Frequency of positive donor rim cultures after penetrating keratoplasty using hypothermic and organ-cultured donor corneas

Gram stain and addition of amphotericin B to improve the microbial safety of human donor corneas

To determine the effectiveness of two methods to improve the microbial safety of human corneas preserved in organ culture. We compared the number of positive preservation solutions of corneas in organ culture in which the initial short-term hypothermic corneal maintenance solution was supplemented with amphotericin B 2.5 µg/mL and the historical data of microbial test results (2015-2019). In addition, we appraised the efficacy of Gram stain to detect bacterial or fungal contamination in the organ culture solutions of corneas from at-risk donors compared to the culture tests of corneas from not-at-risk donors. Statistical analysis was performed using STATA and statistical significance set at p < 0.05. The number of positive culture tests after preservation was 15 (0.5%) in 2020 compared to a mean of 37 (1.2%) in the period 2015-2019 (p < 0.01), with 10 (1.0%) positive samples in the cohort of 998 corneas from at-risk donors and 5 (0.2%) in the 2046 corneas from not-at-risk donors (p < 0.01). All corneas from at-risk donors tested positive at Gram stain and the results were available 1-3 days before those of the conventional culture tests. Amphotericin B supplementation in the short-term maintenance solution markedly reduced the number of positive microbial tests after organ culture and the early detection of contaminants, including slow-growing microorganisms, by Gram stain before the standard culture results. This meant fewer corneas being discarded and a greater likelihood of preventing post-graft infections.

Comparison of Microbial Sampling Sites and Donor-Related Factors on Corneal Graft Contamination

Grafts used for corneal donation should be sterile to avoid transplantation failure and secondary infection. However, there are no clear and globally accepted specifications from eye banks on microbial sampling sites. The objective of this study was to analyze microbial contamination of corneal grafts collected from different sampling sites. We found that the contamination rates and strain compositions significantly differed at different sampling sites. To clarify the effect of the microbial sampling site on corneal graft contamination, microbial sampling was conducted using 30 corneal grafts at the extraocular and intraocular sides of the graft in 2020 from the National Eye Bank of Taiwan. Microbial contamination significantly differed (p < 0.05) between the different sampling sites on the graft according to McNemar’s test. Although the two sampling sites showed the same specificity (33.33%), the sensitivity of sampling on the extraocular side (82.35%) was higher than that on the intraocular side (17.65%) of the graft. Donor-associated factors, including the cause of death, operating place, and cold compression, were analyzed using chi-square statistics, which revealed no significant differences in microbial contamination. Thus, our data provide evidence for the microbial sampling site of donated grafts and clear specifications for maintaining the quality of corneal grafts.

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.

Analysis in Results of Microbiologic Exam Related to Donor Corneas

Purpose: This study analyzed the microorganisms identified in donor corneas and their clinical significance.Methods: The medical records of 94 patients (114 eyes) who underwent keratoplasty and microbiological tests of the donor corneas from October 2008 to December 2020 at our hospital were reviewed retrospectively. During keratoplasty, we conducted microbiological tests of the corneoscleral rim of the donor cornea and preserving solution Optisol™-GS (Bausch & Lomb, Rochester, NY, USA), and examined the antibiotic susceptibility of bacterial isolates from the cultures.Results: Some isolates of domestic donor corneas revealed bacteria, but none of the imported corneas did. Gram-negative bacilli were detected from the corneoscleral rim in three eyes (2.6%): two cases of Acinetobacter baumannii/haemolyticus and one case of Pseudomonas aeruginosa. In one case (0.9%), Acinetobacter baumannii/haemolyticus was identified from preserving solution, with no bacteria found in the corneoscleral rim. Antibiotic susceptibility tests showed multi-drug resistance, except to colistin. In all cases where bacteria were detected, there was no keratitis or endophthalmitis after corneal transplantation.Conclusions: Although rare, bacteria can be identified from donor corneas or the preserving solution used in corneal transplantation. Therefore, caution is needed in all processes dealing with donor corneas. Empirical antibiotics that have sufficient antimicrobial activity to suppress multi-drug resistant bacteria should be selected in corneal transplantation.

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.

Post-keratoplasty Infectious Keratitis: Epidemiology, Risk Factors, Management, and Outcomes

Post-keratoplasty infectious keratitis (PKIK) represents a unique clinical entity that often poses significant diagnostic and therapeutic challenges. It carries a high risk of serious complications such as graft rejection and failure, and less commonly endophthalmitis. Topical corticosteroids are often required to reduce the risk of graft rejection but their use in PKIK may act as a double-edged sword, particularly in fungal infection. The increased uptake in lamellar keratoplasty in the recent years has also led to complications such as graft-host interface infectious keratitis (IIK), which is particularly difficult to manage. The reported incidence of PKIK differs considerably across different countries, with a higher incidence observed in developing countries (9.2-11.9%) than developed countries (0.02-7.9%). Common risk factors for PKIK include the use of topical corticosteroids, suture-related problems, ocular surface diseases and previous corneal infection. PKIK after penetrating keratoplasty or (deep) anterior lamellar keratoplasty is most commonly caused by ocular surface commensals, particularly Gramme-positive bacteria, whereas PKIK after endothelial keratoplasty is usually caused by Candida spp. Empirical broad-spectrum antimicrobial treatment is the mainstay of treatment for both PKIK, though surgical interventions are required in medically refractory cases (during the acute phase) and those affected by visually significant scarring (during the late phase). In this paper, we aim to provide a comprehensive overview on PKIK, encompassing the epidemiology, risk factors, causes, management and outcomes, and to propose a treatment algorithm for systematically managing this challenging condition.

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.

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.

Eye bank and theatre factors for positive microbiological culture of corneoscleral rim and cornea storage medium in the real-world

OBJECTIVES

To evaluate microbiological culture rate and positivity of corneoscleral rim and cornea storage media as well as possible risk factors for contamination with real-world data.

METHODS

Data of consecutive cornea donors implanted in the reference centre from January 2013 to January 2018 were reviewed. Information about cornea characteristics (donor demographic data, endothelial cell density, type of cornea conservation, days of storage, and precut vs full-thickness tissue), and microbiological culture information (corneoscleral rim vs storage sample, positive result) were statistically analysed.

RESULTS

During the study period, 1369 corneas (737 donors) were implanted. Cultures were performed in 76.8% (n = 1052) of them and were positive in 3.2% of cases, mainly bacteria (84.4%). Corneas preserved in hypothermia represented 61.8% of all positive microbiology results (p < 0.001). Other analysed risk factors did not reach statistically significant association with microbiological positivity. None of the 34 cases with positive microbiological cultures reported ocular infection for the recipients in at least 6 months' follow-up.

CONCLUSIONS

Microbiological tests rate in real-world practice are high despite not being compulsory. Organotypic cultured corneas showed a statistically less positivity in corneoscleral and storage medium than hypothermic ones, resulting in another advantage of this kind of cornea storage. Although precut corneas are thought to present less microbiological positivity, a statistically significant association was not found in the present study.

Incidence and outcome of transplantation of fungal-culture-positive donor corneoscleral tissue in optical keratoplasty

PURPOSE

This study aims to determine the incidence of fungal-culture-positive corneoscleral donor rim in patients undergoing keratoplasty and evaluate clinical outcomes of eyes that received these contaminated donor tissues.

METHODS

Patients who had optical keratoplasty between 2006 and 2016 and were found to have fungal-culture-positive donor rim were included. Microbiological and eye bank records were reviewed to determine the incidence of positive fungal rim cultures. Data were collected on visual and clinical outcomes. The main outcome measures were fungal-culture-positive donor rim and development of fungal keratitis or endophthalmitis post keratoplasty. Long-term clinical outcome and associated complications were the secondary outcome measures.

RESULTS

Out of 9620 cases of corneal transplants, 145 (1.5%) had fungal-culture-positive donor rim. Candida was the most common organism, cultured in 127 (87.6%) cases. There were no cases of postoperative fungal keratitis or endophthalmitis. Median follow-up was 4.8 years (interquartile range 3.8-7.2 years). Only eight cases (5.5%) received prophylactic antifungal treatment. There were 34 (23.4%) cases of rejection, 13 (8.9%) developed glaucoma, and 7 (4.8%) developed late bacterial keratitis. At last follow-up, best corrected visual acuity was 20/60 or better in 88 cases (60.7%) and 115 eyes (79.3%) had a clear graft.

CONCLUSION

The incidence of fungal-culture-positive donor rim is extremely low. The risk of developing fungal keratitis or endophthalmitis in patients who received contaminated donor tissue was almost negligible. Further studies are warranted to prove whether prophylaxis or adding amphotericin B in Optisol-GS confers any added benefit.

Intensive care unit time and prolonged enucleation to processing interval are associated with donor cornea contamination

PURPOSE

To determine donor cornea contamination rate and to determine factors associated with cornea contamination. To assess the effect of hospitalization, intensive care unit (ICU) time, and antibiotic use on corneal contamination rate. To determine the spectrum of the contaminating microorganisms.

METHODS

The contamination rate of 212 corneas, obtained by enucleation from April 2014 to January 2015 in a single eye bank, was assessed retrospectively according to age, sex, cause of death, systemic antibiotic use, hospitalization time, ICU time, mechanical ventilation (MV), death to enucleation interval (DEI), enucleation to processing interval (EPI), and corneal epithelial exposure grading. The relative risk (RR) and adjusted RR with a 95% confidence interval were calculated using IBM-SPSS 20.0.

RESULTS

The contamination rate was 35.6% (n = 75). On multivariate analysis, ICU stay of 4 days or longer and enucleation to processing interval (EPI) greater than 7.4 h (RR 1.58, CI 0.96-2.60, P = 0.06) were associated with donor cornea contamination. Corneal contamination risk was highest from 4 to 6 days at the ICU (RR 3.40, CI 1.54-7.51, P < 0.01) and decreased after 7 days (RR 2.22, CI 1.00-4.93, P = 0.05). Coagulase-negative Staphylococcus was the most common isolated bacteria (69.6%). The frequency of gentamicin-resistant bacteria was higher among patients who stayed 4 days or longer at the ICU.

CONCLUSION

Patients staying at the intensive care unit 4 days or longer showed increased risk of corneal contamination. This is an important result to consider further indication for cornea donation.

In vitro susceptibility of microorganisms isolated from cold stored corneas: increased gentamicin-resistance in cornea banking

Donor cornea contamination is one of the major risks for corneal transplants. The use of antibiotics in storage media remains as one of the most important security measurements to minimize the contamination risk in corneal preservation. Since antibiotic resistance among microorganisms have been rising gradually, it is important to gain knowledge about the antimicrobial susceptibility pattern for choosing the most suitable antimicrobial agents. Thus, we evaluated the in vitro susceptibility of microorganisms isolated in donor corneas processed at the Center for Blood Transfusion, Tissues and Cells (Córdoba, Spain) during 4 years in order to evaluate the efficiency, and to promote changes for further antibiotics use. Our results show the high rate of resistance to gentamicin, an antibiotic used in corneal preservation media such as Optisol GS and Eusol-C. Conversely, all the analyzed microorganisms were sensitive to vancomycin. This suggests the possibility of replacing gentamicin with another more effective antibacterial agent such as vancomycin.

Fungal infection after keratoplasty and the role of antifungal supplementation to storage solution: a review

Fungal infection after corneal transplantation is a rare, yet potentially devastating, postoperative complication and has become a growing concern for the transplant surgeon and eye banking community. The Eye Bank Association of America (EBAA) has reported an increasing trend in the rate of postkeratoplasty fungal infections and a reversal in the previously documented predominance of bacterial over fungal infections. Additionally, several studies have confirmed a high correlation between positive corneoscleral donor rim fungal cultures and postoperative infections. Optisol GS (Bausch & Lomb, Irvine, California, USA), the most extensively used corneal storage solution in US eye banks, does not currently contain any antifungal supplementation. Although large randomised control trials evaluating the efficacy and safety of routine antifungal supplementation to corneal storage solution are lacking, several investigative studies have assessed the role of antifungal agents in reducing fungal contamination of donor corneas without causing undue corneal toxicity. This review will present the current epidemiology of postkeratoplasty fungal infections and evidence for obtaining routine fungal rim cultures and antifungal supplementation of storage solution.

Small Incision Femtosecond Laser-assisted X-ray-irradiated Corneal Intrastromal Xenotransplantation in Rhesus Monkeys: A Preliminary Study

BACKGROUND

Gamma-ray irradiation could significantly induce widespread apoptosis in corneas and reduced the allogenicity of donor cornea. And the X-rays may have similar biological effects. The feasibility and effects of X-ray-irradiated corneal lamellae have not been assessed yet.

METHODS

Different doses (10 gray unit (Gy), 20 Gy, 50 Gy, 100 Gy) of X-ray irradiated corneal lamellae were collected from SMILE surgery. These corneal lamellae were assessed by physical characterization, hematoxylin and eosin (H-E) staining, Masson's staining, TdT-mediated dUTP nick end labeling (TUNEL), cell viability assay and transmission electron microscopy (TEM). We selected the optimum dose (100Gy) to treat the corneal lamellae to be the grafts. The human grafts and fresh allogeneic monkey corneal lamellae were implanted into rhesus monkeys via the small incision femtosecond laser-assisted surgery, respectively. Clinical examinations and the immunostaining were performed after surgery.

RESULTS

There were no significant changes in the transparency of the corneal lamellae, but the absorbency of the corneal lamellae was increased. According to the H-E and Masson's staining results, irradiation had little impact on the corneal collagen. The TUNEL assay and cell viability assay results showed that 100Gy X-ray irradiation resulted in complete apoptosis in the corneal lamellae, which was also confirmed by TEM observations. In the following animal model study, no immune reactions or severe inflammatory responses occurred, and the host corneas maintained transparency for 24 weeks of observation. And the expression of CD4 and CD8 were negative in the all host corneas.

CONCLUSION

X-ray irradiated corneal lamellae could serve as a potential material for xenogeneic inlay, and the small incision femtosecond laser-assisted implantation has the potential to become a new corneal transplantation surgical approach.

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.

Microbial Analysis of Donor Corneoscleral Rims and Storage Media

Purpose: We aim to investigate bacterial and fungal cultures of hypothermic donor corneal storage media (Optisol-GS) and donor rims. Methods: All corneal transplants performed from January 1, 2015 to June 30, 2016 by a single surgeon at a single facility were retrospectively reviewed. Aerobic, anaerobic, and fungal cultures were routinely obtained from all donor rims and cornea storage media. Culture results and clinical courses were recorded. Results: Eighty-four corneal transplants were performed. Five of 84 grafts (5.95%) had positive bacteria donor rim cultures. Fungal donor rim cultures were positive in 5/84 grafts (5.95%) of which two grew Candida spp. Storage media bacterial cultures were positive in 2/84 (2.4%) cultures. Storage media fungal cultures were positive in 1/84 (1.2%) cultures. No patients developed any evidence of clinical infection. Conclusions: Given the increasing rates of postkeratoplasty fungal infections, the identification of positive fungal cultures from donor rims and storage media warrants further evaluation of adding antifungals to storage media.

Interface infectious keratitis after anterior and posterior lamellar keratoplasty. Clinical features and treatment strategies. A review

Interface infectious keratitis (IIK) is a novel corneal infection that may develop after any type of lamellar keratoplasty. Onset of infection occurs in the virtual space between the graft and the host where it may remain localised until spreading with possible risk of endophthalmitis. A literature review identified 42 cases of IIK. Thirty-one of them occurred after endothelial keratoplasty and 12 after deep anterior lamellar keratoplasty. Fungi in the form of Candida species were the most common microorganisms involved, with donor to host transmission of infection documented in the majority of cases. Donor rim cultures were useful to address the infectious microorganisms within few days after surgery. Due to the sequestered site of infection, medical treatment, using both topical and systemic antimicrobials drugs, was ineffective on halting the progression of the infection. Injection of antifungals, right at the graft–host interface, was reported successful in some cases. Spreading of the infection with development of endophthalmitis occurred in five cases after Descemet stripping automated endothelial keratoplasty with severe sight loss in three cases. Early excisional penetrating keratoplasty showed to be the treatment with the highest therapeutic efficacy, lowest rate of complications and greater visual outcomes.

Factors influencing the contamination rates of the conjunctival swabs and organ culture media of human donor eyes

This study assessed the influence of donor, environmental, and logistical factors on the contamination rates of the conjunctival swabs and organ culture media of human donor eyes.In total, 1008 conjunctival swabs and 418 organ culture media samples from 504 consecutive human donor eyes were analyzed. Cross-tabulation, chi-squared tests, and Fisher's exact tests were used to assess the influence of the different factors on the contamination rates of the conjunctival swabs and organ culture media.The overall contamination rates were 28.4% for the conjunctival swabs and 1.0% for the organ culture media. A prolonged time between death and the conjunctival swab collection was associated with an increased conjunctival swab contamination rate [odds ratio (OR) = 1.9, 95% confidence interval (CI) = 1.2-3.0, P = .007]. The highest conjunctival swab contamination rate was found in the corneas procured in external institutions (outside the university hospital) (44.1%, OR = 3.6, 95%CI = 1.5-8.4, P = .003). Hospitalization times of 2 to 7 days prior to death were associated with an increased conjunctival swab contamination risk (OR = 2.6, 95%CI = 1.1-5.8, P = .021). However, the sex, age, cause of donor death, differentiation between septic and aseptic donors, differentiation between heart-beating brain-dead multiorgan donors and cadaveric donors, a warmer mean monthly temperature, and death to corneoscleral disc excision time did not significantly increase the conjunctival swab contamination risk. In addition, none of these factors affected the organ culture media contamination risk. Moreover, a positive conjunctival swab did not significantly increase the media contamination risk (P = .08). Surprisingly, the microorganisms causing media contamination were present at 50% of the amount detected on the conjunctival surface of the respective donor eye.A prolonged time between death and the conjunctival swab collection, a hospitalization time of 2 to 7 days prior to death, and corneal collection outside the university hospital seemed to be the main factors responsible for an increased conjunctival swab contamination risk. In addition, our investigation illustrated that a positive conjunctival swab is not a strong indicator for organ culture media contamination. Critical discussion is necessary regarding the validity of conjunctival swabs as prognostic parameters for organ culture media contamination.

Association between positive corneal rim cultures and microbiology screening protocols in Ontario

OBJECTIVE

(i) To assess the rate of positive microbiological cultures of corneas prepared by the Eye Bank of Canada (Ontario Division) between January 1, 2012, and December 31, 2013; (ii) to review the microbiology protocols at the 5 major transplant centres in Ontario; and (iii) to assess the incidence of endophthalmitis during the study period.

DESIGN

Retrospective chart review.

PARTICIPANTS

A total of 4186 consecutive cultured corneal tissues prepared by the Eye Bank from January 1, 2012, to December 31, 2013.

METHODS

Rates of culture-positive cornea rims and incidence of postkeratoplasty endophthalmitis at 5 surgical centres in Ontario were determined, and the protocols used to culture rims at each site were concurrently reviewed. Culture results were analyzed via logistic regression for positive cultures.

RESULTS

The rate of positive cultures at each sites were as follows: centre A, 3.74%; centre B, 3.26%; centre C, 0.51%; centre D, 0.48%; and centre E, 0.04%. Centres A, B, and D were noted to have significantly higher positive rates than centre E. In comparing microbiology protocols, longer incubation period (11 days) was 12 times more likely to be associated with higher positive culture rates than shorter period (4-5 days). Six-month follow-up of all keratoplasties revealed zero reported cases of endophthalmitis.

CONCLUSIONS

A literature review regarding the predictive value of routine culturing reveals conflicting data. Our findings suggest that differences in the microbiology protocols directly influence the rates of positive rim cultures. Without a standardized protocol, it is not possible to evaluate the predictive value of routine corneal rim culturing in predicting postkeratoplasty endophthalmitis.

Factors influencing the contamination rate of human organ-cultured corneas

PURPOSE

To assess the influence of donor, environment and storage factors on the contamination rate of organ-cultured corneas, to consider the microbiological species causing corneal contamination and to investigate the corresponding sensitivities.

METHODS

Data from 1340 consecutive donor corneas were analysed retrospectively. Logistic regression analysis was used to assess the influence of different factors on the contamination rate of organ-cultured corneas for transplantation.

RESULTS

The mean annual contamination rate was 1.8 ± 0.4% (range: 1.3-2.1%); 50% contaminations were of fungal origin with exclusively Candida species, and 50% contaminations were of bacterial origin with Staphylococcus species being predominant. The cause of donor death including infection and multiple organ dysfunction syndrome increased the risk of bacterial or fungal contamination during organ culture (p = 0.007 and p = 0.014, respectively). Differentiating between septic and aseptic donors showed an increased risk of contamination for septic donors (p = 0.0020). Mean monthly temperature including warmer months increased the risk of contamination significantly (p = 0.0031). Sex, donor age, death to enucleation, death to corneoscleral disc excision and storage time did not increase the risk of contamination significantly.

CONCLUSION

The genesis of microbial contamination in organ-cultured donor corneas seems to be multifactorial. The main source of fungal or bacterial contamination could be resident species from the skin flora. The rate of microbial contamination in organ-cultured donor corneas seems to be dependent on the cause of donor death and mean monthly temperature.

Comparison of femtosecond laser-assisted corneal intrastromal xenotransplantation and the allotransplantation in rhesus monkeys

Background

In our previous study, we showed that both allogeneic and autogeneic small-incision femtosecond laser-assisted corneal intrastromal transplantation are safe and effective surgeries. However, the results of small-incision femtosecond laser-assisted intrastromal xenotransplantation have not yet been explored. Additionally, we suggest that glycerol-dehydrated corneal lamellae might provide a possible alternative for this xenogenic implantation approach.

Methods

Corneal inlay lamellae were produced from rabbits and humans using femtosecond laser-assisted surgeries and were dehydrated in glycerol for 1 week at 4 °C. These xenogeneic glycerol-dehydrated grafts and fresh allogeneic monkey lamellae were then implanted into rhesus monkeys using small-incision femtosecond laser assistance. Postoperatively, clinical examinations, AS-OCT measurements and tear inflammatory mediator assays were performed.

Results

There were no significant changes in the transparency of the corneal lamellae after glycerol dehydration. Following implantation, no evidence of tissue rejection or severe inflammatory responses was observed in the monkeys, and the host corneas remained transparent throughout a 6-month observation period. The grafts were clearly visible via AS-OCT. Corneal thickness increased 1 week postoperatively but subsequently declined and remained unchanged 1 month after surgery. Significant changes were observed in all tear inflammatory mediators in the ‘Rabbit to Monkey’ group. The trends in changes of tear inflammatory mediators in the ‘Human to Monkey’ group were similar to those in the ‘Rabbit to Monkey’ group. At 1 month post-surgery, the levels of most tear inflammatory mediators had decreased, with the exception of IL-1β, TGF-β1 and IFN-γ in the allotransplantation group.

Conclusion

Small-incision femtosecond laser-assisted intrastromal transplantation minimized invasiveness and improved surgical efficiency. In addition, the host cornea maintained a high level of biocompatibility. Glycerol-dehydrated corneal lamellae might be potentially useful as an alternative inlay xenogeneic material. In this study, we also describe a new treatment that can be used in keratoconus, corneal ectasia, presbyopia, hyperpresbyopia and other diseases.

The influence of donor factors on corneal organ culture contamination

PURPOSE

To evaluate the contamination rate and the corresponding spectrum of microbes and to identify donor risk factors for corneal organ culture contaminations.

METHODS

A total of 3306 organ-cultured donor corneas were included in the study. We performed a retrospective database analysis to evaluate donor factors such as gender, age, death-to-explantation interval (DEI), procurement site and cause of death and to determine their influence on donor cornea contaminations. Odds ratios (ORs) were calculated for each factor.

RESULTS

The overall contamination rate was 7.8% (n = 259). Younger donor age (OR: 2.2, p = 0.003, chi-squared test), a DEI of more than 24 hr (OR: 1.6, p < 0.001), hospitalization prior to death (OR: 2.2, p < 0.001) and death caused by sepsis (OR: 2.7, p < 0.001) were associated with an increased risk of contamination, whereas donor gender did not have an effect on donor cornea contaminations. The most frequently isolated microbes were Enterococci (19%), Staphylococci (10.8%) and Candida (37.4%).

CONCLUSION

This study helps to estimate the contamination risk of a cultured cornea based on specific donor factors. However, donors with risk factors should not be generally excluded from cornea donation. Further studies including antibiograms might clarify whether a change in the antibiotic composition of the culture medium would be useful to deal with the increasing number of multi-resistant microbes.

The value of corneoscleral rim cultures in keratoplasty: a systematic review and cost-effectiveness analysis

PURPOSE

This study evaluated the performance of donor corneoscleral rim cultures for predicting infection after corneal transplantation, and determines if there is a correlation between positive corneoscleral rim cultures and postkeratoplasty infection.

DESIGN AND DATA SOURCES

This was a systematic review, prognostic accuracy analysis, and cost-effectiveness analysis. Databases searched were: Medline (Ovid), Embase (Ovid), CINAHL, Cochrane Library, Web of Science, and BioSis Previews. Grey literature was also explored.

MATERIALS AND METHODS

A systematic review was conducted to locate published and unpublished studies. All studies examining corneal button contamination and its association with endophthalmitis and keratitis posttransplantation were included. Extracted data were used to calculate sensitivity, specificity, positive predictive value, and negative predictive value. Cost data from the London Laboratory Services Group in London, ON were used to calculate the cost-effectiveness of culturing donor rim cultures.

RESULTS

Of 7,870 grafts, 954 had a positive rim culture (12.1%), with 12 patients going on to develop keratitis or endophthalmitis (1.3%). The prevalence of keratitis and endophthalmitis in this study was 0.15%, and the positive predictive value 1.5%. Of the 12 infections, nine were fungal and three bacterial. The estimated cost of a positive and negative test result was CAD$45.99 and $14.15, respectively. The cost to run all 7,870 tests was estimated to be $141,735.86, with an incremental cost-effectiveness ratio of $40,215.70.

CONCLUSION

There was a significant divergence between bacterial and fungal rim-culture results. Bacterial cultures predicted clinical infection poorly, did not change management, and were expensive. Fungal cultures predicted clinical infection in over 10% of patients, had the potential to change management, and were 40% less expensive than full rim culturing (bacterial and fungal tests). Fungal rim cultures may be considered in areas where fungal infection rates are high.

Incidence and Outcomes of Positive Donor Corneoscleral Rim Fungal Cultures after Keratoplasty

PURPOSE

To determine the incidence of positive corneoscleral donor rim fungal cultures after keratoplasty and to report clinical outcomes of grafts with culture-positive donor rims.

DESIGN

Retrospective cohort study.

PARTICIPANTS

Consecutive donor corneas and keratoplasty recipients at a single tertiary referral center over 20 years.

METHODS

Patient charts were reviewed to determine the incidence of positive donor rim fungal cultures and clinical outcomes of all grafts using contaminated tissue.

MAIN OUTCOME MEASURES

The primary outcome measures were positive donor rim fungal culture results and the development of postkeratoplasty fungal infection using corresponding corneal tissue. The secondary outcome measure was the impact of postoperative prophylaxis on donor tissue-associated infections.

RESULTS

A total of 3414 keratoplasty cases were included in the statistical analysis. Seventy-one cases (2.1%) were associated with a fungal culture-positive donor rim. Candida species were cultured in 40 cases (56.3%). There was a higher incidence of positive rim cultures over the last 5 years of the analytic period compared with the first 15 years (P = 0.018). Fungal keratitis developed in 4 cases (5.6%), and all patients required further surgical intervention to achieve cure. There were no cases of fungal endophthalmitis. Empiric antimycotic prophylaxis initiated at the time of positive culture result reduced the incidence of keratitis from 15.8% in untreated cases to 1.9% in treated cases (P = 0.056).

CONCLUSIONS

Positive donor rim fungal cultures are uncommon, but carry an unacceptably high risk of postoperative fungal infection. This risk may be reduced with prophylactic antimycotic therapy when culture-positive donor rims are identified.

Endophthalmitis after penetrating keratoplasty

PURPOSE

To determine the incidence of endophthalmitis after penetrating keratoplasty (PK) and patient and donor risk factors.

DESIGN

Retrospective cohort study using national transplant registry data.

PARTICIPANTS

All corneal transplant recipients (n = 11 320) registered on the United Kingdom Transplant Registry undergoing their first PK between April 1999 and December 2006.

METHODS

Patients who developed endophthalmitis were identified on the transplant registry. In addition, cases where the fellow cornea from the same donor had been transplanted were included. Clinical information regarding donor and recipient characteristics, surgical details, and postoperative outcomes were collected and analyzed. In cases where endophthalmitis was reported, the diagnosis was verified by a follow-up supplementary questionnaire to the surgeon. Logistic regression was used to investigate differences in the factors associated with the development of endophthalmitis.

MAIN OUTCOME MEASURES

Incidence of endophthalmitis and graft survival.

RESULTS

The overall incidence of endophthalmitis occurring after primary PK in the UK was 0.67%. The incidence of endophthalmitis occurring within 6 weeks of surgery was 0.16%. Graft survival after endophthalmitis was 27% (95% confidence interval, 16-38) at 5 years, with a mean best-corrected visual acuity of 1.13 (logarithm of the minimum angle of resolution) for surviving grafts. Factors associated with endophthalmitis were donor cause of death (infection), high-risk cases, and indication for corneal transplantation.

CONCLUSION

Endophthalmitis remains a serious issue, with those affected having reduced graft survival and poor visual outcomes. Management of the identified recipient and donor risk factors are important to reduce endophthalmitis risk. In particular, the increased incidence of endophthalmitis when the donor dies of infection requires further explanation and review of current donor eye retrieval and eye bank practices. The delayed presentation of endophthalmitis cases also raises questions regarding possible sequestration of microbes within the corneal tissue and the effect of antimicrobials in storage media.

Eye banking and corneal transplantation communicable adverse incidents: current status and project NOTIFY

PURPOSE

Evidence of the transmission of disease via donor ocular tissue has been demonstrated for adenocarcinoma, rabies, hepatitis B virus, cytomegalovirus, herpes simplex virus, Creutzfeldt-Jakob disease, and a variety of bacterial and fungal infections.

METHODS

Although there is no evidence to date of disease transmission for HIV infection, syphilis, hepatitis C, hepatitis A, tuberculosis, HTLV-1 and -2 infection, active leprosy, active typhoid, smallpox, and active malaria, these entities remain contraindications for transplantation for all eye banks nationally and internationally. The potential sources of contamination include infected donors, during the process of removing tissue from cadaveric donors, the processing environment, and contaminated supplies and reagents used during processing. The transmissions of Herpes simplex virus and HSV via corneal graft have been shown to be responsible for primary graft failure. HSV-1 may also be an important cause of PFG.

RESULTS

The long latency period of some diseases, the emergence of new infectious disease, and the reemergence of others emphasize the need for long-term record maintenance and effective tracing capabilities.

CONCLUSIONS

The standardization of definitions for adverse events and reactions will be necessary to support the prevention and transmission of disease. International classification of a unique identification system for donors will be increasingly important for vigilance and traceability in cross-national exportation of human cells, tissues, and cellular- and tissue-based products. Opportunities for continuous improvement exist as does the need for constant vigilance and surveillance.

Thirty years of cornea cultivation: long-term experience in a single eye bank

PURPOSE

To evaluate donor demographics, trends in donor tissue procurement and tissue storage over a long period.

METHODS

A retrospective, longitudinal, descriptive analysis was undertaken of data from the Hamburg Eye Bank Data Base (HEB-DB) that had been collected between 1981 and 2010. Data on 54 parameters of cornea donors [including clinical history, age, death cause, gender and death-to-explantation interval (DEI)] and of cultivated corneas (endothelial quality and development in culture, cultivation period, microbiological contamination) were retrieved. These data were analysed statistically, focusing on the historical development of the eye bank.

RESULTS

At the time of retrieval (June 2010), the HEB-DB contained data on 10 943 corneas (5503 donors). Most donors were men (65%) and had died from cardiopulmonary (n = 801)/cerebral (n = 261) failure or as the result of a polytraumatic accident/suicide (n = 602). Within these years, donor age, DEI and storage time increased. The percentage of stored corneas suitable for transplantation displayed a variable but increasing trend; in 2007, almost 75% of the stored corneas were transplanted. Between 1995 and June 2010, the median microbiological contamination rate was 5.3%. A change in the procurement procedure from enucleation to corneoscleral explantation in 2008 led to a briefly increased contamination rate.

CONCLUSION

  Donor demographic data run parallel to the general demographic development. Our analysis indicates a dynamic development of the eye bank over the last 30 years and emphasizes the need for an active quality management in coping with the challenges of modern eye banking.

Microbiological profile of donor corneas stored for tectonic transplantation purposes in rabbits

This study aimed to evaluate the microbiota of donor rabbit corneas stored for tectonic transplantation purposes. Swabs from both corneas of 20 rabbits were carefully collected and submitted to microorganism isolation and identification. After this first swab collection, rabbits were euthanized for reasons other than this project and the eyes were enucleated. The corneas were collected and stored to compose the cornea tissue bank. Corneas were stored in a 0.3% tobramycin solution at -20ºC. After 30 days, the corneas were thawed at room temperature and removed from the antibiotic. New swabs were obtained from the corneas and submitted to microorganism isolation and identification. Gram positive organisms were predominant in the rabbit corneal flora before storage and the Staphylococcus sp. was the most common microorganism isolated from those samples. No growth was observed on the samples collected after storage. The methods used for collection and storage of the corneas were efficient to constitute a sterile donor corneal tissue bank.

Conjunctival swabs and corneoscleral rim cultures from corneal transplantation donors as possible early indicators for posttransplant endopthalmitis

PURPOSE

To determine by microbiological examinations the rate of conjunctiva and corneoscleral rim contamination of cadaver donor tissues.

METHODS

A prospective review of culture results for 98 cadaver donor conjunctival swabs [mean age 76.4 ± 12.9 years (±SD)]. Transplant patients were evaluated both before and after disinfection with gentamicin. Individual parameters evaluated included detection rates of bacteria, variety of detected bacteria, time interval from donor death to tissue harvest and age of donors.

RESULTS

Before disinfection, 60 out of 98 conjunctival swabs exhibited microbial growth, while only 36 out of 98 exhibited growth after disinfection (p = 0.0006). Longer intervals between death and tissue harvest were associated with higher positive microbial growth rates. Prior to disinfection, culture-positive donors (74.1 ± 13.6 years) were significantly younger than culture-negative donors (79.8 ± 10.8 years) (p = 0.024). Positive donor rim cultures were noted in 2 out of the 22 corneal transplantations. Microorganisms isolated from the corneal grafts matched those found in the conjunctiva.

CONCLUSIONS

It is recommended that the corneoscleral buttons be removed as soon as possible. Cultures of conjunctival swabs collected from donors after disinfection may be useful in determining treatment for postoperative infections occurring after corneal transplantation.

Comparison of in situ excision and whole-globe recovery of corneal tissue in a large, single eye bank series

PURPOSE

To compare the quality of corneal tissue after 2 different procurement techniques, whole-globe enucleation and in situ excision.

DESIGN

Cross-sectional study.

METHODS

Data in the interval 2005 to 2008 were collected from the Lions Eye Bank of Oregon. A total of 3618 eyes underwent whole-globe enucleation (enucleation group) and 2048 eyes were subject to in situ excision (in situ group). Endothelial cell density (ECD) and death-to-preservation time (D-to-P) were analyzed. Grading scores ranging from 0 (excellent) to 4 (unacceptable for transplantation) were used to evaluate the epithelium, stroma, Descemet fold, and overall endothelium. The incidences of ECD less than 2000 cells/mm(2) (ECD <2000), primary graft failure (PGF), and postoperative infection were investigated.

RESULTS

ECD was 2726 +/- 419 cells/mm(2) in the enucleation and 2645 +/- 395 cells/mm(2) in the in situ group (P < .001). D-to-P was 9.81 +/- 3.56 hours and 8.90 +/- 3.65 hours, respectively (P < .001). The mean grade of the stroma was 1.44 +/- 0.51 in the enucleation group and 1.50 +/- 0.56 in the in situ group (P = .001). The mean grades of overall endothelium were 1.51 +/- 0.72 and 1.58 +/- 0.69, respectively (P < .001). The incidence of ECD <2000 was 2.38% in the enucleation group and 2.39% in the in situ group (P > .999), PGF rates were 0.72% and 0.68% (P > .999), and postoperative infection levels were 0.14% and 0.39% (P = .080).

CONCLUSION

Although there were minor differences in parameters related to the endothelium, in situ excision seemed equivalent to whole-globe enucleation when various parameters were evaluated.

Regional variation in the biomechanical properties of the human sclera

The study aimed to determine the variation in thickness and biomechanical properties between the different regions of the human sclera. Thickness measurements were carried out along eight meridian lines extending from the posterior pole to limbus in 36 human donor scleras aged 52-96 years. Strip specimens were extracted from areas close to the limbus, equator and posterior pole, and tested under cycles of uniaxial tension. Two strain rates were considered to assess the viscoelasticity effects on the regional variation in material behaviour. The results were used to derive the stress-strain behaviour of each specimen and to calculate the tangent modulus at each stress level. The scleras had a variable thickness from maximum at the posterior pole to minimum close to the equator, and increasing again towards the limbus. All scleral specimens demonstrated nonlinear behaviour with an initially low tangent modulus (a measure of stiffness) increasing gradually under higher stresses. With reference to specific stress levels, the behaviour comparisons between regions showed a gradual growth in material tangent stiffness with progression from the posterior region towards the limbus. The viscoelasticity of the tissue, which was evident with significant increases in stress (157-203%) and tangent modulus (30.3-38.8%) with strain rate rise (from 8% to 200% per min), was associated with reductions in the regional variation in stiffness. The considerable variation in biomechanical behaviour found in this study should be useful in improving the accuracy of representing the sclera's real-life conditions in numerical simulations.

Whole globe enucleation versus in situ excision for donor corneal retrieval--a prospective comparative study

PURPOSE

The purpose of this study was to compare the results after changing from conventional whole globe enucleation to in situ excision of donor corneas.

METHODS

Donor corneal tissue retrieved by enucleation (n = 50) and in situ excision (n = 50) was quantitatively evaluated prospectively, and the main parameters evaluated were endothelial cell counts, ultrasonic corneal pachymetry, microbial contamination, graft clarity, and postoperative median visual acuity at the end of 3 months.

RESULTS

Mean preoperative donor endothelial cell densities were 2174 +/- 123 and 2132 +/- 149 cells per millimeter square after enucleation and in situ excision, respectively (P = 0.13). The preoperative disease distribution and visual potential of recipients were comparable between the 2 groups. Corneal pachymetry was lower in the whole globe group at the end of 3 months (528 microm, enucleation group; and 539 microm, in situ group; P = 0.01). The mean postoperative endothelial cell counts were comparable in both groups at 3 months (1708 +/- 104.8/mm for whole globe group, measured in 40 eyes, vs 1674 +/- 117.4/mm in in situ group, recorded in 39 eyes; P = 0.18). The number of positive corneoscleral rim cultures postkeratoplasty was statistically comparable in both groups (20% in enucleation group and 24% in in situ group; P = 0.62). At 3 months, 98% and 92% of grafts had a graft clarity of >or=3+ in whole globe and in situ groups, respectively (P = 0.16). Seventy-two percent of patients in whole globe group and 67% in in situ group achieved a best-corrected visual acuity of >or=0.1. Postoperative graft infection developed in 2 cases in the in situ group.

CONCLUSIONS

Changeover from whole globe enucleation technique to in situ excision technique of harvesting donor corneas demonstrated that in situ excision is a viable alternative.