CLINICAL SCIENCE Descemet s Stripping Automated Endothelial Keratoplasty (DSAEK) Using Corneal Donor Tissue Not Acceptable for Use in Penetrating Keratoplasty as a Result of Anterior Stromal Scars, Pterygia, and Previous Corneal Refractive Surgical Procedures Paul M. Phillips, MD,* Mark A. Terry, MD,* Neda Shamie, MD,* Edwin S. Chen, MD,* Karen L. Hoar, MD, FRCSC,* Chris Stoeger, CEBT, CTBS, Daniel J. Friend, MS, and Hisham A. Saad, MD* Purpose: The purpose of this study was to evaluate outcomes of Descemet s stripping automated endothelial keratoplasty (DSAEK) using anterior stromal flawed (ASF) donor corneas that were unsuitable for use in full-thickness penetrating keratoplasty as a result of stromal scars, pterygia, or previous corneal refractive surgery and to compare results with DSAEK using standard tissue. Methods: We conducted a review of our initial 42 (19 with 6-month follow up) consecutive DSAEK surgeries using ASF tissue compared with 357 (199 with 6-month follow up) time-matched controls using standard tissue. Intraoperative and perioperative complications, including dislocations and primary graft failures, were compared. Six-month best spectacle-corrected vision, incidence of rejection episodes, postoperative refractive astigmatism, keratometric values, pre- and postoperative topography-derived surface asymmetry index, and surface regularity index were compared. Results: One surgeon-cut ASF tissue was perforated before surgery and was discarded. No surgeon-cut standard tissue was perforated. No intraoperative complications and no episodes of primary graft failure or pupillary block glaucoma occurred in either group. One (2.4%) postoperative graft dislocation and one (5.2%) graft rejection episode occurred in the study group. There were 10 (2.8%) dislocations and 8 (2.2%) graft rejection in the controls. A statistically similar significant improvement in best spectacle-corrected vision occurred in both groups. Corneal topography, pachymetry, and manifest astigmatism were not significantly different between groups. Conclusion: Postoperative results of DSAEK using donor tissue excluded from use in penetrating keratoplasty as a result of stromal Received for publication June 14, 2008; revision received November 30, 2008; accepted December 21, 2008. From the *Devers Eye Institute, Portland, OR; Lions Vision Research Laboratory of Oregon, Portland, OR; and Lions Eye Bank of Oregon, Portland, OR. Dr. Terry has a financial interest in the specialized instruments used in this surgery. Bausch and Lomb Surgical, St. Louis, MO, manufactured and supplied the specially designed instruments free of charge. Reprints: Mark A. Terry, MD, Devers Eye Institute, 1040 NW 22nd Avenue, Portland, OR 97210 (e-mail: MTerry@DeversEye.org). Copyright Ó 2009 by Lippincott Williams & Wilkins flaws are equivalent to results using standard donor tissue. Central corneal thickness measurements should be performed before cutting to avoid tissue perforation. The use of ASF tissue for DSAEK will expand the cornea donor pool. Key Words: DSAEK, DSEK, descemets stripping automated endothelial keratoplasty, enthothelial, endothelial keratoplasty, donor tissue, cornea (Cornea 2009;28:871 876) INTRODUCTION Penetrating keratoplasty (PK) is a time-tested and effective surgical procedure used to treat vision loss resulting from diseases affecting any or all layers of the cornea. Because this surgery involves replacement of the host cornea with a full-thickness central corneal donor button, the Eye Bank Association of America s (EBAA) Medical Advisory Board has established criteria to ensure the quality of donor tissue used in PK. The criteria excludes the use of corneas with central scarring, pterygia within the central optical area of the cornea, evidence of ectasias, and also those having undergone corneal refractive surgeries for use in standard full thickness PK because these ocular histories may affect the optical outcome of the corneal recipient. 1 Penetrating keratoplasty is presently the standard of care for treatment of corneas with anterior stromal scarring and advanced ectasias; however, endothelial keratoplasty (EK) is viewed by many as the new standard of care for treatment of corneal endothelial failure. 2 4 The field of corneal transplantation has undergone significant advancements in the treatment of endothelial failure, most notably since 1998, when Gerrit Melles first described his method of replacing the posterior corneal surface using only the posterior portion of the donor tissue, which he named posterior lamellar keratoplasty. 5 Endothelial keratoplasty was again modified and further developed, initially as deep lamellar endothelial keratoplasty surgery by Terry 6,7 and then as Descemet s stripping endothelial keratoplasty surgery by Price. 8,9 The procedure was then renamed Descemet s Cornea Volume 28, Number 8, September 2009 www.corneajrnl.com 871
Phillips et al Cornea Volume 28, Number 8, September 2009 stripping automated endothelial keratoplasty (DSAEK) by Gorovoy to distinguish the use of a microkeratome to prepare the donor tissue. 10 The DSAEK procedure is continuing to evolve as more data are presented and techniques are refined. 2,11 19 Soon after the popularization of endothelial keratoplasty for treatment of corneal diseases involving the endothelium, it became clear that anterior stromal flawed (ASF) tissue unsuitable for PK because of anterior scarring, central pterygia, or previous corneal refractive surgery, but which still had excellent endothelium, might effectively be used in EK surgery. Therefore, in 2005, the medical advisory board to the EBAA revised the standard to allow the use of tissue with good endothelial cell densities but with anterior pathology to be transplanted in EK surgery. 1 We have designated this tissue in our eye bank as ASF. The criteria of acceptable tissue was therefore broadened by the EBAA to use additional tissue that would otherwise be unsuitable for PK as a recognition of the perceived value and usefulness of using only the healthy posterior portion of tissue that would otherwise be wasted. With some foresight, it was also recognized that with an aging population, the number of patients requiring corneal transplants will rise while simultaneously, the corneal donor pool of tissue without ASF will, in part, be reduced by the increasing popularity of corneal refractive procedures. Already, it is estimated that approximately 2% of tissue received by the Lions Eye Bank of Oregon cannot be used in PK as a result of previous corneal refractive procedures and this number should only increase in the near future. Additionally, as a result of the rapid recovery and quality outcomes from DSAEK, surgeons are operating on patients with better vision and less severe disease, which means there will be an increase in the overall number of surgeries performed and a rise in the demand for tissue. This, coupled with a higher primary graft failure rate in DSAEK than in PK, found especially with novice surgeons using certain surgical techniques, will lead to increased rates of repeat grafting and may severely diminish donor tissue availability in the near future. In 2007, Armour et al reported the safe use of tissue in deep lamellar endothelial keratoplasty that was deemed unacceptable for use in PK surgery. 20 Since March 2000, our center has performed.800 EK procedures (either deep lamellar endothelial keratoplasty or Descemet s stripping endothelial keratoplasty/dsaek) and in that prospective series, we have accepted ASF donor tissue for transplantation, which would have previously gone unused. Recently, DSAEK has gained wide acceptance. With this in mind, we have now reviewed all of our cases of DSAEK using ASF donor tissue. We have retrospectively reviewed our prospectively obtained results using this tissue and compared the results with a time-matched control group of consecutive DSAEK eyes using standard tissue. The objective of this study was to determine the safety and effectiveness of using microkeratome cut ASF tissue for use in DSAEK surgery. METHODS Institutional Review Board approval was obtained through our hospital for our clinical protocol. An investigational surgical consent form for 5-mm incision DSAEK surgery was approved. DSAEK was then performed and postoperative data were gathered on patients in a prospective, consecutive, nonrandomized series. A retrospective chart review was performed on this prospective series to determine which DSAEK surgeries were performed using ASF donor tissue. The database of the Lions Eye Bank of Oregon was reviewed to find donors that had been used in our DSAEK series that had anterior pathology such as pterygia inside the 8-mm zone, stromal scars, and refractive procedures and had been designated by the medical director as acceptable for endothelial transplant but unusable for PK. We found 42 eyes meeting these criteria. Preoperative and postoperative results of this study group were compared with a control group consisting of the 357 time-matched controls receiving standard donor corneas. Demographic data, including age, sex, and underlying eye diseases, were compared between the 2 groups. Pre- and postoperative evaluation for both groups included Snellen best spectacle-corrected visual acuity (BSCVA), manifest refraction, astigmatism, corneal topographic quality as measured by surface regularity index (SRI) and surface asymmetry index (SAI), and keratometry. Additionally, postoperative complications, including rejection episodes, noted to have occurred at or before the 6-month protocol visit were documented. Further details on the methodology of data acquisition is documented in our previous publications. 2,14 Eyes with comorbidities such as retinal pathology were not excluded from analysis. Surgical Procedure All patients underwent 5.0-mm scleral incision DSAEK by one experienced surgeon (M.A.T.) and 5 novice surgeons (K.H., E.C., N.S., P.P.) from September 2005 to February 2008. The 5.0-mm incision surgical procedure and instrumentation are well described in previous reports. 2,14 When prepared intraoperatively, the donor tissue in this DSAEK series was prepared by the surgeons cutting the tissue with a Moria microkeratome and artificial anterior chamber system (AAC; Moria Systems, Doylestown, PA) always using a 300- mm head, and no pachymetry was performed before the resection. When precut by the eye bank, tissue was cut using an identical system, but the following protocol was used. Tissue thickness is predetermined with ultrasound pachymetry (DGH Pachette 2; DGH technology Inc., Exton, PA). If the tissue is known to have had previous LASIK or if the thickness is,450 mm, then a 250-mm head is used to make the cut. If the tissue is between 451 and 499 mm, a 300-mm head is used and if the tissue is.500 mm, then a 350-mm head is used. The surgeon and the eye bank were consistent in their techniques of tissue preparation for both control and ASF donor tissue. When cut by the eye bank, the microkeratome cuts were all made successfully below the level of the LASIK flaps and other anterior pathology. The tissue preparation was consistent regardless of the presence of pterygium or anterior scarring, because these pathologies did not prevent creation of a good seal on the artificial anterior chamber. Statistical Analysis Snellen visual acuity measurements for BSCVA were converted to logarithm of the minimum angle of resolution 872 www.corneajrnl.com q 2009 Lippincott Williams & Wilkins
Cornea Volume 28, Number 8, September 2009 Evalution of Outcome of DSAEK Using ASF Donor Cornea measurements to allow averaging and statistical analysis. Group comparisons were analyzed by an independent Student t test. Preoperative and postoperative comparisons within the 2 groups were analyzed by a paired t test. RESULTS Donor Tissue The study donor group consisted of 42 corneas; however, one donor was perforated intraoperatively before insertion into the recipient and was replaced by standard tissue, leaving 41 eyes that underwent 5.0-mm incision DSAEK surgeries using ASF tissue. Figure 1 shows examples of 2 donor tissues used in the study group, one with radial keratotomy scars seen preinsertion and postinsertion and one LASIK tissue postcut before insertion. Of these study eyes, 19 had follow up of 6 months. Twenty-nine donors had anterior corneal scars or opacities. Two study corneas had a pterygium within the 8-mm zone, 7 had prior LASIK only, 2 had prior refractive keratoplasty only, and one had both refractive keratoplasty and LASIK (Table 1). The control donor group consisted of 357 consecutive DSAEK surgeries beginning during the same time period performed using standard donor corneas that were suitable for PK. Patient Demographics Patient demographics were similar between the study and control groups (Table 2). Tissue Cutting The initial 10 ASF tissues and 219 control tissues were cut intraoperatively by the surgeon and the following 32 ASF tissues and 138 control tissues were delivered precut by the Lions Eye Bank of Oregon. There was one perforation of a surgeon-cut ASF tissue intraoperatively. The donor was designated ASF as a result of prior LASIK surgery. This one perforation occurred while using a 300-mm head without preresection pachymetry. This tissue was discarded before insertion and therefore not included in the postoperative analysis. No tissue in the control group was reported as TABLE 1. Types of Anterior Stromal Flaws Leading to Tissue Exclusion from PK (N = 41) Anterior Scars Pterygium LASIK RK LASIK + RK 71% (n = 29) 5% (n = 2) 17% (n = 7) 5% (n = 2) 2% (n = 1) PK, penetrating keratoplasty; RK, radial keratotomy. damaged during intraoperative cutting (0% rate of tissue wastage). Intraoperative Data In the study group, concurrent procedures were as follows: 17 (41%) had concurrent phacoemulsification, 2 (5%) had an intraocular lens exchange with an anterior vitrectomy, one patient had a concurrent anterior vitrectomy, and one had an iridoplasty. For the control group patients, 189 (53%) had concurrent phacoemulsification, 8 (2%) had anterior vitrectomies with intraocular lens exchanges, 6 (2%) had concurrent intraocular lens exchange, 4 (1%) had concurrent anterior vitrectomies, 3 had iridoplasty (1%), and 4 (1%) had concurrent surface scraping. The presence of comorbidities such as retinal pathology did not exclude a patient from analysis (study group: 16 [39%]; control group:116 [32%]). There were no significant patient differences between the study group versus control in the data collected on preoperative BSCVA (study 20/111, control 20/91, P = 0.141), K values (study 43.2 D, control 43.5 D, P = 0.556), SRI (study 0.98, control 1.12, P = 0.715), SAI (study 1.42, control 1.73, P = 0.467), refractive astigmatism (study 1.21 D, control 1.03 D, P = 0.317), or pachymetry (study 687 mm, control 686 mm, P = 0.92). The preoperative donor endothelial cell density was not significantly different between the groups (study 2858 cells/mm 2, control 2826 cells/mm 2, P = 0.340). Postoperative Complications Postoperative data were available for 41 eyes that received ASF tissue. All eyes in this study group and 357 eyes in the control group had follow up of at least 1 month, whereas FIGURE 1. A, Intraoperative photograph of a precut donor tissue with refractive keratoplasty (RK) incisions. B, The same RK donor tissue after insertion and positioning within recipient. 1C, Another precut donor with previous LASIK in Optisol storage showing the posterior microkeratome cut below the level of the LASIK flap. q 2009 Lippincott Williams & Wilkins www.corneajrnl.com 873
Phillips et al Cornea Volume 28, Number 8, September 2009 TABLE 2. Demographics ASF Eyes Control Eyes Age 71 612 years (range, 49 90) 69 611 years (range, 37 96) Gender 34% male (n = 14) 66% female (n = 27) 37% male (n = 132) 63% female (n = 225) Reason for transplant 71% Fuchs (n = 29) 24% PBK (n = 10) 5% other endothelial dysfunction (n = 2) 80% Fuchs (n = 285) 14% PBK (n = 51) 6% other endothelial dysfunction (n = 22) ASF, anterior stromal flawed; PBK, pseudophakic bullous keratopathy. 19 in the ASF group and 199 in the control group had follow up of 6 months. There were no cases of primary graft failure or pupillary block in either group. Dislocation of the tissue into the anterior chamber occurred in 10 cases in our control group (2.8%) and one case in our ASF group (2.4%). All were successfully reattached with an air bubble. Eight cases in our control group (2.2%) and one case in our study group (5.2%) experienced a rejection episode. Six-month Data Postoperative parameters are provided in Table 3. The average BSCVA improved in both groups; in the study group from 20/111 (range 20/25 to counting fingers [CF]) preoperatively to 20/33 (range, 20/20 20/63) postoperatively (P = 0.008) and in the control group from 20/91 (range, 20/20 to CF) preoperatively to 20/35 (range, 20/20 20/2000) postoperatively (P, 0.001). However, there was no significant difference in the BSCVA between the 2 groups (P = 0.623). Additionally, there was no difference in the distribution of visual acuities (Table 4). There was no statistically significant topographic difference between the 2 groups (study group: SRI = 0.55, SAI = 0.89, K = 43.09 D; control group: SRI = 0.62, SAI = 0.9, K = 43.49 D; SRI P = 0.499, SAI P = 0.97, K P = 0.362). Refractive astigmatism was similar between the groups (study, 1.11 D; control, 1.12 D; P = 0.964) as was pachymetry (study, 0.652 mm; control, 0.668 mm; P = 0.307). Finally, there was no difference in endothelial cell density between the groups at 6 months (study 1975 cells/ mm 2 versus control 1907 cells/mm 2 ; P = 0.571) and, more importantly, in cell loss from preoperative to postoperative (study 32% cell loss versus control 33% cell loss; P = 0.714). DISCUSSION As the baby boomer population ages and life expectancy increases, the demand for donor corneal tissue may increase. Simultaneously, an ever increasing segment of the population is undergoing refractive surgery leading to an expected decrease in the supply of acceptable tissue for PKs. With these pressures on already stressed eye banks, the demand for healthy donor tissue may begin to overwhelm the supply. With this foresight, the medical advisory board of the EBAA has allowed the use of tissue with good endothelial cell densities, but with anterior pathology, to be used in EK surgery. 1 A review, by one of the authors (C.S.), of donor tissue collected by the Lions Eye Bank of Oregon during the same time period as our study leads to estimates that approximately 6% of additional tissue has now become available for EK surgery. Nearly one third of this tissue was designated as ASF tissue as a result of previous refractive procedures such as refractive keratoplasty, photorefractive keratectomy, and LASIK. Before this designation, this tissue would have been unavailable for transplantation. At the Lion s Eye Bank of Oregon, where precutting of donors is performed, the tissue is evaluated postresection by certified eye bank technicians for damage in the form of uneven cuts, signs of endothelial cell loss or damage, and other abnormalities. Although at this time, there is no set protocol to determine the appropriate postresection thickness of tissue and tissue has been distributed from the Lion s Eye Bank for use in EK as thin as 99 mm and as thick as 265 mm, tissue outside this range might also be discarded at the discretion of the certified eye bank technician or the medical director. When it is determined that postresection tissue is damaged, it is discarded. Evaluation of damaged tissue is logged in the eye bank database. A review of this database during the same time period as our study revealed that there were no full-thickness perforations resulting from cutting 89 ASF tissues and 1043 standard tissues. There were 19 standard tissues (1.8%) and 2 ASF tissues (2.2%) reported as damaged, however. The damage to the 2 ASF tissues occurred during dismounting the tissues and not during the actual cutting; therefore, no damage to ASF TABLE 3. Six-month Results ASF Eyes (n = 19) Control Eyes (n = 199) Significance BSCVA 20/32 (range, 20/20 20/63) 20/33 (range, 20/20 20/200) P = 0.348 Topography SRI = 0.64 SAI = 0.94 K = 43.39 SRI = 0.62 SAI = 0.89 K = 43.49 SRI: P = 0.846 SAI: P = 0.755K: P = 0.817 Astigmatism 1.08 D 1.13 D P = 0.828 Pachymetry 652 mm 668 mm P = 0.259 ECD 1975 (32% cell loss) 1907 (33% cell loss) P = 0.571 ASF, anterior stromal flaws; BSCVA, best spectacle-corrected visual acuity; SRI, surface regularity index; SAI, surface asymmetry index; ECD, endothelial cell density (cells/mm 2 ). 874 www.corneajrnl.com q 2009 Lippincott Williams & Wilkins
Cornea Volume 28, Number 8, September 2009 Evalution of Outcome of DSAEK Using ASF Donor Cornea TABLE 4. Visual Acuities Percentages by Group 20/20 or Better 20/40 or Better Worse Than 20/40 ASF eyes (n = 19) 16% (n = 3) 74% (n = 14) 26% (n = 5) Control eyes (n = 199) 10% (n = 20) 81% (n = 161) 19% (n = 38) ASF, anterior stromal flaws. x 2 for 20/20 or better: P = 0.580; x 2 for 20/40 or better/worse than 20/40: P = 0.653. tissue resulted from the pass of the microkeratome blade, arguably the step of greatest concern when cutting ASF tissue. Similarly, of the 19 damaged standard tissues, 5 (0.5%) were damaged during this cutting step, with other damage occurring during mounting or dismounting the tissue from the anterior chamber or from unknown causes. It is important to address the one episode of perforation of ASF tissue that occurred during intraoperative cutting by the surgeon. Before converting to the use of solely precut tissue at our center, the donors were all cut intraoperatively using a standard 300-mm microkeratome head without the use of ultrasound pachymetry. We now believe that such a method of indiscriminately cutting all tissue with a 300-mm head does not safeguard a surgeon against the undesired complication of tissue perforation. We do feel that intraoperative cutting of tissue can be safely performed, however, if the surgeon knows the corneal thickness and modifies the depth of cut appropriately as is the procedure followed by technicians at the Lions Eye Bank of Oregon. Although knowing the corneal thickness and modifying the microkeratome depth can avoid unnecessary perforation of tissue, it may not be feasible to cut tissue that is excessively thin (,350 mm) from pathology or previous high myopic laser correction. Additionally, it is understood that anterior stromal flaws should be anterior to the depth of the expected microkeratome cut to ensure no central imperfections remain in the donor tissue. When cutting is performed before surgery at an eye bank, the tissue is also checked post cut to be certain that the donor is of appropriate thickness and without flaws. Although it has been reported previously that ASF tissue can be safely used in deep lamellar endothelial keratoplasty surgery 20 and the assumption has been made that it would also be safe and effective in DSAEK, in which tissue cutting is automated with the use of a microkeratome, there have been no data previously published to confirm this. Possible concerns about using ASF tissue in DSAEK might be that the rate of dislocations and primary graft failures would increase with its use. Other concerns include that surface irregularities from scarred donor tissue might be transferred to the bed of the transplanted stromal donor interface from microkeratome preparation or that refractive topography from donors with previous high myopic excimer laser treatment might transfer from the surface to the donor interface and affect refractive outcomes. Armour et al did not find any evidence of these concerns when using ASF tissue in deep lamellar endothelial keratoplasty surgery. 20 They also pointed out that there is a significantly muted contribution of the posterior cornea to the overall refraction of the eye making it very unlikely that even high myopic laser treatments would transfer to affect refractive outcome. Our results using ASF tissue in DSAEK surgery now demonstrate this more clearly and it appears that transfer of such optical irregularities or refractive indices from the donor surface to the interface, if it occurs, does not affect the expected postoperative topographies, refractive outcomes, or BSCVA. This retrospective review of our prospective data on 41 eyes undergoing DSAEK receiving tissue unacceptable for PK confirms both the safety and effectiveness of its use with no increase in dislocations or primary graft failures and the equivalent BSCVA, refractive, and topographic results to those found in DSAEK with standard donor tissue. We have also demonstrated, as might be anticipated, the equivalency of 6-month endothelial cell densities between these populations. DSAEK surgery is now viewed by most as the new standard of care for the treatment of endothelial failure. With early recovery of high-quality visual acuity, most corneal surgeons have converted to this exciting new technique. However, many surgeons, both novice and experienced, have had very high complication rates with high rates of dislocations and even more alarming high rates of primary graft failure 18,21,22 leading to the loss of precious corneal tissue. Although previous studies by Chen et al 19 have shown no clear association between donor tissue characteristics and surgical results, some surgeons may blame high dislocation and primary graft failures rates on the perceived quality of tissue they are receiving. There is a growing demand on eye banks for perfect tissue with higher endothelial cell counts than what has previously been requested for PK. 21,23 We have demonstrated that imperfect tissue with flawed anterior stroma can be safely and effectively used for EK surgery even with automated preparation of the tissue using a microkeratome. Continued prospective data collection is ongoing at our center and will most likely continue to affirm our assertion that the use of tissue that is unacceptable for PK but has healthy endothelium is not only reasonable, but may be necessary to help meet the increasing demands for corneal transplant tissue. The collection of prospective data with continued careful evaluation of outcomes is the preferred course, which will guide us to the most definitive answers. REFERENCES 1. Eye Bank Association of America. Medical Standards. Washington, DC: EBAA; 2005. 2. Terry MA, Chen ES, Shamie N, et al. Endothelial cell loss after Descemet s stripping endothelial keratoplasty in a large prospective series. Ophthalmology. 2008;115:488 496, e3. 3. Price MO, Price FW Jr. Endothelial cell loss after Descemet stripping with endothelial keratoplasty influencing factors and 2-year trend. Ophthalmology. 2008;115:857 865. 4. Bahar I, Kaiserman I, McAllum P, et al. Comparison of posterior lamellar keratoplasty techniques to penetrating keratoplasty. Ophthalmology. 2008; 115:1524 1533. 5. Melles GR, Eggink FA, Lander F, et al. A surgical technique for posterior lamellar keratoplasty. Cornea. 1998;17:618 626. 6. Terry MA, Ousley PJ. Deep lamellar endothelial keratoplasty visual acuity, astigmatism, and endothelial survival in a large prospective series. Ophthalmology. 2005;112:1541 1548. 7. Terry MA, Ousley PJ. Small-incision deep lamellar endothelial keratoplasty (DLEK): six-month results in the first prospective clinical study. Cornea. 2005;24:59 65. q 2009 Lippincott Williams & Wilkins www.corneajrnl.com 875
Phillips et al Cornea Volume 28, Number 8, September 2009 8. 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;32:411 418. 9. Price FW Jr, Price MO. Descemet s stripping with endothelial keratoplasty in 50 eyes: a refractive neutral corneal transplant. J Refract Surg. 2005;21: 339 345. 10. Gorovoy MS. Descemet-stripping automated endothelial keratoplasty. Cornea. 2006;25:886 889. 11. Terry MA, Shamie N, Chen ES, et al. Endothelial keratoplasty a simplified technique to minimize graft dislocation, iatrogenic graft failure, and pupillary block. Ophthalmology 2008;115:1524 1533. 12. 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 1277. 13. Kuo AN, Harvey TM, Afshari NA. Novel delivery method to reduce endothelial injury in Descemet stripping automated endothelial keratoplasty. Am J Ophthalmol. 2008;145:91 96. 14. Chen ES, Terry MA, Shamie N, et al. Descemet s stripping endothelial keratoplasty: six months results in a prospective study of 100 eyes. Cornea. 2008;27:514 520. 15. Koenig SB, Dupps WJ Jr, Covert DJ, et al. Simple technique to unfold the donor corneal lenticule during Descemet s stripping and automated endothelial keratoplasty. J Cataract Refract Surg. 2007;33:189 190. 16. Srinivasan S, Rootman DS. Slit-lamp technique of draining interface fluid following Descemet s stripping endothelial keratoplasty. Br J Ophthalmol. 2007;91:1202 1205. 17. Meisler DM, Dupps WJ Jr, Covert DJ, et al. Use of an air fluid exchange system to promote graft adhesion during Descemet s stripping automated endothelial keratoplasty. J Cataract Refract Surg. 2007;33:770 772. 18. Koenig SB, Covert DJ, Dupps WJ Jr, et al. Visual acuity, refractive error, and endothelial cell density six months after Descemet stripping and automated endothelial keratoplasty (DSAEK). Cornea. 2007;26:670 674. 19. Chen ES, Terry MA, Shamie N, et al. Precut tissue in Descemet s stripping automated endothelial keratoplasty donor characteristics and early postoperative complications. Ophthalmology. 2008;115:497 502. 20. Armour RL, Ousley PJ, Wall J, et al. Endothelial keratoplasty using donor tissue not suitable for full-thickness penetrating keratoplasty. Cornea. 2007;26:515 519. 21. 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 1524. 22. Mearza AA, Qureshi MA, Rostron CK. Experience and 12-month results of Descemet-stripping endothelial keratoplasty (DSEK) with a smallincision technique. Cornea. 2007;26:279 283. 23. Terry MA, Shamie N, Chen ES, et al. Endothelial keratoplasty: the influence of pre-operative donor endothelial cell densities on dislocations, primary graft failure and one year cell counts. Cornea. 2009;28:24 31. 876 www.corneajrnl.com q 2009 Lippincott Williams & Wilkins