Thickness and Curvature Changes of Human Corneal Grafts in Dextran-Containing Organ Culture Medium Before Keratoplasty

Impact of Donor, Host, and Surgical Parameters on High Endothelial Cell Density More Than 5 Years after Penetrating Keratoplasty

OBJECTIVES

To investigate the correlation between postoperative endothelial cell loss (ECL) and donor, host, and surgical parameters, and to assess the clinical impact of maintaining a high endothelial cell density (ECD) of ≥ 1500 cells/mm2 5 years after penetrating keratoplasty (PKP).

METHODS

This retrospective cohort study included 216 eyes with 5 years of follow-up, of which 94 had annual visits, and who underwent normal-risk elective PKP for noninfectious indications by one corneal microsurgeon (B. S.) between 2009 and 2016.

RESULTS

Among the 216 eyes, ECL (39.1%) over 5 years postoperative exhibited weak positive correlations with storage solution time (p = 0.024) and postmortem time (p = 0.028), and moderately positively correlations with the preoperative ECD (p < 0.001). The 5-year postoperative ECL differed significantly between in domo-prepared (36.8%) and ex domo donor corneas (46.3%; p = 0.001). In the 94 eyes, no significant differences were found between the two groups for central pupil pachymetry (CCT) and BCVA (p > 0.074). However, CCT increased significantly between 1 and 4 years (p = 0.034) and 1 and 5 years postoperatively (p = 0.012), respectively. BCVA improved significantly at 1 year postoperatively and continued to improve until 2 years postoperatively (p < 0.001).

CONCLUSION

The Lions corneal bank Saar-Lor-Lux achieved a significantly reduced ECL (36.8%) over 5 years compared to ex domo donor corneas (46.3%). A weak positive correlation was found between ECL with the storage solution time and the postmortem time, as well as a moderate positive correlation with the preoperative ECD. Although CCT increased significantly over 5 years, BCVA improved significantly from the first to the second postoperative year and remained stable thereafter.

Review for special issue: Corneal lamellar surgery: Present outcomes and future perspectives

Since the establishment of the first eye bank in the 1940s, their role has evolved to face new challenges. With the recent development of lamellar keratoplasties, eye banks play an even bigger role in the selection and preparation of donor tissues. The increasing number of keratoplasty techniques and the high demand for "ready-to-use" tissues are challenging eye banks to improve and develop new preparation techniques. Besides necessary examinations, new approaches of tissue analysis in eye banks allow a better/optimized selection of corneal tissues. These new challenges in tissue preservation, preparation, and selection are propelling eye banks into a new era of modern eye banking.

Depth-dependent mechanical properties of the human cornea by uniaxial extension

The purpose of this study was to investigate the depth-dependent biomechanical properties of the human corneal stroma under uniaxial tensile loading. Human stroma samples were obtained after the removal of Descemet's membrane in the course of Descemet's membrane endothelial keratoplasty (DMEK) transplantation. Uniaxial tensile tests were performed at three different depths: anterior, central, and posterior on 2 × 6 × 0.15 mm strips taken from the central DMEK graft. The measured force-displacement data were used to calculate stress-strain curves and to derive the tangent modulus. The study showed that mechanical strength decreased significantly with depth. The anterior cornea appeared to be the stiffest, with a stiffness approximately 18% higher than that of the central cornea and approximately 38% higher than that of the posterior layer. Larger variations in mechanical response were observed in the posterior group, probably due to the higher degree of alignment of the collagen fibers in the posterior sections of the cornea. This study contributes to a better understanding of the biomechanical tensile properties of the cornea, which has important implications for the development of new treatment strategies for corneal diseases. Accurate quantification of tensile strength as a function of depth is critical information that is lacking in human corneal biomechanics to develop numerical models and new treatment methods.

Indications and Results of Emergency Penetrating Keratoplasty With Simultaneous Cataract Surgery ("Triple-PKP à Chaud")

PURPOSE

The purpose of this study was to analyze the indications and clinical results of emergency penetrating keratoplasty with simultaneous cataract surgery ("Triple-PKP à chaud").

METHODS

This study included all subjects who underwent Triple-PKP à chaud between 2006 and 2020 at the Department of Ophthalmology, Saarland University Medical Center, Homburg/Saar in Germany. Data obtained from patient records were retrospectively analyzed.

RESULTS

Triple-PKP à chaud was successfully performed in 27 of 29 eyes with a mean age of 66.0 ± 19.9 years. Previous surgery was performed in 20 eyes (69.0%), most frequently amniotic membrane transplantation in 11 eyes (37.9%) and previous keratoplasty in 9 eyes (31.0%). The most common indication was infectious keratitis (62.1%). In 27 subjects (93.1%), capsulorhexis was performed using the open-sky technique. The most frequent intraoperative complication was positive vitreous pressure (24.1%). In 2 eyes (6.9%), no intraocular lens implantation was performed because of posterior capsule rupture. The preoperative uncorrected visual acuity improved from 2.2 ± 0.6 logMAR (range = 3.0-0.7 logMAR) to 1.3 ± 0.7 logMAR (range = 3.0-0.18 logMAR) postoperatively ( P < 0.001). Common postoperative complications were suture loosening (44.4%) and corneal epithelial defects (33.3%). Repeat keratoplasty was necessary in 14 eyes (51.9%), including 9 eyes (64.2%) within 12 months postoperatively. The mean graft survival was 12.2 ± 17.9 months (range = 1-69 mo).

CONCLUSIONS

Triple-PKP is also feasible in emergency conditions. Nevertheless, the surgery is associated with an increased risk of intraoperative and postoperative complications. Combined surgery should, therefore, only be performed in severely diseased eyes with progressed stage of cataract.

Reliability and efficiency of corneal thickness measurements using sterile donor tomography in the eye bank

To evaluate the reliability and efficiency of sterile pachymetric measurements of donor corneas based on tomographic data using two different methods: a "manual" and a "(semi-)automated" method. Twenty-five (25) donor corneas (50%) stored in MI and 25 (50%) in MII were imaged 5 times consecutively using an anterior segment OCT (AS-OCT). The central corneal thickness (CCT) was measured both with the manual measurement tool of the AS-OCT (= CCTm) and with a MATLAB self-programmed software allowing (semi-)automated analysis (= CCTa). We analyzed the reliability of CCTm and CCTa using Cronbach´s alpha (α) and Wilcoxon signed-Rank Test. Concerning CCTm, 68 measurements (54.4%) in MI and 46 (36.8%) in MII presented distortions in the imaged 3D-volumes and were discarded. Concerning CCTa, 5 (4%) in MI and 1 (0.8%) in MII were not analyzable. The mean (± SD) CCTm was 1129 ± 6.8 in MI and 820 ± 5.1 µm in MII. The mean CCTa was 1149 ± 2.7 and 811 ± 2.4 µm, respectively. Both methods showed a high reliability with a Cronbach´s α for CCTm of 1.0 (MI/MII) and for CCTa of 0.99 (MI) and 1.0 (MII). Nevertheless, the mean SD of the 5 measurements was significantly higher for CCTm compared to CCTa in MI (p = 0.03), but not in MII (p = 0.92). Sterile donor tomography proves to be highly reliable for assessment of CCT with both methods. However, due to frequent distortions regarding the manual method, the (semi-)automated method is more efficient and should be preferred.

Orientation and depth dependent mechanical properties of the porcine cornea: Experiments and parameter identification

The porcine cornea is a standard animal model in ophthalmic research, making its biomechanical characterization and modeling important to develop novel treatments such as crosslinking and refractive surgeries. In this study, we present a numerical model of the porcine cornea based on experimental measurements that captures both the depth dependence and orientation dependence of the mechanical response. The mechanical parameters of the established anisotropic hyperelastic material models of Gasser, Holzapfel and Ogden (HGO) and Markert were determined using tensile tests. Corneas were cut with a femtosecond laser in the anterior (100 μm), central (350 μm), and posterior (600 μm) regions into nasal-temporal, superior-inferior, and diagonal strips of 150 μm thickness. These uniformly thick strips were tested at a low speed using a single-axis testing machine. The results showed that the corneal mechanical properties remained constant in the anterior half of the cornea regardless of orientation, but that the material softened in the posterior layer. These results are consistent with the circular orientation of collagen observed in porcine corneas using X-ray scattering. In addition, the parameters obtained for the HGO model were able to reproduce the published inflation tests, indicating that it is suitable for simulating the mechanical response of the entire cornea. Such a model constitutes the basis for in silico platforms to develop new ophthalmic treatments. In this way, researchers can match their experimental surrogate porcine model with a numerical counterpart and validate the prediction of their algorithms in a complete and accessible environment.

Approval rates for corneal donation and the origin of donor tissue for transplantation at a university-based tertiary referral center with corneal subspecialization hosting a LIONS Eye Bank

BACKGROUND

With the increasing demand for corneas, eye banks must optimize the tissue donation, collection, and selection process. This retrospective monocentric study analyzed the approval rates for corneal donation and the origin of and reasons for discarding donor corneas from 2010 to 2019.

METHODS

Data included the number of deceased, approval or rejection by the family for corneal donation and contraindications. Corneal grafts were included from all deceased persons who were full-body and multi-organ donors at the Saarland University Medical Center (UKS) and from external institutions. Additional analyzed parameters included endothelial cell count (ECC), blood sample serology for infections, and conjunctival swab testing .

RESULTS

A total of 1748 corneoscleral buttons were harvested from 10,265 deceased persons (17% with no contraindication) at the UKS between 2010 and 2019, with a consent rate of 23.3%. The number of keratoplasties increased from 136 in 2010 (15% of the deceased, total = 925) to 251 in 2019 (21%, total = 1214). Both the general and department-specific data showed similar percentages for corneal donation over the years, with intensive care and palliative units recently providing the most corneas. The increase in the number of corneas processed by the cornea bank over the years (368 in 2010 compared with 857 in 2019) was linked both to a better internal supply in 2010 (262, 71.2% of the total) compared with 2019 (519, 60.6%) and to an external supply by reinforcement of cooperation with external hospitals, including Luxembourg in 2010 (106, 28.8% of the total) compared with 2019 (338, 39.4%). A total of 195 of 377 corneas (52%) were discarded in 2009 compared with 260 out of 715 (36%) in 2019. The main reasons for discarding were low ECC (36% of discarded corneas in 2009; 11% in 2019), positive conjunctival swab (11% in 2009; 13% in 2019), and blood sample serology (6% in 2009 and in 2019).

CONCLUSION

Despite an increasing number of donors, the demand for corneas is still rising. Improved cooperation with internal departments and with external clinics has led to an increasing number of explanted corneas. The main reason for discarding corneas was low ECC, followed by a positive conjunctival swab for fungal or bacterial contamination and serology. Increased donation rates and continued improvements in collection and selection processes are necessary to cover the high demand for corneas.

Comparison of clinical outcomes after precut DMEK with or without dextran-containing medium compared to standard DMEK: a prospective pilot study

PURPOSE

To investigate the clinical outcome and complication rate of precut Descemet membrane endothelial keratoplasty (DMEK) in two different culture conditions, dextran-containing and dextran-free medium, and compare the results with the current standard DMEK procedure.

METHODS

A prospective study of 32 eyes suffering from Fuchs endothelial dystrophy were scheduled for DMEK with a follow-up of one year. The eyes were divided into four subgroups. Group + D (n = 7) received a precut DMEK stored in dextran-containing transport medium, and Group - D (n = 9) received a precut DMEK without dextran-containing medium. The respective fellow eyes received a standard DMEK (S) (preparation directly prior to surgery) stored in dextran-containing medium (S-D + ; n = 7) or without (S-D-; n = 9).

RESULTS

Clinical outcome (visual acuity, endothelial cell count, central corneal thickness) and rebubbling rate were comparable for all four groups. None of the patients had a graft failure.

CONCLUSION

The preliminary data of the pilot study show that precut liquid-bubble DMEK leads to comparable clinical results regardless of dextran-containing or dextran-free organ culture medium and is further comparable to the standard DMEK procedure.

OCT Application for Sterile Corneal Graft Screening in the Eye Bank

BACKGROUND AND OBJECTIVE

Sterile donor tomography enables the detection of corneal tissues with refractive anomalies. The aim of this study was to determine the curvature and thickness of donor corneas to support proper selection in the eye bank.

METHODS

704 donor corneas (Klaus Faber Center, LIONS Eye Bank Saar-Lor-Lux, Trier/Westpfalz, in Homburg/Saar) were measured using the anterior segment optical coherence tomograph (AS-OCT) CASIA 2 (Tomey Corp., Nagoya, Japan). The corneoscleral discs were measured in their cell culture flask, which was positioned in a holder on the chin rest of the AS-OCT, after conversion to medium II (with 6% dextran T-500). The measured raw data were analysed and processed in MATLAB (MathWorks Inc., Natick, Massachusetts, USA), after which the refractive power of the steep and flat meridian at the anterior and posterior surface and the central corneal thickness (CCT) of the donor corneas were determined. Results values are expressed as mean x̅ ± standard deviation SD.

RESULTS

The mean refractive power of the steep/flat meridian at the anterior surface was 45.4 ± 1.8 D/44.0 ± 1.3 D, the corresponding values for the posterior surface were - 6.2 ± 0.3 D/- 5.9 ± 0.2 D, and the mean CCT was 616.3 ± 85.1 µm. Of the 704 (100%) measured donor tissues, 590 (83.8%)/670 (95.2%) donor corneas showed no anomaly beyond respectively x̅ ± 2 SD/x̅ ± 3 SD among the 5 examined parameters. 72 (10.3%)/23 (3.3%) donor corneas had only 1 anomaly, 26 (3.7%)/10 (1.4%) had 2 anomalies, 10 (1.4%)/1 (0.1%), 3 anomalies, 5 (0.7%)/0 (0.0%), 4 anomalies, and 1 (0.1%)/0 (0.0%), 5 anomalies.

CONCLUSIONS

AS-OCT provides an objective and sterile screening method to identify corneal tissues with curvature anomalies in order to further optimise donor selection in the eye bank. To avoid postoperative refractive surprises, donor corneas with a total refractive power that deviates > ± 3 SD from the mean should not be used for penetrating or anterior lamellar keratoplasty, but may be suitable for posterior lamellar keratoplasty (DMEK or DSAEK). In the future, sterile donor tomography could enable: (1) the harmonisation of donor and recipient tomography, which may minimise residual astigmatism for a particular donor-recipient pair; and (2) the improvement of IOL power calculation in a classical triple procedure by means of regression analysis between pre- and postoperative total refractive power of corneal grafts.

Vergleich der sterilen Spendertomographie in der Hornhautbank mit der Tomographie des Transplantates nach perforierender Keratoplastik

Hintergrund

Seit 2018 verwenden wir die sterile Spendertomographie in der Hornhautbank routinemäßig, um refraktive Überraschungen nach Keratoplastik zu vermeiden. Ziel dieser Studie war es, Spendertomographieparameter mit Tomographieparametern des Transplantates nach perforierender Keratoplastik (PKP) zu vergleichen.

Methoden

Diese Studie umfasste 193 Spendergewebe der Hornhautbank, die für eine PKP verwendet wurden (Transplantatdurchmesser 8,2 ± 0,7 mm). Messungen wurden mit dem optischen Kohärenztomographen des vorderen Augenabschnittes (VAA-OCT) Casia 2 (Tomey Corp., Nagoya, Japan) präoperativ sowie postoperativ nach 5 ± 4 Monaten bei liegenden Fäden und nach 22 ± 4 Monaten ohne Fäden durchgeführt. Post- und präoperative Werte wurden mithilfe des Wilcoxon-Rangsummentests verglichen.

Ergebnisse

Postoperativ, bei liegenden (bzw. ohne) Fäden, war die Brechkraft (P) der Hornhautvorderfläche (v) im steilen Meridian (S) (PvS) unverändert (−0,2 dpt; p = 0,78) (um 2,7 dpt größer [p < 0,01]) und im flachen Meridian (F) (PvF) um 4,5 dpt (2,8 dpt) niedriger (p < 0,01) im Vergleich zu den Spendertomographiewerten. Der Astigmatismus (v) war um 4,3 dpt (5,4 dpt) größer (p < 0,01). An der Rückfläche (r) war PrS um 0,9 dpt (0,9 dpt) und PrF um 0,3 dpt (p < 0,01) (0,1 dpt [p = 0,42]) kleiner, während der Astigmatismus (r) um 0,7 dpt (0,9 dpt) größer war (p < 0,01). Die zentrale Hornhautdicke war um 55,7 μm (p < 0,01) (27,5 µm [p = 0,01]) kleiner. Die Gesamtbrechkraft ohne Fäden änderte sich nicht signifikant im Vergleich zur Hornhautbankmessung.

Schlussfolgerung

Zentrale Hornhautdicke, Brechkraft (P) und Astigmatismus veränderten sich postoperativ im Vergleich zu den Spendertomographiewerten, mit Ausnahme von P im steilen Meridian der Vorderfläche bei liegenden Fäden sowie von P im flachen Meridian der Rückfläche nach Entfernung aller Fäden. Die Gesamtbrechkraft ohne Fäden ändert sich allerdings nicht signifikant. Diese Informationen könnten für eine Verbesserung der Kunstlinsenberechnung bei klassischer „Triple-Procedure“ von Bedeutung sein.