Evaluation of the endothelium of human donor corneas by induced dilation of intercellular spaces and trypan blue

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

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

Sinasol versus Optisol-GS for cold preservation of human cornea: a prospective ex vivo and clinical study

To compare ex vivo results of donor corneas maintained in Sinasol with those stored in Optisol-GS and reporting clinical outcomes of grafted Sinasol-versus Optisol-GS-stored corneas. In phase I, paired donor corneas were maintained in Sinasol or Optisol-GS. Afterward, the corneas were subjected to slit-lamp biomicroscopic and specular microscopic examinations on days 1 and 7, and then to trypan blue staining on day 7. The same examinations were performed on the corneas that were kept in Sinasol or Optisol-GS for 14 days. In phase II, the post-operative reports of 72 consecutive corneal transplantations were recorded using Sinasol- or Optisol-GS-preserved corneas. In phase I, 128 corneas from 64 donors and 59 corneas from 33 donors were investigated for 7 and 14 days, respectively. The EC indices were comparable between the groups at the measurement periods. The EC losses over 7 and 14 days were 3.7% and 19.9% in Sinasol against 4.6% and 20.8% in Optisol-GS. Although fair quality corneas were more common in Optisol-GS group after 7 (P = 0.04) and 14 days (P = 0.034), changes of stromal edema, Descemet's fold, and other quality ratings during 14 days were not different between the groups. In phase II, all the transplanted corneas were postoperatively clear with no adverse reactions. The overall results indicate that Sinasol is a safe, effective, and affordable intermediate cold storage medium for preservation of corneas.

Safety of Trypan Blue Capsule Staining to Corneal Endothelium in Patients with Diabetic Retinopathy

Purpose

To study the potential corneal endothelial cell toxicity of trypan blue (TB) when used for phacoemulsification to stain the anterior capsule in patients with diabetic retinopathy.

Methods

This was a single-center, prospective, randomized, individual cohort study. One eye in each patient with diabetic retinopathy underwent phacoemulsification without trypan blue capsule staining (control eye), while the other eye underwent phacoemulsification with trypan blue capsule staining (study eye). Both eyes underwent intraocular lens implantation. Preoperative and four-week postoperative quantitative and qualitative morphometric endothelial cell analyses of the cornea were performed using noncontact specular microscopy.

Results

There were no significant differences in endothelial cell density (mean ± SD for the study group: 2506.74 ± 413.99 cells/mm²; mean ± SD for the control eyes: 2466.34 ± 369.12 cells/mm²; P=0.316) or endothelial cell density (CD) loss% (mean CD loss% was 7.23 ± 13.31 for the study eyes and 9.94 ± 9.36 for the control eyes; P=0.157) four weeks after the operation. Additionally, no significant differences were seen in the percentage of hexagonal cells, coefficient of variation, or corneal thickness between the two groups preoperatively and 4 weeks postoperatively.

Conclusions

Direct administration of trypan blue into the anterior chamber for staining of the anterior capsule during cataract surgery did not result in any significant corneal endothelial changes on specular microscopy in patients with severe nonproliferative diabetic retinopathy or high-risk proliferative diabetic retinopathy at 4 weeks postoperatively. This trial is registered with NCT03755752.

Transplantation Blues: Inadvertent Staining of Amyloid Deposits With Trypan Blue

PURPOSE

To describe inadvertent persistent staining of stromal amyloid deposits by trypan blue (TB) after penetrating keratoplasty (PK) and Descemet membrane endothelial keratoplasty (DMEK) performed in patients with corneal amyloidosis.

METHODS

Case series of patients with corneal amyloidosis in whom intraoperative TB was used.

RESULTS

One patient, hospitalized for acute rejection 6 weeks after DMEK, presented with an intense blue staining of small, spindle-shaped structures in the anterior half of the cornea. DMEK had been performed for endothelial failure of a previous PK procedure done 13 years earlier for advanced lattice corneal dystrophy (LCD). After 6 months, the stromal blue tattoo persisted with impaired visual acuity, and PK was performed. Blue-stained structures were amyloid deposits characteristic of LCD recurrence. In parallel, among 85 consecutive triple procedures (PK + cataract + intraocular lens [IOL]) performed over 7 years, in which TB was used, only patients with LCD (n = 18 eyes in 17 patients) or presumed secondary amyloidosis due to chronic inflammation (n = 1), presented an isolated intense blue ring of the graft-host interface. This persisted up to 7 years with no clinical consequence.

CONCLUSIONS

TB can stain corneal amyloid deposits. After PK, staining is limited to the recipient peripheral cornea and has no apparent clinical consequence. However, during DMEK performed after a failed PK, TB stains fibrils accumulated during slow LCD recurrence and scattered on the whole graft. The long-term staining duration indicates strong interactions between TB and amyloid.

Transient leopard spot corneal endothelial staining with trypan blue during cataract surgery in a child with congenital rubella syndrome

We report the complication of corneal endothelial staining with trypan blue that limited the surgical view during cataract extraction in a 10-month-old boy. The boy had presented with a pigmentary retinopathy, microphthalmia, and a dense, white, unilateral congenital cataract. He was suspected of having, and was later diagnosed with, congenital rubella syndrome. We hypothesize that the corneal staining may have resulted from virally induced corneal endothelial damage. To our knowledge, this is the first reported case of trypan blue adversely affecting congenital cataract surgery.

Evaluation of interface quality in organ-cultured lamellar corneal transplants

BACKGROUND

With increasing numbers of lamellar keratoplasties, eye banks are challenged to deliver precut lamellar donor tissue. In Europe, the most common technique of corneal storage is organ culture which requires a deswelling process before surgical processing. The aim of this study was to investigate the influence of different deswelling times on the cutting plane quality after microkeratome-assisted lamellar dissection.

METHODS

Eight paired donor corneas (16 specimens) not suitable for transplantation were organ cultured under standard conditions at the Eye Bank of the Ludwig-Maximilians Universität, Munich, Germany. Pairs of corneal buttons were analyzed during the deswelling process in dextrane-containing medium. While one cornea was cut at an early time point during the deswelling process and put back into deswelling medium thereafter, the partner cornea was completely deswollen and dissected after 72 hours. Specimens were then further processed for scanning electron microscopy. Surface quality was assessed both digitally using Scanning Probe Imaging Processing software, and manually by three blinded graders.

RESULTS

The corneal buttons processed at the beginning of the deswelling process had a smoother surface when compared to the partner cornea that was cut at the end of the deswelling process. In our setting, no relevant difference was detectable between manual and automated microkeratome dissection.

CONCLUSION

For lamellar keratoplasty, organ-cultured corneas should be processed at an early stage during the deswelling process. We interpret the smoother dissection plane during early deswelling as a result of mechanical properties in a highly hydrated cornea.

Robust 3-D reconstruction of surfaces from image focus by local cross-sectional multivariate statistical analyses: application to human ex vivo corneal endotheliums

The considered problem of 3-D reconstruction consists in computationally and passively recovering both topography and texture of a scene surface observed by optical sectioning with a limited depth-of-field imaging system (typically a conventional optical microscope). Throughout a sequence of registered 2-D images, the concepts of shape-from-focus and extended-depth-of-field involve recovering both topography (depth map) and texture image of the surface by researching in-focus information, respectively. Toward that aim, traditional approaches generally follow a 2-D sectional way and thereby fail to deal with noisy and disturbed acquisitions, quite frequent in transmitted light observations and of interest in this paper. Such examples are the acquisitions of human ex vivo corneal endotheliums from the medical issue addressed in this paper, which are mainly damaged by cellular fragments in the sample immersion medium and by emphasized contrast reversals. To achieve with such noisy and disturbed acquisitions, a new focus analysis is introduced that originally adopts a 3-D strategy throughout the image sequence. This method exploits simultaneously all available cross-sectional cues that effectively strengthens the robustness. More precisely, it locally performs multivariate statistical analyses over cross-sectional spatial windows so as to find sectional in-focus positions. Comparisons to state-of-the-art methods on both synthetic data and real acquisitions from the deal-with medical issue demonstrate the efficiency and the robustness of the proposed approach.

Optimizing the deswelling process of organ-cultured corneas

PURPOSE

During deswelling of organ-cultured human corneas, endothelial cell loss occurs. Therefore, it is necessary to minimize the deswelling time and achieving an optimal central corneal thickness (CCT) of approximately 550 microm at the same time. We investigated the minimal deswelling time necessary and analyzed endothelial cell loss.

METHODS

Fifty-eight human corneas were stored between 13 and 81 days in organ culture. CCT was measured by optical coherence tomography. Measurements were performed before preparation, during culturing, before deswelling, and after varying deswelling periods (1-72 hours) using 5% dextran. Additionally, vital staining was performed in 6 human corneas to assess endothelial cell loss between 24 and 30 hours of deswelling. To evaluate absolute cell loss, endothelial cells were counted on human corneal pairs after 24 and 30 hours of deswelling.

RESULTS

After organ culture, mean CCT was 1194 microm. After 24 hours of deswelling in dextran-containing medium, mean CCT was 600 microm, whereas after 30 hours, mean CCT was 510 microm and hardly any corneas showed a CCT of more than 550 microm. Almost no further decrease in CCT was observed thereafter. No factors could be identified predicting the necessary deswelling time; however, paired corneas showed significant correlation of deswelling characteristics. We did not see any differences in endothelial cell loss 24 and 30 hours of deswelling or the ratio of living to dead endothelial cell counts.

CONCLUSIONS

Deswelling for 24 hours does not provide an optimal corneal thickness. Because endothelial cell loss does not increase between 24 and 30 hours of deswelling, a period of 30 hours is more suitable for obtaining sufficient corneal thickness.

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

Most of the tissue used for penetrating keratoplasty is issued through eye banks that store the corneoscleral button either in hypothermic storage at 2-6 degrees C or in organ culture at 31-37 degrees C. These two preservation techniques differ in technical aspects, tissue evaluation possibilities, storage time and microbiological safety. Hypothermic storage is simple and requires little expensive equipment. In general a pre-storage evaluation of the endothelium is performed by specular microscopy and storage time is usually around 7-10 days. Organ culture is a relatively complicated technique requiring more expertise and well-equipped facilities. Evaluation of the endothelium is not only performed before storage, but is routinely performed after storage through the use of light microscopy. With organ culture the allowed storage period is longer, up to four weeks. The vulnerability of organ culture to microbial contamination can be turned into an advantage because it allows the detection of residual micro-organisms on the cornea before surgery. Both preservation techniques seem to result in similar graft survival. The method of choice for preservation of the donor cornea is dictated by a number of factors mentioned in this review and this helps to explain the geographical differences in the use of the different techniques.

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.

Endothelial cell density in porcine corneas after exposure to hypotonic solutions

PURPOSE

To evaluate exposure to sucrose solution (1.8%) and hypotonic balanced salt solution (BSS) for its effects on endothelial cell density of porcine corneas.

METHODS

Two groups of central discs from pig corneas were organ-cultured for 24 h. Twelve corneas per group were exposed to sucrose solution (1.8%) or hypotonic BSS for 4 min each. The paired corneal discs were not treated and served as controls. After further organ culture with and without dextran for 48 h, corneal endothelium was stained with alizarin red and examined by light microscopy. The endothelial cell densities were determined manually on three central images.

RESULTS

The endothelial cell density differed significantly between corneas exposed to sucrose and the control corneas (3982+/-382 cells/mm(2) and 4360+/-331 cells/mm(2) respectively, and 3876+/-364 cells/mm(2) versus 4374+/-168 cells/mm(2) respectively with 6% dextran). In contrast, the endothelial cell density did not differ significantly between corneas exposed to hypotonic BSS and the control corneas (4374+/-296 cells/mm(2) and 4317+/-193 cells/mm(2) respectively, and 4348+/-151 cells/mm(2) versus 4426+/-175 cells/mm(2), respectively with 6% dextran).

CONCLUSIONS

Exposure to 1.8% sucrose for 4 min induces a significant endothelial cell loss of 10% on average, whereas exposure to hypotonic BSS did not significantly influence the endothelial cell density.

Staining Properties of Deepithelialized Human Amniotic Membrane

PURPOSE

The surgical use of human amniotic membrane (HAM) can be challenging because of its transparency, thin structure, and adhesive quality. Staining of HAM has been proposed to facilitate intraoperative visualization. We evaluated the in vitro staining properties of deepithelialized HAM using 5 vital dyes.

METHODS

Deepithelialized HAM was stained with indocyanine green (1.0%, 0.5%, 0.1%), fluorescein sodium (1.0%, 0.25%, 0.1%), lissamine green (0.5%, 0.1%), rose bengal (1.0%, 0.1%), and trypan blue (0.5%, 0.1%). The staining of each dyed sample was evaluated using a x10 operating microscope by a single observer. Each membrane was then rinsed, resuspended (3 mL of balanced salt solution), and then reevaluated for staining at 30-minute intervals for a total of 4 hours. All remaining stained samples were then placed in 5 mL balanced salt solution and then reevaluated for staining at 24 hours.

RESULTS

All concentrations of the 5 dyes stained the membrane initially. After 120 minutes, fluorescein sodium 0.1% and lissamine green 0.5% and 0.1% no longer stained the membrane. Fluorescein sodium 0.5% no longer stained at 210 minutes, and fluorescein sodium 1.0% no longer stained at 24 hours. All concentrations of indocyanine green, rose bengal, and trypan blue stained positively at 24 hours.

CONCLUSIONS

All 5 dyes stain deepithelialized HAM initially. Tested concentrations of fluorescein sodium and lissamine green may be superior to other tested dyes for intraoperative use because these dyes stain the membrane and then fade. Tested concentrations of rose bengal, trypan blue, and ICG may not be ideal for clinical use because they demonstrate persistent staining at 24 hours.

Automated tri-image analysis of stored corneal endothelium

BACKGROUND

Endothelial examination of organ culture stored corneas is usually done manually and on several mosaic zones. Some banks use an image analyser that takes account of only one zone. This method is restricted by image quality, and may be inaccurate if endothelial cell density (ECD) within the mosaic is not homogeneous. The authors have developed an analyser that has tools for automatic error detection and correction, and can measure ECD and perform morphometry on multiple zones of three images of the endothelial mosaic.

METHODS

60 human corneas were divided into two equal groups: group 1 with homogeneous mosaics, group 2 with heterogeneous ones. Three standard microscopy video images of the endothelium, graded by quality, were analysed either in isolation (so called mono-image analysis) or simultaneously (so called tri-image analysis), with 50 or 300 endothelial cells (ECs) counted. The automated analysis was compared with the manual analysis, which concerned 10 non-adjacent zones and about 300 cells. For each analysis method, failures and durations were studied according to image quality.

RESULTS

All corneas were able to undergo analysis, in about 2 or 7.5 minutes for 50 and 300 ECs respectively. The tri-image analysis did not increase analysis time and never failed, even with mediocre images. The tri-image analysis of 300 ECs was always most highly correlated with the manual count, particularly in the heterogeneous cornea group (r=0.94, p<0.001) and prevented serious count errors.

CONCLUSIONS

This analyser allows reliable and rapid analysis of ECD, even for heterogeneous endothelia mosaics and mediocre images.

Evaluation of potential organ culture media for eye banking using human donor corneas

AIM

To evaluate the ability of different commercially available cell culture solutions to preserve human donor corneas during 3 weeks of "closed system" organ culture at physiological temperature. This screening was performed in an attempt to establish a rational basis for the development of a serum-free organ culture medium for eye banking.

METHODS

72 normal human donor corneas were organ cultured for 21 days at 31 degrees C in eight different test media (nine corneas in each group). The basic culture solutions included: minimal essential medium (MEM), MEM with stabilised L-glutamine, M199, DIF-1000, SFM, F99, and F99 with ascorbic acid, insulin, bFGF, transferrin, selenium, and lipids (termed F99-Sr). All media were supplemented with 2% fetal calf serum (FCS), except for MEM, which was also studied at 8% FCS. The evaluation parameters included: (1) the endothelial cell loss as evaluated using trypan blue staining; (2) the ability of keratocytes and endothelial cells to incorporate tritiated uridine into RNA as evaluated using autoradiography and digital image analysis; (3) the leakage of immunogenic keratan sulphate as assessed using ELISA; and (4) changes in storage medium pH, glucose, and lactate content.

RESULTS

SFM induced the lowest endothelial cell loss of 14% (SD 2%) and the highest RNA synthesis rates of all test solutions supplemented with 2% FCS. Corneas stored in SFM also showed the least leakage of keratan sulphate and the highest glucose consumption and lactate production. In five media (MEM with 2% FCS, MEM with stabilised L-glutamine, M199, F99, and F99-Sr), comparable and intermediate potentials for organ culture were observed with endothelial cell loss of 16-19%. By contrast, 29% (4%) of the endothelium was lost after storage in DIF-1000. Interestingly, the use of 8% FCS (in MEM) had a marked protective effect on the endothelium, which showed the highest RNA synthetic activity combined with a cell loss of only 11% (4%), compared with 19% (6%) at 2% FCS (p<0.05).

CONCLUSION

Among the present test solutions, SFM appears to be the most prominent candidate for a new corneal organ culture medium and should be further tested and possibly refined to effectively substitute serum addition.

Modulation of HLA-DR and CD1a expression on human cornea with low-dose UVB irradiation

PURPOSE

To evaluate the effects of low-dose UVB irradiation of HLA and CD1a expression and the toxic effects of UVB on human corneas.

METHODS

24 pairs of human corneas from 24 donors were studied. One cornea from each pair was randomly irradiated with UVB (100 mJ/cm2) after enucleation. All corneas were then organ-cultured for 2, 7, 14 or 21 days. Endothelium was studied after enucleation and organ culture. Following preservation, corneas were evaluated by means of light microscopy, morphometry and TEM. HLA and CD1a staining was performed using an immuno-alkaline-phosphatase technique.

RESULTS

Endothelial cell loss during organ culture averaged 9.1% in the UVB group and 9.2% in the control group (NS). The number of rosette and reformation figures (p = 0.004) and the coefficient of variation (p = 0.014) were higher in the control group. Epithelial sloughing was more accentuated in the UVB group. We observed the same moderate ultrastructural injuries in both groups. In the epithelium, the average number of HLA-DR+ cells per field was 0.12 in the UVB group and 0.42 in the control group (p = 0.035). In the stroma, these figures were respectively 1.04 and 1.34 (p = 0.026). In the epithelium, the average number of CD1a + cells was respectively 0. 025 and 0.078 (p = 0.019). In the preservation mediums, the average percentage of CD1a + cells was 0.07% in the UVB group and 0.27% in the control group (p = 0.014).

CONCLUSIONS

Low-dose UVB (100 mJ/cm2) decreases HLA-DR and CD1a expression of organ-cultured human corneas and induces moderate corneal injuries. Low-dose UVB might be useful for preventing allograft rejection.