The cornea consists of five layers:

1. EPITHELIUM: 5-7 layers of stratified squamous cells that form the protective outer covering of the cornea. This layer acts as a barrier to infection. A breakdown of the epithelium allows moisture and bacteria into the stroma.

2. BOWMANíS MEMBRANE: A thin membrane separating the epithelium and the stroma. Injuries or damage to this layer result in permanent scars that may reduce vision.

3. STROMA: The largest layer of the cornea, accounting for most of the thickness. The stroma is made up of collagen fibrils arranged in a lattice configuration. The stroma is transparent, however, a breakdown of the epithelium and Bowmanís membrane can let moisture and bacteria into the stroma, leaving it clouded thus reducing vision.

4. DESCEMETíS MEMBRANE: A basement membrane produced by the delicate layer of endothial cells that line the inner cornea.

5. ENDOTHELIUM: A single layer of squamous cells whose function is to pump water out of the cornea. This pumping action not only keeps the layers of the cornea transparent, but plays an important role in oxygen transport. A healthy endothelium is vital to a successful cornea transplant.