Stem Cells and Ocular Regeneration.

The surface of the eye is a peculiar and extraordinary area, since the functions of all regions of the ocular surface system (OSS) are closely integrated forming a unique functional unit composed of different tissues and organs. Anatomically the ocular surface is composed principally by cornea and conjunctiva, but it also includes the lacrimal gland and the lacrimal drainage system for the tear film homeostasis, and the eyelids. Additional components as Meibomian glands, eyelashes and eyebrows complete the picture, contributing to the outermost lipid layer and to particle clearance (Fig. 1). Cornea and conjunc- tiva are generally covered by a complex liquid known as the tear film, providing a continuous moist environment connecting all areas at the front of the eye ball and protecting them from pathogens and small solid particles. This interconnected system provides the necessary conditions for the maintenance of functions needed for the vision process, as the final goal of eye function. The dysfunction of this apparatus could lead to several pathologies, such as corneal opacity or dry eye diseases (DED). Each component plays an important role for ocular surface maintenance, therefore some recent findings in stem cell biology aimed at the regeneration of different components of the ocular surface by tissue engineering, are examined in the following paragraphs.