On the nature and the role of the subsurface vesicles in the outer epithelial cells of the conjunctiva.

The layer of the tear film in contact with the conjunctiva is mucus. This mucus comes from two sources, the conjunctival goblet cells and the subsurface vesicles. These vesicles are found just below the surface of the conjunctival cells. They contain long chain mucus glycoprotein molecules that are joined to the vesicle membrane. The vesicles fuse with the surface membrane of the conjunctival cells and expose their mucus glycoprotein chains to the overlying mucus. Chemical and physical bonds between the two types of mucus help to bind the mucus layer to the conjunctiva. The vesicle membrane becomes incorporated in the cell membrane and supplies the membranes for the microvilli that cover the exposed surface.