Abstract
In the human cornea, regeneration of the epithelium is regulated by the stem cell reservoir of the limbus, which is the marginal region of the cornea representing the anatomical and functional border between the corneal and conjunctival epithelium. In support of this concept, extensive limbal damage, e.g., by chemical or thermal injury, inflammation, or surgery, may induce limbal stem cell deficiency (LSCD) leading to vascularization and opacification of the cornea and eventually vision loss. These acquired forms of limbal stem cell deficiency may occur uni- or bilaterally, which is important for the choice of treatment. Moreover, a variety of inherited diseases, such as congenital aniridia or dyskeratosis congenita, are characterized by LSCD typically occurring bilaterally. Several techniques of autologous and allogenic stem cell transplantation have been established. The limbus can be restored by transplantation of whole limbal grafts, small limbal biopsies or by ex vivo-expanded limbal cells. In this review, the physiology of the corneal epithelium, the pathophysiology of LSCD, and the therapeutic options will be presented.
Highlights
In 1868, the term “stem cell” was first proposed in the worldwide scientific literature by the German biologist Ernst Haeckel [1]
In 1971, Davanger and Evensen proposed that renewal of the corneal epithelium is driven by migration of epithelial cells located at the limbus of the cornea [13]
limbal epithelial stem cells (LESCs) and corneal stromal stem cells and endothelial stem cells appear to exist in the cornea, which are all considered to play a vital role in maintaining corneal homeostasis and repair [20,21,22,23]
Summary
In 1868, the term “stem cell” was first proposed in the worldwide scientific literature by the German biologist Ernst Haeckel [1]. Stem cells became attractive for therapeutic applications in many branches of medicine, and a growing amount of knowledge is being gathered in this field [2] Based on their differentiation potential, stem cells can be classified into totipotent, pluripotent, multipotent, oligopotent, and unipotent stem cells [2]. The World Health Organization estimates that around 4.2 million worldwide are suffering from moderate to severe distance vision loss or blindness due to corneal opacities, which has become the fourth leading cause of visual impairment [26].There is a wide variety of corneal diseases that can cause corneal opacification or deformation, e.g., corneal trauma, microbial infection, neurotrophic keratopathy, endothelial dystrophy, or limbal stem cell deficiency, which can be acquired or inherited [27,28,29,30]. We discuss novel potential treatments aimed at improving corneal regeneration
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