The cornea is the transparent end of the eyeball. It is the transparent front surface of the eye through which the iris and pupil can be seen.
It has no blood vessels and is particularly sensitive due to the high density of sensitive nerves.
It is made up of 5 layers from the outside in:
1. epithelium: outer protective cell layer that is able to regenerate itself. The tear film adheres to it.
2. bowman membrane: separates the epithelium from the stroma and serves as the basis for the epithelial cell layer on top of it. It is not completely regenerable in the event of injury.
3. stroma: The stroma makes up approx. 90% of the corneal thickness. It contains collagen fibers and is mainly responsible for the shape, firmness and refractive power of the cornea.
4. descemet’s membrane: This separates the stroma from the underlying endothelium and acts as the basis of the endothelial cell layer.
5. endothelium: The single-layer endothelial cell layer has a pumping function whose task is to regulate the water balance of the stroma so that its clear transparency is maintained.
In a healthy eye, the cornea is regularly curved. This allows an object to be focused on a focal point and a sharp image to be produced in the eye on the retina (this corresponds to a film in a camera).
In the normal eye, the focal point is on the retina and the eye can see sharply without any other visual aids. In the case of “normal” short-sightedness or long-sightedness, the focal point is in front of or behind the retina – the eye is relatively too long or too short. In this case, glasses or contact lenses are necessary or a minimally invasive operation is possible to move the focal point to the retina and achieve sharp vision.
The eye disease keratoconus is a non-inflammatory disease of the cornea in which the cornea thins out due to a lack of biomechanical stability and continues to bulge until it takes on a conical shape. The protrusion often appears in the lower part of the eye. Around one in 2000 people are affected, usually with a time delay in both eyes.
Keratoconus usually occurs in the second to third decade of life and comes to a standstill after the fourth decade of life following a mostly progressive course.
In some patients, however, the progressive form of keratoconus may not only make it impossible to wear special contact lenses, but may also require a corneal transplant.
There is a risk that this rare eye disease may be mistaken for astigmatism in the early stages and therefore treated incorrectly. Only experienced doctors are able to reliably diagnose keratoconus by examining the corneal surface, the back surface of the cornea (endothelium), the corneal thickness and, if necessary, a cell count of the endothelium.
Keratoconus is presumably a disorder affecting the collagen structure within the connective tissue framework of the cornea, leading to reduced collagen cross-linking and, consequently, diminished biomechanical stability of the cornea.
The causes are complex and not yet fully understood. A genetic predisposition is suggested by the fact that keratoconus often runs in families. Immunological factors may also play a role. However, what is clear so far is that severe and frequent eye rubbing over many years — for example, in people with allergies — is a major risk factor for developing keratoconus.
Keratoconus is also associated with other conditions, such as neurodermatitis and Down syndrome (trisomy 21). Thyroid dysfunction is also being considered as a possible contributing factor.
Possible consequences of keratoconus and the associated irregular astigmatism include unusual fluctuations and a decline in visual acuity, the perception of rings around light sources—known as “halos”—as well as increased sensitivity to light and glare. For many patients, it is not possible to achieve sufficiently good visual acuity with glasses alone. Most patients benefit from wearing rigid (hard) gas-permeable contact lenses. These lenses help improve vision by compensating for the irregular shape of the cornea, but they do not stop the progression of the disease.
In advanced stages, folds in the cornea (Vogt’s striae) and permanent corneal scarring may develop, which can significantly impair vision even when using rigid contact lenses.
In rare and severe cases, a condition called corneal hydrops can occur. This happens when the Descemet’s membrane tears, allowing fluid from inside the eye to enter the cornea, leading to sudden and significant vision loss.
Keratoconus typically begins during puberty or early adulthood. It is usually a progressive condition that continues to worsen over several years, often stabilizing by the fourth or fifth decade of life. The severity of the disease varies greatly from person to person, and in most cases, both eyes are affected to differing degrees. The range of severity extends from asymptomatic incidental findings to advanced stages involving corneal scarring and the potential need for a corneal transplant.
If the disease remains in an early stage where the characteristic cone-shaped protrusion of the cornea has not fully developed, it is referred to as forme fruste keratoconus.
Early detection of keratoconus is crucial. Due to the genetic component of the disease, family history often provides important clues. It is not uncommon for close relatives—such as children, parents, or siblings—to also be affected. Therefore, if a family member is diagnosed, their relatives should undergo ophthalmologic screening as well.
A noticeable decline in visual acuity that can no longer be fully corrected with glasses is often the first sign of keratoconus.
Today, the diagnosis is typically made using corneal topography and tomography with advanced imaging technology.
At our center, we utilize two of the most advanced diagnostic devices available worldwide:
The MS-39 by SCHWIND and the Anterion by Heidelberg Engineering.