The eye cornea

The eye cornea is the transparent front elastic and the mostly curved part of the exterior ligamentous layer of the human eye. It has the shape of horizontally placed convex and comprises 20% of the surface of the eyeball. It is colorless, completely transparent and avascular. Together with the conjunctiva, sclera and tear film it represents a mechanical and chemically impermeable barrier between interior and exterior environment. On the outside it borders with the air and on the inside it is in contact with the aqueous humour. Due to its refractive power the eye cornea is the most important part of the visual system and it is a critical factor as far as the quality of the vision is concerned.

The cornea has a diameter of approximately about 11.5mm vertically and 12mm horizontally. This does not hold true for everyone and there are people who have a diameter which is substantially smaller or even larger. When approaching the edge of the cornea, the corneal limbus, the cornea flattens and gradually transforms into the sclera. The surface of the eye cornea is covered by tear film which is important from the immunology’s point of view and also because it protects the corneal epithelium.

From the histological point of view the cornea consists of five layers. From the anterior to posterior there is corneal epithelium, Bowman´s membrane, corneal stroma, Descemet's membrane and corneal endothelium.

The structure of the cornea

Corneal epithelium

It has a good and fast regeneration ability and is exceptionally sensitive thanks to many loose nerve endings.

Bowman's membrane

It is transparent under normal circumstances but pathological states can make it blurry.

Corneal stroma

It comprises 9/10 of the total thickness of the cornea; consists of arrangements of collagen fibers and its structure causes that the rays of light which enter the eye are not influenced by traversing through the cornea.

Descemet's membrane

It is rich in glycoproteins which help it to stay firmly attached to the endothelium; it prevents leucocytes from penetrating into the corneal stroma and is very immune to injuries and infections.

Corneal endothelium

It plays a central role in active transfer of fluids, nourishment and innervation of the cornea.

The cornea does not contain any blood vessels and together with the sclera, lens and vitreous body belongs to the group of bradytrophic (without blood supplementation) tissues. Because of the fact that the cornea is avascular it is very important for its nourishment that it has a supply of oxygen from the outside. Other parts that account for the nourishment are the quality of tears, tear film and partially also aqueous humour.

Steady hydration is very important for the cornea as it prevents the corneal desiccation which could result in unpleasant feelings of discomfort, worse vision and even the formation of unpleasant inflammations. The cornea is the most sensitive tissue of human organism because it has the highest number of sensitive nerve fibers. The disruption of the corneal epithelium (for example as a consequence of the presence of some foreign body, erosion or inflammation) causes unpleasant pain which is followed by spontaneous lachrymation and blepharospasm.