by transplanting the Descemet’s membrane/endothelial disc without any attached stroma. Melles et al.31,32 and Tappin33 have recently reported successful transplantation of Descemet’s membrane and endothelium without stromal support. This procedure is termed Descemet’s membrane endothelial keratoplasty (DMEK). DMEK is still at an early stage, and donor detachments and primary graft failure remain problematic. In a series of 10 patients there were 3 patients with 20/20 vision, 3 dislocations, and 6-month average EC counts of 2030 cells/mm.32 DMEK may become more widespread if technical advances improve the reliability of graft adherence and if visual acuity outcomes demonstrate an improvement over DSAEK. An alternative way to eliminate stromal haze may be to transplant endothelial cells alone, without Descemet’s membrane or stromal tissue. Sumide et al.34 harvested human corneal endothelial cells, cultivated them in tissue culture, and confirmed active Na/K ATPase activity, indicating that they would retain their vital pump function. Transplanting such cells may require a supporting material that would encourage them to adhere to host tissue. This approach was successfully demonstrated in a monkey model35 in which corneal endothelial cells were cultivated on collagen sheets, transplanted into recipients, and found to reduce corneal edema. Use of the femtosecond laser for donor preparation in EK has been explored.36,37 It has already proven useful in host and donor trephination for PK. In EK donor preparation, the femtosecond laser may be capable of creating a deeper and more consistent cutting depth, resulting in a thinner posterior donor tissue than can be produced with the microkeratome. One potential problem with using the femtosecond laser for EK donor preparation is that it has been found to produce a less smooth, more stucco-like interface.38 This may be due to several factors, including increased scattering of laser energy at greater stromal depths or in edematous donor corneas. The first case of DSAEK using a donor disc prepared with a femtosecond laser was reported by Cheng et al.,39 resulting in a BSCVA of 20/50. The authors stated that this patient had a pre-existing maculopathy, but it is not clear how much interface disturbances may have contributed to the postoperative visual limitation. Conclusions
For patients with endothelial dysfunction, EK has revolutionized the corneal transplant experience. The advantages
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of EK include rapid recovery of vision, lifelong tectonic stability of the eye, and no dependency on contact lenses. The long-term safety of EK is also a benefit for those at higher risk from PK, such as elderly or monocular patients. Future results regarding long-term graft survival will be important to monitor. With such high rates of EC loss, it is possible that replacement of posterior grafts may impose a heightened demand for corneal tissue in the future. We look forward to continued improvements in the technique, including modifications that minimize endothelial damage. Ultimately, the ability to transplant EC without stroma, such as with the DMEK technique, may represent the next major step in the evolution of EK surgery. References 1. Melles GR, Eggink FA, Lander F, et al. A surgical technique for posterior lamellar keratoplasty. Cornea 1998;17:618–26. 2. Melles GR, Lander F, Beekhuis WH, Remeijer L, Binders PS. Posterior lamellar keratoplasty for a case of pseudophakic bullous keratopathy. Am J Ophthalmol 1999;127:340–1. 3. Terry MA, Ousley PJ. Deep lamellar endothelial keratoplasty in the first United States patients: early clinical results. Cornea 2001;20:239–43. 4. Melles GR, Lander F, Nieuwendaal C. Sutureless, posterior lamellar keratoplasty: a case report of a modified technique. Cornea 2002;21:325–7. 5. Melles GR, Lander F, Rietveld FJ. Transplantation of Descemet’s membrane carrying viable endothelium through a small scleral incision. Cornea 2002;21:415–8. 6. Melles GR, Wijdh RH, Nieuwendaal CP. A technique to excise the descemet membrane from a recipient cornea (descemetorhexis). Cornea 2004;23:286–8. 7. Price FW, Jr., Price MO. Descemet’s stripping with endothelial keratoplasty in 200 eyes: early challenges and techniques to enhance donor adherence. J Cataract Refract Surg 2006;32:411–8. 8. Gorovoy MS. Descemet-stripping automated endothelial keratoplasty. Cornea 2006;25:886–9. 9. Terry MA, Shamie N, Chen ES, Hoar KL, Friend DJ. Endothelial keratoplasty a simplified technique to minimize graft dislocation, iatrogenic graft failure, and pupillary block. Ophthalmology 2008;115:1179–86. 10. Bahar I, Kaiserman I, McAllum P, Slomovic A, Rootman D. Comparison of posterior lamellar keratoplasty techniques to penetrating keratoplasty. Ophthalmology 2008;115:1525–33. 11. Bahar I, Sansanayudh W, Levinger E, Kaiserman L, Srinivasan S, Rootman D. Posterior lamellar keratoplasty–comparison of DLEK and DSAEK in the same patients: a patient’s perspective. Br J Ophthalmol 2009;93:186–90. 12. Rose L, Briceno CA, Stark WJ, Gloria DG, Jun AS. Assessment of eye bank-prepared posterior lamellar corneal tissue for endothelial keratoplasty. Ophthalmology 2008;115:279–86. 13. Price MO, Baig KM, Brubaker JW, Price FW, Jr. Randomized, prospective comparison of precut vs surgeon-dissected grafts for Descemet stripping automated endothelial keratoplasty. Am J Ophthalmol 2008;146:36–41. 14. Terry MA, Shamie N, Chen ES, Phillips PM, Hoar KL, Friend DJ. Precut tissue for Descemet’s stripping automated endothelial keratoplasty: vision, astigmatism, and endothelial survival. Ophthalmology 2009;116:248–56.
Endothelial keratoplasty—Rose et al. 15. Lee JK, Eghrari AO, Desai NR, Stark WJ, Gottsch JD. Presoaking donor corneas reduces graft detachment rates in Descemet stripping endothelial keratoplasty. Am J Ophthalmol 2009;147:439–41. 16. Srinivasan S, Rootman DS. Slit-lamp technique of draining interface fluid following Descemet’s stripping endothelial keratoplasty. Br J Ophthalmol 2007;91:1202–5. 17. Bahar I, Kaiserman I, Sansanayudh W, Levinger E, Rootman DS. Busin guide vs forceps for the insertion of the donor lenticule in Descemet stripping automated endothelial keratoplasty. Am J Ophthalmol 2009;147:220–6. 18. Price FW, Jr., Price MO. Descemet’s stripping with endothelial keratoplasty in 50 eyes: a refractive neutral corneal transplant. J Refract Surg 2005;21:339–45. 19. Koenig SB, Covert DJ. Early results of small-incision Descemet’s stripping and automated endothelial keratoplasty. Ophthalmology 2007;114:221–6. 20. Price MO, Price FW. Descemet’s stripping endothelial keratoplasty. Curr Opin Ophthalmol 2007;18:290–4. 21. Hindman HB, McCally RL, Myrowitz E, et al. Evaluation of deep lamellar endothelial keratoplasty surgery using scatterometry and wavefront analyses. Ophthalmology 2007;114:2006–12. 22. Allan BD, Terry MA, Price FW, Jr., Price MO, Griffin MB, Claesson M. Corneal transplant rejection rate and severity after endothelial keratoplasty. Cornea 2007;26:1039–42. 23. Price MO, Price FW, Jr. Endothelial cell loss after descemet stripping with endothelial keratoplasty influencing factors and 2-year trend. Ophthalmology 2008;115:857–65. 24. Terry MA, Chen ES, Shamie N, Hoar KL, Friend DJ. Endothelial cell loss after Descemet’s stripping endothelial keratoplasty in a large prospective series. Ophthalmology 2008;115:488–96 e3. 25. Terry MA. Endothelial keratoplasty: clinical outcomes in the two years following deep lamellar endothelial keratoplasty (an American Ophthalmological Society thesis). Trans Am Ophthalmol Soc 2007;105:530–63. 26. Suh LH, Yoo SH, Deobhakta A, et al. Complications of Descemet’s stripping with automated endothelial keratoplasty: survey of 118 eyes at one institute. Ophthalmology 2008;115:1517–24. 27. Covert DJ, Koenig SB. New triple procedure: Descemet’s stripping and automated endothelial keratoplasty combined with phacoemulsification and intraocular lens implantation. Ophthalmology 2007;114:1272–7.
28. Mehta JS, Por YM, Beuerman RW, Tan DT. Glide insertion technique for donor cornea lenticule during Descemet’s stripping automated endothelial keratoplasty. J Cataract Refract Surg 2007;33:1846–50. 29. Bradley JC, McCartney DL. Descemet’s stripping automated endothelial keratoplasty in intraoperative floppy-iris syndrome: suture-drag technique. J Cataract Refract Surg 2007;33:1149–50. 30. Aralikatti A, Dean S, Busin M, Shah S. Pull-through technique for graft insertion in DSAEK. J Cataract Refract Surg 2008;34:341; author reply 341–2. 31. Melles GR, Ong TS, Ververs B, van der Wees J. Descemet membrane endothelial keratoplasty (DMEK). Cornea 2006;25:987–90. 32. Melles GR, Ong TS, Ververs B, van der Wees J. Preliminary clinical results of Descemet membrane endothelial keratoplasty. Am J Ophthalmol 2008;145:222–7. 33. Tappin M. A method for true endothelial cell (Tencell) transplantation using a custom-made cannula for the treatment of endothelial cell failure. Eye 2007;21:775–9. 34. Sumide T, Nishida K, Yamato M, et al. Functional human corneal endothelial cell sheets harvested from temperature- responsive culture surfaces. FASEB J 2006;20:392–4. 35. Koizumi N, Sakamoto Y, Okumura N, et al. Cultivated corneal endothelial cell sheet transplantation in a primate model. Invest Ophthalmol Vis Sci 2007;48:4519–26. 36. Cheng YY, Pels E, Cleutjens JP, van Suylen RJ, Hendrikse F, Nuijts RM. Corneal endothelial viability after femtosecond laser preparation of posterior lamellar discs for Descemet-stripping endothelial keratoplasty. Cornea 2007;26:1118–22. 37. Sikder S, Snyder RW. Femtosecond laser preparation of donor tissue from the endothelial side. Cornea 2006;25:416–22. 38. Soong HK, Mian S, Abbasi O, Juhasz T. Femtosecond laserassisted posterior lamellar keratoplasty: initial studies of surgical technique in eye bank eyes. Ophthalmology 2005;112:44–9. 39. Cheng YY, Pels E, Nuijts RM. Femtosecond-laser-assisted Descemet’s stripping endothelial keratoplasty. J Cataract Refract Surg 2007;33:152–5.
Keywords: endothelial keratoplasty, penetrating keratoplasty
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