Posterior corneoscleral limbus: Architecture, stem cells, and clinical implications

• Published in: Progress in retinal and eye research Vol. 96; p. 101192
• Main Authors: Yam, Gary Hin-Fai, Pi, Shaohua, Du, Yiqin, Mehta, Jodhbir S.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.09.2023
• Subjects: Corneal cell therapy; Corneal endothelial progenitors; Corneal stromal stem cells; Posterior limbus; Trabecular meshwork stem cells; Transition zone; Trabecular meshwork stem cells; Posterior limbus; Transition zone; Corneal endothelial progenitors; Corneal cell therapy; Corneal stromal stem cells
• ISSN: 1350-9462; 1873-1635; 1873-1635
• DOI: 10.1016/j.preteyeres.2023.101192

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. •Posterior limbus contains limbal stroma, Schwalbe's line and trabecular meshwork.•The complex structure housing different cell types is crucial for corneal health.•Limbal stroma has complex cell types and keratocyte progenitors inhibit opacities.•Transition zone contains endothelial progenitors with regenerative potency.•Trabecular meshwork regeneration by stem cells improved aqueous outflow.