The cornea is the crystal-clear, wetted by tear fluid end of the eyeball. With 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 created in the eye on the retina (corresponds to the film in the camera).
In the normal eye, the focal point is on the retina and the eye can see clearly without any further aids. In the case of “normal” nearsightedness or farsightedness, the focal point lies in front of or behind the retina – the eye is relatively too long or too short. In this last case glasses or a contact lens (see “optics studio”) is necessary or a minimally invasive operation is conceivable (see “no need for glasses”) to shift the focus to the retina to see clearly.
The keratoconus eye disease is a non-inflammatory disorder of the eye’s cornea in which it thins and bulges further and further until it takes on a conical shape. The bulge is often seen in the lower area of the eye. Approximately one in 2,000 people are affected, usually with a delay in both eyes. A keratoconus usually occurs in the second to third decade of life and comes to a standstill between the fourth and fifth decade of life. In some patients, the progressive shape of the keratoconus may not only make it impossible to wear special contact lenses, but may also require a corneal transplant. In the early stages, this rare eye disease is often mistaken for astigmatism and treated incorrectly.
Possible consequences of keratoconus are unusual fluctuations and decreased visual acuity, irregular astigmatism, the perception of light rings around light sources, the so-called “halos”, and increased sensitivity to light and glare. If the disease remains at a stage in which the full cone shape has not yet developed, one speaks of “Forme Fruste Keratoconus (FFK)”.
In 20% of patients, however, a progressive keratoconus develops rapidly. This can cause cracks in the posterior cornea, through which liquid from the anterior chamber penetrates the cornea, causing it to become cloudy. One then speaks of an acute keratoconus. Often only a corneal transplant helps in the late stage.
Presumably, a keratoconus is a disruption between the collagen molecules of the connective tissue support structure of the cornea, which leads to less cross-linking of the collagen and thus to a reduced biomechanical stability of the cornea.
The causes are complex and not yet fully understood. A genetic predisposition is indicated by the fact that it often occurs in families. Immunological factors can also play a role. So far, however, it is only certain that violent and frequent rubbing of the eyes for years, for example in allergy sufferers, represents a high risk factor for the development of keratoconus. Thyroid dysfunction could also be a cause.
For this reason, we recommend our keratoconus patients to have their thyroid examined in order to have therapy with thyroid hormones if necessary. The thyroid hormone thyroxine seems to have a significant influence on the biomechanics of the cornea: it increases the growth and stiffness of corneal tissue and affects the nature or properties of the collagen-protein compound.
The symptoms of the forme fruste are not much different from normal astigmatism and are often discovered by chance during a close ophthalmological check-up. It can be corrected with glasses or a contact lens and does not need to be treated if it is stable, but must be observed and checked regularly. The forme fruste is ten times more common than the progressive shape.
The progressive form of the keratoconus is aggressive and is often noticeable even in teenage years. The progressive bulge causes a curvature of the cornea called astigmatism. This irregularity in the cornea makes correction with glasses increasingly difficult. Contact lenses are more suitable because they apply pressure on the cornea and can compensate for the roughest unevenness. If the disease is not too advanced, a good correction can be achieved with lenses, up to the maximum eyesight.
However, if the bulging of the cornea continues to increase, even hard contact lenses are less stable and can fall out. In addition, as the bulging progresses, the cornea below the center becomes ever thinner and scarred, which irreparably worsens visual acuity.