Evaluation of various preservation media for storage of donor corneas

Role of sulfated GAGs in shear mechanical properties of human and porcine cornea

The corneal extracellular matrix is mainly composed of collagen fibers, proteoglycans (PGs), and glycosaminoglycans (GAGs). The present work was done to investigate the effect of GAGs on linear viscoelastic shear properties of human and porcine cornea. A clear understanding of structural functions of GAGs could result in the development of new intervention methods for diseased conditions that involve changes to the expression of GAGs/PGs. Here, we used keratanase II enzyme to deplete sulfated GAGs from porcine and human donor corneal disks. After quantifying the GAG content, collagen fiber diameter, and interfibrillar spacings of control and GAG-depleted specimens using the Blyscan assay and transmission electron microscopy, we performed torsional rheometry to determine their shear properties at different levels of axial strain. We found that the GAG content of control human (52.35 ± 3.40 μg/mg dry tissue) and porcine cornea (48.59 ± 7.79 μg/mg dry tissue) significantly reduced following keratanase II enzyme treatment. Moreover, we observed that the diameter of collagen fibers (28.78 ± 2.33 nm) and interfibrillar spacing (45.93 ± 2.33 nm) of human specimens were significantly smaller than the collagen fiber diameter (34.77 ± 21.90 nm) and interfibrillar spacing (54.28 ± 3.99 nm) of porcine corneal samples. Although GAG depletion did not have any significant effect on the collagen fiber diameter, it significantly increased the interfibrillar spacing in both porcine and human samples. Within the range of linear viscoelastic behavior, the shear stiffness of human and porcine corneal samples did not depend on the shear strain but significantly increased with increasing the applied axial strain. The average complex shear modulus was found to be between 1.0 KPa and 6.5 KPa and between 8.5 KPa and 31 KPa for control porcine and human corneal discs, respectively. The GAG removal caused significant reduction of shear stiffness in both human and porcine corneal samples. Based on these findings, we conclude that sulfated GAGs are important in defining shear properties of porcine and human corneas and significant GAG content variation adversely affects corneal shear modulus.

Comparative Analysis of Endothelial Cell Density and Central Thickness of Corneas Used for Endothelial Keratoplasty Procedures Using Various Storage Solutions

PURPOSE

The goal of this study was to evaluate the effect of various Food and Drug Administration-approved storage solutions on endothelial cell density (ECD) and central corneal thickness (CCT).

METHOD

We analyzed 6220 tissues used for endothelial keratoplasty procedures between January 2022 and June 2023 that were stored in either Life4°C, Optisol-GS, Kerasave, or Eusol-C under hypothermic conditions. We analyzed preprocessing CCT, success rate of meeting surgeon's Descemet stripping automated endothelial keratoplasty (DSAEK) thickness preferences, and preprocessing and postprocessing ECD. Results were analyzed using one-way analysis of variance, followed by multiple pairwise comparisons using the Tukey test.

RESULTS

Mean preprocessing CCT was significantly lower in the Life4°C group (532 μm) than in Optisol-GS (549 μm), Kerasave (582 μm), and Eusol-C (589 μm) groups (all P < 0.0001). Preprocessing CCT in the Optisol-GS group was significantly lower than in Kerasave and Eusol-C groups (F (3, 3273) = 153.1, all P < 0.0001). Success rate of meeting surgeon DSAEK preferences was statistically similar among all 4 groups. Preprocessing ECD of the Kerasave group (2821 cells/mm 2 ) was numerically higher than of the Eusol-C (2791 cells/mm 2 ), Life4°C (2759 cells/mm 2 ), and Optisol-GS (2768 cells/mm 2 ) groups ( P = 0.3232, 0.0004, and 0.0015, respectively).

CONCLUSIONS

Corneal tissues stored in Kerasave and Eusol-C are significantly thicker than those in Life4°C and Optisol-GS. However, the success rate of meeting surgeon DSAEK preferences is similar among all 4 storage solutions.

A Comprehensive Review of Donor Corneal Preservation Strategies

ABSTRACT

Successful corneal transplantation relies on the viability of the corneal endothelium. Although various preservation systems have been developed in the field of eye banking, long-term storage of the corneal endothelium poses challenges and is costly. Optisol-GS in the past has been the most commonly used solution for intermediate-term corneal storage in the United States. However, disruptions in the availability of Optisol-GS, caused by rising costs and supply shortages, have necessitated alternative methods of corneal preservation. Previously described preservation methods include hypothermia (2-8°C) for short-term storage (7-14 days), organ culture (28-37°C) for intermediate storage (4-7 weeks), and cryopreservation for longer-term storage. In this review, we examine standard practice and alternative methods for corneal storage.

Culturing Limbal Epithelial Cells of Long-term Stored Corneal Donors (Organ Culture) In Vitro - A Stepwise Linear Regression Algorithm

PURPOSE

To assess various potential factors on human limbal epithelial cell (LEC) outgrowth in vitro using corneal donor tissue following long-term storage (organ culture) and a stepwise linear regression algorithm.

METHODS

Of 215 donors, 304 corneoscleral rings were used for our experiments. For digestion of the limbal tissue and isolation of the limbal epithelial cells, the tissue pieces were incubated with 4.0 mg/mL collagenase A at 37 °C with 95% relative humidity and a 5% CO2 atmosphere overnight. Thereafter, limbal epithelial cells were separated from limbal keratocytes using a 20-µm CellTricks filter. The separated human LECs were cultured in keratinocyte serum-free medium medium, 1% penicillin/streptomycin (P/S), 0.02% epidermal growth factor (EGF), and 0.3% bovine pituitary extract (BPE). The potential effect of donor age (covariate), postmortem time (covariate), medium time (covariate), size of the used corneoscleral ring (360°, 270°180°, 120°, 90°, less than 90°) (covariate), endothelial cell density (ECD) (covariate), gender (factor), number of culture medium changes during organ culture (factor), and origin of the donor (donating institution and storing institution, factor) on the limbal epithelial cell outgrowth was analyzed with a stepwise linear regression algorithm.

RESULTS

The rate of successful human LEC outgrowth was 37.5%. From the stepwise linear regression algorithm, we found out that the relevant influencing parameters on the LEC growth were intercept (p < 0.001), donor age (p = 0.002), number of culture medium changes during organ culture (p < 0.001), total medium time (p = 0.181), and size of the used corneoscleral ring (p = 0.007), as well as medium time × size of the corneoscleral ring (p = 0.007).

CONCLUSIONS

The success of LEC outgrowth increases with lower donor age, lower number of organ culture medium changes during storage, shorter medium time in organ culture, and smaller corneoscleral ring size. Our stepwise linear regression algorithm may help us in optimizing LEC cultures in vitro.

Comparison of corneal endothelial cell density and morphology with Optisol GS and Life4C storage media in the eye bank: a 5-year retrospective analysis

Purpose

Optisol GS and Life4C are corneal storage media used by eye banks worldwide. We sought to determine if either solution was associated with superior corneal endothelial cell density (ECD) or morphology in a large cohort of donor corneas.

Methods

From January 2016 through December 2020, 10,316 corneas from 5,624 unique donors were acquired and analyzed at Rocky Mountain Lions Eye Bank. In April 2019, Life4C replaced Optisol GS as the sole storage medium. We compared ECD and morphology before and after April 2019, and excluded corneas processed within the transition period. Univariable and multivariable regression analyses accounted for age, sex, tobacco use, heavy alcohol use, and diabetes. Only right corneas were analyzed to account for the correlation between eyes.

Results

Of 5042 right corneas analyzed, 3486 were stored in Optisol GS and 1556 in Life4C. There was no significant difference in ECD across groups (2794 vs. 2793 cells/mm2 in Optisol GS and Life4C, p=0.88). In multivariate analyses, there was no significant difference in corneal ECD (0.6 cells/mm2 higher with Life4C, p=0.96) or hexagonality (0.22% higher with Life4C, p=0.31). However, the coefficient of variation was significantly lower in the Life4C group (-0.0039, p=0.03). After adjustment for above factors, corneas in Life4C demonstrated a 3.1% decreased likelihood of exhibiting CV values greater than 0.40 (p=0.009).

Conclusions

This study demonstrates comparable and favorable outcomes using both storage media and confirms their overall efficacy. The decreased CV in Life4C is not of clinically significant magnitude, but merits further research in clinical and long-term settings.

Corneal blindness and eye banking: Current strategies and best practices

Corneal blindness (CB) is one of the leading causes of blindness in India and globally, affecting around 8 million population worldwide. Many of these corneal blind patients may be visually rehabilitated by corneal transplantation (CT). Eye banking plays a crucial role in facilitating CT and ocular research. Many countries have adopted regulatory frameworks, quality assurance programs, and technological advancements to enhance the efficacy and safety of CT. Various infrastructural and organizational frameworks of eye banks (EBs) in India, according to the Eye Bank Association of India (EBAI), aid in establishing guidelines and standards for EB practices. Initiatives such as the National Programme for Control of Blindness (NPCB) have significantly contributed to eye donation rates and improved access to donor corneas. This review article discusses the established eye banking networks in countries such as India, the United States (USA), and Europe, where dedicated EB organizations work collaboratively to ensure efficient procurement, processing, and distribution of corneal tissue. It also highlights specific strategies employed in India and global countries to address EBs' challenges. These challenges include the shortage of donor corneas, improving donor screening and tissue processing techniques, ensuring timely distribution of corneal tissue, and maintaining high-quality standards. Interestingly, the comparative analysis between India and other developed countries highlights the similarities and differences in eye banking strategies. By understanding the strategies employed by different regions, EBs can learn from each other's experiences and work toward achieving optimal outcomes in CT and ocular research worldwide. It underscores the importance of knowledge sharing and collaborative efforts in addressing common challenges and implementing best practices in eye banking.

Cold Storage Media versus Optisol-GS in the Preservation of Corneal Quality for Keratoplasty: A Systematic Review

Optisol-GS is the most widely used pharmaceutical composition to preserve corneas for transplantation. This systematic review investigated the effects of different cold corneal storage media (CCSM) compared with Optisol-GS on the quality of stored corneas. The literature was searched throughout May 2022 on six databases and grey literature. Studies including corneas (population) exposed to distinct cold storage media (exposure) and Optisol-GS (comparison) that reported qualitative and/or quantitative parameters of cornea quality (outcome) were included. Methodological quality was assessed using ToxRTool. From 4520 identified studies, fourteen were included according to the eligibility criteria, comprising 769 evaluated cornea samples comparing Optisol-GS with commercial and noncommercial media. All studies showed good methodological quality. Experimental times ranged from 1–28 days, mainly using 4 °C as the preservation temperature. Viable endothelial cell density (ECD) and endothelial cell morphology (EC) were the most assessed parameters. ECD results for Cornisol were higher than Optisol-GS in 10 days (p = 0.049) and favored Cornea ColdTM up to 4 weeks (p < 0.05), which also showed better qualitative results. While the standardization of test protocols could improve comparisons, evidence indicates that most CCSM present similar performances on cornea preservation for transplantation at seven days, while some formulations may increase preservation at extended times.