cornea

The cornea is the transparent, anterior portion of the eye that covers the iris, pupil, and anterior chamber. It serves as the eye’s primary refractive element, contributing about two-thirds of the eye’s total optical power and helping to focus light onto the retina. The cornea is avascular and highly organized to maintain clear vision, relying on nourishment from tears and the aqueous humor.

Anatomically, the cornea consists of five cellular–extracellular layers: the epithelium, Bowman's layer, the stroma, Descemet's membrane, and the endothelium. The central thickness is about 0.5 mm, with a diameter of roughly 11–12 mm and a curvature that gives a radius of about 7.8 mm in adults. The stroma provides most of the cornea’s thickness and strength, while the endothelium maintains corneal dehydration to preserve transparency.

Nerve supply and nutrition are key features. The cornea receives rich sensory innervation from the trigeminal nerve, contributing to blinking and protective reflexes. It is nourished mainly by diffusion from the tear film and the aqueous humor, with the endothelium actively maintaining deturgescence to prevent edema.

Clinical relevance includes injuries, infections, and degenerative conditions. The cornea can heal from minor abrasions, but injuries can scar and reduce vision. Diseases such as keratoconus (thinning and cone-like protrusion), and Fuchs' endothelial dystrophy (endothelial cell loss) can impair clarity. When vision is compromised, corneal transplantation (keratoplasty) or lamellar procedures may be performed, ranging from penetrating keratoplasty to endothelial replacement techniques like DMEK.