Background and Objective: Limbal stem cell deficiency (LSCD) is characterized by the insufficiency of limbal stem cells to maintain the corneal epithelium. Severe cases of LSCD may be treated with limbal transplantation from healthy autologous or allogeneic limbal tissue. Multiple cell-based therapies have been studied as alternative treatments to improve success rates and minimize immunosuppressive regimens after allogeneic transplants. In this review, we describe the success rates, and complications of different cell-based therapies for LSCD. We also discuss each therapy’s relative strengths and weaknesses, their history in animal and human studies, and their effectiveness compared to traditional transplants.

Methods: PubMed was searched for publications using the terms LSCD, cell-based therapy, cultivated limbal epithelial transplantation (CLET), cultivated oral mucosal epithelial transplantation (COMET),and mesenchymal stem cells from 1989 to August 2022. Inclusion criteria were English language articles.Exclusion criteria were non-English language articles.

Key Content and Findings: current cell-based therapies for LSCD are CLET and non-limbal epithelial cells. Non-limbal epithelial cell methods include COMET, conjunctival epithelial autografts, and mesenchymal stem/stromal cells (MSCs). Moreover, several alternative potential sources of non-limbal cells have described, including induced pluripotent stem cells (iPSCs), human embryonic stem cells (hESCs),human dental pulp stem cells, hair follicle bulge-derived epithelial stem cells, amniotic membrane epithelial cells, and human umbilical cord lining epithelial cells.

Conclusions: Cell-based therapies are a promising treatment modality for LSCD. While CLET is currently the only approved cell-based therapy and is only approved in the European Union, more novel methods have also been shown to be effective in human or animal studies thus far. Non-limbal epithelial cells such as COMET are also an alternative treatment to allogeneic transplants especially as a surface stabilizing procedure. iPSCs are currently being studied in early phase trials and have the potential to revolutionize the way LSCD is treated. Lastly, cell-based therapies for restoring the limbal niche such as mesenchymal stem cells have also shown promising results in the first human proof-of-concept study. Several potential sources of non-limbal cells are under investigation.

Background and Objective: Nearly 30 years have passed since limbal stem cell deficiency (LSCD) was first identified by pioneers and given clinical attention. LSCD remains a difficult disease to treat. It can potentially lead to blinding. At present, understanding of limbal stem cells (LSCs) has deepened and various treatment options for LSCD have been devised. The objective of this review is to summarize basic knowledge of LSCD and current treatment strategies.

Methods: PubMed search was performed to find studies published in English on LSCs and LSCD including original reports and reviews. Literatures published from 1989 to 2022 were reviewed.
Key Content and Findings: LSCs are enigmatic stem cells for which no specific marker has been discovered yet. Although LSCD is not difficult to diagnose, it is still challenging to treat. An important advancement in the treatment of LSCD is the provision of guidelines for selecting systematic surgical treatment according to the patient’s condition. It is also encouraging that stem cell technologies are being actively investigated for their potential usefulness in the treatment of LSCD.

Conclusions: Although various treatment options for LSCD have been developed, it should be kept in mind that the best chance of treatment for LSCD is in the early stage of the disease. Every effort should be made to preserve as many LSCs as possible in the early treatment of LSCD.

Conjunctival flaps have previously proven to be effective in preserving the globe for individuals with severe ocular surface disease. Infectious keratitis, neurotrophic keratitis, nontraumatic corneal melts, descemetoceles, perforations, and corneal burns are all indications for this procedure. The flaps promote nutrition, metabolism, structure, and vascularity, as well as reduce pain, irritation, inflammation, and infection. Furthermore, patients avoid the emotional and psychological repercussions of enucleation or evisceration, while requiring fewer postoperative medications and office visits. Currently, fewer flaps are performed due to the emergence of additional therapeutic techniques, such as serum tears, bandage lenses, corneal grafting, Oxervate, amniotic membrane, and umbilical cord grafting. However, despite newer conservative medical methods, conjunctival flaps have been demonstrated to be useful and advantageous. Moreover, future technologies and approaches for globe preservation and sight restoration after prior conjunctival flaps are anticipated. Herein, we review the history, advantages, and disadvantages of various surgical techniques: Gundersen’s bipedicle flap, partial limbal advancement flap, selective pedunculated conjunctival flap with or without Tenon’s capsule, and Mekonnen’s modified inferior palpebral-bulbar conjunctival flap. The surgical pearls and recommendations offered by the innovators are also reviewed, including restrictions and potential complications. Procedures for visual rehabilitation in selective cases after conjunctival flap are reviewed as well.

Abstract: Primary vitreoretinal lymphoma (PVRL), as a subset of primary central nervous system lymphoma (PCNSL), is a rare and fatal ocular malignancy. Most PVRL masquerades as chronic posterior uveitis, which makes the clinical diagnosis challenging. Vitreous cells, subretinal lesions and imaging techniques are essential for clinical diagnosis. Importantly, cytopathology/histopathology identification of malignant cells is the gold standard for the diagnosis of PVRL. In addition, molecular detection of immunoglobulin heavy chain (IgH) or T cell receptor (TCR) gene rearrangements, immunophenotyping for cell markers, and cytokine analysis of interleukine-10 elevation are often used as adjunct procedures. Current management of PVRL involves local radiation, intravitreal chemotherapy (methotrexate and rituximab), with or without systemic chemotherapy depending on the involvement of non-ocular tissues. In cases with concomitant PCNSL, systemic high-dose methotrexate/rituximab based therapy in conjunction with local therapy, whole brain radiotherapy and/or autologous stem cell transplantation is considered. Although PVRL normally responds well to initial treatment, high rates of relapse and CNS involvement usually lead to poor prognosis and limited survival. A professional team of medical experts in ophthalmologists, ocular pathologists, neuro-oncologists and hemato-oncologists is essential for optimizing patient management.

Abstract: Vision loss in retinal disease is often secondary to neural cell loss. Neural loss of any type including that of the retina has always been considered irreversible as these cells rarely retain the ability to regenerate. The recent identification of stable stem cell sources and the advances in stem cell technology have transformed this area of research science into an important area of strong therapeutic possibility. These sources include human embryonic stem cells (hESC), induced pleuripotent stem cell sources (iPS) as well as adult sources. The main advantage of using a stem cell source is that there is an infinite capacity to reproduce and therefore an infinite capacity to produce cells, including neural cells for transplantation. The challenge more recently has been to transform these stem cells into differentiated cells that are useful for transplantation in disease. In terms of the retina, hESC have been successfully developed into retinal pigment epithelial cells. These cells have been characterised as identical to native human RPE cells structurally, functionally and biochemically. Previous studies of macular translocation and RPE/choroidal transplantation have shown that vision loss from AMD can be reversed. Early animal studies show that the transplanted HESC RPE survive and can prevent vision loss in animal models of disease. Initial hESC based RPE transplantation trials using suspension cultures were successful in demonstrating safety of the cells in the context of disease and sub-retinal delivery. More recently, we have carried out the first 2 transplantations of sheets of hESC based RPE on a coated artificial Bruch’s membrane, in the London Project’s RPE transplantation trial, with promising results. As well as RPE— Bruch’s transplantation I will also briefly discuss the recent advances in neuro-retinal and vascular reconstructions using stem cells.

Abstract: Glaucoma is now the second leading reason of blindness in the world and is characterized by gradual loss of retinal ganglion cells. Stem cells have the ability to regenerate human structures. Although there are still problems unsolved, stem cell therapy might provide brighter future for treatment of glaucoma.

Background: Rods and cones are critical for light detection. Although there has been considerable work done in elucidating the molecular mechanisms involved in rod development, not much is known about how the cone cell fate decision is made by the multipotent retinal progenitor cells during development. Analysis of the promoter regions of Nrl and trβ2, rod and cone differentiation factors respectively, revealed DNA binding motifs of two POU-domain containing transcription factors, Pou2f1 and Pou2f2. Preliminary experiments showed that Pou2f1/2 are expressed during the peak of cone genesis in the embryonic retina. Therefore, we hypothesize that Pou2f1/2 specify cone cell fate in the developing retina.

Methods: We used immunofluorescence and in situ hybridization to establish the spatiotemporal expression of Pou2f1/2 during retinogenesis. We performed in vivo electroporation in post-natal mice to misexpress Pou2f1/2 and used antibodies specific to proteins expressed in cones such as Rxrγ and S-opsin to count cones. Using ex vivo electroporation of embryonic retinal explants, we knocked out Pou2f1 and Pou2f2 using CRISPR/Cas9 gRNAs at the peak of cone production window. Finally, we transfected post-natal retinal explants with a combination of regulatory elements of Nrl or thrb with control backbone vector, Pou2f1 or Pou2f2 using electroporation.

Results: We found that Pou2f1/2 are expressed in retinal progenitor cells in the developing retina and subsequently in the differentiated cones. Pou2f1/2 misexpression outside the cone genesis window led to an increase in cones at the expense of rods. Pou2f1/2 indel knockouts generated by CRISPR/Cas9 gRNAs led to a decrease in cones and a converse increase in rods. Finally, we found that Pou2f1/2 activate the cis-regulatory module (CRM) of the thrb gene and repress the activity of the CRM of Nrl.

Conclusions: These results uncover novel players that establish the complex gene regulatory network for cone photoreceptor fate specification in the retinal progenitor cells. We anticipate that this work should help us devise improved replacement therapies in the future utilizing stem cells for retinal degenerative diseases such as aged-related macular degeneration (AMD) and Stargardt’s disease.

Abstract: The inverted retina is a basic characteristic of the vertebrate eye. This implies that vertebrates must have a common ancestor with an inverted retina. Of the two groups of chordates, cephalochordates have an inverted retina and urochordates a direct retina. Surprisingly, recent genetics studies favor urochordates as the closest ancestor to vertebrates. The evolution of increasingly complex organs such as the eye implies not only tissular but also structural modifications at the organ level. How these configurational modifications give rise to a functional eye at any step is still subject to debate and speculation. Here we propose an orderly sequence of phylogenetic events that closely follows the sequence of developmental eye formation in extant vertebrates. The progressive structural complexity has been clearly recorded during vertebrate development at the period of organogenesis. Matching the chain of increasing eye complexity in Mollusca that leads to the bicameral eye of the octopus and the developmental sequence in vertebrates, we delineate the parallel evolution of the two-chambered eye of vertebrates starting with an early ectodermal eye. This sequence allows for some interesting predictions regarding the eyes of not preserved intermediary species. The clue to understanding the inverted retina of vertebrates and the similarity between the sequence followed by Mollusca and chordates is the notion that the eye in both cases is an ectodermal structure, in contrast to an exclusively (de novo) neuroectodermal origin in the eye of vertebrates. This analysis places cephalochordates as the closest branch to vertebrates contrary to urochordates, claimed as a closer branch by some researchers that base their proposals in a genetic analysis.