Corneal transplantation in the aftermath of the COVID-19 pandemic: an international perspective

Mutational dynamics of SARS-CoV-2: Impact on future COVID-19 vaccine strategies

The rapid emergence of multiple strains of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) has sparked profound concerns regarding the ongoing evolution of the virus and its potential impact on global health. Classified by the World Health Organization (WHO) as variants of concern (VOC), these strains exhibit heightened transmissibility and pathogenicity, posing significant challenges to existing vaccine strategies. Despite widespread vaccination efforts, the continual evolution of SARS-CoV-2 variants presents a formidable obstacle to achieving herd immunity. Of particular concern is the coronavirus spike (S) protein, a pivotal viral surface protein crucial for host cell entry and infectivity. Mutations within the S protein have been shown to enhance transmissibility and confer resistance to antibody-mediated neutralization, undermining the efficacy of traditional vaccine platforms. Moreover, the S protein undergoes rapid molecular evolution under selective immune pressure, leading to the emergence of diverse variants with distinct mutation profiles. This review underscores the urgent need for vigilance and adaptation in vaccine development efforts to combat the evolving landscape of SARS-CoV-2 mutations and ensure the long-term effectiveness of global immunization campaigns.

Photothermal hydrogels for infection control and tissue regeneration

In this review, we report investigating photothermal hydrogels, innovative biomedical materials designed for infection control and tissue regeneration. These hydrogels exhibit responsiveness to near-infrared (NIR) stimulation, altering their structure and properties, which is pivotal for medical applications. Photothermal hydrogels have emerged as a significant advancement in medical materials, harnessing photothermal agents (PTAs) to respond to NIR light. This responsiveness is crucial for controlling infections and promoting tissue healing. We discuss three construction methods for preparing photothermal hydrogels, emphasizing their design and synthesis, which incorporate PTAs to achieve the desired photothermal effects. The application of these hydrogels demonstrates enhanced infection control and tissue regeneration, supported by their unique photothermal properties. Although research progress in photothermal hydrogels is promising, challenges remain. We address these issues and explore future directions to enhance their therapeutic potential.

Global impact of COVID-19 on corneal donor tissue harvesting and corneal transplantation

Introduction

The purpose of this review is to consolidate and examine the available literature on the coronavirus disease 2019 pandemic and its effect on corneal transplantation and eye banking.

Methods

A primary literature search was conducted using the PubMed (Medline) database with keywords and MeSH terms such as "corneal transplantation," "eye banks," "keratoplasty" and then were combined with COVID-19. Relevant articles through September 2022 were assessed and 25 articles were included in this review.

Results

Donor tissue volumes declined globally during lockdown periods due to a lower number of referrals and tighter tissue screening guidelines. Rates of elective surgeries decreased in the lockdown period compared to respective periods in previous years. However, changes in rates of emergency procedures were not uniform across different regions. Moreover, rates of different elective corneal grafts [i.e., penetrating keratoplasty (PK), endothelial keratoplasty (EK), or anterior lamellar keratoplasty (ALK)] were affected differently with the pattern of change being dependent on region-specific factors.

Conclusion

Both donor tissue volumes and rates of corneal transplant procedures were affected by lockdown restrictions. The underlying etiology of these changes differed by region. Examining the range of impact across many countries as well as the contributing factors involved will provide guidance for future global pandemics.

Effect of Covid-19 on Eye Banks and Corneal Transplantations: Current Perspectives

The coronavirus disease 2019 (COVID-19) pandemic exerted a great impact on medical practice, which was reframed according to the actual needs. Ophthalmological services and procedures including corneal transplantation did not represent an exception. The adoption and implementation of new standard operating procedures as well as of new technologies for remote consultation and smart-working reshaped daily activities of both eye bankers, physicians, researchers, and patients. Regulatory restrictions were issued redefining corneal donor eligibility criteria, as well as handling and harvesting procedures of donor ocular tissues. Surgical schedules underwent an abrupt contraction with prioritization of urgent procedures. Local lockdowns and confinement strategies resulted in both a reduction and redirection of research activities. The evaluation of SARS-CoV-2 colonization of ocular tissues, long-term corneal storage techniques, new disinfection strategies, split corneal transplants and cell-based therapies for the treatment of corneal disease peaked in the pipeline. Aim of this article is to summarizes the overall impact of the pandemic on the corneal transplantation machinery, and the current and future perspectives for the corneal transplant community.

A Review of Corneal Transplantation: An Insight on the Overall Global Post-COVID-19 Impact

The coronavirus disease 2019 (COVID-19) pandemic made us reframe a lot of the strategies followed in medical practice and ophthalmological services and procedures were also not spared, including corneal transplantation or keratoplasty, the most routine procedure performed worldwide. The prevalence of viral presence in the ocular tissue necessitates a focus on the handling of donor ocular tissue and the functioning of eye banks, ensuring it doesn't risk the patient and the doctor's safety. Restrictions in the movement of people during the pandemic limited the number of donations, causing a shortage of tissues, with a large number of people already waitlisted for tissue needs. The lesson from the COVID-19 pandemic directs us to look for long-term corneal storage techniques taking into consideration the tissue viability time and the possibility of post-pandemic shortages. Although there is not a significant number of reports, the cases of corneal graft rejection post-vaccination against COVID-19 are highlighted and thus should form a part of the lookout while evaluating the possible cause of rejection of grafts. This article summarises the overall impact of the pandemic on corneal transplantation and the possible future of storage techniques, which need to evolve and be adapted.

COVID-19 and the eye: alternative facts The 2022 Bowman Club, David L. Easty lecture

In addition to catastrophic loss of life, and dramatic and unwanted alterations to the daily lives of those left behind, the COVID-19 pandemic has fostered the publication and dissemination of an unprecedented quantity of peer-reviewed medical and scientific publications on a single subject. In particular, the ophthalmic literature is now replete with clinical and laboratory studies on putative eye involvement by SARS-CoV-2, the aetiologic agent of COVID-19. In this review, we critically appraise the published literature on COVID-19, and suggest that the quality of scientific peer review and editorial decision-making also suffered during the COVID-19 pandemic.

Effect of the First Year of COVID-19 Pandemic on Ophthalmological Practice: A Multi-Centre Italian Study with a Focus on Medico-Legal Aspects

During the COVID-19 era, several restrictions on surgery have been imposed to reduce the infectious risk among patients and staff and further preserve the availability of critical care resources. The aim of the study was to assess their impact on the ophthalmological practice and its medico-legal implications. A retrospective review of electronic medical records of the ophthalmological departments of the University of Cagliari (SGD) and University Magna Græcia of Catanzaro (UMG), from 16 March 2020 to 14 March 2021 (52 weeks), were compared with data from the corresponding period of the previous year. Weekly data on the number and type of diagnoses and procedures performed were collected and analysed in relation to the weekly average of the total number of COVID-19 patients in intensive care units (ICUs) and inpatients in Sardinia and Calabria. Results showed a significant decrease in cataract surgery operations by 47% and 31%, respectively, in the SGD and UMG (p < 0.05) during the second semester of the year; this drop occurred at the same time as the increase in COVID-19 patients in ICU and those hospitalised in both regions. Additionally, anterior segment surgery decreased at the UMG by 30% (p < 0.05). Vitreoretinal surgery decreased by 27% at the SGD, differently increased amount 31.5% at UMG (p < 0.05). The pandemic had a dramatic impact on elective surgery in ophthalmology, quantifying the backlog is the first step in order to understanding the measures to be taken in near future.

Use of biomaterials in corneal endothelial repair

Human corneal endothelium (HCE) is a single layer of hexagonal cells that lines the posterior surface of the cornea. It forms the barrier that separates the aqueous humor from the rest of the corneal layers (stroma and epithelium layer). This layer plays a fundamental role in maintaining the hydration and transparency of the cornea, which in turn ensures a clear vision. In vivo, human corneal endothelial cells (HCECs) are generally believed to be nonproliferating. In many cases, due to their nonproliferative nature, any damage to these cells can lead to further issues with Descemet’s membrane (DM), stroma and epithelium which may ultimately lead to hazy vision and blindness. Endothelial keratoplasties such as Descemet’s stripping automated endothelial keratoplasty (DSAEK) and Descemet’s membrane endothelial keratoplasty (DEK) are the standard surgeries routinely used to restore vision following endothelial failure. Basically, these two similar surgical techniques involve the replacement of the diseased endothelial layer in the center of the cornea by a healthy layer taken from a donor cornea. Globally, eye banks are facing an increased demand to provide corneas that have suitable features for transplantation. Consequently, it can be stated that there is a significant shortage of corneal grafting tissue; for every 70 corneas required, only 1 is available. Nowadays, eye banks face long waiting lists due to shortage of donors, seriously aggravated when compared with previous years, due to the global COVID-19 pandemic. Thus, there is an urgent need to find alternative and more sustainable sources for treating endothelial diseases, such as utilizing bioengineering to use of biomaterials as a remedy. The current review focuses on the use of biomaterials to repair the corneal endothelium. A range of biomaterials have been considered based on their promising results and outstanding features, including previous studies and their key findings in the context of each biomaterial.

Canadian demand and access to corneal transplantation: a provincial comparison

To gather information from stakeholders involved in corneal donation and transplantation to inform discussion at the "National Consensus Forum on Improving Cornea Donation and Transplantation Access in Canada" held in February 2020, survey questions were posed to eye banks, transplanting ophthalmologists and organ donation organizations across Canada to learn more about demand, wait times, and access to tissue for transplant. The survey response rate was one hundred percent (100%) for eye banks and organ donation organizations while 64 percent (64%) of transplant ophthalmologists provided feedback. A number of opportunities for improvement were identified including: demand forecasting; infrastructure and strategies to align supply with demand; data collection and benchmarking of wait times for assessment and transplant to support consistency, equitability and transparency in access; and national collaboration in the development of a data strategy to accurately measure demand and access to cornea transplants in a consistent manner across all provinces to facilitate equity in access nationally.

Biofabrication of Artificial Stem Cell Niches in the Anterior Ocular Segment

The anterior segment of the eye is a complex set of structures that collectively act to maintain the integrity of the globe and direct light towards the posteriorly located retina. The eye is exposed to numerous physical and environmental insults such as infection, UV radiation, physical or chemical injuries. Loss of transparency to the cornea or lens (cataract) and dysfunctional regulation of intra ocular pressure (glaucoma) are leading causes of worldwide blindness. Whilst traditional therapeutic approaches can improve vision, their effect often fails to control the multiple pathological events that lead to long-term vision loss. Regenerative medicine approaches in the eye have already had success with ocular stem cell therapy and ex vivo production of cornea and conjunctival tissue for transplant recovering patients' vision. However, advancements are required to increase the efficacy of these as well as develop other ocular cell therapies. One of the most important challenges that determines the success of regenerative approaches is the preservation of the stem cell properties during expansion culture in vitro. To achieve this, the environment must provide the physical, chemical and biological factors that ensure the maintenance of their undifferentiated state, as well as their proliferative capacity. This is likely to be accomplished by replicating the natural stem cell niche in vitro. Due to the complex nature of the cell microenvironment, the creation of such artificial niches requires the use of bioengineering techniques which can replicate the physico-chemical properties and the dynamic cell-extracellular matrix interactions that maintain the stem cell phenotype. This review discusses the progress made in the replication of stem cell niches from the anterior ocular segment by using bioengineering approaches and their therapeutic implications.

Impact of SARS-CoV-2 on Ocular Surface Pathology and Treatment Practices: a Review

Purpose of Review

The ocular surface is a potential site of ocular involvement by SARS-CoV-2 infection. We performed a review of the literature to understand the pathogenesis of SARS-CoV-2 disease manifestations on the ocular surface as well as to elucidate emerging treatment patterns and practice changes during the COVID-19 pandemic.

Recent Findings

The ocular manifestations of SARS-CoV-2 are likely limited to a mild and transient conjunctivitis. Other manifestations have not been validated in larger cohorts. Ocular surface tissue should be considered potentially infectious due to the presence of host receptors on surface tissues. The availability of donor tissue in lower-middle income countries has been greatly impacted by the pandemic and would benefit from further investigation into transmissibility through donor tissue.

Summary

Transmission of SARS-CoV-2 through the ocular surface has yet to be confirmed. The most common ocular manifestation is a mild conjunctivitis. Ocular surface surgeons face specific challenges in the use of donor tissues and aerosolizing procedures and have adapted practice patterns accordingly.

Corneal Donation: Current Guidelines and Future Direction

PURPOSE

This review aims to outline current practices and guidelines of corneal donation and eye banking, describes the implications of COVID-19 and emerging diseases on the corneal donor pool, and discusses future trends to improve and increase the efficiency of the processes involved in corneal donation and eye banking.

SUMMARY

Corneal screening, preservation, corneal storage, and prevention of systemic disease transmission from donor to recipient have been crucial in shaping the policies of the FDA and eye banks across the world. Eye banks globally have developed varying guidelines and criteria for evaluating the viability of donor corneas. Variables such as the age of the donor, medical history, and potential disease transmission are important screening parameters. While known infectious diseases may be transmissible through the cornea, emerging infectious diseases that are not well studied may be more transmissible than other infections. In particular, coronavirus has impacted corneal transplantation as SARS-CoV-2 expression has been detected in corneal tissue and conjunctiva. In recent years, partial-thickness corneal transplantations have been introduced. Lamellar grafts and other corneal layers are now utilized for transplantation of the specific areas that are damaged.

Proliferation Increasing Genetic Engineering in Human Corneal Endothelial Cells: A Literature Review

The corneal endothelium is the inner layer of the cornea. Despite comprising only a monolayer of cells, dysfunction of this layer renders millions of people visually impaired worldwide. Currently, corneal endothelial transplantation is the only viable means of restoring vision for these patients. However, because the supply of corneal endothelial grafts does not meet the demand, many patients remain on waiting lists, or are not treated at all. Possible alternative treatment strategies include intracameral injection of human corneal endothelial cells (HCEnCs), biomedical engineering of endothelial grafts and increasing the HCEnC density on grafts that would otherwise have been unsuitable for transplantation. Unfortunately, the limited proliferative capacity of HCEnCs proves to be a major bottleneck to make these alternatives beneficial. To tackle this constraint, proliferation enhancing genetic engineering is being investigated. This review presents the diverse array of genes that have been targeted by different genetic engineering strategies to increase the proliferative capacity of HCEnCs and their relevance for clinical and research applications. Together these proliferation-related genes form the basis to obtain a stable and safe supply of HCEnCs that can tackle the corneal endothelial donor shortage.

Ophthalmic practice during COVID-19 pandemic

Coronavirus disease 2019 (COVID-19) pandemic has caused significant changes in ophthalmic practice. The initial strategy of strict restriction of elective activities has been replaced with various guidelines to revitalize ophthalmic procedures considering the new safety concerns. In this manuscript, we reviewed recent recommendations for ophthalmic practice in different fields of ophthalmology during the COVID-19 pandemic.

The Impact of COVID-19 on Acute and Elective Corneal Surgery at Moorfields Eye Hospital London

Purpose

Moorfields Eye Hospital sits as a major tertiary centre for ophthalmic care in the United Kingdom and became a central hub to provide safe and effective ophthalmic care across London and surrounding regions during the COVID-19 pandemic. We explore the impact on both the acute and elective corneal services during the first wave of this pandemic.

Methods

A retrospective review of the proportion of corneal transplants and anterior segment trauma repairs was performed during the period of March 23rd to July 1st 2020 compared with an identical period in 2019. Data were acquired from our in-house electronic patient records.

Results

A 92% reduction in corneal elective work was observed during the lockdown period compared with an identical period in 2019, with only 10 elective cases in total being performed. In addition, 91 corneal cross-linking and 76 therapeutic lasers were cancelled. There were 15 cases of primary repair for anterior segment trauma compared with 6 cases pre-COVID-19. A similar scenario occurs with removal of foreign body (4 cases during COVID-19 period versus no cases during pre-COVID-19 era) and with traumatic lens aspirations (6 cases during COVID-19 compared with 2 pre-COVID-19). Interestingly, a statistical difference (p=0.03) was found in the time interval from presentation of symptoms to emergency corneal surgery. During the COVID-19 period, a delay of 1.5 days ± 2.29 (range 0–10 days) occurred compared with 0.8 days ± 1.54 (range 0–6 days) pre-COVID-19.

Conclusion

Stringent risk stratification reduced elective corneal surgery capacity during the lockdown thereby preserving social distancing requirements. However, an apparent increase in emergency corneal surgery seen is likely attributed to centralisation of ophthalmic services during the pandemic crisis, alongside increased domestic injuries. Despite the challenges posed, successful delivery of corneal surgery occurred whilst helping to identify lessons in preparations for future pandemics and current inefficiencies in healthcare delivery.

Corneal transplantation during COVID-19 pandemic: need for special considerations-A live review

Corneal blindness is the fourth leading cause of blindness worldwide, with 10 million people having bilateral corneal blindness, nearly 80% of all corneal blindness cases are avoidable and are reversible. Corneal transplantation (CT) is the most frequently performed type of transplant across the world. This review was conducted with the objective of identifying if it is safe to harvest the cornea from the patients died due to COVID-19 and preventing the chances of transmission from donor to the recipient or healthcare worker handling the harvested cornea. A total of 45 articles were found with the keywords and out of all, only 16 fulfilled the inclusion criteria. RT-PCR is the technique of choice for detection of virus in the corpse and the sample analyzed was a pharyngeal swab. Available literature states unavailability of sufficient evidence-based studies proving presence of virus in the cornea or tear of COVID affected patients There is no proven consensus on presence of Virus in cornea. It is important to follow preferred practice guidelines so as to restart eye banking and do at least the emergency surgeries without having risk of disease transmission and keeping ourselves safe.

Prevalence of SARS-CoV-2 in human post-mortem ocular tissues

BACKGROUND

SARS-CoV-2 is found in conjunctival swabs and tears of COVID-19 patients. However, the presence of SARS-CoV-2 has not been detected in the human eye to date. We undertook this study to analyze the prevalence of SARS-CoV-2 in human post-mortem ocular tissues.

METHODS

The expression of SARS-CoV-2 RNA was assessed by RT-PCR in corneal and scleral tissues from 33 surgical-intended donors who were eliminated from a surgical use per Eye Bank Association of America (EBAA) donor screening guidelines or medical director review or positive COVID-19 test. Ocular levels of SARS-CoV-2 RNA (RT-PCR), Envelope and Spike proteins (immunohistochemistry) and anti-SARS-CoV-2 IgG and IgM antibodies (ELISA) in blood were evaluated in 10 COVID-19 donors.

FINDINGS

Of 132 ocular tissues from 33 surgical-intended donors, the positivity rate for SARS-CoV-2 RNA was ~13% (17/132). Of 10 COVID-19 donors, six had PCR positive post-mortem nasopharyngeal swabs whereas eight exhibited positive post-mortem anti-SARS-CoV-2 IgG levels. Among 20 eyes recovered from 10 COVID-19 donors: three conjunctival, one anterior corneal, five posterior corneal, and three vitreous swabs tested positive for SARS-CoV-2 RNA. SARS-CoV-2 spike and envelope proteins were detected in epithelial layer of the corneas that were procured without Povidone-Iodine (PVP-I) disinfection.

INTERPRETATIONS

Our study showed a small but noteworthy prevalence of SARS-CoV-2 in ocular tissues from COVID-19 donors. These findings underscore the criticality of donor screening guidelines, post-mortem nasopharyngeal PCR testing and PVP-I disinfection protocol to eliminate any tissue harboring SARS-CoV-2 being used for corneal transplantation.