Explain the barrier function in the cornea.

Barrier Function:

It is the first line of barrier between the external environment and the corneal stroma. The superficial epithelial cells are encircled by tight junctions (zonula occludens).

These superficial epithelial cells serve as semi-pernieable high resistance (12- 16kQ) membrane. It prevents niovement of fluid from tear to stroma. It is useful for maintenance of epithelial barrier. The maintenance is done by mitosis of basal cells and migration of new basal cells from the limbal stern cells. So the corneal epithelium is maintained by a balance among the process of centripetal cell migration (120pm/wk), mitosis, and shedding of superficial cells. The XYZ hypothesis of corneal epithelial maintenance by Thoft and Friend is X+Y=Z. The limbal epithelium has the highest mitotic rate followed by peripheral cells and central cells have the lowest mitotic mte.