الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Stem cells are cells that can proliferate with almost unlimited potential, maintaining a pool of growing and dividing cells, with the added ability that some cells can differentiate into specific cell types. Stem cells are present in all self reviewing tissue and have unique characteristics that enable them to control cell replacement during homeostasis and tissue repair. The ocular surface is made up of two distinct types of epithelial cells, constituting the conjunctival and corneal epithelia. These epithlia are stratified, sequamous and non keratinized. Although anatomically continuous with each other at the corneo-scleral limbus. limbal stem cells have been localized to the palisades of Vogt in the corneal limbus. The microenvironment of the limbus is considered to be important in maintaining stemness of stem cells. They also act as” barrier” to conjunctival epithelial cells and prevent them from migrating on to the corneal surface. In certain pathologic conditions, the limbal stem cells may be destroyed partially or completely resulting in varying degree of stem cell deficiency with its characteristic clinical features. These include ” conjunctivalization” of the cornea with vascularization, appearance of goblet cells and irregular and unstable epithelium. Limbal stem cell deficiency disorders are divided into two major categories. Category I diseases are characterized by having clear pathogenic cause identifiable from past history which has destroyed the limbal stem cell population.