The stratified epithelium of the cornea is part of the corneo-scleral coat that forms the outer tunic of the eyeball, protecting its inner structures and, together with the pressure of the intraocular fluid, maintaining the eye’s shape and consistency. The anterior surface of the cornea is built up by the corneal epithelium shown in this figure.

The corneal epithelium exhibits all characteristics of a simple stratified squamous epithelium of five to seven layers of cells. In the most basal layer, high polygonal cells are aligned along the basal lamina. They are anchored to the basal lamina and to the adjacent Bowman’s layer by hemidesmosomes (cf. Fig. 161). The Bowman’s layer represents the anterior part of the corneal stroma and is visible in the most basal section of the figure. Basal cells are mitotically active and replace the differentiated cells of the upper layers. The corneal epithelium has a remarkable wound healing capacity. Cytokeratin intermediate filaments are associated with multiple desmosomes that attach the cells to one another. In the basal layers, cells are connected by long bridges that span the wide intercellular spaces.

The cells change shape during differentiation, migration, and transport to the upper layers, increasingly becoming flat. The squamous superficial cells in the outermost layer are particularly rich in cytokeratin filaments. They protect the cells lying beneath from the external environment. On their apical domains, short microvilli are present. They are in contact with a protective film of tear, by which the surface of the corneal epithelium is continually kept wet. Mucins in the tear film lubricate the epithelial surface during the blinking of the eyelid. They stabilize the tear film, preventing desiccation of the underlying epithelial cells, and form a barrier to penetration of pathogens.

A barrier leading to impermeability of the corneal epithelium to water-soluble substances is formed by tight junctions between the superficial cells. Tight junctions are established during differentiation from the basal to the superficial cells and may regenerate within one hour after abrasion of the superficial cells.

For maintenance of corneal transparency, a precise regulation of water content is necessary (cf. Fig. 160). Data provide evidence that the water-transporting proteins aquaporin 5 and 1, expressed in the corneal epithelium and in the corneal endothelium, respectively, provide main routes for water transport across the epithelial and endothelial barriers of the cornea.

The biophysical properties of each layer (cf. Figs. 108, 160, and 161) of the rabbit cornea from the epithelium to the endothelium in comparison to the human cornea have been determined by atomic force microscopy. The differences found between the two species are particularly interesting, inasmuch as the rabbit cornea is commonly used for evaluation of new keratoprosthetics and substrates for in vitro studies of corneal cellular behavior.