ORIGINAL ARTICLE
Tissue quality of eye-bank–prepared precut corneas for Descemet’s stripping automated endothelial keratoplasty Brian A. Nelson, MD, Rusty J. Ritenour, MD, FRCSC ABSTRACT ● RÉSUMÉ Objective: To evaluate endothelial cell density (ECD) of eye-bank–prepared tissue for use in Descemet’s stripping automated endothelial keratoplasty (DSAEK). Design: Prospective case series of consecutive corneal tissue prepared for DSAEK surgery. Participants: Sixty-seven sequential corneal-scleral tissue specimens representing 48 human donors processed for use in DSAEK surgery by the Regional Tissue Bank (Halifax, Nova Scotia). Methods: Corneal-scleral donor tissue was obtained by in situ recovery. ECD was recorded using the EB-3000 XYZ (HAI Laboratories Inc, Lexington, MA) specular microscope within 24 hours of preservation. Before the tissue was dissected, the corneal thickness was measured using the DGH-550 PACHETTE 2 (DGH Technology, Exton, PA) ultrasound pachymeter. The dissection was performed using a 300-μm Moria ALTK model microkeratome (Moria Inc). The posterior bed thickness was measured, and the anterior flap was replaced. Endothelial cell count density was obtained after re-preservation. Results: Complete measurements were obtained for 42 of 67 corneas. In 25 corneas it was not possible to obtain a postdissection ECD measurement. The mean ECD before dissection was 2806 ⫾ 317 cells/mm2. The mean ECD after dissection was 2772 ⫾ 318 cells/mm2. There was an average loss of 34 cells/mm2 (95% CI –110 to 40 cells/mm2, p ¼ 0.3). Conclusions: This case series confirms that ECD is preserved when DSAEK tissue is prepared in advance of surgery by trained eyebank technicians in a low-volume Canadian eye bank. It was difficult to obtain clear images of the endothelial cell layer postdissection, possibly because of tissue swelling or distortion. Sixty-six of 67 corneas included in the study were used for surgery. Objet : Évaluation de la densité des cellules endothéliales (DCE) des tissus préparés par la banque d’yeux pour la kératoplastie endothéliale automatisée avec décapage de la Descemet (KEADD). Nature : Série de cas prospectifs de tissus cornéens consécutifs préparés pour la chirurgie de KEADD. Participants : 67 spécimens séquentiels de tissu scléro-cornéen provenant de 48 donneurs humains pour utilisation dans la chirurgie KEADD, de la Banque régionale de tissu de Halifax, Nouvelle-Écosse. Méthodes : Le tissu scléro-cornéen des donneurs a été obtenu par récupération sur place. La DCE a été relevée avec le microscope spéculaire EB-3000 XYZ (HAI Labs, USA) sous 24 heures de préservation. Avant la dissection du tissu, l’épaisseur de la cornée avait été mesurée avec le pachymètre à l’ultrason DGH-550 PACHETTE 2 (DGH Technology, USA). La dissection a été exécutée avec un microkératome de 300 um de modèle Moria ALTK (Moria Inc., USA). L’épaisseur du lit postérieur a été mesurée et le lambeau antérieur, replacé. La DCE a été obtenu à la suite de la représervation. Résultats : Les mesures complètes ont été obtenues pour 42 cornées sur 67. Dans 25 cornées, il n’a pas été possible d’obtenir une mesure DCE après la dissection. Avant la dissection, la DCE moyenne était de 2806 + 317 cellules/2mm. La moyenne de DCE après dissection était de 2772 + 318 cellules/2mm (95 % CI - 110 à 40 cellules/2mm, p=0,3). En moyenne, il y a eu une perte de 34 cellules/mm2 (95% IC -110 à 40 cellules/mm2 p=0.3). Conclusion : Cette série de cas confirme que la DCE est conservée lorsque le tissu de la KEADD est préparé d’avance en petit volume par des techniciens qualifiés dans une banque d’yeux canadienne pour la chirurgie. Il était difficile d’obtenir des images claires de la couche cellulaire endothéliale après la dissection, ce qui est peut-être dû à l’enflure ou à la distorsion du tissu. 66 des 67 cornées incluses dans l’étude ont servi à la chirurgie.
Endothelial keratoplasty (EK) describes corneal transplantation surgeries that use a posterior lamellar graft of donor endothelium, either with Descemet’s membrane alone or with stromal tissue. EK is an area of rapid development since the first technique was described by Melles et al.1 in 1999. Advancements in technique have greatly improved visual outcomes2 and reduced graft failure rates.3,4 EK is seeing rapidly growing utilization rates compared with penetrating keratoplasty for endothelial dysfunction.5,6 For Descemet’s stripping automated endothelial keratoplasty (DSAEK), the graft dissection is most commonly performed using a microkeratome,7 with some centres using a femtosecond laser.8–10 Worldwide popularity of DSAEK has surpassed that of other EK techniques because
of the simplicity of donor tissue preparation, increasing supply of eye-bank–prepared tissue, and an increasing body of evidence supporting the safety and efficacy of the procedure. DSAEK has been shown to reduce incidence of donor perforation and reduce recovery time without any reduction in visual outcome over manual dissection.3 In DSAEK, the surgeon either prepares the donor tissue at the time of surgery or uses eye-bank–prepared tissue.11,12 Tissue prepared before surgery by a technician reduces the length and complexity of DSEAK surgery. Surgeonprepared and eye-bank–prepared tissue have been shown to have similar final endothelial cell loss, visual and refractive outcomes, and dislocation rates.11,13 Predissected tissue carries several other advantages, including avoidance of
From the Dalhousie University, Halifax, N.S
Correspondence to Brian A. Nelson, MD, Dalhousie University, 1276 South Park Street, Halifax NS B3H 2Y9; [email protected]
Presented at the Canadian Ophthalmological Society Annual Meeting in Vancouver, B.C., June 11, 2011. Originally received Jan. 26, 2013. Final revision Sep. 12, 2013. Accepted Sep. 17, 2013
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Tissue quality of precut corneas for DSAEK—Nelson and Ritenour surgical delays because of tissue damage at the time of surgery. Technician-prepared tissue from high-volume eye banks has been shown to have acceptable rates of endothelial cell density (ECD) loss and consistent graft thickness.12,14 Kelliher et al.14 reported 913 technician-prepared corneas from a single eye bank and found an average gain in ECD of 136 cells/mm2. Chen et al.12 reported 80 corneas from 2 independent eye banks and found an average loss in ECD of 99 cells/mm2. In Canada, because of geographic constraints and a smaller population, there are many eye banks with a lower tissue volume than those reported in the literature. The purpose of this article is to evaluate tissue quality parameters of ECD and microkeratome cut depth in a low-volume Canadian eye bank with newly trained technicians performing the dissection.
METHODS Data were prospectively collected for consecutive DSAEK tissue processed by Regional Tissue Bank technicians at the Queen Elizabeth II Health Sciences Centre (Halifax, Nova Scotia). The Tissue Bank is approved by Health Canada and is an International Associate Member of the Eye Bank Association of America. Approval of the study protocol was obtained from the local institution’s research ethics board. The first tissue was processed by the tissue bank technicians for transplantation in May 2010. Consecutive tissue was included in the study until February 2011. The 2 technicians performing the dissections were trained by local ophthalmologists using tissue not suitable for transplantation but for which consent was obtained for research and education use. In situ excisions of corneal-scleral rims were performed by local technicians in Halifax and a satellite eye bank in St. John, New Brunswick. Within 24 hours of preservation, the tissue was evaluated by slit lamp and ECD measurements were obtained using an EB-3000 XYZ specular microscope (HAI Laboratories Inc, Lexington, MA). Study corneas underwent the standard tissue bank protocol for screening. In short, suitable tissue (donor age o 70 years, ECD 4 2000) undergoes serology screening and a medical social interview with the donor’s next of kin and family physician. Suitable tissues are then offered to the cornea transplant service where the decision is made regarding its use for DSAEK surgery. To be considered for DSAEK, tissue must have ECD greater than 2200, few or no corneal folds, clear stroma, and few or no guttae. The tissue is predissected no more than 24 hours before the surgery. The tissue is mounted on a Moria Artificial Anterior Chamber (Moria Inc). The anterior chamber is pressurized using a syringe with balanced salt solution until the cornea is firm to digital tonometry. The corneal epithelium is then removed using a sterile cellulose sponge eye spear. The thickness of the remaining donor tissue is then measured 3 times using a
DGH-550 PACHETTE 2 (DGH Technology, Lexington, MA) pachymeter. An alignment mark is made using a marking pen in the periphery of the cornea. The cornea is then cut using a Moria ALTK Microkeratome (Moria Inc, Antony, France) with 300-μm head, creating a free cap. The cap is set aside and the thickness of the remaining posterior lamella is measured 3 times. The surface is dried using a cellulose surgical spear and the flap replaced. Centration of the flap is confirmed using the peripheral mark made earlier. The tissue is then preserved in OptisolGS (Bausch & Lomb, Rochester, NY). Tissue is evaluated after dissection with slit-lamp biomicroscopy and ECD.
RESULTS One hundred and thirty-nine corneas were prepared by the eye bank for corneal transplantation during the study period. Of these, 67 corneas representing 58 human donors were selected by the transplant surgeon for DSAEK preparation. All remaining tissues were used for other corneal transplantation techniques. The donors consisted of 33 males and 25 females (Table 1). The mean donor age was 51 years, with a range of 12 to 69 years. The most common cause of donor death was cardiovascular disease. One cornea was lost during the study period because of anterior chamber collapse during preparation. This occurred because the tissue was initially excised with a thin scleral rim, and an adequate seal to the artificial anterior chamber was not obtained. This cornea was not included in the analysis. The remaining 66 corneas included in the study were all used for surgery. Tissue was preserved in Optisol GS. The mean time to preservation from pronouncement of cardiac death by the attending physician was 9.1 hours. Once preserved in Optisol, tissue was then a mean of 7 days later (Table 2). The mean ECD at the time of preservation was 2810 cells/ mm2. Mean ECD measured after preparation was 2770 cells/mm2 in the 41 corneas where postcut measurements were successfully obtained. The mean ECD loss was 35 cells/mm2, which was not statistically significant. ECD loss in each sequential cut is shown in Figure 1. In the 26 corneas where postcut measurements were not obtained, the technician was unable to visualize the endothelial layer using the specular microscope. Tissue that had a high predissection ECD tended to measure lower ECD postdissection. Likewise, low initial ECD measurements led to higher final ECD measurement Table 1—Donor characteristics Donor sex Donor age, y Cause of death, n (%) Cardiovascular Cerebrovascular Lung cancer Trauma
33 (57%) males, 25 (43%) females Mean 51, range 12–69 19 (33%) 7 (12%) 4 (7%) 4 (7%)
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Tissue quality of precut corneas for DSAEK—Nelson and Ritenour Table 2—Tissue characteristics Result Time from death to preservation Time from preservation to dissection ECD at initial preservation, cells/mm2 ECD postdissection, cells/mm2 ECD change, cells/mm2
Mean (range) 9:04 h (3:19 to 15:45) 7 þ 2.5 days (3–13) 2810 þ 320 (2200–3490) 2770 þ 320 (2220–3390) –35 (95% CI –110 to 40, p ¼ 0.3)
ECD, endothelial cell density.
in some corneas. Technician technique was expected to improve with volume of cut procedures performed. To quantify an improved outcome because of learning, we compared ECD loss in the first 33 corneas with the last 34 using the paired t test. No significant difference was detected. There was, however, an improvement in the success rate of obtaining cell density measurement postdissection. In the first 33 dissections, final ECD measurements were obtained in 17 corneas (51.5%). In the final 34 dissections, final ECD measurements were obtained in 25 corneas (73.5%). In all corneas, the 300-μm microkeratome head was used. The expected cut depth assumed by other eye banks is 370 μm.14 Of the 67 corneas included in the study, 60 had complete pachymetry measurements before and after the cut. The average precut pachymetry measured immediately after removal of the epithelium was 529 ⫾ 50 μm. The average cut depth was 347 ⫾ 53 μm, calculated by subtracting the posterior bed thickness from the predissection corneal thickness (Fig. 2). The 3 deepest cuts were 446, 459, and 540 μm, and were associated with higher predissection corneal thickness of 565, 549, and 663 μm, respectively.
DISCUSSION The comparatively low-volume Canadian Eye Bank studied demonstrated tissue quality metrics on par with those reported in larger centres elsewhere.14,15 As in other studies, there were corneas where a physiologically impossible gain in ECD was observed, as well as large losses in
Fig. 1 — Change in endothelial cell density (ECD) of sequential dissections.
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Fig. 2 — Depth of microkeratome cut of sequential dissections.
ECD. These tended to occur in corneas that were outliers in initial ECD testing and could be explained by regression to the mean or inaccurate initial measurements. This same effect was observed by Kelliher et al.,14 who reported a mean ECD gain of 136 cells/mm2, with a standard deviation of 305 cells/mm2 in 913 corneas. Chen et al.12 reported an average loss of 99 cells/mm2, with a standard deviation of 179 and a range of –351 to 531 in 80 corneas using the same specular microscope as our study. Rose et al.15 reported measurements in 6 corneas before and after dissection, and demonstrated an average loss of 328 cells/mm2 with a range of –163 to 1380 cells/mm2, although the measurements were taken at 48 hours after dissection and a EKA-98 Keratoanalyzer (Konan Medical Inc, Rancho Palos Verdes, Calif.) was used. Terry et al.16 reported clinical outcomes of 90 consecutive DSAEK procedures and demonstrated that predissection ECD had no effect on post-op ECD or the incidence of graft dislocation and primary graft failure. In our study, large outliers are best explained by measurement error. For example, 1 cornea measured 655 cells/mm2 higher after dissection. There was no significant loss of ECD during tissue handling throughout the study. Only 1 tissue was lost during handling. The collapse of the artificial chamber during cutting was related to insufficient scleral rim tissue when the cornea was initially excised from the donor. Our results are comparable with the published rates of tissue loss during dissection range from 1.5% in 913 corneas14 to 2.5% in 100 corneas.12 There were difficulties obtaining clear specular microscopy images after the dissections. Tissue distortion and corneal edema caused by excess manipulation of the corneal tissue may be implicated. This is further suggested by improvement in the rate of successful specular microscopy image acquisition in the later dissections, when the technicians had more experience with the procedure. The technicians had extensive experience with specular microscopy before the eye bank began preparing DSAEK tissue. The lack of postdissection
Tissue quality of precut corneas for DSAEK—Nelson and Ritenour ECD measurements in 25 of 66 corneas introduces a potential bias in the analysis of cell loss, because tissue that was difficult to image may have experienced more cell loss. The majority of literature on eye-bank–prepared tissue for DSAEK comes from high-volume surgical centres and large eye banks in the United States and Europe. Our study demonstrates that technicians in lower volume tissue banks can perform the procedure effectively and safely. A rigorous training program initiated by local corneal transplant surgeons using nontransplantable human corneas was effective. Cost savings are achieved by reducing operating room time required by the surgeon. These data should encourage low-volume eye banks to become involved in DSAEK tissue preparation.
Disclosure: The authors have no proprietary or commercial interest in any materials discussed in this article.
Acknowledgements: The authors acknowledge Paul Artes, PhD (Department of Ophthalmology and Vision Sciences, Dalhousie University) for assistance with statistical analysis, Catherine Hackett (Regional Tissue Bank, QEII Health Sciences Centre, Halifax, Nova Scotia), and Mary Gatien (New Brunswick Eye Bank, Saint John, Nova Scotia). REFERENCES 1. Melles GR, Lander F, Rietveld FJ, Remeijer L, Beekhuis WH, Binder PS. A new surgical technique for deep stromal, anterior lamellar keratoplasty. Br J Ophthalmol. 1999;83:327-33. 2. Melles GR, Wijdh RH, Nieuwendaal CP. A technique to excise the Descemet membrane from a recipient cornea (descemetorhexis). Cornea. 2004;23:286-8. 3. 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.
4. Allan BD, Terry MA, Price FW Jr, Price MO, Griffin NB, Claesson M. Corneal transplant rejection rate and severity after endothelial keratoplasty. Cornea. 2007;26:1039-42. 5. Boimer C, Lee K, Sharpen L, Mashour RS, Slomovic AR. Evolving surgical techniques of and indications for corneal transplantation in Ontario from 2000 to 2009. Can J Ophthalmol. 2011;46:360-6. 6. Cunningham WJ, Brookes NH, Twohill HC, et al. Trends in the distribution of donor corneal tissue and indications for corneal transplantation: the New Zealand National Eye Bank Study 20002009. Clin Experiment Ophthalmol. 2012;40:141-7. 7. Gorovoy MS. Descemet-stripping automated endothelial keratoplasty. Cornea. 2006;25:886-9. 8. Cheng YY, Tahzib NG, van Rij G, et al. Femtosecond laser-assisted inverted mushroom keratoplasty. Cornea. 2008;27:679-85. 9. Cheng YY, Schouten JS, Tahzib NG, et al. Efficacy and safety of femtosecond laser-assisted corneal endothelial keratoplasty: a randomized multicenter clinical trial. Transplantation. 2009;88: 1294-302. 10. Monterosso C, Fasolo A, Caretti L, Monterosso G, Buratto L, Böhm E. Sixty-kilohertz femtosecond laser-assisted endothelial keratoplasty: clinical results and stromal bed quality evaluation. Cornea. 2011;30:189-93. 11. 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. 12. Chen ES, Terry MA, Shamie N, Hoar KL, Friend DJ. Precut tissue in Descemet’s stripping automated endothelial keratoplasty donor characteristics and early postoperative complications. Ophthalmology. 2008;115:497-502. 13. 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. 14. Kelliher C, Engler C, Speck C, Ward D, Farazdaghi S, Jun AS. A comprehensive analysis of eye bank-prepared posterior lamellar corneal tissue for use in endothelial keratoplasty. Cornea. 2009;28:966-70. 15. Rose L, Briceño CA, Stark WJ, Gloria DG, Jun AS. Assessment of eye bank-prepared posterior lamellar corneal tissue for endothelial keratoplasty. Ophthalmology. 2008;115:279-86. 16. Terry MA, Shamie N, Chen ES, Hoar KL, Phillips PM, Friend DJ. Endothelial keratoplasty: the influence of preoperative donor endothelial cell densities on dislocation, primary graft failure, and 1-year cell counts. Cornea. 2008;27:1131-7.
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Tissue quality of eye-bank–prepared precut corneas for Descemet’s stripping automated endothelial keratoplasty Brian A. Nelson, MD, Rusty J. Ritenour, MD, FRCSC ABSTRACT ● RÉSUMÉ Objective: To evaluate endothelial cell density (ECD) of eye-bank–prepared tissue for use in Descemet’s stripping automated endothelial keratoplasty (DSAEK). Design: Prospective case series of consecutive corneal tissue prepared for DSAEK surgery. Participants: Sixty-seven sequential corneal-scleral tissue specimens representing 48 human donors processed for use in DSAEK surgery by the Regional Tissue Bank (Halifax, Nova Scotia). Methods: Corneal-scleral donor tissue was obtained by in situ recovery. ECD was recorded using the EB-3000 XYZ (HAI Laboratories Inc, Lexington, MA) specular microscope within 24 hours of preservation. Before the tissue was dissected, the corneal thickness was measured using the DGH-550 PACHETTE 2 (DGH Technology, Exton, PA) ultrasound pachymeter. The dissection was performed using a 300-μm Moria ALTK model microkeratome (Moria Inc). The posterior bed thickness was measured, and the anterior flap was replaced. Endothelial cell count density was obtained after re-preservation. Results: Complete measurements were obtained for 42 of 67 corneas. In 25 corneas it was not possible to obtain a postdissection ECD measurement. The mean ECD before dissection was 2806 ⫾ 317 cells/mm2. The mean ECD after dissection was 2772 ⫾ 318 cells/mm2. There was an average loss of 34 cells/mm2 (95% CI –110 to 40 cells/mm2, p ¼ 0.3). Conclusions: This case series confirms that ECD is preserved when DSAEK tissue is prepared in advance of surgery by trained eyebank technicians in a low-volume Canadian eye bank. It was difficult to obtain clear images of the endothelial cell layer postdissection, possibly because of tissue swelling or distortion. Sixty-six of 67 corneas included in the study were used for surgery. Objet : Évaluation de la densité des cellules endothéliales (DCE) des tissus préparés par la banque d’yeux pour la kératoplastie endothéliale automatisée avec décapage de la Descemet (KEADD). Nature : Série de cas prospectifs de tissus cornéens consécutifs préparés pour la chirurgie de KEADD. Participants : 67 spécimens séquentiels de tissu scléro-cornéen provenant de 48 donneurs humains pour utilisation dans la chirurgie KEADD, de la Banque régionale de tissu de Halifax, Nouvelle-Écosse. Méthodes : Le tissu scléro-cornéen des donneurs a été obtenu par récupération sur place. La DCE a été relevée avec le microscope spéculaire EB-3000 XYZ (HAI Labs, USA) sous 24 heures de préservation. Avant la dissection du tissu, l’épaisseur de la cornée avait été mesurée avec le pachymètre à l’ultrason DGH-550 PACHETTE 2 (DGH Technology, USA). La dissection a été exécutée avec un microkératome de 300 um de modèle Moria ALTK (Moria Inc., USA). L’épaisseur du lit postérieur a été mesurée et le lambeau antérieur, replacé. La DCE a été obtenu à la suite de la représervation. Résultats : Les mesures complètes ont été obtenues pour 42 cornées sur 67. Dans 25 cornées, il n’a pas été possible d’obtenir une mesure DCE après la dissection. Avant la dissection, la DCE moyenne était de 2806 + 317 cellules/2mm. La moyenne de DCE après dissection était de 2772 + 318 cellules/2mm (95 % CI - 110 à 40 cellules/2mm, p=0,3). En moyenne, il y a eu une perte de 34 cellules/mm2 (95% IC -110 à 40 cellules/mm2 p=0.3). Conclusion : Cette série de cas confirme que la DCE est conservée lorsque le tissu de la KEADD est préparé d’avance en petit volume par des techniciens qualifiés dans une banque d’yeux canadienne pour la chirurgie. Il était difficile d’obtenir des images claires de la couche cellulaire endothéliale après la dissection, ce qui est peut-être dû à l’enflure ou à la distorsion du tissu. 66 des 67 cornées incluses dans l’étude ont servi à la chirurgie.
Endothelial keratoplasty (EK) describes corneal transplantation surgeries that use a posterior lamellar graft of donor endothelium, either with Descemet’s membrane alone or with stromal tissue. EK is an area of rapid development since the first technique was described by Melles et al.1 in 1999. Advancements in technique have greatly improved visual outcomes2 and reduced graft failure rates.3,4 EK is seeing rapidly growing utilization rates compared with penetrating keratoplasty for endothelial dysfunction.5,6 For Descemet’s stripping automated endothelial keratoplasty (DSAEK), the graft dissection is most commonly performed using a microkeratome,7 with some centres using a femtosecond laser.8–10 Worldwide popularity of DSAEK has surpassed that of other EK techniques because
of the simplicity of donor tissue preparation, increasing supply of eye-bank–prepared tissue, and an increasing body of evidence supporting the safety and efficacy of the procedure. DSAEK has been shown to reduce incidence of donor perforation and reduce recovery time without any reduction in visual outcome over manual dissection.3 In DSAEK, the surgeon either prepares the donor tissue at the time of surgery or uses eye-bank–prepared tissue.11,12 Tissue prepared before surgery by a technician reduces the length and complexity of DSEAK surgery. Surgeonprepared and eye-bank–prepared tissue have been shown to have similar final endothelial cell loss, visual and refractive outcomes, and dislocation rates.11,13 Predissected tissue carries several other advantages, including avoidance of
From the Dalhousie University, Halifax, N.S
Correspondence to Brian A. Nelson, MD, Dalhousie University, 1276 South Park Street, Halifax NS B3H 2Y9; [email protected]
Presented at the Canadian Ophthalmological Society Annual Meeting in Vancouver, B.C., June 11, 2011. Originally received Jan. 26, 2013. Final revision Sep. 12, 2013. Accepted Sep. 17, 2013
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Can J Ophthalmol 2014;49:92–95 0008-4182/14/$-see front matter & 2014 Canadian Ophthalmological Society. Published by Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jcjo.2013.09.017
Tissue quality of precut corneas for DSAEK—Nelson and Ritenour surgical delays because of tissue damage at the time of surgery. Technician-prepared tissue from high-volume eye banks has been shown to have acceptable rates of endothelial cell density (ECD) loss and consistent graft thickness.12,14 Kelliher et al.14 reported 913 technician-prepared corneas from a single eye bank and found an average gain in ECD of 136 cells/mm2. Chen et al.12 reported 80 corneas from 2 independent eye banks and found an average loss in ECD of 99 cells/mm2. In Canada, because of geographic constraints and a smaller population, there are many eye banks with a lower tissue volume than those reported in the literature. The purpose of this article is to evaluate tissue quality parameters of ECD and microkeratome cut depth in a low-volume Canadian eye bank with newly trained technicians performing the dissection.
METHODS Data were prospectively collected for consecutive DSAEK tissue processed by Regional Tissue Bank technicians at the Queen Elizabeth II Health Sciences Centre (Halifax, Nova Scotia). The Tissue Bank is approved by Health Canada and is an International Associate Member of the Eye Bank Association of America. Approval of the study protocol was obtained from the local institution’s research ethics board. The first tissue was processed by the tissue bank technicians for transplantation in May 2010. Consecutive tissue was included in the study until February 2011. The 2 technicians performing the dissections were trained by local ophthalmologists using tissue not suitable for transplantation but for which consent was obtained for research and education use. In situ excisions of corneal-scleral rims were performed by local technicians in Halifax and a satellite eye bank in St. John, New Brunswick. Within 24 hours of preservation, the tissue was evaluated by slit lamp and ECD measurements were obtained using an EB-3000 XYZ specular microscope (HAI Laboratories Inc, Lexington, MA). Study corneas underwent the standard tissue bank protocol for screening. In short, suitable tissue (donor age o 70 years, ECD 4 2000) undergoes serology screening and a medical social interview with the donor’s next of kin and family physician. Suitable tissues are then offered to the cornea transplant service where the decision is made regarding its use for DSAEK surgery. To be considered for DSAEK, tissue must have ECD greater than 2200, few or no corneal folds, clear stroma, and few or no guttae. The tissue is predissected no more than 24 hours before the surgery. The tissue is mounted on a Moria Artificial Anterior Chamber (Moria Inc). The anterior chamber is pressurized using a syringe with balanced salt solution until the cornea is firm to digital tonometry. The corneal epithelium is then removed using a sterile cellulose sponge eye spear. The thickness of the remaining donor tissue is then measured 3 times using a
DGH-550 PACHETTE 2 (DGH Technology, Lexington, MA) pachymeter. An alignment mark is made using a marking pen in the periphery of the cornea. The cornea is then cut using a Moria ALTK Microkeratome (Moria Inc, Antony, France) with 300-μm head, creating a free cap. The cap is set aside and the thickness of the remaining posterior lamella is measured 3 times. The surface is dried using a cellulose surgical spear and the flap replaced. Centration of the flap is confirmed using the peripheral mark made earlier. The tissue is then preserved in OptisolGS (Bausch & Lomb, Rochester, NY). Tissue is evaluated after dissection with slit-lamp biomicroscopy and ECD.
RESULTS One hundred and thirty-nine corneas were prepared by the eye bank for corneal transplantation during the study period. Of these, 67 corneas representing 58 human donors were selected by the transplant surgeon for DSAEK preparation. All remaining tissues were used for other corneal transplantation techniques. The donors consisted of 33 males and 25 females (Table 1). The mean donor age was 51 years, with a range of 12 to 69 years. The most common cause of donor death was cardiovascular disease. One cornea was lost during the study period because of anterior chamber collapse during preparation. This occurred because the tissue was initially excised with a thin scleral rim, and an adequate seal to the artificial anterior chamber was not obtained. This cornea was not included in the analysis. The remaining 66 corneas included in the study were all used for surgery. Tissue was preserved in Optisol GS. The mean time to preservation from pronouncement of cardiac death by the attending physician was 9.1 hours. Once preserved in Optisol, tissue was then a mean of 7 days later (Table 2). The mean ECD at the time of preservation was 2810 cells/ mm2. Mean ECD measured after preparation was 2770 cells/mm2 in the 41 corneas where postcut measurements were successfully obtained. The mean ECD loss was 35 cells/mm2, which was not statistically significant. ECD loss in each sequential cut is shown in Figure 1. In the 26 corneas where postcut measurements were not obtained, the technician was unable to visualize the endothelial layer using the specular microscope. Tissue that had a high predissection ECD tended to measure lower ECD postdissection. Likewise, low initial ECD measurements led to higher final ECD measurement Table 1—Donor characteristics Donor sex Donor age, y Cause of death, n (%) Cardiovascular Cerebrovascular Lung cancer Trauma
33 (57%) males, 25 (43%) females Mean 51, range 12–69 19 (33%) 7 (12%) 4 (7%) 4 (7%)
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Tissue quality of precut corneas for DSAEK—Nelson and Ritenour Table 2—Tissue characteristics Result Time from death to preservation Time from preservation to dissection ECD at initial preservation, cells/mm2 ECD postdissection, cells/mm2 ECD change, cells/mm2
Mean (range) 9:04 h (3:19 to 15:45) 7 þ 2.5 days (3–13) 2810 þ 320 (2200–3490) 2770 þ 320 (2220–3390) –35 (95% CI –110 to 40, p ¼ 0.3)
ECD, endothelial cell density.
in some corneas. Technician technique was expected to improve with volume of cut procedures performed. To quantify an improved outcome because of learning, we compared ECD loss in the first 33 corneas with the last 34 using the paired t test. No significant difference was detected. There was, however, an improvement in the success rate of obtaining cell density measurement postdissection. In the first 33 dissections, final ECD measurements were obtained in 17 corneas (51.5%). In the final 34 dissections, final ECD measurements were obtained in 25 corneas (73.5%). In all corneas, the 300-μm microkeratome head was used. The expected cut depth assumed by other eye banks is 370 μm.14 Of the 67 corneas included in the study, 60 had complete pachymetry measurements before and after the cut. The average precut pachymetry measured immediately after removal of the epithelium was 529 ⫾ 50 μm. The average cut depth was 347 ⫾ 53 μm, calculated by subtracting the posterior bed thickness from the predissection corneal thickness (Fig. 2). The 3 deepest cuts were 446, 459, and 540 μm, and were associated with higher predissection corneal thickness of 565, 549, and 663 μm, respectively.
DISCUSSION The comparatively low-volume Canadian Eye Bank studied demonstrated tissue quality metrics on par with those reported in larger centres elsewhere.14,15 As in other studies, there were corneas where a physiologically impossible gain in ECD was observed, as well as large losses in
Fig. 1 — Change in endothelial cell density (ECD) of sequential dissections.
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Fig. 2 — Depth of microkeratome cut of sequential dissections.
ECD. These tended to occur in corneas that were outliers in initial ECD testing and could be explained by regression to the mean or inaccurate initial measurements. This same effect was observed by Kelliher et al.,14 who reported a mean ECD gain of 136 cells/mm2, with a standard deviation of 305 cells/mm2 in 913 corneas. Chen et al.12 reported an average loss of 99 cells/mm2, with a standard deviation of 179 and a range of –351 to 531 in 80 corneas using the same specular microscope as our study. Rose et al.15 reported measurements in 6 corneas before and after dissection, and demonstrated an average loss of 328 cells/mm2 with a range of –163 to 1380 cells/mm2, although the measurements were taken at 48 hours after dissection and a EKA-98 Keratoanalyzer (Konan Medical Inc, Rancho Palos Verdes, Calif.) was used. Terry et al.16 reported clinical outcomes of 90 consecutive DSAEK procedures and demonstrated that predissection ECD had no effect on post-op ECD or the incidence of graft dislocation and primary graft failure. In our study, large outliers are best explained by measurement error. For example, 1 cornea measured 655 cells/mm2 higher after dissection. There was no significant loss of ECD during tissue handling throughout the study. Only 1 tissue was lost during handling. The collapse of the artificial chamber during cutting was related to insufficient scleral rim tissue when the cornea was initially excised from the donor. Our results are comparable with the published rates of tissue loss during dissection range from 1.5% in 913 corneas14 to 2.5% in 100 corneas.12 There were difficulties obtaining clear specular microscopy images after the dissections. Tissue distortion and corneal edema caused by excess manipulation of the corneal tissue may be implicated. This is further suggested by improvement in the rate of successful specular microscopy image acquisition in the later dissections, when the technicians had more experience with the procedure. The technicians had extensive experience with specular microscopy before the eye bank began preparing DSAEK tissue. The lack of postdissection
Tissue quality of precut corneas for DSAEK—Nelson and Ritenour ECD measurements in 25 of 66 corneas introduces a potential bias in the analysis of cell loss, because tissue that was difficult to image may have experienced more cell loss. The majority of literature on eye-bank–prepared tissue for DSAEK comes from high-volume surgical centres and large eye banks in the United States and Europe. Our study demonstrates that technicians in lower volume tissue banks can perform the procedure effectively and safely. A rigorous training program initiated by local corneal transplant surgeons using nontransplantable human corneas was effective. Cost savings are achieved by reducing operating room time required by the surgeon. These data should encourage low-volume eye banks to become involved in DSAEK tissue preparation.
Disclosure: The authors have no proprietary or commercial interest in any materials discussed in this article.
Acknowledgements: The authors acknowledge Paul Artes, PhD (Department of Ophthalmology and Vision Sciences, Dalhousie University) for assistance with statistical analysis, Catherine Hackett (Regional Tissue Bank, QEII Health Sciences Centre, Halifax, Nova Scotia), and Mary Gatien (New Brunswick Eye Bank, Saint John, Nova Scotia). REFERENCES 1. Melles GR, Lander F, Rietveld FJ, Remeijer L, Beekhuis WH, Binder PS. A new surgical technique for deep stromal, anterior lamellar keratoplasty. Br J Ophthalmol. 1999;83:327-33. 2. Melles GR, Wijdh RH, Nieuwendaal CP. A technique to excise the Descemet membrane from a recipient cornea (descemetorhexis). Cornea. 2004;23:286-8. 3. 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.
4. Allan BD, Terry MA, Price FW Jr, Price MO, Griffin NB, Claesson M. Corneal transplant rejection rate and severity after endothelial keratoplasty. Cornea. 2007;26:1039-42. 5. Boimer C, Lee K, Sharpen L, Mashour RS, Slomovic AR. Evolving surgical techniques of and indications for corneal transplantation in Ontario from 2000 to 2009. Can J Ophthalmol. 2011;46:360-6. 6. Cunningham WJ, Brookes NH, Twohill HC, et al. Trends in the distribution of donor corneal tissue and indications for corneal transplantation: the New Zealand National Eye Bank Study 20002009. Clin Experiment Ophthalmol. 2012;40:141-7. 7. Gorovoy MS. Descemet-stripping automated endothelial keratoplasty. Cornea. 2006;25:886-9. 8. Cheng YY, Tahzib NG, van Rij G, et al. Femtosecond laser-assisted inverted mushroom keratoplasty. Cornea. 2008;27:679-85. 9. Cheng YY, Schouten JS, Tahzib NG, et al. Efficacy and safety of femtosecond laser-assisted corneal endothelial keratoplasty: a randomized multicenter clinical trial. Transplantation. 2009;88: 1294-302. 10. Monterosso C, Fasolo A, Caretti L, Monterosso G, Buratto L, Böhm E. Sixty-kilohertz femtosecond laser-assisted endothelial keratoplasty: clinical results and stromal bed quality evaluation. Cornea. 2011;30:189-93. 11. 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. 12. Chen ES, Terry MA, Shamie N, Hoar KL, Friend DJ. Precut tissue in Descemet’s stripping automated endothelial keratoplasty donor characteristics and early postoperative complications. Ophthalmology. 2008;115:497-502. 13. 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. 14. Kelliher C, Engler C, Speck C, Ward D, Farazdaghi S, Jun AS. A comprehensive analysis of eye bank-prepared posterior lamellar corneal tissue for use in endothelial keratoplasty. Cornea. 2009;28:966-70. 15. Rose L, Briceño CA, Stark WJ, Gloria DG, Jun AS. Assessment of eye bank-prepared posterior lamellar corneal tissue for endothelial keratoplasty. Ophthalmology. 2008;115:279-86. 16. Terry MA, Shamie N, Chen ES, Hoar KL, Phillips PM, Friend DJ. Endothelial keratoplasty: the influence of preoperative donor endothelial cell densities on dislocation, primary graft failure, and 1-year cell counts. Cornea. 2008;27:1131-7.
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