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Yam GHF, Pi S, Du Y, Mehta JS. Posterior corneoscleral limbus: Architecture, stem cells, and clinical implications. Prog Retin Eye Res 2023; 96:101192. [PMID: 37392960 DOI: 10.1016/j.preteyeres.2023.101192] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2023] [Revised: 06/22/2023] [Accepted: 06/23/2023] [Indexed: 07/03/2023]
Abstract
The limbus is a transition from the cornea to conjunctiva and sclera. In human eyes, this thin strip has a rich variation of tissue structures and composition, typifying a change from scleral irregularity and opacity to corneal regularity and transparency; a variation from richly vascularized conjunctiva and sclera to avascular cornea; the neural passage and drainage of aqueous humor. The limbal stroma is enriched with circular fibres running parallel to the corneal circumference, giving its unique role in absorbing small pressure changes to maintain corneal curvature and refractivity. It contains specific niches housing different types of stem cells for the corneal epithelium, stromal keratocytes, corneal endothelium, and trabecular meshwork. This truly reflects the important roles of the limbus in ocular physiology, and the limbal functionality is crucial for corneal health and the entire visual system. Since the anterior limbus containing epithelial structures and limbal epithelial stem cells has been extensively reviewed, this article is focused on the posterior limbus. We have discussed the structural organization and cellular components of the region beneath the limbal epithelium, the characteristics of stem cell types: namely corneal stromal stem cells, endothelial progenitors and trabecular meshwork stem cells, and recent advances leading to the emergence of potential cell therapy options to replenish their respective mature cell types and to correct defects causing corneal abnormalities. We have reviewed different clinical disorders associated with defects of the posterior limbus and summarized the available preclinical and clinical evidence about the developing topic of cell-based therapy for corneal disorders.
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Affiliation(s)
- Gary Hin-Fai Yam
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA; Tissue Engineering and Cell Therapy Group, Singapore Eye Research Institute, Singapore; McGowan Institute for Regenerative Medicine, Pittsburgh, PA, USA.
| | - Shaohua Pi
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Yiqin Du
- Department of Ophthalmology, University of South Florida, Tampa, FL, USA
| | - Jodhbir S Mehta
- Tissue Engineering and Cell Therapy Group, Singapore Eye Research Institute, Singapore; Department of Cornea and External Eye Disease, Singapore National Eye Centre, Singapore; Ophthalmology and Visual Sciences Academic Clinical Program, Duke-National University of Singapore (NUS) Medical School, Singapore.
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Mirzayev I, Gündüz AK, Aydın Ellialtıoğlu P, Gündüz ÖÖ. Clinical applications of anterior segment swept-source optical coherence tomography: A systematic review. Photodiagnosis Photodyn Ther 2023; 42:103334. [PMID: 36764640 DOI: 10.1016/j.pdpdt.2023.103334] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2022] [Revised: 01/25/2023] [Accepted: 02/07/2023] [Indexed: 02/11/2023]
Abstract
Optical coherence tomography (OCT) is a non-invasive method that provides the opportunity to examine tissues by taking cross-sectional images. OCT is increasingly being used to evaluate anterior segment (AS) pathologies. Swept-source (SS) OCT allows greater penetration and achieves better visualization of the internal configuration of AS tissues due to the longer wavelength employed and high scan speeds. We reviewed the utilization of AS SS-OCT in various conditions including glaucoma, ocular surface pathologies, iris tumors, refractive surgery, cataract surgery, and scleral diseases. A systematic literature search was carried out on PubMed, Scopus, and Web of Science databases between January 1, 2008, and September 1, 2022 using the following keywords: AS SS-OCT; dry eye and SS-OCT; ocular surface and SS-OCT; cornea and SS-OCT; dystrophy and SS-OCT; glaucoma and SS-OCT; ocular surface tumors and SS-OCT; conjunctival tumors and SS-OCT; refractive surgery and SS-OCT; cataract and SS-OCT; biometry and SS-OCT; sclera and SS-OCT; iris and SS-OCT; ciliary body and SS-OCT; artificial intelligence and SS-OCT. A total of 221 studies were included in this review. Review of the existing literature shows that SS-OCT offers several advantages in the diagnosis of AS diseases. Exclusive features of SS-OCT including rapid scanning, deeper tissue penetration, and better image quality help improve our understanding of various AS pathologies.
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Affiliation(s)
- Ibadulla Mirzayev
- Department of Ophthalmology, Ankara University Faculty of Medicine, Ankara, Turkey; Halil Şıvgın Çubuk State Hospital, Ophthalmology Clinic, Ankara, Turkey
| | - Ahmet Kaan Gündüz
- Department of Ophthalmology, Ankara University Faculty of Medicine, Ankara, Turkey; Private Eye Clinic, Ankara, Turkey.
| | | | - Ömür Özlenen Gündüz
- Department of Ophthalmology, Ankara University Faculty of Medicine, Ankara, Turkey
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Pujari A, Agarwal D, Sharma N. Clinical role of swept source optical coherence tomography in anterior segment diseases: a review. Semin Ophthalmol 2021; 36:684-691. [PMID: 33689554 DOI: 10.1080/08820538.2021.1897854] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
PURPOSE To note the comprehensive role of swept source anterior segment optical coherence tomography (SS-ASOCT) in anterior segment diseases. METHODS A systematic literature search was carried out on various medical databases using the keywords, swept source anterior segment optical coherence tomography; SS-ASOCT; Cornea and SS-ASOCT; SS-ASOCT and glaucoma; SS-ASOCT and cataract; SS-ASOCT and biometer; SS-ASOCT and tear film and ocular surface.Original works and novel reports describing the potential role of SS-ASOCT in various anterior segment conditions were included. RESULTS After a thorough assessment of literature, it was clear that the SS-ASOCT did provide newer insights into many anterior eye conditions. The rapid scan acquisition, deeper tissue penetration, and higher magnification did enhance many of our understandings, which were previously not possible. In addition, lenticular assessment under complex clinical scenarios with automated values on objective scale has made it a worthy tool with immense future possibilities. CONCLUSIONS SS-ASOCT unveiled various anterior segment findings which were of clinical importance.
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Affiliation(s)
- Amar Pujari
- Dr Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India
| | - Divya Agarwal
- Dr Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India
| | - Namrata Sharma
- Dr Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India
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Regenerative capacity of the corneal transition zone for endothelial cell therapy. Stem Cell Res Ther 2020; 11:523. [PMID: 33276809 PMCID: PMC7716425 DOI: 10.1186/s13287-020-02046-2] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2020] [Accepted: 11/23/2020] [Indexed: 12/13/2022] Open
Abstract
The corneal endothelium located on the posterior corneal surface is responsible for regulating stromal hydration. This is contributed by a monolayer of corneal endothelial cells (CECs), which are metabolically active in a continuous fluid-coupled efflux of ions from the corneal stroma into the aqueous humor, preventing stromal over-hydration and preserving the orderly arrangement of stromal collagen fibrils, which is essential for corneal transparency. Mature CECs do not have regenerative capacity and cell loss due to aging and diseases results in irreversible stromal edema and a loss of corneal clarity. The current gold standard of treatment for this worldwide blindness caused by corneal endothelial failure is the corneal transplantation using cadaveric donor corneas. The top indication is Fuchs corneal endothelial dystrophy/degeneration, which represents 39% of all corneal transplants performed. However, the global shortage of transplantable donor corneas has restricted the treatment outcomes, hence instigating a need to research for alternative therapies. One such avenue is the CEC regeneration from endothelial progenitors, which have been identified in the peripheral endothelium and the adjacent transition zone. This review examines the evidence supporting the existence of endothelial progenitors in the posterior limbus and summarizes the existing knowledge on the microanatomy of the transitional zone. We give an overview of the isolation and ex vivo propagation of human endothelial progenitors in the transition zone, and their growth and differentiation capacity to the corneal endothelium. Transplanting these bioengineered constructs into in vivo models of corneal endothelial degeneration will prove the efficacy and viability, and the long-term maintenance of functional endothelium. This will develop a novel regenerative therapy for the management of corneal endothelial diseases.
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Yam GHF, Seah X, Yusoff NZBM, Setiawan M, Wahlig S, Htoon HM, Peh GSL, Kocaba V, Mehta JS. Characterization of Human Transition Zone Reveals a Putative Progenitor-Enriched Niche of Corneal Endothelium. Cells 2019; 8:cells8101244. [PMID: 31614883 PMCID: PMC6829622 DOI: 10.3390/cells8101244] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2019] [Revised: 10/09/2019] [Accepted: 10/10/2019] [Indexed: 12/12/2022] Open
Abstract
: The corneal endothelium regulates corneal hydration to maintain the transparency of cornea. Lacking regenerative capacity, corneal endothelial cell loss due to aging and diseases can lead to corneal edema and vision loss. There is limited information on the existence of corneal endothelial progenitors. We conducted ultrastructural examinations and expression analyses on the human transition zone (TZ) at the posterior limbus of corneal periphery, to elucidate if the TZ harbored progenitor-like cells, and to reveal their niche characteristics. Within the narrow TZ (~190 μm width), the inner TZ-adjacent to the peripheral endothelium (PE)-contained cells expressing stem/progenitor markers (Sox2, Lgr5, CD34, Pitx2, telomerase). They were located on the inner TZ surface and in its underlying stroma. Lgr5 positive cells projected as multicellular clusters into the PE. Under transmission electron microscopy and serial block face-scanning electron microscopy and three-dimensional (3D) reconstruction, the terminal margin of Descemet's membrane was inserted beneath the TZ surface, with the distance akin to the inner TZ breadth. Porcine TZ cells were isolated and proliferated into a confluent monolayer and differentiated to cells expressing corneal endothelial markers (ZO1, Na+K+ATPase) on cell surface. In conclusion, we have identified a novel inner TZ containing progenitor-like cells, which could serve the regenerative potential for corneal endothelium.
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Affiliation(s)
- Gary Hin-Fai Yam
- Tissue Engineering and Stem Cell Group, Singapore Eye Research Institute, Singapore 169856, Singapore.
- Eye-Academic Clinical Program, Duke-National University of Singapore (NUS) Graduate Medical School, Singapore 169857, Singapore.
| | - Xinyi Seah
- Tissue Engineering and Stem Cell Group, Singapore Eye Research Institute, Singapore 169856, Singapore.
| | | | - Melina Setiawan
- Tissue Engineering and Stem Cell Group, Singapore Eye Research Institute, Singapore 169856, Singapore.
| | - Stephen Wahlig
- Tissue Engineering and Stem Cell Group, Singapore Eye Research Institute, Singapore 169856, Singapore.
- Department of Ophthalmology, Duke University School of Medicine, Durham, NC 27705, USA.
| | - Hla Myint Htoon
- Eye-Academic Clinical Program, Duke-National University of Singapore (NUS) Graduate Medical School, Singapore 169857, Singapore.
- Data Science Group, Singapore Eye Research Institute, Singapore 169856, Singapore.
| | - Gary S L Peh
- Tissue Engineering and Stem Cell Group, Singapore Eye Research Institute, Singapore 169856, Singapore.
- Eye-Academic Clinical Program, Duke-National University of Singapore (NUS) Graduate Medical School, Singapore 169857, Singapore.
| | - Viridiana Kocaba
- Tissue Engineering and Stem Cell Group, Singapore Eye Research Institute, Singapore 169856, Singapore.
- Department of Ophthalmology, Claude Bernard Lyon 1 Université, 69622 Villeurbanne, France.
| | - Jodhbir S Mehta
- Tissue Engineering and Stem Cell Group, Singapore Eye Research Institute, Singapore 169856, Singapore.
- Eye-Academic Clinical Program, Duke-National University of Singapore (NUS) Graduate Medical School, Singapore 169857, Singapore.
- Singapore National Eye Centre, Singapore, Singapore 168751, Singapore.
- School of Material Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore.
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Basak SK, Basak S. Clinical Outcomes and Endothelial Cell Density After Descemet Membrane Endothelial Keratoplasty Using Peripherally-trephinated Donor Tissue (DMEK-pD) in Fuchs Endothelial Corneal Dystrophy. Cornea 2019; 39:437-442. [DOI: 10.1097/ico.0000000000002149] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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