Meibomian Gland Dysfunction in Ocular Graft vs. Host Disease: A Need for Pre-Clinical Models and Deeper Insights

Despite decades of experience with hematopoietic stem cell transplantation, we are still faced with the delicate equipoise of achieving stable ocular health post-transplantation. This is because ocular graft-versus-host disease (oGvHD) following hematopoietic stem cell transplantation frequently occurs (≥50%) among transplant patients. To date, our understanding of the pathophysiology of oGvHD especially the involvement of the meibomian gland is still limited as a result of a lack of suitable preclinical models among other. Herein, the current state of the etiology and, pathophysiology of oGvHD based on existing pre-clinical models are reviewed. The need for additional pre-clinical models and knowledge about the involvement of the meibomian glands in oGvHD are emphasized.

Knowledge and attitude towards eye donation among health professionals of northern India.

Background: We aimed to assess the knowledge and attitude of health professionals towards eye donation at an apex tertiary care centre of northern India. Methods: We interviewed 600 health professionals, comprising doctors, nurses, medical as well as nursing students, social workers and allied paramedical staff. A structured questionnaire (12 questions for assessing knowledge and 5 questions for assessing attitude) was used to estimate the awareness of eye donation and willingness to pledge eyes for donation. The responses pertaining to knowledge were graded as 'excellent', 'good' and 'poor' and those pertaining to attitude were grouped into 'positive' and 'negative'. Results: Of the 600 participants, 138 participants (23%) had 'excellent' knowledge and 234 participants (39%) had 'good' knowledge about eye donation. Awareness of eye donation was positively related to the level of literacy (odds ratio [OR] 8.5 [2.30-31.2]; p<0.001). Medical social workers and health supervisors had better knowledge about eye donation (OR 2.01 [1.08-3.72]; p=0.026) than other professional groups. Knowledge of eye donation had no significant association with age, gender, religion, family type and marital status of the respondent. Willingness to pledge eyes for donation was observed in only 6% of the participating health professionals. Pledging of eyes for donation was higher among older participants (OR 7.8 [2.67-22.77]; p<0.001). Conclusion: Our study shows that there is sufficient knowledge about eye donation, but an alarmingly low willingness to pledge eyes for donation among health professionals. Concerted efforts are required to alter their attitude to strengthen the Hospital Cornea Retrieval Programme.

Immunological considerations and concerns as pertinent to whole eye transplantation.

PURPOSE OF REVIEW: The advent of clinical vascularized composite allotransplantation (VCA), offers hope for whole eye transplantation (WET) in patients with devastating vison loss that fails or defies current treatment options. Optic nerve regeneration and reintegration remain the overarching hurdles to WET. However, the realization of WET may indeed be limited by our lack of understanding of the singular immunological features of the eye as pertinent to graft survival and functional vision restoration in the setting of transplantation. RECENT FINDINGS: Like other VCA, such as the hand or face, the eye includes multiple tissues with distinct embryonic lineage and differential antigenicity. The ultimate goal of vision restoration through WET requires optimal immune modulation of the graft for successful optic nerve regeneration. Our team is exploring barriers to our understanding of the immunology of the eye in the context of WET including the role of immune privilege and lymphatic drainage on rejection, as well as the effects ischemia, reperfusion injury and rejection on optic nerve regeneration. SUMMARY: Elucidation of the unique immunological responses in the eye and adnexa after WET will provide foundational clues that will help inform therapies that prevent immune rejection without hindering optic nerve regeneration or reintegration.

Distribution of potential eye and tissue donors within an Australian teaching hospital.

Eye and Tissue donation has the capacity to transform lives, yet the vast majority of potential in-hospital donors are not recognised. Studies which describe the relative importance of specific units or wards in determining the size of the donor pool are limited. The aim of this study was to map the distribution of potential Eye and Tissue donors within the study hospital. A 12-month retrospective analysis of all patient deaths at the study hospital was undertaken. The ability to donate corneal, heart valve, bone and skin tissue was investigated. Patients were classified as potential donors if they met specific age criteria and had an absence of contraindications based on electronic database search. There were 985 deaths during the study period. Deaths occurred under the care of 26 separate clinical units, and within 28 unique wards and treatment spaces. Four hundred and forty nine (45.6%) patients were identified as potential eye or tissue donors. The majority of potential donors occurred in ICU, Emergency and palliative care units. Of the subset of 328 deaths ≤ 70 years, the frequency of potential tissue donors was 55% (n = 181). ED and ICU had significantly higher frequencies of potential donor than other wards (86 and 77%, p < 0.01). The current study has identified the ED, ICU and PCUs are being important sites for potential Eye and Tissue Donors within our hospital. These will provide an important focus for future interventions to improve the rate of eye and tissue donation.

Development of national system performance metrics for tissue donation, production, and distribution activity.

Canada's federal, provincial, and territorial governments gave Canadian Blood Services a mandate for organ and tissue donation and transplantation, including system performance, data and analytics. In 2012 Canadian Blood Services facilitated an eye and tissue banking workshop focused on standardized specifications and practices. At the workshop, the Canadian tissue community directed Canadian Blood Services to facilitate the development and implementation of a national data stream and analytics. Prior to this no national data was prospectively collected or collated on tissue donation, production or distribution activity. An eye and tissue data committee was formed with representation from eye and tissue banks in all Canadian jurisdictions. A minimum data set, standardized definitions, a data submission form and a quality assurance process was developed. Training was provided to data personal identified by each eye and tissue bank. Data collection was initiated January 1, 2013; with quarterly data submitted to Canadian Blood Services via excel spreadsheet. Data was submitted by sixteen Canadian eye and tissue banks, located in eight of Canada's thirteen provinces and territories, representing a census of activity. Annual data reports, with trend analysis, are generated and distributed to the tissue community to inform operational strategy and system performance improvement. This report provides an overview of the data process and provides visibility to the Canadian tissue donation, production and distribution activities for 3 years; January 1, 2013 to December 31, 2015.

Clinical Considerations for Vascularized Composite Allotransplantation of the Eye.

Vascularized composite allotransplantation represents a potential shift in approaches to reconstruction of complex defects resulting from congenital differences as well as trauma and other acquired pathology. Given the highly specialized function of the eye and its unique anatomical components, vascularized composite allotransplantation of the eye is an appealing method for restoration, replacement, and reconstruction of the nonfunctioning eye. Herein, we describe conventional treatments for eye restoration and their shortcomings as well as recent research and events that have brought eye transplantation closer to a potential clinical reality. In this article, we outline some potential considerations in patient selection, donor facial tissue procurement, eye tissue implantation, surgical procedure, and potential for functional outcomes.

Ethical Considerations of Whole-Eye Transplantation.

Whole eye transplantation (WET) remains experimental. Long presumed impossible, recent scientific advances regarding WET suggest that it may become a clinical reality. However, the ethical implications of WET as an experimental therapeutic strategy remain largely unexplored. This article evaluates the ethical considerations surrounding WET as an emerging experimental treatment for vision loss. A thorough review of published literature pertaining to WET was performed; ethical issues were identified during review of the articles.

Dendritic cell physiology and function in the eye.

The eye and the brain are immunologically privileged sites, a property previously attributed to the lack of a lymphatic circulation. However, recent tracking studies confirm that these organs have good communication through classical site-specific lymph nodes, as well as direct connection through the blood circulation with the spleen. In addition, like all tissues, they contain resident myeloid cell populations that play important roles in tissue homeostasis and the response to foreign antigens. Most of the macrophage and dendritic cell (DC) populations in the eye are restricted to the supporting connective tissues, including the cornea, while the neural tissue (the retina) contains almost no DCs, occasional macrophages (perivascularly distributed), and a specialized myeloid cell type, the microglial cell. Resident microglial cells are normally programmed for immunological tolerance. The privileged status of the eye, however, is relative, as it is susceptible to immune-mediated inflammatory disease, both infectious and autoimmune. Intraocular inflammation (uveitis and uveoretinitis) and corneal graft rejection constitute two of the more common inflammatory conditions affecting the eye leading to considerable morbidity (blindness). As corneal graft rejection occurs almost exclusively by indirect allorecognition, host DCs play a major role in this process and are likely to be modified in their behavior by the ocular microenvironment. Ocular surface disease, including allergy and atopy, also comprise a significant group of immune-mediated eye disorders in which DCs participate, while infectious disease such as herpes simplex keratitis is thought to be initiated via corneal DCs. Intriguingly, some more common conditions previously thought to be degenerative (e.g. age-related macular degeneration) may have an autoimmune component in which ocular DCs and macrophages are critically involved. Recently, the possibility of harnessing the tolerizing potential of DCs has been applied to experimental models of autoimmune uveoretinitis with good effect. This approach has considerable potential for use in translational clinical therapy to prevent sight-threatening disease caused by ocular inflammation.

Awareness Regarding Eye Donation and Effects of COVID-19 on Its Perception: A Community-Based Cross-Sectional Study From India.

OBJECTIVES: This study aimed to assess awareness toward eye donation and the effects of COVID-19 on perceptions about eye donation in an urban community of West Bengal, India. MATERIALS AND METHODS: Eligible adults residing in the area under study were chosen by simple random sampling and interviewed using a predesigned and pretested data collection schedule to assess awareness and perception. Based on their total awareness score, the participants were classified as having good awareness or poor awareness toward eye donation. RESULTS: Among 423 participants, 52.0% were male, 34.0% were 18 to 30 years old, 38.3% were educated up to secondary level, and 85.6% had eye disease in their family. Of total participants, 70.2% had heard about eye donation, with 59.9% of this group having knowledge of eye donation only after death and 57.9% having knowledge that donation must occur within 6 hours of death. In addition, 52.9% were aware about donation from home, 30.6% said only the cornea is transplantable, and 52.2% knew it can be preserved. Participants with higher education, higher socioeconomic status, and outside of the house occupational engagement had significantly higher chance of good eye donation awareness. Of total participants, 32.0% said that COVID-19 could be transmitted through eye donation, with 58.2% of participants opining that the pandemic was not a suitable time to consider donation of eyes. CONCLUSIONS: COVID-19 has had a negative impact on eye donation perceptions. Although most of our participants had heard about eye donation, their awareness regarding important aspects about eye donation were still lacking, thus calling for a more focused action plan and implementation of the same.

Development of a New Large-Animal Model for Composite Face and Whole-Eye Transplantation: A Novel Application for Anatomical Mapping Using Indocyanine Green and Liquid Latex.

BACKGROUND: Recent advances in the field of vascularized composite allotransplantation have revolutionized reconstructive surgery and demonstrated opportunity for restoration of orbital content and perhaps vision. The development of an animal model that would facilitate study of surgical technique, nerve regeneration, vision restoration, and immunosuppression is needed. The aim of this study is to describe three different large-animal cadaveric models suitable for composite face and whole-eye transplantation. In addition, the authors introduce a novel colored liquid latex and indocyanine green mixture for vasculature identification and visualization. METHODS: The authors studied three different flap designs using cadaveric Yorkshire swine and modified them for face and whole-eye transplant harvest. Flaps harvested included a chimeric flap, a monobloc flap, and a bipedicled free flap. The authors injected selected vasculature with colored latex to better delineate vascular anatomy supplying the orbit and face. Indocyanine green was added to the latex solution to allow for visualization of the vascular supply using near-infrared imaging. RESULTS: Colored latex and indocyanine green injections were successfully visualized in all cadaveric dissections. All three modified flap designs showed a well-defined and consistent vascular network within each face and whole-eye transplantation flap using laser-assisted near-infrared imaging. CONCLUSIONS: The authors present the feasibility of composite face and whole-eye transplantation models using a novel mixture of liquid latex and indocyanine green in a porcine cadaver. Further study in large animals is needed to appraise the surgical feasibility of this procedure and potential for clinically relevant outcomes, including vision restoration. The authors believe this study establishes a foundation for translation into live animal models for optic nerve regeneration.

Central projection of optic tract from translocated eyes in the leopard frog (Rana pipiens).

In Rana pipiens embryos, eye anlagen were moved to the evacuated ear position, where they continued to differentiate and sent their optic nerve fibers into the hindbrain. Upon entering the medulla, the optic fibers turned caudally, penetrated the spinal cord, and traversed the dorsolateral white matter to the caudal end. We found this pattern of growth in every animal; the optic fibers did not enter the tecta. These results suggest the existence within the neural tube of a three-dimensional gradient system to which embryonic optic fibers are responsive and which may guide the normal development of the visual pathway.

Eyes transplanted to tadpole tails send axons rostrally in two spinal-cord tracts.

Axons from eyes transplanted to the tail in Xenopus larvae enter the caudal spinal cord and follow two adjacent tracts rostrally to the level of the cerebellum. When eyes are transplanted to the ear area, optic axons enter the hindbrain and follow the same tracts rostrally and caudally. These sensory pathways normally contain the embryonic sensory system of the Rohon-Beard axons and the descending and ascending tracts of nerve V. We propose that the transplanted optic axons have followed a continuous substrate sensory pathway normally shared by a number of different sensory tracts.

Eye-specific termination bands in tecta of three-eyed frogs.

An extra eye primordium was implanted into the forebrain region of embryonic Rana pipiens. During development both normal and supernumerary optic tracts terminated within a single, previously uninnervated tectal lobe. Autoradiographic tracing of either the normal or supernumerary eye's projection revealed distinct, eye-specific bands of radioactivity running rostrocaudally through the dually innervated tectum. Interactions among axons of retinal ganglion cells, possibly mediated through tectal neurons, must be invoked to explain this stereotyped disruption of the normally continuous retinal termination pattern.

astray, a zebrafish roundabout homolog required for retinal axon guidance.

As growing retinotectal axons navigate from the eye to the tectum, they sense guidance molecules distributed along the optic pathway. Mutations in the zebrafish astray gene severely disrupt retinal axon guidance, causing anterior-posterior pathfinding defects, excessive midline crossing, and defasciculation of the retinal projection. Eye transplantation experiments show that astray function is required in the eye. We identify astray as zebrafish robo2, a member of the Roundabout family of axon guidance receptors. Retinal ganglion cells express robo2 as they extend axons. Thus, robo2 is required for multiple axon guidance decisions during establishment of the vertebrate visual projection.

Tissue micromanipulation in zebrafish embryos.

Although a common approach in large vertebrate embryos such as chick or frog, manipulation at the tissue level is only rarely applied to zebrafish embryos. Despite its relatively small size, the zebrafish embryo can be readily used for micromanipulations such as tissue and organ primordium transplantation, explantation, and microbead implantation, to study inductive tissue interactions and tissue autonomy of pleiotropic, mutant phenotypes or to isolate tissue for organotypic and primary cell culture or RNA isolation. Since this requires special handling techniques, tools, and tricks, which are rarely published and thus difficult to apply without hands-on demonstration, this article provides detailed instructions and protocols on tissue micromanipulation. The goal is to introduce a broader scientific audience to these surgical techniques, which can be applied to a wide range of questions and used as a starting point for many downstream applications in the genetically tractable zebrafish embryo.

Demonstration of technical feasibility and viability of whole eye transplantation in a rodent model.

INTRODUCTION: Whole eye transplantation (WET) holds promise for vision restoration in devastating/disabling visual loss (congenital or traumatic) not amenable to surgical or neuroprosthetic treatment options. The eye includes multiple tissues with distinct embryonic lineage and differential antigenicity. Anatomically and immunologically, the eye is unique due to its avascular (cornea) and highly vascular (retina) components. Our goal was to establish technical feasibility, demonstrate graft viability, and evaluate histologic changes in ocular tissues/adnexae in a novel experimental model of WET that included globe, adnexal, optic nerve (ON), and periorbital soft tissues. METHODS: Outbred Sprague-Dawley rats (n = 5) received heterotopic vascularized WET from donors. Each WET included the entire globe, adnexa, ON, and periorbital soft tissues supplied by the common carotid artery and external jugular vein. Viability and perfusion were confirmed by clinical examination, angiography and magnetic resonance imaging (MRI). Globe, adnexal, and periorbital tissues were analyzed for histopathologic changes, and the ON was examined for neuro-regeneration at study endpoint (30 days) or Banff Grade 3 rejection in the periorbital skin (whichever was earlier). RESULTS: Gross examination confirmed transplant viability and corneal transparency. Average operative duration was 64.0 ±â€¯5.8 min. Average ischemia time was 26.0 ±â€¯4.2 min. MRI revealed loss of globe volume by 36.0 ±â€¯2.8% after transplantation. Histopathology of globe and adnexal tissues showed unique and differential patterns of inflammatory cell infiltration. The ON revealed a neurodegeneration pattern. CONCLUSION: The present study is the first in the literature to establish an experimental model of WET. This model holds significant potential in investigating mechanistic pathways, monitoring strategies or developing management approaches involving ocular viability, immune rejection, and ON regeneration after WET.

Precocious pathfinding: retinal axons can navigate in an axonless brain.

The developing axons of retinal ganglion cells follow a stereotyped trajectory through the diencephalon to the optic tectum. In Xenopus, this trajectory closely parallels that of a preexisting fiber tract, the tract of the postoptic commissure (TPOC). This tract comprises part of the early CNS scaffold and has been proposed to play a critical role in guiding the later growing optic axons. We have tested this possibility using heterochronic and xenoplastic transplants of eye primordia to force optic axons to enter the brain before scaffold tracts have arisen in the forebrain. We show that optic axons can navigate appropriately in the absence of the TPOC or any other axons, indicating that axonal pathfinding cues are present in the axonless neuroepithelial sheet. We suggest that molecularly distinct heterogeneities within the neuroepithelium are used for pathfinding by early and late developing axons alike in normal development.

A New Composite Eyeball-Periorbital Transplantation Model in Humans: An Anatomical Study in Preparation for Eyeball Transplantation.

BACKGROUND: Vascularized composite allotransplantation offers a new hope for restoration of orbital content and perhaps vision. The aim of this study was to introduce a new composite eyeball-periorbital transplantation model in fresh cadavers in preparation for composite eyeball allotransplantation in humans. METHODS: The composite eyeball-periorbital transplantation flap borders included the inferior border, outlined by the infraorbital rim; the medial border, created by the nasal dorsum; the lateral border, created by the lateral orbital rim; and the superior border, created by the superior part of the eyebrow. The pedicle of the flap included the facial artery, superficial temporal artery, and external jugular vein. The skin and subcutaneous tissues of the periorbital region were dissected and the bony tissue was reached. A coronal incision was performed and the frontal lobe of the brain was reached by means of frontal osteotomy. Ophthalmic and oculomotor nerves were also included in the flap. After a "box osteotomy" around the orbit, the dissection was completed. Methylene blue and indocyanine green injection (SPY Elite System) was performed to show the integrity of the vascular territories after facial flap harvest. RESULTS: Adequate venous return was observed within the flap after methylene blue dye injection. Laser-assisted indocyanine green angiography identified a well-defined vascular network within the entire composite eyeball-periorbital transplantation flap. CONCLUSIONS: For the first time, a novel composite eyeball-periorbital transplantation model in human cadavers was introduced. Good perfusion of the flap confirmed the feasibility of composite eyeball-periorbital transplantation in the clinical setting. Although harvesting of the flap is challenging, it introduces a new option for reconstruction of the periorbital region including the eyeball.

The Barcelona Principles: An Agreement on the Use of Human Donated Tissue for Ocular Transplantation, Research, and Future Technologies©.

PREAMBLE: The Barcelona Principles: An Agreement on the use of human donated tissue for ocular transplantation, research, and future technologies (Agreement) is a global bioethical framework (GBF), developed by the eye bank and ophthalmic communities, to inform on the management of altruistic and voluntary donations; their subsequent utility within ophthalmology and research; their retention as a public resource for the shared benefit of all; and their accessibility by waiting recipients.The Agreement is the result of global sector engagement over a 12-month period-led by the Global Alliance of Eye Bank Associations. Its aim is to provide leadership, guidance and recommendations that inform and support sound policy, and sector wide strategic planning and implementation at local, national, regional, and international levels.Inspired by the Declaration of Istanbul on Organ Trafficking and Transplant Tourism, this Agreement affirms the importance of the missions of the United Nations Sustainable Development Goals (Transforming our World: the 2030 Agenda for Sustainable Development); Universal Declaration of Human Rights; World Medical Association's Declaration of Helsinki-Ethical Principles for Medical Research Involving Human Subjects, and their Statement on Organ and Tissue Donation; The Council for International Organizations of Medical Science's International Ethical Guidelines for Health-related Research Involving Humans 2016; and accords with the World Health Organization's 2010 Guiding principles on human cell, tissue, and organ transplantation-WHA63.22.With millions waiting for a corneal transplant at any given moment-and the majority residing in lower resource locations, a significant component of this Agreement promotes equitable allocation systems for waiting recipients, and the development of self-sufficient services. It recognises important instruments, such as the International Council of Ophthalmology 2017 Position Statement: Donation, Processing, Allocation, Advocacy, and Legislation Supporting Human Corneal Tissue for Ocular Transplant; the World Health Organization's Universal Eye Health-Global Action Plan 2014 to 2019, and the mission of the International Agency for the Prevention of Blindness.Future biological innovations/technologies are also addressed within the Agreement, promoting research and development that seek to improve donation utility, reduce burden, and improve therapeutic options for recipients, without ethical compromise.The Agreement has been developed by the Global Alliance of Eye Bank Associations in conjunction with the International Council of Ophthalmology, International Agency for the Prevention of Blindness, The Corneal Society, Asian Eye Bank Association, European Eye Bank Association, Eye Bank Association of America, Eye Bank Association of Australia and New Zealand, Eye Bank Association of India, the Pan American Association of Eye Banks, and in countries and regions without eye bank organizations, their ophthalmic societies-such as the Ophthalmological Society of the West Indies, and the Pacific Eye Care Society.Finally, we endorse the current international consensus that prohibits trafficking and transplant tourism.

Self-organization and progenitor targeting generate stable patterns in planarian regeneration.

During animal regeneration, cells must organize into discrete and functional systems. We show that self-organization, along with patterning cues, govern progenitor behavior in planarian regeneration. Surgical paradigms allowed the manipulation of planarian eye regeneration in predictable locations and numbers, generating alternative stable neuroanatomical states for wild-type animals with multiple functional ectopic eyes. We used animals with multiple ectopic eyes and eye transplantation to demonstrate that broad progenitor specification, combined with self-organization, allows anatomy maintenance during regeneration. We propose a model for regenerative progenitors involving (i) migratory targeting cues, (ii) self-organization into existing or regenerating eyes, and (iii) a broad zone, associated with coarse progenitor specification, in which eyes can be targeted by progenitors. These three properties help explain how tissues can be organized during regeneration.