The influence of donor age and post mortem time on corneal graft survival and thickness when employing banked donor material (A five-year follow-up)

Influence of Organ Culture on the Characteristics of the Human Limbal Stem Cell Niche

Organ culture storage techniques for corneoscleral limbal (CSL) tissue have improved the quality of corneas for transplantation and allow for longer storage times. Cultured limbal tissue has been used for stem cell transplantation to treat limbal stem cell deficiency (LSCD) as well as for research purposes to assess homeostasis mechanisms in the limbal stem cell niche. However, the effects of organ culture storage conditions on the quality of limbal niche components are less well described. Therefore, in this study, the morphological and immunohistochemical characteristics of organ-cultured limbal tissue are investigated and compared to fresh limbal tissues by means of light and electron microscopy. Organ-cultured limbal tissues showed signs of deterioration, such as edema, less pronounced basement membranes, and loss of the most superficial layers of the epithelium. In comparison to the fresh limbal epithelium, organ-cultured limbal epithelium showed signs of ongoing proliferative activity (more Ki-67+ cells) and exhibited an altered limbal epithelial phenotype with a loss of N-cadherin and desmoglein expression as well as a lack of precise staining patterns for cytokeratin ((CK)14, CK17/19, CK15). The analyzed extracellular matrix composition was mainly intact (collagen IV, fibronectin, laminin chains) except for Tenascin-C, whose expression was increased in organ-cultured limbal tissue. Nonetheless, the expression patterns of cell-matrix adhesion proteins varied in organ-cultured limbal tissue compared to fresh limbal tissue. A decrease in the number of melanocytes (Melan-A+ cells) and Langerhans cells (HLA-DR+, CD1a+, CD18+) was observed in the organ-cultured limbal tissue. The organ culture-induced alterations of the limbal epithelial stem cell niche might hamper its use in the treatment of LSCD as well as in research studies. In contrast, reduced numbers of donor-derived Langerhans cells seem associated with better clinical outcomes. However, there is a need to consider the preferential use of fresh CSL for limbal transplants and to look at ways of improving the limbal stem cell properties of stored CSL tissue.

Donor and recipient characteristics associated with rebubbling rate, endothelial cell loss, and graft failure in primary descemet membrane endothelial keratoplasty

Aim: To determine whether donor and recipient characteristics are associated with rebubbling rate, endothelial cell loss (ECL), and graft failure 3 years after primary Descemet membrane endothelial keratoplasty (DMEK). Material and Method: Records of 295 consecutive DMEK surgery and match with corresponding donor data were reviewed at a tertiary referral clinic. Recipients with intraoperative complications and coexisting ocular pathologies were excluded. Age, sex of donor and recipient, cause of donor death, death-to-preservation time (DtPT), storage time, donor endothelial cell density (ECD), and indications for surgery were analyzed for correlation with rebubbling rate, postoperative ECL, and graft failure. Further, subgroup analyses of the cause of death, donor sex, DtPT (median value, 3.5 h), and indications were performed. Multiple regression and receiver operating characteristics (ROC) analysis were used to determine the independent risk factors for graft failure. Results: This study included 114 eyes that underwent DMEK for bullous keratopathy (BK; 64%) and for Fuchs’ endothelial corneal dystrophy (FECD; 36%). The graft failure percentage was the only parameter that was higher in patients with DtPT > 3.5 h (p=0.047) than those with shorter DtPT. The probability of graft failure was seven times higher in eyes with DtPT > 3.5 h than with shorter DtPT (odds ratio 7.36, 95% confidence interval CI 1.34‒40.53) and 10 times higher in eyes with BK than those with FECD (odds ratio 10.29, 95% CI 1.01‒104.54). Conclusion:. DtPT and recipients with BK diagnosis were found to be independent risk factors for graft failure. Therefore, surgeons should consider DtPT for DMEK in eyes with BK.

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.

Endothelial failure and rejection in recipients of corneas from the same donor

Objective

To determine whether patients who receive corneas from the same donor have similar risks of endothelial failure and rejection.

Methods and Analysis

Patients with Fuchs endothelial dystrophy (FED) and pseudophakic bullous keratopathy (PBK) who received their first corneal transplant between 1999 and 2016 were analysed. Patients receiving corneas from donors who donated both corneas for the same indication were defined as ‘paired’. Gray’s test was used to compare the cumulative incidence of endothelial failure and rejection within 5 years post-transplant for ‘paired’ and ‘unpaired’ groups. Cox regression models were fitted to determine whether there was an association between recorded donor characteristics (endothelial cell density (ECD), age and sex and endothelial graft failure and rejection.

Results

10 838 patients were analysed of whom 1536 (14%) were paired. The unpaired group comprised 1837 (69%) recipients of single corneal donors and 7465 (69%) donors who donated both corneas for another indication. ECD was lower for unpaired single cornea donors (p<0.01). There was no significant difference in endothelial graft failure or rejection between paired and unpaired groups for FED (p=0.37, p=0.99) or PBK (p=0.88, p=0.28) nor for donor ECD, age, sex and paired donation after adjusting for transplant factors (across all models p>0.16 for ECD, p>0.32 for donor age, p>0.14 for sex match and p>0.17 for the donor effect).

Conclusion

The absence of a significant difference in graft outcome for corneal transplants for FED and PBK between paired and unpaired donors may reflect a homogeneous donor pool in the UK.

Effect of Body Refrigeration Time on Cornea Donor Tissue

PURPOSE

To determine how early body refrigeration affects corneal donor transplant suitability and endothelial cell density.

METHODS

Donor information was obtained from the CorneaGen Eye Bank including demographics, time of death to preservation, and body refrigeration status, for donors between 2012 and 2016. The death to preservation interval was classified into 3 categories: 0 to 10, 10 to 20, and 20+ hours. Two primary logistic method models were fit using a main effects model and an interaction model to determine the association of body refrigeration on unsuitability of transplantation and endothelial cell density.

RESULTS

Analysis was from 42,929 donor eyes, with a mean (standard deviation) endothelial cell count of 2743 (415) cells/mm2. Fifty-nine percent of donor eyes were from male donors in the eye bank data set, and the mean death to preservation interval was 11.0 (5.6) hours for all eyes. Unsuitability for transplantation demonstrated a reduced adjusted odds ratio by 22% (OR = 0.78, P = 0.009) when the body was refrigerated during the death to preservation interval versus when the body was not refrigerated. Eyes that were refrigerated, however, exhibited no statistically significant difference in endothelial cell count from eyes that were not refrigerated (P = 0.12).

CONCLUSIONS

We demonstrate an appreciable effect of early body refrigeration on transplant suitability in this large cohort of eye bank eyes. There was no beneficial effect of body refrigeration on endothelial cell count.

Cornea Procurement and Processing up to 72 Hours: No Risk for Cornea Transplant Quality

Background

The realization of tissue donations is bound to a tight timeframe. Depending on the type of tissue, time limits are specified within which the donation must be procured and processed. Otherwise, there is a risk of tissue quality loss with increasing time intervals from cardiovascular arrest. According to the European Directorate for the Quality of Medicines and HealthCare (EDQM) guide, cornea must be procured and processed within 72 h after death. The question arises whether this time interval has an influence on the quality of transplanted tissues and how it affects the accomplishment of tissue donations.

Methods

In order to obtain information on this, the numbers of tissue donations in the network of the German Society for Tissue Transplantation (DGFG) were evaluated as a function of the death to retrieval time (DRT) as well as the death to preservation time (DPT). For this purpose, 21,454 database entries of cornea donations made in the period from 2014 to 2018 were included.

Results

The results show that nearly 50% of donations realized in the DGFG network could be processed only 48 h or later after cardiovascular death due to the opt-in regulation in Germany. For these donations, there seems to be a higher discard rate compared to donations taken earlier. Nevertheless, there is a transplantation rate for these grafts of more than 65%, which is comparable to average transplantation rates stated in the literature.

Conclusion

All corneas finally selected for transplantation must meet the specified quality parameters. Since this naturally also applies to transplants that could only be procured at later time points, it can be concluded that DPT up to 72 h for corneal tissue is adequate and has no influence on the quality of corneas that are ultimately transplanted.

Outcome of transplanted donor corneas with more than 6 h of death-to-preservation time

Purpose:

In tropical countries, physicians are skeptic in using corneas with death-to-preservation time (DTPT) >6 h, concerns being endothelial cell viability and microbial contamination on prolonged DTPT. The objective of the study was to investigate these concerns by analyzing the outcomes of corneal transplants performed using donor corneas with DTPT >6 h.

Materials and Methods:

The study was a retrospective case series of 65 transplants performed in 2013 with donor corneas that had DTPT >6 h (range, 6.1–9.8 h). The information on donor cornea tissues and the recipient details were collected from the eye bank and the medical records department of our tertiary eye care center. The main outcome measures were slit lamp assessment of the donor corneas, primary graft failure, graft survival, and postoperative adverse reactions, especially infections, if any.

Results:

Median DTPT was 7 h. Forty-four (67.7%) corneas were evaluated as optical grade and 21 (32.3%) were deemed as therapeutic grade; 36 (55.4%) were used for optical indications. There was no relationship between DTPT and the tissue grading of corneas or endothelial cell density. Of the 23 keratoplasties for purely optical indications with a minimum follow-up of 3 months, 15 (65.2%) remained clear whereas 7 (30.4%) failed (mean follow-up 15.1 ± 6.7 months). The causes of failure were primary graft failure (n = 1) and secondary graft failure (n = 6).

Conclusion

: The donor corneas with DTPT 6 h to 10 h can be utilized for optical indications provided that they meet the criteria of tissue acceptance for optical use.

Anatomical characterization of central, apical and minimal corneal thickness

AIM

To anatomically locate the points of minimum corneal thickness and central corneal thickness (pupil center) in relation to the corneal apex.

METHODS

Observational, cross-sectional study, 299 healthy volunteers. Thickness at the corneal apex (AT), minimum corneal thickness (MT) and corneal thickness at the pupil center (PT) were determined using the pentacam. Distances from the corneal apex to MT (MD) and PT (PD) were calculated and their quadrant position (taking the corneal apex as the reference) determined: point of minimum thickness (MC) and point of central thickness (PC) depending on the quadrant position. Two multivariate linear regression models were constructed to examine the influence of age, gender, power of the flattest and steepest corneal axes, position of the flattest axis, corneal volume (determined using the Pentacam) and PT on MD and PD. The effects of these variables on MC and PC were also determined in two multinomial regression models.

RESULTS

MT was located at a mean distance of 0.909 mm from the apex (79.4% in the inferior-temporal quadrant). PT was located at a mean distance of 0.156 mm from the apex. The linear regression model for MD indicated it was significantly influenced by corneal volume (B=-0.024; 95%CI: -0.043 to -0.004). No significant relations were identified in the linear regression model for PD or the multinomial logistic regressions for MC and PC.

CONCLUSION

MT was typically located at the inferior-temporal quadrant of the cornea and its distance to the corneal apex tended to decrease with the increment of corneal volume.

Evaluation of grafted patients with donor corneas that today are more than 100 years old

PURPOSE

Life expectancy is increasing. When corneal donors become older and corneal-grafted patients live longer with their graft, the need for good-quality donor tissue becomes more crucial. The aim of the present investigation is to study grafted recipients with a donor cornea with a total tissue age of more than 100 years.

METHODS

One thousand consecutive donor records from the Danish Cornea Bank were initially reviewed. After applying different inclusion criteria, 35 recipients with corneal donor tissue of more than 100 years of age were invited for a follow-up visit. Visual acuity, corneal transparency and thickness, and intraocular pressure were measured. Corneal topography and endothelial photos were taken.

RESULTS

  Seventeen of the invited patients attended the examination. The average age of the grafts at examination was 107 years old; the oldest being 118 years. Most grafts were still clear 23-35 years after transplantation, and almost one-fourth had best spectacle-corrected visual acuity (BSCVA) ≥ 0.50. Cell morphology showed irregularity in size and shape for both grafted and healthy corneas, but the alterations were more extensive in the grafted corneas. The average endothelial cell density (ECD) was 1360 mm(2) in the grafted corneas. Sixty per cent had ECD > 1000 cells/mm(2). No signs of decompensation were observed for those with <1000 cells. The average central corneal thickness of the grafts was 0.582 mm (SD = 0.067) compared with 0.494 mm (SD = 0.043) in the fellow cornea.

CONCLUSION

  This study shows a trend of moderate long-term survival and quality for very old grafts despite low ECD. Most recipients had a clear transplant, and one-fifth had BSCVA of 0.80.

Effect of postmortem interval on the graft endothelium during preservation and after transplantation for keratoconus

PURPOSE

To investigate the effect of postmortem intervals and prognostic factors on endothelial cell density (ECD) of human donor corneas during preservation and at 1 and 3 years after transplantation in patients transplanted for keratoconus.

METHODS

Two different studies were performed: (1) with 733 donor corneas selected for the preservation study and (2) 64 patients with keratoconus selected retrospectively from 2 hospital clinics. The corneas were evaluated on the basis of the ECD during preservation, study A, and at 1 and 3 years after transplantation, study B. The effect of ≥ 10 hours of postmortem interval on the percentage of corneal endothelial cell loss (ECL) was determined.

RESULTS

The multiple regression showed no statistical significance (P = 0.827) of postmortem interval on ECL during preservation. However, for patients with keratoconus, the postmortem interval was statistically significant at both 1 year (P < 0.0001) and 3 years after transplantation (P < 0.0001).

CONCLUSIONS

The postmortem interval has no influence on the ECD during preservation. However, it has a statistically significant effect on the ECL after transplantation for patients transplanted for keratoconus, and therefore, it becomes eligible to be one of the potential factors affecting the ECD apart from surgical trauma.

Influence of donor age, post-mortem time and cold storage on metabolic profile of human cornea

PURPOSE

Limited knowledge exists about the influence of donor age and death-to-preservation interval (DPI) on the metabolic properties of the cornea. The aim of this study is to investigate the relationship between both factors and metabolite content of the cornea.

METHODS

Corneas from 15 human donors (age: 41-78 years) were obtained within 16 hrs post-mortem and kept in cold storage for 8 days. The metabolic profiles of the samples were investigated using high-resolution, magic angle spinning (1) H nuclear magnetic resonance spectroscopy before and after 8 days of preservation.

RESULTS

Twenty-two metabolites were detected and assigned in the corneal spectra. The significant metabolic differences before and after hypothermic storage were revealed between younger and older donors. DPI-related significant differences revealed before preservation of the corneas were not displayed after 8 days of cold storage.

CONCLUSIONS

Age of donor as well as post-mortem time influences the biochemical properties of the cornea. Cold storage decreases the metabolite differences between the tissues collected at different post-mortem time.

Regeneration with proliferation of the endothelium of cultured human donor corneas with extended postmortem time

PURPOSE

To examine the endothelium of donor corneas with extended postmortem time for survival and reparative mechanisms in an eye bank organ culture storage system.

METHODS

We obtained 14 pairs of donor corneas with a postmortem time ranging from 29 to 163 hours. One cornea of a pair was immediately fixed for the study of structural changes postmortem and to serve as a control. The second was stored in organ culture for 3 days and thereafter fixed to be studied for reparative processes. Examination was done with light microscopy and scanning electron microscopy. Immunohistochemical staining with antibodies against proliferating cell nuclear antigen, Ki-67, and n-cadherin was performed to examine for cell proliferation and to characterize the cells.

RESULTS

The control corneas showed increasing endothelial cell damage with increasing postmortem time. After 5-7 days postmortem, most cells were structurally damaged. After 3 days in organ culture, all corneas acquired an endothelial covering of the posterior surface, with cells, suggesting proliferation in both scanning preparations and in cross-sections. Positive endothelial cell staining with proliferating cell nuclear antigen was found in all cultured corneas. Ki-67 staining of the endothelium was found in 9 of the cultured corneas.

CONCLUSIONS

The study showed survival of the corneal endothelium up to 7 days postmortem, and accordingly, the potential clinical use of donor corneas with extended postmortem time. Our results furthermore suggest that repair of the endothelium in donor corneas during organ culture storage occurs also by proliferation and not only by migration and enlargement of existing cells. If we uncover the mechanisms regulating cell proliferation in corneal endothelium, it should be possible to develop better storage methods of corneal transplants to improve quality and supply.

Impact of short-term versus longterm topical steroid treatment on 'idiopathic' endothelial cell loss after normal-risk penetrating keratoplasty

PURPOSE

Chronic endothelial cell loss after penetrating keratoplasty (PK) is suspected to result from a subclinical immune reaction. The aim of this study was to investigate whether the prolonged use of a topical steroid after normal-risk PK has a favourable impact on chronic endothelial cell loss.

METHODS

The study included 305 eyes from the prospective Erlangen Normal-risk Keratoplasty Study, with a mean follow-up of 3.1 +/- 0.9 years. Postoperative treatment was initiated with prednisolone acetate 1% eyedrops five times a day and was tapered slowly over the first 6 months. Patients were then randomized into two treatment groups: a short-term group (n = 161), which stopped topical steroid treatment, and a longterm group (n = 144), which continued topical treatment with prednisolone acetate 1% eyedrops once a day until 12 months postoperatively. Endothelial cell counts were determined at each follow-up examination (after 6 weeks, then every 3 months until 2 years, then once a year).

RESULTS

Endothelial cell density in the short-term and longterm groups decreased significantly from 1941 +/- 550 cells/mm(2) and 1957 +/- 568 cells/mm(2) to 1535 +/- 535 cells/mm(2) and 1472 +/- 549 cells/mm(2), respectively, from 6 weeks to 2 years postoperatively (p < 0.001). In a linear regression model, cell count in the short-term group decreased by 216 +/- 93 cells/mm(2) and in the longterm group by 206 +/- 111 cells/mm(2) per year. There was no significant difference in endothelial cell loss between the short-term and longterm groups (p = 0.5).

CONCLUSIONS

Longterm, low-dose, topical steroid treatment does not seem to prohibit chronic endothelial cell loss after normal-risk penetrating keratoplasty, in contrast to its favourable effect on immunological graft reactions. Our results may indicate that the aetiology of chronic endothelial cell loss is not of inflammatory origin. Further studies are needed to investigate this phenomenon.

Regeneration of the epithelium in organ-cultured donor corneas with extended post-mortem time

PURPOSE

The maximum post-mortem time limit for obtaining donor corneas varies between eye banks. It is not known for how long a time the epithelial cells survive post-mortem, nor is it known if donor corneas with extended post-mortem time are able to regenerate the epithelium. Therefore, we wanted to examine the epithelium in donor corneas for regenerative ability during storage in an eye bank organ culture system.

METHODS

Twenty-four paired donor corneas with post-mortem time from 28 to 163 hr were obtained. One cornea of a pair was fixed immediately to serve as a control, and the second was cultured in eye bank medium at 32 degrees C for 3 days. Examination of the specimens was performed with light and scanning electron microscopy. Immunohistochemical staining methods with antibodies against K 3, K 19, vimentin and p63 were used to further characterize the cells.

RESULTS

The control corneas showed decreasing amounts of epithelial cells with increasing post-mortem time. All the cultured corneas demonstrated rapid regeneration of the epithelium. After 3 days in organ culture, 10 of 12 donor corneas were covered with epithelium.

CONCLUSION

Even up to 7 days post-mortem, viable cells reside in the corneal epithelium. The study demonstrates the hardiness and enormous regenerative potential of peripheral corneal cells. Donor corneas processed in an eye bank organ culture storage system will obtain an intact epithelial layer within a few days.

Donor corneas for transplantation: a scanning electron microscopic study of the epithelium

PURPOSE

Donor corneas are processed in eye banks and used for transplantation as a standard routine. The maximum time limit post-mortem for harvesting donor tissue varies greatly between eye banks. This study aimed to examine the corneal epithelium for structural changes post-mortem.

METHODS

A total of 51 corneas harvested between 14 and 163 hours post-mortem were examined using scanning electron and light microscopy.

RESULTS

Cell loss occurred through desquamation of flat superficial cells during the first days. In corneas with a post-mortem time of more than 2-3 days, large superficial cell sheets and deeper cells detached, starting centrally. Deep peripheral cells remained. The loss of the superficial cells revealed the 3-dimensional structure of the epithelium and the membrane characteristics of deeper cells.

CONCLUSION

The longer the time post-mortem, the greater the epithelial cell loss. However, a rim of peripheral cells remained, even after 7 days. The superficial cell layer showed signs of strong lateral attachment and broke up in a sheet-like fashion. The intercellular adhesion between deeper cells and adhesion between the basal cells and the basement membrane appeared to be weak post-mortem. The cell membrane structures of the remaining cells were surprisingly well retained. The clinical implication of the study is discussed.

Sterile structural imaging of donor cornea by optical coherence tomography

PURPOSE

The purpose of the study was to demonstrate a new noncontact method for sterile measurement of structure and thickness of donor cornea with use of optical coherence tomography (OCT).

METHODS

A commercially available OCT instrument designed for retinal measurements was used for noncontact assessment of human corneas. Structural changes occurring during organ culture were evaluated in 29 corneas. Comparison with histology was performed, and the ability of OCT to detect corneal scars and corneal thickness was investigated.

RESULTS

Corneal epithelium, stroma, and posterior curvature, as well as thickness, can be measured by standard OCT while the cornea remains in its storage bottle. Epithelial changes leading to a reduction of epithelial thickness, stromal structural changes, and hydration folds can be visualized. OCT scans correlate well with histology. Preexisting and developing corneal scars can be detected by OCT.

CONCLUSIONS

Corneal structural imaging can be performed under sterile conditions by OCT. This provides a method for improvement of corneal storage and a screening method for signs of photorefractive surgery and scarring in donor cornea.

Cornea procurement from very old donors: post organ culture cornea outcome and recipient graft outcome

AIM

To study the suitability of corneas from very old donors for graft after banking and their clinical and endothelial outcomes in recipients.

METHODS

419 corneas stored in organ culture were divided into group 1, donors under 85 years (330 corneas) and group 2, "very old" donors aged 85 years and over (89 corneas). Endothelial cell density (ECD) before and after organ culture, discard rate before and after storage, and clinical and endothelial outcomes of the 196 penetrating keratoplasties (PKP) (158 in group 1 and 38 in group 2) were compared in a prospective longitudinal study.

RESULTS

Initial ECD was lower in group 2 than in group 1 and elimination for low ECD was more frequent in group 2 (respectively 38% v 20.2%, p=0.001). At the end of storage, because very old corneas lost fewer ECs than younger ones (respectively 4.2% v 9.5%, p=0.022), ECD was comparable between the two groups. The corneas of very old donors had a poorer macroscopic appearance at procurement and during surgery. Despite this, in grafted patients, overall graft survival in groups 1 and 2 (respectively 87.4% v 80.6%, p=0.197), visual acuity, and ECD did not differ at completion of the study (mean follow up 25 months).

CONCLUSION

This study suggests that endothelial cell count during banking ensures that functional and cellular results of PKPs are not dramatically influenced by very old donor age. Considering Europe's ageing population, the very elderly should not be deemed off limits for corneal procurement.