Cornea is the outermost layer of the eye, facing the external world. The avascular and transparent cornea is histologically divided into six layers. From the surface and inwards: Corneal epithelium, basement membrane, Bowman’s layer, stroma, Descemet’s membrane and the endothelium. The corneal epithelium is subject to amazingly challenging and specialized demands: It not only serves as an outer barrier against microbes and injuries, it also serves as an accurate optical medium. A constant self-renewal of the epithelium is therefore necessary. During the last decades, new understanding and knowledge on this area has greatly increased. The limbus is the transformation-zone between the cornea and the conjunctiva. It represents an exciting location on the eye. Certain stem cells, called limbal stem cells (LSC), are proved to situate among the vascularized, basal layer of the limbus. The LSC are the source of mature corneal epithelium cells, via proliferation, transmigration and differentiation. Hence an injury or illness to the LSC will result in complications for the corneal epithelium. Acid or alkali burns, Stevens-Johnson syndrome, severe microbial infections and pterygium are examples of conditions that can lead to limbal stem cell deficiency (LSCD). One can observe conjunctivalisation, i.e. ingrowth of the vascular and atransparent conjunctiva into the cornea. According to the degree of LSCD, the findings can be neovascularisation, persisting erosions and ulcers and ingrowth of fibrous tissue. The symptoms can be photophobia, pain, reduced vision and even blindness.
According to the new knowledge on LSC, we are now able to offer treatment for LSCD. Both auto-transplantation and allo-transplantaion of LSC have shown promising results. Other stem cells, like embryonic stem cells and mesenchymal stem cells from bone marrow, have also shown good results in treating LSCD. Still, more research needs to be done to find the perfect treatment for LSCD.
This article serves as an overview of international literature on the area, and aims to give a summary of, and introduction to, the new knowledge on LSC and experiences in therapy of LSCD.