Cornea

About the Cornea

The cornea is the transparent dome that forms the front surface of the eye, covering the iris and pupil. It provides most of the focusing power of the eye, more than the lens, because of the large difference in refractive index between air and corneal tissue. It has five main layers: an outer epithelium that regenerates quickly, Bowman layer, a thick stroma made of precisely arranged collagen fibrils whose regular spacing makes it transparent, Descemet membrane, and a single layer of endothelial cells that pump fluid out of the stroma to keep it clear. The cornea contains no blood vessels and receives oxygen mainly from the air and tear film, and nutrients from the aqueous humor. It is one of the most densely innervated tissues in the body, which is why even small scratches are very painful. Its shape determines refractive errors such as astigmatism, and it is reshaped in laser vision correction. Diseases include keratitis, keratoconus, and Fuchs dystrophy, and corneal transplantation is among the most common and successful tissue transplants.