Corneal anatomy

The cornea is the most anterior part of the eyeball, in direct contact with the external environment.

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What is the cornea?

The cornea is a transparent, avascular tissue. Its anterior surface is covered by the tear film, while its posterior surface is bathed in the aqueous humor. The cornea consists of five distinct tissue layers: the epithelium, Bowman’s layer, the stroma, Descemet’s membrane, and the endothelium. It is one of the most innervated and sensitive tissues in the human body due to the extremely high number of nerve endings it contains.

Further details about the cornea

The surface of the cornea is covered by a tear film that protects it from dehydration and maintains the regularity of the epithelial surface. The thickness of the corneal epithelium is 50 μm. The arrangement of collagen fibers within the stroma is responsible for the cornea’s transparency. The endothelium is a cellular layer that functions as a pump, with its main role being the regulation of corneal hydration.

The cornea is convex and aspherical (prolate), which gives it refractive power. In adults, its average diameter ranges from 9 to 11 mm. The mean central thickness is about 500 microns, gradually increasing towards the periphery to reach 700 microns.

The radius of curvature of the cornea is not uniform across its surface. It is more curved at the center (7.5 to 8 mm over the central 3 mm) and flattens towards the periphery. With a refractive power of +43.5 diopters, the cornea provides two-thirds of the eye’s total refractive power.

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This page was written by Dr. Camille Rambaud, an ophthalmologist based in Paris and a specialist in refractive surgery.