Intrinsic ultrastructural abnormalities of the Descemet membrane were observed in 7 of 16 grafts; this included abnormal banded and fibrillary collagen inclusions within the normally non-banded posterior layer, which is indicative of pre-existing corneal endothelial dysfunction (Fig. 3B–D). Abnormal fibrillary inclusions and posterior deposition of collagen fibers were also found in some of the specimens (Fig. 3B). Of the 7 specimens, 1 showed signs of beginning guttae formation, indicating the presence of early stages of Fuchs’ dystrophy in the donor (Fig. 3D). Only 1 of 16 specimens showed no abnormalities of the Descemet membrane.
Donor graft preparation, a successful surgical procedure, and a lack of postoperative complications are crucial for the success of DMEK. Complications in any surgical step can lead to primary or secondary graft failure.
Of the 16 specimens that we analyzed, 3 showed upside down transplantation that led to graft failure. We strongly recommend presurgical marking of the donor Descemet membrane to avoid this complication.[11,12] We think that the need for numerous failing re-bubbling procedures may be a strong sign of upside down transplantation.
Studies show that graft failure after DMEK occurs in 1.6% to 8% of patients.[13–15]
The majority of patients with primary or secondary graft failure show ultrastructural anomalies of the donor Descemet membrane, including intrinsic abnormal inclusions in the Descemet membrane and/or posterior collagenous layers deposited onto the membrane.[5,16] Abnormal inclusions within the Descemet membrane may reflect pre-existing subclinical endothelial dysfunction prior to transplantation, whereas retrocorneal collagen deposits and fibroblast-like endothelial cells indicate peri- and postoperative endothelial damage.
Ultrastructural changes with abnormal banded and fibrillary collagen inclusions (like a duplicated anterior banded layer within the posterior nonbanded layer in Fig. 3B) within the normally nonbanded posterior layer may also be a sign of incomplete removal of recipient's Descemet membrane. Brockmann et al found that incomplete removal of the Descemet membrane from the recipient's stroma can increase the detachment rate. They discovered an increased thickness of the anterior banded layer in patients with graft detachment and concluded that residual anterior banded layer fragments on the recipients’ stroma can create an anatomical border.
Ultrastructural changes observed in a donor Descemet membrane may be preexisting or may be acquired during tissue harvesting, tissue storage, graft preparation, or surgery. Weller et al also concluded that ultrastructural anomalies can be signs of preoperative corneal endothelial dysfunction. The donor tissue we used did not show any noticeable problems during examination in our eye bank. However, the presence of early stages of pseudoexfoliation-associated keratopathy and cornea guttata may have gone undetected.
Of the 16 specimens, 9 showed an abnormal PCL. Weller et al postulated that a PCL may be indicative of intraoperative or postoperative trauma and is thought to be produced by damaged, fibroblast-like endothelial cells. In our study, there was no mathematical correlation between the thickness of the abnormal PCL (which ranged from 0.65 to 20 μm) and the time period until repeat surgery (which ranged from 2 to 39 months). However, this could be due to the small number of cases. In our case series, we could not evaluate potential risk factors during organ culture, graft preparation, or intraoperative manipulation in all patients, because 8 of the patients were referred to our department from other hospitals.
Important indicators for graft preparation and unfolding include donor age, the presence of diabetes mellitus, previous phacoemulsification of the donor, and storage medium during organ culture.[7,9,10] The storage medium may also influence the detachment rate. Heinzelmann et al discussed storage in dextran as a risk factor for ultrastructural anomalies that could lead to primary graft failure after DMEK, especially in precut tissues, but the study only included 11 eyes. We also found that dextran in prestripped tissue had a negative impact on graft survival because there was a higher rate of repeat keratoplasty after DMEK when the tissues were stored in culture medium with dextran. On the other hand, Yoeruek and Bayyoud reported only a moderate loss of endothelial cells in precut tissue and safe donor graft preparation with or without dextran.[20,21] Parekh et al concluded that dextran should be used in precut tissues to prevent the loss of endothelial cells.
We think that the presence of pigment granules in the interface may decrease adhesion between the donor graft and recipient stroma. Pseudoexfoliation or pigment dispersion syndrome, both of which are associated with pigment liberation from the iris pigment epithelium, may cause pigment accumulation in the interface. However, further investigations in a larger study population are required. Peri-operative YAG iridotomy is another potential source of pigment, so we now perform YAG iridotomy at the 6 o’clock position many weeks before DMEK rather than the day before surgery. This may help avoid pigment dispersion during DMEK surgery.
To summarize, major causes of graft failure include previously undetected endothelial dysfunction or disease in the donor, endothelial damage during surgery, or surgical mistakes, such as inverted transplantation and damage to iris tissue, that results in the accumulation of pigmented cells or pigment granules in the Descemet–stroma interface, resulting in poor graft adhesion.[10,16,24]
After repeat surgery, postoperative visual acuity improved significantly in all of our patients, and central cornea thickness decreased significantly. We conclude that repeat penetrating keratoplasty and repeat DMEK can lead to satisfactory functional results after failed DMEK and new triple procedure.
This study had some limitations, in that it was a retrospective study with a small number of cases. Prospective studies are warranted, including a larger case series, especially to investigate the culture conditions (e.g. role of dextran) to strengthen the interpretation of our results. A better understanding of graft failure may help in the development of preventive methods in the future.
Conceptualization: Ursula Schlötzer-Schrehardt, Berthold Seitz.
Data curation: Ursula Schlötzer-Schrehardt, Berthold Seitz.
Formal analysis: Achim Langenbucher.
Investigation: Ursula Schlötzer-Schrehardt, Annette Zimpfer.
Methodology: Achim Langenbucher, Berthold Seitz.
Project administration: Berthold Seitz.
Software: Achim Langenbucher, Timo Eppig.
Supervision: Ursula Schlötzer-Schrehardt, Timo Eppig, Tobias Hager, Berthold Seitz.
Validation: Achim Langenbucher, Berthold Seitz.
Writing – original draft: Isabell Schmidt.
Writing – review & editing: Ursula Schlötzer-Schrehardt.
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Keywords:Copyright © 2019 The Authors. Published by Wolters Kluwer Health, Inc. All rights reserved.
Descemet membrane; DMEK; graft failure; transmission electron microscopy; ultrastructural findings