Eye bank issues: II. Preservation techniques: warm versus cold storage

Risk of tuberculosis transmission by tissue transplantation: a quantitative risk assessment

Two recent tuberculosis outbreaks in the United States implicated a contaminated bone graft product containing living cells. Evidence-based donor selection criteria may help prevent future tragic events like these. However, the development of such criteria must be informed by estimates of the risk of tuberculosis transmission by tissue transplantation, which are currently lacking. Therefore, we aimed to estimate the risk of tuberculosis transmission through tissue transplantation in Québec, Canada. We developed a deterministic model to assess the risk of tuberculosis transmission through the transplantation of skin, cardiovascular, musculoskeletal, and ocular tissues. Transmission risk was estimated according to three scenarios (i.e., most-likely, optimistic, and pessimistic). Except for ocular tissues, the estimated risk was consistently < 1 in 1 million transplantations, even after inflating some parameters by 50% or 100%. In the most-likely scenario, the risk of transmission by ocular tissue transplantation was estimated at only 1 in 312,160. The calculated risk of tuberculosis transmission by tissue transplantation is extremely low in our jurisdiction and does not warrant the implementation of additional risk mitigation measures beyond those currently in place. Albeit low, the estimated risk was higher for ocular grafts in part because they contain living cells, which is not the case of gamma-irradiated tissues. Our work showcases how the selection criteria of tissue donors can be informed by risk estimates derived from mathematical models.

A corneal and whole eye globe bovine ex vivo model to mimic human donor corneal storage conditions and eye surgeries

PURPOSE

This study aimed to develop a bovine ex vivoex vivo model to simulate human donor corneal storage conditions and assess the feasibility of human eye surgeries in bovine eye bulbs.

METHODS

Calf eye bulbs (n = 19) were obtained from local slaughterhouses. Ten corneas were excised, with five maintained in hypothermic storage (2-8 °C): corneal quality parameters, including endothelial cell (EC) density (ECD), EC mortality and morphology, corneal transparency, and central corneal thickness, were monitored up to 14 days of preservation. Five corneas were assigned to non-vital imaging techniques to investigate cell and nuclei morphology. Human donor corneas (n = 5) in hypothermic storage were assessed as a control group. Nine bovine eye bulbs were used to mimic human eye surgeries, including capsulorhexis and open-sky vitrectomy with inner limiting membrane (ILM) removal, to evaluate their feasibility in the bovine model.

RESULTS

Calf corneal endothelia exhibited a regular mosaic of hexagonal-shaped cells with oval-shaped nuclei and occurrence of binucleated cells. Calf ECD and EC morphology remained stable during the storage, although EC mortality and CCT increased, and corneal transparency and VECD decreased over time. ECD, EC mortality, and CCT were significantly higher in calf than in human corneas, while corneal transparency was lower. ECD change and EC morphology were statistically comparable between the two species. In the whole eye bulb, the narrow horizontal pupil reduced posterior chamber visualization, necessitating an open-sky approach for vitrectomy and ILM removal. Capsulorhexis was performed following complete iridectomy.

CONCLUSIONS

The presented bovine model offers a reliable alternative to human donor tissues for preliminary studies on corneal preservation and ophthalmic surgical procedures.

Incidence and Implications of Culture-Positive Corneoscleral Rims in Corneal Transplantation

Background

Corneal transplantation is a critical procedure for restoring vision affected by different corneal pathologies. However, postoperative infections threaten graft survival, particularly microbial keratitis and endophthalmitis.

Objective

This study aims to evaluate the incidence of culture-positive corneoscleral rims (CPCR) among transplanted corneas at a tertiary eye hospital and explore its association with death-preservation and preservation-surgery times.

Methods

A retrospective analysis of keratoplasty surgeries performed in 2015 was conducted, involving 603 cases meeting the study criteria.

Results

The incidence of CPCR was found to be 4.6%, predominantly bacterial (68%), with Methicillin-resistant Staphylococcus epidermidis (MRSE) being the most common isolate, followed by fungal (32%) species, notably Candida. However, none of the cases developed subsequent keratitis or endophthalmitis post-transplantation. Statistical analysis revealed no significant association between CPCR occurrence and death-preservation or preservation-surgery times.

Conclusion

The study underscores the reduced impact of contaminated CPCR on graft outcomes, advocating for targeted fungal culturing, intraoperative practices to mitigate post-transplant infections, and maintaining current prophylactic antibiotic regimens, such as optisolGS ™, which contains streptomycin and gentamicin.

Biomimetic Air-Lifted Organ Culture System with a Protective Coverage Membrane for Full-Thickness Corneal Preservation

Effective storage and utilization of limited donor corneal resources are in high demand to alleviate the shortage of donor corneal tissue. Here, we designed a static air-lifted organ culture system equipped with a protective coverage membrane, namely, an air-lifted OC-P system, to provide a biomimetic physiological environment for full-thickness corneal preservation. The air-lifted OC-P system features a unique collagen-based protective coverage membrane that can offer a moist, oxygen-rich environment for corneal epithelium, produce an appropriate intraocular pressure onto the cornea by gravity, and facilitate the maintenance of the organ culture medium level for nutrient supply during corneal preservation. Compared with conventional submerged and air-lifted corneal preservation methods, the air-lifted OC-P system remarkably improved the overall quality of the preserved corneas. These preserved corneas not only exhibited superior controllability of corneal swelling and extraordinary maintenance of the morphology and viability of all three types of corneal cells (i.e., corneal epithelium, keratocytes, and endothelium) but also demonstrated optimal optical, thermal, and mechanical properties. This air-lifted OC-P system presents a biomimetic strategy that provides a static and efficient method to replicate the corneal natural conditions for corneal preservation effectively.

Expression of Yes-associated protein in endothelial cells of human corneas before and after storage in organ culture

The cornea, the anterior meniscus-shaped transparent and refractive structure of the eyeball, is the first mechanical barrier of the eye. Its functionality heavily relies on the health of its endothelium, its most posterior layer. The treatment of corneal endothelial cells (CECs) deficiency is allogeneic corneal graft using stored donor corneas. One of the main goals of eye banks is to maintain endothelial cell density (ECD) and endothelial barrier function, critical parameters influencing transplantation outcomes. Unlike in vivo, the stored cornea is not subjected to physiological mechanical stimuli, such as the hydrokinetic pressure of the aqueous humor and intraocular pressure (IOP). YAP (Yes-Associated Protein), a pivotal transcriptional coactivator, is recognized for its ability to sense diverse biomechanical cues and transduce them into specific biological signals, varying for each cell type and mechanical forces. The biomechanical cues that might regulate YAP in human corneal endothelium remain unidentified. Therefore, we investigated the expression and subcellular localization of YAP in the endothelium of corneas stored in organ culture (OC). Our findings demonstrated that CEC morphology, ECD and cell-cell interactions are distinctly and differentially associated with modifications in the expression, subcellular localization and phosphorylation of YAP. Notably, this phosphorylation occurs in the basal region of the primary cilium, which may play central cellular roles in sensing mechanical stimuli. The sustained recruitment of YAP in cellular junctions, nucleus, and cilium under long-term OC conditions strongly indicates its specific role in maintaining CEC homeostasis. Understanding these biophysical influences could aid in identifying molecules that promote homeostasis and enhance the functionality of CECs.

Retrospective Clinical Outcomes of Keratoplasty Using Human Donor Corneas Preserved in Eusol-C Hypothermic Storage Medium

Objective: To evaluate the clinical outcomes of cornea transplantation (penetrating keratoplasty, Descemet membrane endothelial keratoplasty, Descemet stripping automated endothelial keratoplasty, and deep anterior lamellar keratoplasty) using donor corneas stored in Eusol-C hypothermic storage medium compared to corneas stored in organ-culture. Methods: The clinical outcomes of 92 patients who underwent corneal transplantation with human donor corneas stored in Eusol-C medium at 2-8 °C were retrospectively evaluated. The control group consisted of 169 patients who received corneas organ-cultured at 31 °C. Donor age, sex, death-to-preservation time, and storage time were recorded. Endothelial cell (EC) density (ECD), EC mortality, and EC morphology scores were evaluated during storage in both groups. Complication rates, visual outcomes, and corneal transparency were monitored for up to six months. Results: The mean storage in Eusol-C time was 7.7 ± 2.5 days, while organ-culture time was 14.2 ± 4.0 days. In the Eusol-C group, ECD was 2398 ± 354 cells/mm2, with an average EC morphology score of 3.4 ± 0.7/4. Approximately 28% of the corneas in the Eusol-C group had no EC mortality. In the organ-culture group, ECD was 2256 ± 328 cells/mm2, with an average EC morphology score of 3.5 ± 0.5/4, and 42% were devoid of EC mortality. No complications, such as re-bubbling, were observed in both groups during surgery. Transparent corneas were achieved in 81.3% of the Eusol-C group the day after surgery. Mean corrected distance visual acuity (CDVA) at 3 and 6 months was 4.5 ± 4.0/10 and 5.4 ± 3.7/10 for the Eusol-C group and 5.0 ± 2.9/10 and 5.7 ± 2.8/10 for the organ-culture group, with no statistical differences observed between the groups. No graft failure was observed up to three months. Graft rejection occurred in the Eusol-C group and in the organ-culture group in, respectively, one and two cases at the six-month follow-up. Conclusions: Comparable surgical outcomes were achieved with donor corneas stored in both hypothermic Eusol-C and organ-culture media.

Trends in infectious adverse events after elective optical keratoplasty (PK, EK, and ALK) - Ten years' analysis from an eye bank

PURPOSE

To report the clinical profile and donor characteristics of post-optical keratoplasty adverse events notified at an eye bank.

METHODS

Between January 2013 and December 2022, 37,041 donor corneas were utilized for keratoplasty, of which 16,531 were used for penetrating keratoplasty (PK), 12,171 for endothelial keratoplasty (EK), and 1356 for anterior lamellar keratoplasty (ALK). EK included 10,956 Descemet stripping automated endothelial keratoplasty (DSAEK) and 1215 Descemet membrane endothelial keratoplasty (DMEK). The adverse events reported within the first 6 weeks of optical keratoplasty were analyzed for donor-related parameters.

RESULTS

A total of 41 (0.11%) recipients had post-keratoplasty infections. Of these, 33 occurred after EK (29 after DSAEK, and four after DMEK), two after ALK, and six after PK. The clinical presentation was keratitis alone in 16 eyes and associated with endophthalmitis in 25 eyes. The organisms isolated were gram-negative bacteria in 26 eyes, fungus in eight eyes, gram-positive bacteria in four eyes, mixed infection in five eyes, and microbiology inconclusive in seven eyes. The majority (78%) of the gram-negative infections were due to multidrug-resistant organisms. Most (88%) donor corneas were harvested from hospital premises. The most common cause of donor mortality was trauma. The median duration of presentation from surgery was 4.46 (range: 1-30) days. The death to preservation time was 4.18 (1.5-7.65) hours. The death to utilization time was 3 (2-4.7) days.

CONCLUSION

The overall risk of infectious adverse events after keratoplasty was 0.11%, ranging from 0.08% to 0.36%. Most (80.4%) of the adverse events occurred after EK. The majority (78.9%) of the adverse events were of bacterial etiology, of which gram-negative infections (68.4%) were the most common. The trends and microbiological spectrum of organisms associated with infections should be thoroughly documented in eye banks to gain insights and formulate guidelines on the management of adverse events.

Investigating the Influence of Temperature and Supplementation Timing on Antifungal Efficacy in Storage Medium for Corneal Transplantation

INTRODUCTION

Although antifungal supplementation reduces the fungal load in the corneal storage medium, consensus is lacking on the influence of dosing and temperature. The study aims to evaluate the impact of eye bank warming protocol and timing of antifungal supplements on efficacy in Optisol-GS and tissue.

METHODS

Corneoscleral rims contaminated with Candida albicans (C. albicans) were incubated in Optisol-GS, either without antifungal agents or with the addition of amphotericin B or voriconazole at various concentrations (2 ×, 5 ×, 10 ×, and 20 × MIC), at different time points, and under various preservation temperatures (2-8 °C versus 2 h-room temperature exposure). Antifungal efficacy was evaluated by counting viable yeast colonies cultured from Optisol-GS samples. Tissue sterility was determined through direct tissue culture and histological examination of the contaminated rims after a 14-day incubation period.

RESULTS

Room temperature exposure did not increase colony growth at the same multiple MIC of antifungal agents. Although antifungal addition reduced C. albicans growth in a concentration-dependent manner, yeast growth was still observed in all Optisol-GS samples with a single supplementation after a 14-day incubation. Only groups with additional antifungal supplementation on either day 2 or day 6 showed a 99% or greater reduction of C. albicans growth in Optisol-GS samples and yielded negative results in direct tissue culture.

CONCLUSIONS

The eye bank warming protocol did not compromise antifungal efficacy. To sustain the required concentration and effectively reduce C. albicans growth in Optisol-GS and contaminated tissue, additional antifungal supplementation on either day 2 or day 6 was necessary during a 2-week preservation period.

The expanding roles of eye banks in India: Past, present, and future

This review highlights the evolution in the scope of eye banking activities in India. The roles and responsibilities of the eye banks have expanded to match the requirements and necessities that arose because of advancements in keratoplasty techniques and the need for corneal surgeons. Adoption of different types of corneal preservation solutions and methods of donor cornea preservation was a consequence of the changing and unprecedented times. The growth of eye banking in India has been a commendable journey and has placed the country in an "almost sufficient" category in eye banking and corneal transplantation. There exists a potential to reach the status of cornea surplus country in the future. The rules and laws governing eye banking operations need dynamic amendments based on the trends in keratoplasty, surgical practice patterns, and status of self-sufficiency. Newer technological advances and quality measures must be adopted in donor cornea evaluation and tissue preparation. Research should be integrated as an important component of eye banking, especially in developing novel methods of donor preservation, and evaluating and validating the existing and changing practices of eye banking.

Quality assurance in corneal transplants: Donor cornea assessment and oversight

The cornea is the most frequently transplanted human tissue, and corneal transplantation represents the most successful allogeneic transplant worldwide. In order to obtain good surgical outcome and visual rehabilitation and to ensure the safety of the recipient, accurate screening of donors and donor tissues is necessary throughout the process. This mitigates the risks of transmission to the recipient, including infectious diseases and environmental contaminants, and ensures high optical and functional quality of the tissues. The process can be divided into 3 stages: (1) donor evaluation and selection before tissue harvest performed by the retrieval team, (2) tissue analysis during the storage phase conducted by the eye bank technicians after the retrieval, and, (3) tissue quality checks undertaken by the surgeons in the operating room before transplantation. Although process improvements over the years have greatly enhanced safety, quality, and outcome of the corneal transplants, a lack of standardization between centers during certain phases of the process still remains, and may impact on the quality and number of transplanted corneas. Here we detail the donor screening process for the retrieval teams, eye bank operators. and ophthalmic surgeons and examine the limitations associated with each of these stages.

An untargeted metabolomics approach to study changes of the medium during human cornea culture

INTRODUCTION

Two main approaches (organ culture and hypothermia) for the preservation and storage of human donor corneas are globally adopted for corneal preservation before the transplant. Hypothermia is a hypothermic storage which slows down cellular metabolism while organ culture, a corneal culture performed at 28-37 °C, maintains an active corneal metabolism. Researchers, till now, have just studied the impact of organ culture on human cornea after manipulating and disrupting tissues.

OBJECTIVES

The aim of the current work was to optimize an analytical procedure which can be useful for discovering biomarkers capable of predicting tissue health status. For the first time, this research proposed a preliminary metabolomics study on medium for organ culture without manipulating and disrupting the valuable human tissues which could be still used for transplantation.

METHODS

In particular, the present research proposed a method for investigating changes in the medium, over a storage period of 20 days, in presence and absence of a human donor cornea. An untargeted metabolomics approach using UHPLC-QTOF was developed to deeply investigate the differences on metabolites and metabolic pathways and the influence of the presence of the cornea inside the medium.

RESULTS

Differences in the expression of some compounds emerged from this preliminary metabolomics approach, in particular in medium maintained for 10 and 20 days in presence but also in the absence of cornea. A total of 173 metabolites have been annotated and 36 pathways were enriched by pathway analysis.

CONCLUSION

The results revealed a valuable untargeted metabolomics approach which can be applied in organ culture metabolomics.

Corneal endothelial validation in the eye bank: differences in automated methods and repeatability

PURPOSE

To evaluate reproducibility of endothelial cell density (ECD) measurements using the Konan Cell Check D in donor corneas by two different ophthalmologists and to compare the two automated cell count methods (center and flex-center) available in the software of this specular microscope.

METHODS

ECD values were quantified in 54 donor corneas by two independent investigators using the Cell Check D (Konan Medical USA Inc) with both automated cell count methods. In the center method, at least 30 contiguous cells are marked. For the flex-center method, an area is delineated and only the cells within the designated area are counted.

RESULTS

The mean ECD was 2473.81±378.22 cells/mm2. Good ECD intergrader reproducibility for the center (ICC=0.821) and the flex-center method (ICC=0.784) were noted. Poor reliability was observed for coefficient of variation and hexagonality (ICC≤0.265). When both methods for ECD analysis were compared, a moderate correlation for the two independent graders using the two manual (center and flex-center) methods was detected (correlation coefficient of 0.678 and 0.745 for each of the investigators). Comparison between methods yielded significantly higher ECD with the flex-center method (P=0.013). When corneas were divided by ECD, those under 2200 cells/mm2 and those between 2200 and 2700 cells/mm2 also had significantly higher ECD with the flex-center method (P<0.022).

CONCLUSIONS

ECD values are reproducible with both methods, although the flex-center method ECDs tend to be higher, particularly in cases of low ECD. Eye banks and surgeons should exercise caution in making decisions based only on small differences in ECD.

Assessment of performance and safety of Corneal Chamber hypothermic storage medium and PSS-L corneal rinsing solution in human and porcine corneas

PURPOSE

To prove the safety and performance of the hypothermic corneal storage medium "Corneal Chamber" and the rinsing solution "PSS-L" in support of the new Conformité Européenne (CE) certification process in accordance with the Medical Device Regulation.

METHODS

Fifteen (n=15) human donor corneas and 11 (n=11) porcine corneas were evaluated for the following parameters: endothelial cell density (ECD) and mortality, percentage of hexagonal cells (HEX%), coefficient of cellular area variation (CV%) and corneal transparency at Day 0 and after 14±1 days of storage in Corneal Chamber medium at 2-8°C. Then, the same parameters were assessed after rinsing of corneas in PSS-L for 1 min at room temperature. Evaluation of gentamicin sulfate carryover after corneal storage and PSS-L rinsing was performed by ultra-high performance liquid chromatography analysis on human corneas homogenates.

RESULTS

Human and porcine corneas stored in Corneal Chamber medium showed a good overall quality of the tissue according to the quality parameters evaluated. In particular, mean ECD, HEX% and CV% did not show statistically significant changes at the end of storage and endothelial mortality increased to 3.1±3.3 and 7.8±3.5% in human and porcine corneas, respectively. Tissue rinsing with PSS-L did not affect the quality parameters evaluated before and gentamicin sulfate residues were absent in human corneas.

CONCLUSIONS

Corneal preservation in Corneal Chamber medium at 2-8°C for 14 days and the corneal rinse with PSS-L are safe and effective procedures allowing the preservation of the corneal quality parameters as well as the complete elimination of gentamicin sulfate from the tissues before transplantation.Cite Now.

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.

Donor related corneal graft infection: a review of literature and preventive strategies

PURPOSE

Donor-related infections are a serious threat to patient safety after corneal transplantation. We provide a concise review of literature from the last decade on donor-related graft infections, sources of contamination and means to reduce the contamination of donor tissue and preservation media.

METHODS

We reviewed 50 papers from year 2005 to 2021 related to donor-related graft infections. We included 14 studies related to the risk factors associated with post-keratoplasty infection and preventive methods.

RESULTS

Incidence of post-keratoplasty infections has been reported to be approximately 0.2%-0.77% for endophthalmitis and 6.5%-10.5% for microbial keratitis. We analyzed six important studies regarding the risk factors related to donor contamination. It was observed that younger donor age, increased death to retrieval time, warming cycles and increased eye bank processing time and positive corneo-scleral rim cultures were important risk factors for donor-related infections post keratoplasty. Eye banks have adapted newer protocols over the time period for prevention of donor-related contamination. Recommended preventive strategies were published in about eight important studies over the past decade. In addition to meticulous donor screening, rapid warming cycles, double contact with povidone iodine during retrieval and addition of antifungals like amphotericin B, Voriconazole and cycloheximide have been suggested over the last decade although their use is still in debate with regard to the efficacy, toxicity and cost-effectiveness.

CONCLUSION

The last decade has witnessed a relative rise of fungal infections and multidrug resistant bacterial infections post-keratoplasty. Eye bank prepared corneas for lamellar surgeries are at increased risk for donor contamination due to increased exposure to the higher temperatures during their processing. Addition of antifungals and broad spectrum antibiotics to the hypothermic preservation media needs to be considered in the new era of increasing trends of lamellar keratoplasty.

Cytoprotective Effects of Human Platelet Lysate during the Xeno-Free Culture of Human Donor Corneas

We evaluated the suitability of 2% human platelet lysate medium (2%HPL) as a replacement for 2% fetal bovine serum medium (2%FBS) for the xeno-free organ culture of human donor corneas. A total of 32 corneas from 16 human donors were cultured in 2%FBS for 3 days (TP1), then evaluated using phase contrast microscopy (endothelial cell density (ECD) and cell morphology). Following an additional 25-day culture period (TP2) in either 2%FBS or 2%HPL, the pairs were again compared using microscopy; then stroma and Descemet membrane/endothelium (DmE) were processed for next generation sequencing (NGS). At TP2 the ECD was higher in the 2%HPL group (2179 ± 288 cells/mm²) compared to 2%FBS (2113 ± 331 cells/mm²; p = 0.03), and endothelial cell loss was lower (ECL HPL = -0.7% vs. FBS = -3.8%; p = 0.01). There were no significant differences in cell morphology between TP1 and 2, or between 2%HPL and 2%FBS. NGS showed the differential expression of 1644 genes in endothelial cells and 217 genes in stromal cells. It was found that 2%HPL led to the upregulation of cytoprotective, anti-inflammatory and anti-fibrotic genes (HMOX1, SERPINE1, ANGPTL4, LEFTY2, GADD45B, PLIN2, PTX3, GFRA1/2), and the downregulation of pro-inflammatory/apoptotic genes (e.g., CXCL14, SIK1B, PLK5, PPP2R3B, FABP5, MAL, GATA3). 2%HPL is a suitable xeno-free substitution for 2%FBS in human cornea organ culture, inducing less ECL and producing potentially beneficial alterations in gene expression.

Role of Oxidative Stress in the Disruption of the Endothelial Apical Junctional Complex During Corneal Cold Storage

Purpose: To characterize the impact of corneal cold storage (CS) on the endothelial apical junctional complex (AJC). Methods: Porcine corneas were held in CS (4°C; 1-7 days) with Cornisol™ preservation medium supplemented with epothilone B (EpoB; microtubule stabilizer; 100 nM), SB-203580 (p38 mitogen-activated protein [MAP] kinase inhibitor; 20 μM), or antioxidants (quercetin, 100 μM; vitamin E, 1 mM; deferoxamine, an iron chelator, 10 mM). After CS termination, the damage to endothelial AJC was characterized by imaging perijunctional actomyosin ring (PAMR) and zonula occludens (ZO-1). The effects of EpoB and SB-203580 were characterized by imaging microtubules. The loss in the barrier function was assessed in cultured cells grown on biotin-coated gelatin by permeability to fluorescein isothiocyanate (FITC)-avidin. The accumulation of reactive oxygen species (ROS), altered mitochondrial membrane potential (MMP), lipid peroxidation, and lactate dehydrogenase (LDH) release were also determined in response to CS. Results: CS led to the loss of microtubules, destruction of PAMR, and breakdown of ZO-1 in the endothelium. The severity of damage increased when CS was prolonged. Although rewarming of the tissue increased the damage, the effect was marginal. CS also induced accumulation of ROS, alteration in MMP, lipid peroxidation, enhanced LDH release, and increased permeability to FITC-avidin. These changes were opposed by EpoB, SB-203580, and antioxidants. Conclusion: Corneal CS destroys AJC of the endothelium, leading to loss of its barrier function. The effects were surmounted by microtubule stabilization, p38 MAP kinase inhibition, and antioxidants. Thus, there is potential for reformulation of the preservation medium to maintain the health of the donor corneal endothelium before transplantation.

Influence of the Postmortem/Storage Time of Human Corneas on the Properties of Cultured Limbal Epithelial Cells

Besides being a powerful model to study the mechanisms of corneal wound healing, tissue-engineered human corneas (hTECs) are sparking interest as suitable substitutes for grafting purposes. To ensure the histological and physiological integrity of hTECs, the primary cultures generated from human cornea (identified as human limbal epithelial cells (hLECs) that are used to produce them must be of the highest possible quality. The goal of the present study consisted in evaluating the impact of the postmortem/storage time (PM/ST) on their properties in culture. hLECs were isolated from the entire cornea comprising the limbus and central cornea. When grown as monolayers, short PM/ST hLECs displayed increased daily doublings and generated more colonies per seeded cells than long PM/ST hLECs. Moreover, hLECs with a short PM/ST exhibited a markedly faster wound closure kinetic both in scratch wound assays and hTECs. Collectively, these results suggest that short PM/ST hLECs have a greater number of highly proliferative stem cells, exhibit a faster and more efficient wound healing response in vitro, and produce hTECs of a higher quality, making them the best candidates to produce biomaterial substitutes for clinical studies.

Influence of time to procurement, incubation and release of organ cultured donor corneas on graft failure after Descemet Stripping Automated Endothelial Keratoplasty

PURPOSE

The aim of the present study was to investigate whether the time from death to procurement, to preservation or the storage time of donor corneas preserved in organ culture influenced the clinical outcome of patients undergoing Descemet stripping automated endothelial keratoplasty (DSAEK) for Fuchs endothelial keratoplasty.

METHODS

We conducted a registry-based study on 776 patients undergoing DSAEK. Data on time from donor death to cornea retrieval (DRT), time from death to preservation (DPT), the preservation time and donor cornea characteristics: age, sex and endothelial cell density (ECD) at the time of release for surgery, were extracted from The Danish Cornea Bank Registry. Data on recipient follow-up were collected from a corneal graft registry. The primary outcome was presence of graft failure within a period from 2 months to 2 years after surgery. Secondary outcomes were DRT, DPT, ECD ≤2300 and gender mismatch between donor and recipient.

RESULTS

Graft failure occurred in 26 patients. The mean preservation time for failed grafts was 34.1 ± 10.0 days (mean ± SD) and 27.3 ± 10.6 days (mean ± SD) for the clear, functional grafts at the 2-year follow-up. A preservation time of >29 days compared with ≤29 days was associated with a lower survival (HR 2.33, 95% CI on 1.06-5.14, p = 0.036) and an increased risk of graft failure (RR 1.53, 95% CI on 1.11-2.10, p = 0.009). For the secondary outcome variables, no difference in the risk of graft failure was observed and did not appear to impact the survival rate of DSAEK patients.

CONCLUSION

Preservation time of donor cornea was associated with graft survival and a prolonged preservation time of more than 4 weeks seemed to lower the 2-year survival.

Long-Term Graft Survival and Decline in Endothelial Cell Density Following Penetrating Keratoplasty with Organ-Cultured Corneas

INTRODUCTION

Endothelial cell density (ECD) changes long after penetrating keratoplasty (PKP) of organ-cultured corneas have been little studied. We aim to calculate the point when ECD decline stabilises following PKP with organ culture stored corneas.

METHODS

This is an observational study of first-ever PKPs and first-ever re-grafts, performed over 17 years under a single surgeon. ECDs were acquired at 3 and 6 months, 1 year post-graft and annually thereafter by specular microscopy. Time-dependent ECD data was fitted to a log-biexponential model.

RESULTS

We studied 465 first-ever grafts and 128 re-grafts. Mean recipient age was 59 years (range 0-96 years; SD 22). Median follow-up was 5.7 (range 0.2-17.1) years. Probability of ED at 5 years in first grafts and re-grafts was 4.4% (2.6-7.1%) and 14.8% (8.3-23.2%). In first grafts, ECD loss reached 0.6% per annum at 7.9 (6.2-9.6) years post-operatively. The half-lives of ECD loss during the immediate post-operative period for first grafts, re-grafts, dystrophies, ectasias, and previous ocular surgery are 20.1 (14.9-30.9), 12.8 (6.9-79.4), 19.5 (13.1-37.7), 26.2 (16.2-68), and 11.6 (6.7-41.3) months, respectively. The half-life during this rapid phase of ECD loss has an inverse correlation with graft survival at 10 years (r = - 0.89, p = 0.02).

CONCLUSIONS

Rate of endothelial decompensation is higher in first grafts than re-grafts. ECD decline stabilises 7.9 years post-operatively in first grafts but then becomes lower than the physiological loss expected. Further work is needed to verify whether organ-cultured grafts reach physiological levels of ECD loss faster than hypothermically stored grafts.

The importance of donor characteristics, post-mortem time and preservation time for use and efficacy of donated corneas for posterior lamellar keratoplasty

PURPOSE

The aim of this study is to examine whether donor age, death-to-retrieval time (DRT) and death-to-preservation time (DPT) as well as total preservation time affect donor cornea suitability for endothelial keratoplasty (EK) or penetrating keratoplasty (PK).

METHODS

A registry-based study was performed identifying 3248 corneas donated between 2011 and 2017. Data regarding donated corneas were extracted from The Danish Cornea Bank and donor medical records and evaluated for missing information. The primary outcome was whether ECD at preservation (ECD-P) or at release (ECD-R) was >2000 cells/mm² .

RESULTS

Logistic regression for ECD-P showed a significant negative effect of increasing age (OR: 1.07, 95%CI: 1.05;1.08, p < 0.001) on donor suitability. Higher ECD-P had a significant positive effect on graft eligibility (OR: 1.007 95%CI: 1.003;1.010, p < 0.001). No significant effect of donor sex (p = 0.547), DRT (p = 0.289) or DPT (p = 0.102) on donor suitability for EK or PK (Chi-squared test).

CONCLUSION

High donor age and low ECD-P negatively affect the suitability of donor corneas for EK/PK whereas DRT and DPT did not affect graft suitability.

Near infra-red labelling and tracking of corneal endothelial cells in-vivo

Following corneal transplantation, there is an initial, rapid decline in corneal endothelial cells (CECs) following surgery. Direct imaging of post-transplantation endothelial cells is only possible weeks after surgery and with a limited field of view. We have developed a labelling approach using 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindotricarbocyanine iodide (DIR) dye solution, that enables tracking of labelled CECs in vivo for at least 1 month. Initial in vitro optimization, with assessments of dye concentration on fluorescence, cellular toxicity and cell migration, performed in propagated primary CECs. Subsequently, in vivo evaluation of cellular labelling was assessed within a rabbit wound healing model. Finally, real-time visualization of human cadaver donor tissue incubated in DIR transplanted into rabbits was achieved using a clinical confocal microscope. Results revealed detectable fluorescence increased with concentration to a plateau of 100 µg/ml, with no toxicity of CECs at any concentration evaluated. DIR-labelled CECs were detectable in vivo up to 1 month, and transplanted labelled donor graft could be visualized and were trackable in vivo. Acute endothelial rejection in 1 rabbit was evidenced by detectable DIR positive cells within the anterior chamber. DIR imaging allowed for detailed imaging of the transplanted human corneal endothelium, and enabled non-invasive observation of the corneal endothelial morphology following transplantation.

Overview of Short-Term and Intermediate-Term Corneal Storage Solution: Comparison of Clinical Outcomes and Need For Future Research

ABSTRACT

Corneal donor tissue preservation techniques have incrementally improved since the introduction of McCarey-Kaufman storage solution from short-term storage to intermediate duration of storage with the advent of organ culture and Optisol GS storage solutions. Improved understanding of the corneal endothelial cell physiology has helped in designing newer storage solutions, such as the Life 4C and Cornea Cold. The incorporation of antibiotics, ATP precursors, minerals, and vitamins has improved the viability of tissues. In addition, these modifications to the newer storage solutions have increased the endothelial longevity and metabolic activity. Despite these advances, the duration of tissue storage has largely been restricted to 2 weeks in Optisol GS and 4 weeks in organ culture. The role and cost-effectiveness of antifungal supplementation and the need for improved epithelial preservation are additional areas that need to be explored. This review intends to summarize the efficacy and viability of donor corneas in different tissue storage solution and compare clinical outcomes while providing an insight into the challenges in developing newer methods of corneal preservation.

Killing efficacy of a new hypothermic corneal storage medium against the micro-organisms frequently found in human donor cornea intended for transplantation

Objective

To study the in vitro killing efficacy of Kerasave (AL.CHI.MI.A Srl), a medium provided with amphotericin B tablet for hypothermic storage of human donor corneas, against relevant contaminants associated with postkeratoplasty infections.

Methods and Analysis

The antimicrobial activity of Kerasave was determined after 0, 3 and 14 days of incubation at 2°C-8°C, inoculating Kerasave and the control medium with 10⁵-10⁶ colony forming units (CFU) of Candida albicans (CA), Fusarium solani (FS), Aspergillus brasiliensis (AB), Staphylococcus aureus (SA), Enterococcus faecalis (EF), Bacillus subtilis spizizenii (BS), Pseudomonas aeruginosa (PA), Enterobacter cloacae (EC) and Klebsiella pneumoniae (KP). Log₁₀ reductions at different time intervals were determined by assessing the number of viable CFU using the serial dilution plating technique.

Results

After 3 days, Kerasave induced the highest log₁₀ decrease in the concentrations of KP, PA, CA and EC (5.37, 4.15, 2.97 and 2.67, respectively; all p<0.001). The log₁₀ decreases of SA and EF were 2.27 and 2.11, respectively (all p<0.001). The lowest log₁₀ decrease was observed in BS, AB and FS concentrations (0.25, 0.30 and 0.67, respectively; p<0.001 for BS and AB and p=0.004 for FS). After 14 days, the microbial count of CA, FS, SA, EF, PA and EC further decreased (p=0.006 for FS; p<0.001 for the others).

Conclusion

Kerasave effectively reduced or kept unchanged the microbial concentration of almost all tested strains after 3 days. Thus, this novel medium represents a valuable tool to control the microbial contamination of human donor corneas during hypothermic storage for up to 14 days before transplantation.

Antifungal Efficacy and Safety of Cycloheximide as a Supplement in Optisol-GS

PURPOSE

The incidence of fungal infection after corneal transplant has increased significantly in recent years, especially Candida spp. This study aimed to evaluate the efficacy and safety of the addition of cycloheximide in Optisol-GS media in decreasing the growth of Candida spp. strains.

METHODS

This in vitro laboratory efficacy study measured fungal colony growth in 24 vials of Optisol-GS that were divided into 6 groups of 4 vials each, as follows: (1) MIC/2 cycloheximide, (2) MIC cycloheximide, (3) MICx5 cycloheximide, (4) MICx10 cycloheximide, from MIC values obtained for each strain, (5) unsupplemented optisol-GS as a positive control (added inoculum), and (6) unsupplemented optisol-GS as a negative control (no inoculum). In each group was added Candida albicans, C. glabrata and C. parapsilosis, except in the negative control. The evaluated variables were fungal colony growth from the Optisol-GS vials, corneal endothelial cell density and endothelial cell viability at different concentrations of cycloheximide.

RESULTS

In the efficacy study, all strains showed a reduction in fungal cell growth from the second day at all evaluated concentrations of optisol-GS supplemented with cycloheximide, even at subinhibitory concentrations (MIC/2). For C. glabrata, the colony count was reduced to 99%. No evidence of corneal endothelial toxicity was found at any concentration, in the safety study, compared with the paired control.

CONCLUSION

The addition of cycloheximide to optisol-GS decreased the fungal growth, demonstrating fungicide action against C. glabrata and fungistatic action against C. albicans and C. parapsilosis. This drug did not demonstrate toxicity to the corneal endothelium at different concentrations.

Synthetic media for preservation of corneal tissues deemed for endothelial keratoplasty and endothelial cell culture

PURPOSE

To compare the difference between various endothelial graft preparation methods and endothelial cell culture from tissues that are preserved in serum-based and synthetic medium.

METHODS

In a randomized masked study, the tissues (n = 64) were preserved in Cornea Max (serum-based) and Cornea Syn (synthetic) series for 36 days at their respective preservation conditions. Following organ culture, corneal tissues (n = 48) were used to prepareDescemet stripping automated endothelial keratoplasty (DSAEK), preloaded ultra-thin (UT) -DSAEK, prestripped Descemet membrane endothelial keratoplasty (DMEK), free-floating DMEK, and preloaded DMEK with endothelium inward and outward grafts. These tissues were preserved for another 4days at room temperature in dextran supplemented media following which they were subjected to trypan blue, alizarin red, live/dead and Zonula Occludens-1 (ZO-1) staining. A separate set of tissues (n = 16) from both the series was used for human corneal endothelial cell (HCEnC) culture. At confluence, the proliferation and cell doubling rate was calculated and the cultured cells were subjected to live/dead, ZO-1, 2A12 and Ki-67 staining. Mann-Whitney test was performed with p < 0.05 deemed statistically significant.

RESULTS

After preparation and preservation of the tissues for endothelial keratoplasty, alizarin red showed standard endothelial morphology from both the groups. Endothelial cell loss, hexagonality and uncovered areas did not show statistically significant differences (p > 0.05) between both groups. For HCEnC, cell doubling rate was 4.7 days (p > 0.05). All the antibodies were expressed in both the groups. Hexagonality, polymorphism, cell area, viable/dead cells and Ki-67 positivity were not statistically significant (p > 0.05).

CONCLUSIONS

Complete synthetic organ culture series is safe and advantageous for carrying out advanced endothelial keratoplasty graft preparation procedures and for HCEnC culture as it is free from animal or animal-derived products.

Usefulness of Prestorage Corneal Swab Culture in the Prevention of Contaminated Corneal Tissue in Corneal Transplantation

PURPOSE

To assess the efficacy of the prestorage corneal swab (PCS) culture to screen for corneal graft contamination after storage in Optisol-GS.

METHODS

A retrospective analysis of all PCS cultures was performed at the Eye Bank of Québec in Hôpital Maisonneuve-Rosemont from September 2013 to June 2016. Whole corneal culture was performed on rejected grafts because of a positive PCS, and a contamination rate was calculated. In addition, contamination rates of corneoscleral rims were compared between corneas tested with PCS and those of imported corneas which did not have PCS.

RESULTS

Among the 1966 PCS cultures performed, 814 (41.4%) were positive for growth. Pathogenic bacteria were present in 144 (7.3%) corneas, including Staphylococcus aureus (n = 96, 11.8% of all positive cultures), Enterobacteriaceae (n = 14, 1.7%), and Pseudomonas aeruginosa (n = 6, 0.7%). After preservation in Optisol-GS, only 7 (6.9%) corneas remained contaminated (95% confidence interval 5.1-9.3). The sensitivity of the PCS culture was 87.5% (95% confidence interval 47.4-99.7). There was no significant difference in corneoscleral rim contamination between corneas tested with PCS (1/388; 0.2%) compared with imported, nonswabbed corneas (3/214; 1.4%) (P = 0.131). Therefore, the cost to recover the loss of tissue rejected because of false-positive PCS by purchasing corneal tissue was calculated to be $142,884 (CAD) per year.

CONCLUSIONS

Despite the high sensitivity of PCS cultures, there was no significant reduction of infection after corneal transplantation using this technique. In consequence, 93% of the corneas possibly suitable for transplantation were rejected. This suggests that the PCS culture alone is a poor test for detecting clinically relevant corneal contamination.

Corneal endothelial cell therapy: feasibility of cell culture from corneas stored in organ culture

In 2013, a clinical trial was initiated to investigate cell therapy for the treatment of corneal endothelial decompensation. Cultivating human corneal endothelial cells (CECs) while maintaining their functional phenotype is challenging; therefore, establishment of a confirmed protocol is pivotal for obtaining approval from regulatory authorities for use of cellular therapy products. In this study, we evaluated organ culture (OC) as a storage method for donor corneas used as a raw material for establishing CEC cultures. OC allows storage of corneal tissue for conventional corneal transplantation at 31-37 °C for up to 5 weeks, whereas storage at 4 °C is limited to 2 weeks. We investigated 20 pairs of corneas: one cornea of each pair was stored in OC and the other in cold storage for one week before CEC culture. In 15/20 cases, the CECs assumed a hexagonal sheet-like monolayer structure and expressed endothelial function-related markers. CECs were also obtained from OC corneas that had been stored for 1 (n = 19) and 2 (n = 7) months. As a further test, CECs were cultivated from 5 OC corneas that had been transported from France to Japan. In all cases, these corneas, even after international transport, generated CECs that formed hexagonal monolayers with clinically applicable and sufficiently high cell densities. In conclusion, the CEC cultures required for endothelial cell therapy can be obtained from OC corneas without changing the standard storage operating procedures of the eye banks.

Process development and safety evaluation of ABCB5+ limbal stem cells as advanced-therapy medicinal product to treat limbal stem cell deficiency

Background

While therapeutic success of the limbal tissue or cell transplantation to treat severe cases of limbal stem cell (LSC) deficiency (LSCD) strongly depends on the percentage of LSCs within the transplanted cells, prospective LSC enrichment has been hampered by the intranuclear localization of the previously reported LSC marker p63. The recent identification of the ATP-binding cassette transporter ABCB5 as a plasma membrane-spanning marker of LSCs that are capable of restoring the cornea and the development of an antibody directed against an extracellular loop of the ABCB5 molecule stimulated us to develop a novel treatment strategy based on the utilization of in vitro expanded allogeneic ABCB5⁺ LSCs derived from human cadaveric limbal tissue.

Methods

We developed and validated a Good Manufacturing Practice- and European Pharmacopeia-conform production and quality-control process, by which ABCB5⁺ LSCs are derived from human corneal rims, expanded ex vivo, isolated as homogenous cell population, and manufactured as an advanced-therapy medicinal product (ATMP). This product was tested in a preclinical study program investigating the cells’ engraftment potential, biodistribution behavior, and safety.

Results

ABCB5⁺ LSCs were reliably expanded and manufactured as an ATMP that contains comparably high percentages of cells expressing transcription factors critical for LSC stemness maintenance (p63) and corneal epithelial differentiation (PAX6). Preclinical studies confirmed local engraftment potential of the cells and gave no signals of toxicity and tumorgenicity. These findings were sufficient for the product to be approved by the German Paul Ehrlich Institute and the U.S. Food & Drug Administration to be tested in an international multicenter phase I/IIa clinical trial (NCT03549299) to evaluate the safety and therapeutic efficacy in patients with LSCD.

Conclusion

Building upon these data in conjunction with the previously shown cornea-restoring capacity of human ABCB5⁺ LSCs in animal models of LSCD, we provide an advanced allogeneic LSC-based treatment strategy that shows promise for replenishment of the patient’s LSC pool, recreation of a functional barrier against invading conjunctival cells and restoration of a transparent, avascular cornea.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02272-2.

Translational and Regulatory Challenges of Corneal Endothelial Cell Therapy: A Global Perspective

Cell therapies are emerging as a unique class of clinical therapeutics in medicine. In 2015, Holoclar (ex vivo expanded autologous human corneal epithelial cells containing stem cells) gained the regulatory approval for treating limbal stem cell deficiency after chemical eye burn. This has set a precedent in ophthalmology and in medicine, reinforcing the therapeutic promise of cell therapy. However, to generalize and commercialize cell therapies on a global scale, stringent translational and regulatory requirements need to be fulfilled at both local and international levels. Over the past decade, the Singapore group has taken significant steps in developing human corneal endothelial cell (HCEnC) therapy for treating corneal endothelial diseases, which are currently the leading indication for corneal transplantation in many countries. Successful development of HCEnC therapy may serve as a novel solution to the current global shortage of donor corneas. Based on the experience in Singapore, this review aims to provide a global perspective on the translational and regulatory challenges for bench-to-bedside translation of cell therapy. Specifically, we discussed about the characterization of the critical quality attributes (CQA), the challenges that can affect the CQA, and the variations in the regulatory framework embedded within different regions, including Singapore, Europe, and the United States. Impact statement Functional corneal endothelium is critical to normal vision. Corneal endothelial disease-secondary to trauma, surgery, or pathology-represents an important cause of visual impairment and blindness in both developed and developing countries. Currently, corneal transplantation serves as the current gold standard for treating visually significant corneal endothelial diseases, although limited by the shortage of donor corneas. Over the past decade, human corneal endothelial cell therapy has emerged as a promising treatment option for treating corneal endothelial diseases. To allow widespread application of this therapy, significant regulatory challenges will need to be systematically overcome.

Changes of Contamination Rate and Microorganism Evaluation in Organ-Cultured Human Corneas: A 14-Year Review From a French Regional Eye Bank

PURPOSE

This study aimed to assess how the contamination rate of organ-cultured corneas has evolved and to analyze the evolution of microorganisms involved.

METHODS

Data from the Besançon eye bank were reviewed over 14 years (2005-2018). The changes in the contamination rate and the contaminant species found during the organ culture storage were analyzed. Microbiological tests were performed twice on the storage media-at day 5 and before the deswelling phase.

RESULTS

Among the 17,979 donor corneas collected, 1240 corneas were microbiological-test positive. The average annual contamination rate was 6.8% (range: 5.2%-8.9%). Seventy-five percent of contaminations were bacterial. The most frequently found bacterium was Staphylococcus spp. (31.3%), followed by non-Enterobacteriaceae Gram-negative Bacilli (GNB) (27.3%), with most Sphingomonas spp. and Pseudomonas spp. Fungal contamination (21.9%) was dominated by Candida (82.7%). Seventy-seven types of microorganisms were identified. The Staphylococcus rate tended to decrease, whereas non-Enterobacteriaceae GNB rate has increased in the past few years to reach 46% of bacteria. Most of the contaminations were detected in the early phase of organ culture at day 5 (89.2%). The second microbiological test found 44.8% of fungal contaminations (predominantly Candida spp.).

CONCLUSIONS

The annual contamination rate was stable and remains low, but the types of contaminating microorganisms varied from year to year. Staphylococcus spp. and non-Enterobacteriaceae GNB accounted for a significant proportion of the contaminations. We found a significant proportion of contamination, especially fungal, at the late phase of storage. Reassessing the antibiotics and antifungals in the storage medium may be useful to limit corneal disposal.

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

PURPOSE

To determine the changes of corneal thickness and curvature of human corneal grafts in organ culture medium II, containing dextran T500 6%, before keratoplasty.

METHODS

We examined the tomography of 24 corneas from our eye bank transferred from medium I into medium II. Images were repeated hourly during 24 hours using an anterior segment optical coherence tomography. The central corneal thickness (CCT) was measured with the manual measurement tool of the anterior segment optical coherence tomography. The radii of curvature (anterior flat and steep and posterior flat and steep) were measured with a MATLAB self-programmed software for "sterile donor tomography."

RESULTS

The mean CCT (±SD) at baseline (T0) was 727 ± 156 μm. It reached 581 ± 103, 506 ± 84, 472 ± 79, and 456±7 μm after 6, 12, 18, and 24 hours, respectively. After 12 hours, 83% of the final deswelling was achieved. The radii of curvature (±SD) at baseline (T0) were (posterior flat, posterior steep, anterior flat, and anterior steep) 6.6 ± 0.5, 6.2 ± 0.5, 7.7 ± 0.4, and 7.4 ± 0.4 mm, respectively. After 24 hours, the radii of curvature reached 6.8 ± 0.1, 6.6 ± 0.3, 7.6 ± 0.1, and 7.4 ± 0.2 mm, respectively.

CONCLUSIONS

The kinetics of the deswelling process in medium II follow a hyperbolic curve. Considering a CCT of 506 μm at T12, we assume that a time interval of 12 hours in medium II might be enough for clinical purposes. This result might help to keep storage in medium II as short as possible to escape potential toxic effects of dextran in medium II. The radius of curvature does not seem to change within 24 hours for all measured surfaces.

Microvesicle delivery of a lysosomal transport protein to ex vivo rabbit cornea

Therapeutic use of transmembrane proteins is limited because of irreversible denaturation when away from their native lipid membrane. Mutations in lysosomal membrane transport proteins cause many lethal disorders including cystinosis which results from mutations in CTNS, which codes for the lysosomal cystine transport protein, cystinosin. Cystinosin-deficient fibroblasts, including keratocytes (corneal fibroblasts) accumulate lysosomal cystine. Cystinosis patients develop highly painful corneal cystine crystals, resulting in severe visually debilitating photophobia. The only available therapy is daily treatment with cysteamine eye drops. We have previously shown that microvesicles containing functional cystinosin are spontaneously produced by infecting Spodoptera frugiperda cells (Sf9) with baculovirus containing human wt CTNS. Infecting Sf9 cells for 3 days at a MOI of 1 yields 10¹¹microvesicles /ml with a modal diameter of 90 nm. Addition of these vesicles to cultures of cystinotic fibroblasts produces cystine depletion over the course of 96 h, which persists for 2 weeks. In this paper we show that addition of such microvesicles containing cystinosinGFP to ex vivo rabbit ocular globes yields punctate perinuclear green fluorescence in the corneal keratocytes. These results support potential therapeutic use of these cystinosin containing microvesicles in treating cystinotic corneal keratopathy with the advantage of administering twice/month instead of daily topical administration.

Femtosecond Laser-Assisted Small Incision Sutureless Intrastromal Lamellar Keratoplasty (SILK) for Corneal Transplantation in Keratoconus

PURPOSE

To describe a femtosecond laser-assisted small incision sutureless intrastromal lamellar keratoplasty in an eye with severe keratoconus and report on the outcome with a 1-year follow-up.

METHODS

A 20-year-old man with a history of keratoconus presented for evaluation at the Tilganga Institute of Ophthalmology, Kathmandu, Nepal. The patient had previously undergone a deep anterior lamellar keratoplasty in the left eye. Examination of the right eye revealed an uncorrected distance visual acuity (UDVA) of counting fingers with a manifest refraction of -5.00 -3.50 × 170, giving a corrected distance visual acuity (CDVA) of 20/80. Thinnest pachymetry was 425 µm and progression of both anterior and posterior corneal elevation tomography and maximum keratometry was noted compared to examination 2 years prior. The VisuMax femtosecond laser (Carl Zeiss Meditec, Jena, Germany) was used to prepare the donor and recipient cornea. The donor graft was inserted into the recipient through the 3-mm small incision. No sutures were applied.

RESULTS

At 2 weeks postoperatively, UDVA was 20/50 with a manifest refraction of -1.00 -5.00 × 145 (20/32). One year postoperatively, UDVA was 20/80 with a manifest refraction of -2.50 -3.50 × 125 (20/40^-2), with the maximum keratometry decreasing from 64.08 to 56.74 diopters.

CONCLUSIONS

This femtosecond laser-assisted sutureless intrastromal corneal transplantation technique may provide an option to improve the quality of vision for some patients with keratoconus, affording a simpler postoperative follow-up course compared to traditional anterior lamellar or full-thickness corneal transplantation. [J Refract Surg. 2019;35(10):663-671.].

Optimisation of Storage and Transportation Conditions of Cultured Corneal Endothelial Cells for Cell Replacement Therapy

As the cornea is one of the most transplanted tissues in the body it has placed a burden on the provision of corneas from cadaveric donors. Corneal endothelial dysfunction is the leading indication for cornea transplant. Therefore, tissue engineering is emerging as an alternative approach to overcome the global shortage of transplant-grade corneas. The propagation and expansion of corneal endothelial cells has been widely reported. However, one obstacle to overcome is the transport and storage of corneal endothelial cells. In this study we investigated whether tissue engineered corneal endothelial cells can be preserved in hypothermic conditions. Human corneal endothelial cells (HCEnCs) were exposed to various temperatures (4 °C, 23 °C, and 37 °C) in both adherent and suspension storage models. Optimal storage media and storage duration was tested along with post-storage viability. Following storage and subsequent recovery at 37 °C, cell phenotype was assessed by immunofluorescence, gene and protein expression, and proliferative capacity analysis. Functionality was also assessed within a rabbit model of bullous keratopathy. Our data support our hypothesis that functional HCEnCs can be preserved in hypothermic conditions.

Investigation of factors associated with ABCB5-positive limbal stem cell isolation yields from human donors

PURPOSE

To identify factors associated with isolation yields of ATP-binding cassette (ABC) superfamily member B5 (ABCB5)-positive limbal stem cells (LSCs) from human cadaveric donor eyes.

METHODS

Whole eye globes were obtained from the Saving Sight eye bank, Kansas City, MO and the CorneaGen eye bank, Seattle, WA. ABCB5-positive LSCs were sorted by flow cytometry upon anti-ABCB5 monoclonal antibody staining within one week after donor death. The yields of live limbal epithelial cells in their entirety and of isolated pure ABCB5-positive LSC subsets were correlated with variables contained in the eye donors' medical information.

RESULTS

The mean isolation yield of live limbal epithelial cells and ABCB5-positive LSCs per donor eye was (340,000 ± 160,000 and 2,608 ± 1,842 respectively, mean ± SD). Stepwise regression analysis showed that cardiac disease-related death was the strongest negative predictor of the ABCB5-positive LSC isolation yield (p = 0.01). While we observed a trend for an age-related decline in the yield of ABCB5-positive LSCs, a statistically significant association could not be established (2% decrease/year, p = 0.11). Additionally, despite a trend for decreased isolation yields of total live limbal epithelial cells isolated from single donors with a longer time between death and tissue processing (p = 0.04), this did not affect the yields of purified ABCB5-positive LSC, which was independent of increasing time between death and tissue processing (p = 0.50).

CONCLUSIONS

Our study identifies cardiac disease-related death as a donor variable significantly associated with lower ABCB5-positive LSC isolation yields.

Ethical issues in living-related corneal tissue transplantation

The cornea was the first human solid tissue to be transplanted successfully, and is now a common procedure in ophthalmic surgery. The grafts come from deceased donors. Corneal therapies are now being developed that rely on tissue from living-related donors. This presents new ethical challenges for ophthalmic surgeons, who have hitherto been somewhat insulated from debates in transplantation and donation ethics. This paper provides the first overview of the ethical considerations generated by ocular tissue donation from living donors and suggests how these might be addressed in practice. These are discussed in the context of a novel treatment for corneal limbal stem cell deficiency. This involves limbal cell grafts which are transplanted, either directly or after ex vivo expansion, onto recipient stem cell-deficient eyes. Where only one eye is diseased, the unaffected eye can be used as a source of graft tissue. Bilateral disease requires an allogenic donation, preferably from a genetically related living donor. While numerous papers have dealt with the theory, surgical approaches and clinical outcomes of limbal stem cell therapies, none has addressed the ethical dimensions of this form of tissue donation.

Effect of Cornea Preservation Time on Success of Descemet Stripping Automated Endothelial Keratoplasty: A Randomized Clinical Trial

Importance

Demonstrating that success of Descemet stripping automated endothelial keratoplasty is similar across donor cornea preservation times (PTs) could increase the donor pool.

Objective

To determine whether the 3-year rate of graft success using corneal donor tissue preserved 8 to 14 days is noninferior to that of donor tissue preserved 7 days or less.

Design, Setting, and Participants

A multicenter, double-masked, randomized noninferiority clinical trial was conducted from April 16, 2012, to June 5, 2017, at 40 clinical sites (70 surgeons) in the United States, with donor corneas provided by 23 US eye banks. A total of 1090 individuals (1330 study eyes) underwent Descemet stripping automated endothelial keratoplasty (1255 eyes [94.4%] for Fuchs endothelial corneal dystrophy).

Interventions

Descemet stripping automated endothelial keratoplasty with random assignment of a donor cornea with a PT of 7 days or less (0-7d PT) or 8 to 14 days (8-14d PT).

Main Outcomes and Measures

Graft success at 3 years.

Results

Of the 1090 participants (1330 study eyes; 60.2% women and 39.8% men; median age at enrollment, 70 years [range, 42-90 years]), the 3-year cumulative probability of graft success was 95.3% (95% CI, 93.6%-96.9%) in the 0-7d PT group and 92.1% (95% CI, 89.9%-94.2%) in the 8-14d PT group (difference, 3.2%). The upper limit of the 1-sided 95% CI on the difference was 5.4%, exceeding the prespecified noninferiority limit of 4%. The difference was mostly owing to more primary donor failures in the 8-14d PT group, with the conditional probability of failure after the first month being 2.4% in the 0-7d PT group and 3.1% in the 8-14d PT group. In preplanned secondary analyses, longer PT was associated with a lower rate of graft success (unadjusted hazard ratio for graft failure per additional day of PT, 1.10; 95% CI, 1.03-1.18; P = .008 [PT analyzed as days]), with success rates of 96.5% (95% CI, 92.3%-98.4%) for PT of 4 days or less, 94.9% (95% CI, 92.5%-96.6%) for PT of 5 to 7 days, 93.8% (95% CI, 91.0%-95.8%) for PT of 8 to 11 days, and 89.3% (95% CI, 84.4%-92.7%) for PT of 12 to 14 days (P = .01 [PT analyzed as categorical variable]).

Conclusions and Relevance

The 3-year success rate in eyes undergoing Descemet stripping automated endothelial keratoplasty was high irrespective of PT. However, the study was unable to conclude that the success rate with donor corneas preserved 8 to 14 days was similar to that of corneas preserved 7 days or less with respect to the prespecified noninferiority limit. Although longer PT was associated with a lower success rate, the difference in rates was small when PT was less than 12 days.

Microbiological Screening of Hypothermic Preserved Donor Corneas in Keratoplasty

Purpose: To determine the prevalence, risk factors and microbial profiles of donor corneal contamination and its association with postoperative infection. Materials and Methods: 1348 hypothermic preserved donor corneas were screened during keratoplasty to assess the impacts of donor age, gender, cause of death and corneal preservation time on the contamination risk. The microbial spectrum and antibiotic sensitivity of causative microorganisms and the prognostic role of corneoscleral rim cultures were analyzed. Results: 111 donor corneas (8.2%) had positive microbial cultures, with 84 contaminated by bacteria, 25 by fungi and 2 by both. Acinetobacter baumannii complex (19.8%) and Candida spp. (9.0%) were the most commonly isolated bacteria and fungi, respectively. Two patients (1.8%) who received contaminated corneal buttons developed postoperative infections. Death due to cardiac disease led to more corneal contaminations than death due to brain disease (odds ratio (OR) = 2.59, P = .009). Longer preservation time was associated with a trend toward increasing contamination rate (from 8.3% to 15.0%). Moreover, fungal-contaminated corneas were preserved longer than bacterial-contaminated corneas (6.6 ± 4.5 versus 10.2 ± 5.4 days, P = .001). Corneas from donors who died from cardiac diseases and trauma showed the highest prevalence of bacterial (10.9%) and fungal (2.6%) contamination, respectively. Antibiotic sensitivity testing revealed that the third-generation fluoroquinolone levofloxacin had high rates of susceptibility to both gram-positive (G+) (60.0%) and gram-negative (G-) (44.6%) bacteria. Conclusions: The causes of donor corneal contamination are multifactorial. The antibiotic resistance rate of contaminating microbes seems to be increasing. Whether antibiotic usage in storage medium and postoperative prophylaxis should be updated accordingly warrants further investigation.

Monitoring the microbial contamination of donor cornea during all preservation phases: A prospective study in the Eye Bank of Rome

BACKGROUND

In most European eye banks, human donor corneas are microbiologically tested after storage in organ culture conditions, and the tissues that are free of contamination are distributed for transplantation. In this prospective study, 100 donor corneas were tested for microbial contamination after cold storage, corneal culture and corneal deswelling at the Eye Bank of Rome.

METHODS

Samples of cold storage medium (EUSOL-C), corneal culture medium (TISSUE-C) and deswelling medium (CARRY-C) were tested after three, seven and one days of corneal storage, respectively. The CARRY-C medium, used to transport the cornea to the operation theatre, was retested 1 day after transplantation. The TISSUE-C and CARRY-C media were also tested after removing antimicrobial and antifungal agents using a dedicated device.

RESULTS

We found 67% of the EUSOL-C samples were contaminated mainly by Staphylococcus spp, 14% of TISSUE-C media were contaminated by bacteria and fungi and 3% of CARRY-C media by Staphylococcus spp The analysis performed after removing the antimicrobial and antifungal agents showed growth in three additional TISSUE-C samples (S viridans, S haemolyticus and E faecalis) and one CARRY-C (S cerevisiae and P acnes).

CONCLUSION

Tissue contamination was unexpectedly high on arrival to the eye bank, indicating the need to review and update decontamination procedures during tissue recovery, and renew training for the recovery teams. Storing donor corneas in organ culture conditions significantly reduced the microorganism burden. Using devices to remove antimicrobial and antifungal agents from samples before testing can increase the sensitivity of the standard microbiological method, and thus help further reduce the risk of microbial transmission.

Survival of corneal nerve/sheath structures in organ-cultured donor corneas

PURPOSE

To study the morphology of human corneal nerves in eye bank organ-cultured corneas and in corneal grafts post-transplantation.

METHODS

Thirty-seven organ-cultured corneas were divided into: Group-A, anterior 300-400 μm of 20 corneas used for Descemets stripping endothelial keratoplasty, and Group-B, 17 full-thickness corneas unsuitable for transplantation. Corneas whole mounts were stained for nerves using acetylcholinesterase technique and examined by NanoZoomer digital pathology microscope. Central and sub-Bowman's stromal nerves and the sub-basal nerve plexus including perforation sites and terminal bulbs were studied. Ten eyes were imaged following penetrating keratoplasty using in-vivo confocal microscopy (IVCM) for the presence of sub-basal and stromal nerves at 1, 4-5 and 7-8 weeks postoperatively (five eyes) and in all the other five eyes, the final follow-up was at 12 weeks.

RESULTS

Fifteen of twenty (75%) corneas had stromal nerves in Group-A and 15 of 17 (88.2%) in Group-B. Average number of stromal nerves entering peripherally were 9.1 (range: 1-36). 7.5 in Group-A and 10.8 in Group-B. Central stromal nerves were seen in eight samples in Group-A and nine in Group-B. Many stromal nerves terminated abruptly without demonstrable continuity through Bowman's membrane. No terminal bulbs or sub-basal nerves were detected. In-vivo confocal microscopy (IVCM) showed 4 of 5 in 9 of 10 (90%) donor corneas had stromal nerves 1 week postoperatively, which remained present in 8 of 10 (80%) corneas at 4-5 weeks and in 9 of 10 (90%) at 7-8 weeks postoperatively. All 5 corneas analysed at 12 weeks showed the same stromal nerves from 1 to 12 weeks postoperatively. Sub-basal nerves were absent in all corneas over the 12-week study period.

CONCLUSION

This study provides further insight into the behaviour of corneal nerves in transplanted corneas. Corneal stromal nerves/nerve-sheaths are preserved in organ-cultured eye bank eyes and persist post-transplantation up to 3 months. These could provide directional guidance to regenerating nerves from host stroma.