Synonym
Keratoplasty
Introduction
The cornea covers the front part of the eye. It is a thin transparent collagenous layer of approximately 550 micrometers to 700 micrometers that is not visible to the naked eye. It protects the eyeball and refracts the incident light rays.
Structure of the cornea
The cornea consists of several layers (structure). The multilayer corneal epithelium protects the corneal surface and repels germs. Together with the tear fluid, it forms the smooth refractive surface of the optical system.
The basal epithelial cells are anchored in a basal membrane, which merges into the so-called Bowman membrane (a thicker and tougher layer) and contributes to the stability of the cornea. The corneal stroma is formed by parallel layers of collagenous fibers and is transparent due to its regular and narrow grid structure. On the inside of the corneal cornea is the single-layer corneal endothelium.
Its basement membrane is also crossed by elastic fibers and is called the descent membrane. The corneal endothelium seals the corneal stroma from the aqueous humor. Penetrated fluid is pumped back into the anterior chamber. The cornea is not able to regenerate after deeper injuries. The structure of the cornea remains permanently damaged.
Tasks of the cornea
Initially, the cornea serves as a front lens, i.e. it contributes with its own refractive power to imaging the image onto the retina. Its refractive power is 43 diopters. Besides its contribution to vision, the cornea also has a protective function. It can cushion the intraocular pressure generated in the eye. The cornea is a very important part of the optical apparatus that cannot be dispensed with.
Diseases of the cornea: Corneal astigmatism
Astigmatism is also known as astigmatism. It is a harmless and very common corneal anomaly, which can be observed in about 70% of all spectacle wearers. Literally translated, astigmatism means “pointlessness”.
In German, astigmatism is also called “Stabsichtigkeit”. A normal and healthy cornea has a uniform curvature in all directions of its radius. In people with astigmatism, which is usually congenital and does not recede during life, the cornea is now slightly more curved in one direction than in the other.
As a result, the rays of light that hit the eye are no longer point-like, but rather as lines on the retina. The horizontal rays of light are refracted more strongly than the vertical ones. As a result, the rays do not merge into a single sharp focal point on the retina.
Instead, two different rod-shaped focal lines are created: the image appears slightly distorted. This explains the term “astigmatism”. Very often, astigmatism can be observed in combination with other refractive errors of the eye, for example in combination with short- or long-sightedness. Once the astigmatism has been recognized and diagnosed, it can easily be corrected with glasses, contact lenses or even a refractory corneal surgery.
