Evolving Techniques in Corneal Transplantation

The landscape of clinical trials in corneal regeneration: A systematic review of tissue engineering approaches in corneal disease

The limited availability of a healthy donor cornea and the incidence of allograft failure led researchers to seek other corneal substitutes via tissue engineering. Exploring the trend of clinical trials of the cornea with the vision of tissue engineering provides an opportunity to reveal future potential corneal substitutes. The results of this clinical trial are beneficial for future study designs to overcome the limitations of current therapeutic approaches. In this study, registered clinical trials of bio-based approaches were reviewed for corneal regeneration on March 22, 2024. Among the 3955 registered trials for the cornea, 392 trials were included in this study, which categorized in three main bio-based scaffolds, stem cells, and bioactive macromolecules. In addition to the acellular cornea and human amniotic membrane, several bio-based materials have been introduced as corneal substrates such as collagen, fibrin, and agarose. However, some synthetic materials have been introduced in recent studies to improve the desired properties of bio-based scaffolds for corneal substitutes. Nevertheless, new insights into corneal regenerative medicine have recently emerged from cell sheets with autologous and allogeneic cell sources. In addition, the future perspective of corneal regeneration is described through a literature review of recent experimental models.

Biopolymeric corneal lenticules by digital light processing based bioprinting: a dynamic substitute for corneal transplant

Digital light processing (DLP) technology has gained significant attention for its ability to construct intricate structures for various applications in tissue modeling and regeneration. In this study, we aimed to design corneal lenticules using DLP bioprinting technology, utilizing dual network bioinks to mimic the characteristics of the human cornea. The bioink was prepared using methacrylated hyaluronic acid and methacrylated gelatin, where ruthenium salt and sodium persulfate were included for mediating photo-crosslinking while tartrazine was used as a photoabsorber. The bioprinted lenticules were optically transparent (85.45% ± 0.14%), exhibited adhesive strength (58.67 ± 17.5 kPa), and compressive modulus (535.42 ± 29.05 kPa) sufficient for supporting corneal tissue integration and regeneration. Puncture resistance tests and drag force analysis further confirmed the excellent mechanical performance of the lenticules enabling their application as potential corneal implants. Additionally, the lenticules demonstrated outstanding support for re-epithelialization and stromal regeneration when assessed with human corneal stromal cells. We generated implant ready corneal lenticules while optimizing bioink and bioprinting parameters, providing valuable solution for individuals suffering from various corneal defects and waiting for corneal transplants.

DNA methylation changes and increased mRNA expression of coagulation proteins, factor V and thrombomodulin in Fuchs endothelial corneal dystrophy

Late-onset Fuchs endothelial corneal dystrophy (FECD) is a disease affecting the corneal endothelium (CE), associated with a cytosine-thymine-guanine repeat expansion at the CTG18.1 locus in the transcription factor 4 (TCF4) gene. It is unknown whether CTG18.1 expansions affect global methylation including TCF4 gene in CE or whether global CE methylation changes at advanced age. Using genome-wide DNA methylation array, we investigated methylation in CE from FECD patients with CTG18.1 expansions and studied the methylation in healthy CE at different ages. The most revealing DNA methylation findings were analyzed by gene expression and protein analysis. 3488 CpGs had significantly altered methylation pattern in FECD though no substantial changes were found in TCF4. The most hypermethylated site was in a predicted promoter of aquaporin 1 (AQP1) gene, and the most hypomethylated site was in a predicted promoter of coagulation factor V (F5 for gene, FV for protein). In FECD, AQP1 mRNA expression was variable, while F5 gene expression showed a ~ 23-fold increase. FV protein was present in both healthy and affected CE. Further gene expression analysis of coagulation factors interacting with FV revealed a ~ 34-fold increase of thrombomodulin (THBD). THBD protein was detected only in CE from FECD patients. Additionally, we observed an age-dependent hypomethylation in elderly healthy CE.Thus, tissue-specific genome-wide and gene-specific methylation changes associated with altered gene expression were discovered in FECD. TCF4 pathological methylation in FECD because of CTG18.1 expansion was ruled out.

Triplet of doubles: Double anterior chamber, double descemet membranes, and double rhexis

A 52-year-old women underwent penetrating keratoplasty for total corneal opacity after healed microbial keratitis with an uneventful postoperative period until six months when she developed gross diminution of vision. During examination, she was detected to have a membrane in the anterior chamber, creating a double anterior chamber with a total cataract. The graft was clear, and sutures were intact. Anterior segment optical coherence tomography (OCT) showed the membrane in the anterior chamber crossing the graft host junction, suggesting this membrane to be retained host descemet membrane. This was confirmed on histopathological examination. Double rhexis (descemetorhexis and capsulorhexis) was performed with cataract removal and intraocular lens (IOL) implantation, and patient had good visual recovery postoperatively.

Design of functional biomaterials as substrates for corneal endothelium tissue engineering

Corneal endothelium defects are one of the leading causes of blindness worldwide. The actual treatment is transplantation, which requires the use of human cadaveric donors, but it faces several problems, such as global shortage of donors. Therefore, new alternatives are being developed and, among them, cell therapy has gained interest in the last years due to its promising results in tissue regeneration. Nevertheless, the direct administration of cells may sometimes have limited success due to the immune response, hence requiring the combination with extracellular mimicking materials. In this review, we present different methods to obtain corneal endothelial cells from diverse cell sources such as pluripotent or multipotent stem cells. Moreover, we discuss different substrates in order to allow a correct implantation as a cell sheet and to promote an enhanced cell behavior. For this reason, natural or synthetic matrixes that mimic the native environment have been developed. These matrixes have been optimized in terms of their physicochemical properties, such as stiffness, topography, composition and transparency. To further enhance the matrixes properties, these can be tuned by incorporating certain molecules that can be delivered in a sustained manner in order to enhance biological behavior. Finally, we elucidate future directions for corneal endothelial regeneration, such as 3D printing, in order to obtain patient-specific substrates.

Trends in Corneal Transplantation in a Tertiary Hospital in Brazil

PURPOSE

The purpose of this study was to analyze the evolving trends of surgical techniques and indications of corneal transplantation (CT) at a tertiary hospital in Brazil.

METHODS

The medical records of all patients who underwent CT at the Hospital Oftalmológico de Sorocaba (Sorocaba Eye Hospital) from the Banco de Olhos de Sorocaba (Sorocaba Eye Bank) group in Sorocaba, Brazil, from January 1, 2012, to December 31, 2019, were analyzed. Data regarding age, sex, transplant indication, and surgical technique were collected.

RESULTS

A total of 16,250 CTs were performed. There was a statistically significant decreasing trend of keratoconus-related CT ( P < 0.0001), with rates dropping from 41.7% among all CTs in 2012 to 25.5% in 2019. Penetrating keratoplasty, anterior lamellar keratoplasty, and endothelial keratoplasty (EK) accounted for 59.3%, 27.1%, and 7.8% of the CTs performed in 2012 and 33.3%, 16.4%, and 39.9% in 2019, respectively. A statistically significant decreasing trend was observed for penetrating keratoplasty ( P < 0.0001) and anterior lamellar keratoplasty ( P < 0.0001), whereas EK showed a statistically significant increasing trend during the period ( P < 0.0001). Among EKs, Descemet membrane EK increased statistically significantly from 12.8% in 2012 to 74.4% in 2019 ( P < 0.0001).

CONCLUSIONS

This study shows relevant evolving trends in indications and preferred CT techniques in a tertiary hospital in Brazil.

Surgical management of glaucoma following different keratoplasty techniques

PURPOSE

To investigate the results of surgical management of glaucoma following different keratoplasty techniques.

METHODS

Medical records of 628 cases who underwent keratoplasty were reviewed. One hundred and eighty-eight patients (29.9%) who developed post-keratoplasty glaucoma were evaluated. Patients who could not be controlled with maximal medical treatment and underwent glaucoma surgery were included in this study. Trabeculectomy, Ahmed glaucoma valve (AGV) implantation or diode laser cyclophotocoagulation (DLC) were applied.

RESULTS

Glaucoma surgery was performed in 55 (29.3%) patients who had uncontrolled post-keratoplasty glaucoma. In penetrating keratoplasty group (n = 42), DLC was applied to 30 (71.4%) eyes, AGV to 11 (26.2%) eyes, and trabeculectomy in 1 (2.4%) eye. In Descemet's membrane endothelial keratoplasty group (n = 8), DLC was applied to 4 (50%) eyes, trabeculectomy for 3 (37.5%) eyes and AGV for 1 (12.5%) eye. In deep anterior lamellar keratoplasty group (n = 5), DLC was applied to 2 (40%) eyes, trabeculectomy to 2 (40%) eyes and AGV to 1 (20%) eye. While a statistically significant decrease was found in intraocular pressure (IOP) and anti-glaucomatous medication after surgery (p < 0.05 for each), no significant difference was found in best corrected visual acuity (BCVA). During follow-up, DLC was applied as re-glaucoma surgery in 19 (34.5%) cases. A significant reduction in IOP together with number of anti-glaucomatous medications was found with re-operation; however, a significant decrease in BCVA was noted (p < 0.05 for each).

CONCLUSION

Glaucoma surgeries after keratoplasty are effective in decreasing IOP and the number of anti-glaucomatous medication. While BCVA doesn't change after the first glaucoma surgery, after re-operation significant decrease may occur.

Posterior lamellar keratoplasty: techniques, outcomes, and recent advances

Over the past 2 decades, posterior lamellar keratoplasty (PLK) has emerged as an alternative to penetrating keratoplasty in the treatment of corneal endothelial disorders. The reasons for this trend include the search for a safer procedure to replace diseased endothelium that provides faster and better visual rehabilitation and reduces the need for postoperative care. Different surgical techniques, surgical instruments, devices, and lasers have been introduced to overcome technical difficulties, thus improving clinical outcomes. Yet, surgeons and eye banks must address the complications and limitations that arise during the transition to these new techniques. This review discusses the most significant aspects of the evolution of PLK, including a detailed description of current techniques and the direction of future treatment for corneal endothelial disease with the use of laser-assisted surgery, bioengineered corneas, cell therapy, and new pharmacologic therapy.

Trends of Corneal Transplantation in Adults from 2010 to 2019 in East China: A 10-Year Experience

INTRODUCTION

The aim of the study was to provide an overview of trends in the indications and surgical techniques for corneal transplantation in adults in East China from 2010 to 2019.

METHODS

The medical charts of all patients (aged ≥18 years old) undergoing keratoplasty at the Eye, Ear, Nose and Throat Hospital of Fudan University between January 2010 and December 2019 were retrospectively reviewed. The indications for keratoplasty and the surgical techniques were collected.

RESULTS

A total of 2,929 cases were included. Acquired nontraumatic corneal diseases (n = 1,927, 65.8%) have been the leading indication for corneal transplantation during the past decade. Although infectious keratitis was still the leading indication among acquired nontraumatic diseases, its absolute number and proportion gradually decreased during this decade (p < 0.001). In contrast, the proportion of endothelial dysfunction/bullous keratopathy increased from 7.8% in 2010 to 12.4% in 2019 (p = 0.029). Penetrating keratoplasty (PKP) has been the predominant surgical technique (n = 1,854, 63.3%), followed by deep anterior lamellar keratoplasty (DALK) (n = 361, 12.3%) and endothelial keratoplasty (EK) (n = 305, 10.4%). Nevertheless, the proportion of PKP decreased from 77.6% in 2010 to 56.9% in 2019 (p = 0.002) and was gradually replaced by DALK (from 7.8% to 16.3%, p < 0.001) and EK (from 3.4% to 10.4%, p = 0.009).

CONCLUSIONS

Over the past decade, infectious keratitis and endothelial dysfunction/bullous keratopathy have been the leading indications for keratoplasty in adults. Preferred surgical techniques for keratoplasty have been shifting from PKP to more customized lamellar keratoplasties.

Novel Microforceps Technique Developed for Endothelial Surgical Procedures

PURPOSE

To develop a more efficient and less traumatic method of Descemet membrane removal in endothelial surgery.

METHODS

A novel, vertically oriented, reverse-grasping microforceps (named the Rabiyah Descemet Membrane Removal Microforceps) were created to facilitate grasping and extraction of a host Descemet membrane.

RESULTS

This new instrument has been used successfully and safely in more than 85 endothelial keratoplasty cases among 4 surgeons.

CONCLUSIONS

The Rabiyah Descemet Membrane Removal Microforceps provides surgeons with a safe and an efficient option to remove Descemet membrane in endothelial surgical procedures.

Incidence and Risk Factors of Ocular Hypertension/Glaucoma After Descemet Stripping Automated Endothelial Keratoplasty

Purpose

To evaluate the incidence, demographics, associated risk factors, management and clinical outcomes of ocular hypertension/glaucoma after Descemet stripping automated endothelial keratoplasty (DSAEK).

Methods

A cohort review of 81 DSAEK cases was performed at Queen Victoria Hospital, United Kingdom. Patients with pre-existing glaucoma, transient increased IOP within the first 48 hours post-graft, additional post-transplant surgery, or failed to complete one year follow-up were excluded from the study. Ocular hypertension was defined as intraocular pressure (IOP) elevation >21mmHg or ≥6mmHg from baseline at any postoperative visit. The study looked at the incidence, risk factors, response to anti-glaucoma treatment, graft failure and best corrected visual acuity.

Results

The incidence of post-DSAEK ocular hypertension and glaucoma was 51.9% and 13.6%, respectively. Steroid-induced IOP elevation was the most frequent cause, with an incidence of 38.3%. Risk factors such as pseudophakia (p=0.024) and preoperative IOP>16 (p=0.003) were found to be associated with post-DSAEK ocular hypertension. Preoperative IOP>16 had 5.27 times risk of IOP elevation. Eyes with graft dislocation and/or detachment were significantly associated with post-DSAEK glaucoma (p=0.038). There was no negative effect of OHT on visual acuity and graft status.

Conclusion

Glaucoma and OHT are common postoperative complications of DSAEK. Although steroid-induced IOP elevation was the most frequent cause, there are other reasons associated with development of post-DSAEK glaucoma, including graft dislocation and detachment. Eyes with preoperative IOP>16 mm Hg may require a close monitoring of IOP. In addition, management by medical treatment results in good visual acuity and graft clarity.

Recent indications of endothelial keratoplasty at a tertiary eye care center in South India

PURPOSE

To describe the patient demographics and recent clinical indications of endothelial keratoplasty (EK) in patients presenting to a tertiary eye care center in India.

METHODS

This cross-sectional hospital-based study included 2,182 patients who underwent EK between Jan 2016 and Dec 2019 (4 years period). The data were collected using an electronic medical record system.

RESULTS

Overall, 2,632 eyes of 2,182 patients underwent EK during the study period. Median age was 62 (IQR: 48-70) years and adults (94.45%) comprised most of the cohort. More commonly, the patients were male (55.59%) and from the higher socioeconomic strata (67.51%). The corneal signs included corneal edema (70.93%), corneal scarring (29.60%), corneal vascularization (16%) and guttae (12.88%). The major indications of EK were post-cataract surgery corneal edema in 1331 (50.57%) patients, endothelial dystrophy in 537 (20.4%) patients, failed graft in 535 (20.33%) patients causing a vision impairment of > 20/400-20/1200 in about a half (45.55%) of the patients. Descemet stripping endothelial keratoplasty (DSEK) and Descemet membrane endothelial keratoplasty (DMEK) were performed in 2075 (78.84%) and 557(21.16%) patients, respectively.

CONCLUSION

EK is commonly performed during the sixth decade of life and in males. The most performed procedure is DSEK. The commonest indication was post-cataract surgery corneal edema.

Cornea donation process and tissue quality for transplantation

Introduction

The quality of the corneal tissue can be influenced by several factors inherent to the recipient, donor, and to the donation and transplantation process. The donated corneal tissue can be classified by its quality as excellent, good, regular, bad, or unacceptable for transplantation, evaluating it in a slit lamp.

Objective

To analyze the relationship between the clinical and sociodemographic variables of the donors and the donation process and the classification of the quality of the corneal tissue collected for transplantation.

Methods

This is an epidemiologic study, retrospective cohort type, which addressed the process of cornea donation by the Human Eye Tissue Bank in a reference service in Northeast Brazil. The sample consisted of corneas processed by the Human Eye Tissue Bank of Rio Grande do Norte (n = 419). For descriptive and inferential analysis, the study used the Statistical Package for the Social Sciences (SPSS) software, version 25.0, and considered a significance level of 0.05. Logistic regression analysis was used for the adjustment of the final model.

Results

It was verified that the epidemiological profile showed a prevalence of individuals with a mean age of 42.54 years old, male (73.99%), and living in the metropolitan region of the state capital (75.66%). When analyzing the relationship between the clinical and sociodemographic variables of the donors, it was identified that those aged 45 years old or less had better quality corneas (excellent and good), while the chronological variables were predictive factors for corneas of regular and bad qualities.

Conclusion

The identification of the factors inherent to the donation process and predictors of corneal tissue quality contribute to minimizing the risk of transplantation and to a better ocular prognosis.

Current development of alternative treatments for endothelial decompensation: Cell-based therapy

Current treatment for corneal endothelial dysfunction consists in the replacement of corneal endothelium by keratoplasty. Owing to the scarcity of donor corneas and the increasing number of transplants, alternative treatments such as cell-based therapies are necessary. In this article, we highlight the biological aspects of the cornea and the corneal endothelium, as well as the context that surrounds the need for new alternatives to conventional keratoplasty. We then review some of those experimental treatments in more detail, focusing on the development of the in vitro and preclinical phases of two cell-based therapies: tissue-engineered endothelial keratoplasty (TE-EK) and cell injection. In the case of TE-EK graft construction, we analyse the current progress, considering all the requirements it must meet in order to be functional. Moreover, we discuss the inherent drawbacks of endothelial keratoplasties, which TE-EK grafts should overcome in order to make surgical intervention easier and to improve the outcomes of current endothelial keratoplasties. Finally, we analyse the development of preclinical trials and their limitations in terms of performing an optimal functional evaluation of cell-based therapy, and we conclude by discussing early clinical trials in humans.

First case of Kluyveromyces marxianus (Candida kefyr) late onset keratitis after lamellar endothelial corneal graft

We present a case of Kluyveromyces marxianus keratitis nine months after Descement's membrane endothelial keratoplasty (DMEK) in a patient with Fuchs endothelial disease. Endothelial scraping revealed this rare yeast infection at the interface between graft and host cornea. Immediate antifungal treatment with intracameral and corneal intrastromal injections of voriconazole and amphotericin B remained unsuccessful, requiring penetrating keratoplasty. This case highlights the challenging management of keratomycosis in patients with endothelial grafts.

Evaluation of the quality of life related to vision after penetrating keratoplasty

INTRODUCTION

Organ and tissue donation and transplantation represent the most important therapeutic advance of current times. The cornea is, by far, one of the most transplanted tissues worldwide due to the immune privilege of this tissue, as well as the advances in microsurgery, existence of cornea banks, preservation of corneas, and use of anti-rejection therapy. However, many patients with successful corneal transplants (with clear corneas) experience poor vision in the post-operative period due to irregular astigmatism, or other complications.

OBJECTIVE

To evaluate the quality of life related to vision in patients undergoing penetrating keratoplasty.

MATERIAL AND METHODS

A cross-analytical study including patients with a history of penetrating keratoplasty, over 18years of age, and at least 6months after surgery. The patients answered the Visual Function Questionnaire25 (VFQ-25) of visual function, a tool validated for use in Spanish, in which the higher the score, the better the quality of life.

RESULTS

Thirty patients (20men and 10women), with a mean age of 61.2±18.7years, were included. The time of evolution after the transplant was 17.7±4months. The total quality of life score was 74.9±21.9, with significance in visual acuity (P<.001), and the presence of systemic comorbidities (P=.018). There was no significance between the transplant reason (P=.098) or ocular comorbidities (P=.119).

CONCLUSION

The results suggest that visual acuity, as well as the presence of systemic comorbidities, has a significant impact on quality of life.

Comparison of long-term results after manual and femtosecond assisted corneal trephination in deep anterior lamellar keratoplasty for keratoconus

AIM

To compare long-term postoperative outcomes of manual and femtosecond assisted corneal trephination in deep anterior lamellar keratoplasty (FS-DALK) for keratoconus.

METHODS

In the retrospective study, 17 consecutive eyes that underwent vertical side cut incision FS-DALK and 22 eyes that underwent trephine incision DALK were collected over a 2-year period. Main measurements included postoperative uncorrected-visual acuity (UCVA), corrected distance visual acuity (CDVA), refractive sphere and cylinder, manifest refraction spherical equivalent (MRSE), flat and steep corneal keratometry (K1 and K2), endothelial cell density (ECD), and time of epithelium healing and suture removal.

RESULTS

Groups were comparable for diagnosis and preoperative visual acuity. Follow-up averaged 23mo (range, 12-36mo). At 12mo, the mean UCVA was better in the manual-DALK group (P=0.039), and the refractive sphere was lower in the FS-DALK group (P=0.040). MRSE between groups differed at 1, 6, and 12mo postoperatively (P=0.047, 0.025, 0.042, respectively). Mean CDVA, cylinder, K1, K2, corneal astigmatism, ECD, and time of epithelium healing were similar between groups. Stability of MRSE, ECD, and K1 returned sooner after FS-DALK. Initial loosened suture removal time was earlier in the manual-DALK group (P=0.042) while complete suture removal time was similar (P=0.122).

CONCLUSION

Manual and femtosecond assisted corneal trephination in DALK are options for advanced keratoconus. FS-DALK do not result in improved visual acuity but it is more stable during the follow-up period. FS-DALK in the present form show limited benefit, so surgical design and parameters still need to be optimized and explored.

Late-onset fungal interface keratitis following endothelial keratoplasty with positive donor fungal culture

Purpose

To describe late-onset fungal keratitis after Descemet's stripping endothelial keratoplasty (DSEK) with positive fungal culture of the donor corneal rim.

Observations

A case report of a patient undergoing DSEK is described whereby the donor corneal rim culture grew fungus. No infection was initially noted, but the patient developed fungal keratitis 1 year after the original DSEK procedure, despite prophylactic treatment at the time of the positive donor culture. The patient responded to antifungal therapy, but fungal keratitis recurred following completion of a 1-year course of antifungal treatment. The patient eventually underwent full thickness keratoplasty.

Conclusions and importance

A positive fungal culture of the donor rim tissue at the time of endothelial keratoplasty is a risk factor for fungal keratitis. Even with prophylactic antifungal treatment, fungal keratitis may eventually develop as late as 1 year after the initial endothelial keratoplasty procedure. Treatment may need to be aggressive, but keratitis may recur despite resolution with antifungal treatment.

Myh11 Lineage Corneal Endothelial Cells and ASCs Populate Corneal Endothelium

Purpose

To establish Myh11 as a marker of a subset of corneal endothelial cells (CECs), and to demonstrate the feasibility of restoring the corneal endothelium with Myh11-lineage (Myh11-Lin[+]) adipose-derived stromal cells (ASCs).

Methods

Intraperitoneal administration of tamoxifen and (Z)-4-hydroxytamoxifen eyedrops were used to trace the lineage of Myh11-expressing cells with the Myh11-Cre-ERT2-flox-tdTomato mouse model. Immunostaining and Western blot characterized marker expression and spatial distribution of Myh11-Lin(+) cells in the cornea, and administration of 5-ethynyl-2'-deoxyuridine labeled proliferating cells. ASCs were isolated from epididymal adipose Myh11+ mural cells and treated with cornea differentiation media to evaluate corneal endothelial differentiation potential. Differentiated ASCs were injected into the anterior chamber to test for incorporation into corneal endothelium following scratch injury.

Results

A subset of CECs express Myh11, a marker previously thought restricted to only mural cells. Myh11-Lin(+) CECs marked a stable subpopulation of cells in the cornea endothelium. Myh11-Lin(+) ASCs undergo CEC differentiation in vitro and incorporate into injured corneal endothelium.

Conclusions

Dystrophy and dysfunction of the corneal endothelium accounts for almost half of all corneal transplants, the maintenance of the cornea endothelium is poorly understood, and there are a lack of mouse models to study specific CEC populations. We establish a mouse model that can trace the cell fate of a subpopulation of CECs based on Myh11 expression. A subset of ASCs that share this Myh11 transcriptional lineage are capable of differentiating into CECs that can incorporate into injured corneal endothelium, revealing a potential cell source for creating engineered transplant material.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Angiogenesis and lymphangiogenesis in corneal transplantation-A review

Corneal transplantation has been proven effective for returning the gift of sight to those affected by corneal disorders such as opacity, injury, and infections that are a leading cause of blindness. Immune privilege plays an important role in the success of corneal transplantation procedures; however, immune rejection reactions do occur, and they, in conjunction with a shortage of corneal donor tissue, continue to pose major challenges. Corneal immune privilege is important to the success of corneal transplantation and closely related to the avascular nature of the cornea. Corneal avascularity may be disrupted by the processes of angiogenesis and lymphangiogenesis, and for this reason, these phenomena have been a focus of research in recent years. Through this research, therapies addressing certain rejection reactions related to angiogenesis have been developed and implemented. Corneal donor tissue shortages also have been addressed by the development of new materials to replace the human donor cornea. These advancements, along with other improvements in the corneal transplantation procedure, have contributed to an improved success rate for corneal transplantation. We summarize recent developments and improvements in corneal transplantation, including the current understanding of angiogenesis mechanisms, the anti-angiogenic and anti-lymphangiogenic factors identified to date, and the new materials being used. Additionally, we discuss future directions for research in corneal transplantation.

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.

Corneal Transplantation in Disease Affecting Only One Eye: Does It Make a Difference to Habitual Binocular Viewing?

BACKGROUND

Clarity of the transplanted tissue and restoration of visual acuity are the two primary metrics for evaluating the success of corneal transplantation. Participation of the transplanted eye in habitual binocular viewing is seldom evaluated post-operatively. In unilateral corneal disease, the transplanted eye may remain functionally inactive during binocular viewing due to its suboptimal visual acuity and poor image quality, vis-à-vis the healthy fellow eye.

METHODS AND FINDINGS

This study prospectively quantified the contribution of the transplanted eye towards habitual binocular viewing in 25 cases with unilateral transplants [40 yrs (IQR: 32-42 yrs) and 25 age-matched controls [30 yrs (25-37 yrs)]. Binocular functions including visual field extent, high-contrast logMAR acuity, suppression threshold and stereoacuity were assessed using standard psychophysical paradigms. Optical quality of all eyes was determined from wavefront aberrometry measurements. Binocular visual field expanded by a median 21% (IQR: 18-29%) compared to the monocular field of cases and controls (p = 0.63). Binocular logMAR acuity [0.0 (0.0-0.0)] almost always followed the fellow eye's acuity [0.00 (0.00 --0.02)] (r = 0.82), independent of the transplanted eye's acuity [0.34 (0.2-0.5)] (r = 0.04). Suppression threshold and stereoacuity were poorer in cases [30.1% (13.5-44.3%); 620.8 arc sec (370.3-988.2 arc sec)] than in controls [79% (63.5-100%); 16.3 arc sec (10.6-25.5 arc sec)] (p<0.001). Higher-order wavefront aberrations of the transplanted eye [0.34 μ (0.21-0.51 μ)] were higher than the fellow eye [0.07 μ (0.05-0.11 μ)] (p<0.001) and their reduction with RGP contact lenses [0.09 μ (0.08-0.12 μ)] significantly improved the suppression threshold [65% (50-72%)] and stereoacuity [56.6 arc sec (47.7-181.6 arc sec)] (p<0.001).

CONCLUSIONS

In unilateral corneal disease, the transplanted eye does participate in gross binocular viewing but offers limited support to fine levels of binocularity. Improvement in the transplanted eye's optics enhances its participation in binocular viewing. Current metrics of this treatment success can expand to include measures of binocularity to assess the functional benefit of the transplantation process in unilateral corneal disease.