The limbus is the transition zone between transparent cornea and opaque sclera. This area harbors corneal epithelial stem cells, which are responsible for the normal homeostasis and wound repair of the corneal epithelium. The palisades of Vogt, which are concentrated in the superior and inferior limbus, are thought to be the site of the limbal stem cells’ niche and can be observed biomicroscopically as radially oriented fibrovascular ridges concentrated along the corneoscleral limbus (Fig 1-6). The posterior limbus appears to be responsible for stem cell maintenance, while the function of the anterior limbus may be to prompt regeneration of corneal epithelium. Renewal occurs from basal cells, with centripetal migration of stem cells from the periphery. This is known as the XYZ hypothesis, where X represents proliferation and stratification of limbal basal cells; Y, centripetal migration of basal cells; and Z, desquamation of superficial cells. The health of the cornea depends on the sum of X and Y being equal to Z. Damage to epithelial stem cells impairs long-term regeneration of corneal epithelial cells. Damage to the limbus leads to loss of the barrier that prevents invasion of the conjunctiva and neovascularization of the ocular surface.
Figure 1-6 Slit-lamp photograph showing the corneoscleral limbus with radially oriented fibrovascular ridges (palisades of Vogt).
(Courtesy of Cornea Service, Paulista School of Medicine, Federal University of São Paulo.)
Singh V, Shukla S, Ramachandran C, et al. Science and art of cell-based ocular surface regeneration. Int Rev Cell Mol Biol. 2015;319:45–106.
Yoon JJ, Ismail S, Sherwin T. Limbal stem cells: central concepts of corneal epithelial homeostasis. World J Stem Cells. 2014;6(4):391–403.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.