corneae

The corneae, or corneas, are the pair of transparent anterior structures of the eye that cover the iris and pupil. They account for about two-thirds of the eye's total optical power and play a central role in focusing light onto the retina. Humans have two corneae, one in each eye.

Each cornea consists of five layers: the epithelium; Bowman's layer; the stroma; Descemet's membrane; and the endothelium. The epithelium is a stratified squamous layer that protects the surface; the stroma, comprising about 90% of corneal thickness, contains regularly arranged collagen lamellae that maintain transparency; Descemet's membrane and the endothelium maintain structure and deturgescence; the endothelium regulates corneal hydration.

The cornea is avascular; it receives nutrients from tears and the aqueous humor. It is densely innervated, especially by sensory nerves from the ophthalmic division of the trigeminal nerve, contributing to high sensitivity to touch and pain.

Developmentally, the cornea arises from the surface ectoderm and neural crest. Wound healing shows rapid epithelial regeneration but slower stromal repair, which can lead to scarring and vision loss. The endothelium has limited regenerative capacity.

Clinically important conditions include keratoconus, keratitis, corneal ulcers, and dystrophies such as Fuchs endothelial dystrophy. Management ranges from contact lens correction and cross-linking for keratoconus to corneal transplantation, including penetrating keratoplasty and lamellar techniques (DSAEK, DMEK, DALK), to restore vision.