Diseases of the cornea
The cornea of the eye is so to say our window onto the outer world. Diseases of the cornea may lead to opacifications, scars or a protrusion, and can durably impair our eyesight.
Irregular deformation of the cornea (e.g. keratoconus)
An irregular curvature of the cornea may result from a disease or an injury – the surface of the cornea is undulated and irregular. A tissue alteration (keratoconus) may also cause blurry or distorted vision, due to a progressive bulging out (protrusion) of the cornea.
With time, visual acuity may decrease considerably and the protrusion may become so pronounced that the cornea gets thinner and thinner – in extreme cases it may cicatrize or even rupture. A corneal transplant may be avoided through a surgical stabilization of the cornea, because in many cases the irregular deformation of the cornea can be reduced markedly and stabilized. With the same procedure, the corneal surface can be made more symmetrical (and regular) again.
Kera rings
Kera rings, also called intracorneal ring segments, are corneal implants. In persons suffering from an irregular deformation of the cornea (e.g. keratoconus), the cornea can be stabilized to a great extent. The surface of the cornea can be made more symmetrical again with this procedure, which leads to an improved visual acuity.
In order to implant the kera rings that will stabilize the cornea, one, or, if necessary, two semicircular channels are pierced into the cornea with the femtosecond laser (also used in laser corrections). The kera rings are then inserted into these channels. The rings produce a tension on the cornea, causing the central part of the cornea to flatten and the asymmetrical distortion of the cornea to be corrected.
The implantation of kera rings usually provides a good basis for a further procedure used to stabilize the cornea: corneal cross-linking.
Properties of kera rings:
- Good predictability of the results
- Fast recovery
- Treatment is reversible, the rings can be surgically removed again
- Implant material characterized by optimal tissue tolerance
- The implantation of kera rings can be combined with the implantation of an artificial lens to compensate for a visual defect such as myopia (the combined treatment is not performed at the same time)
- The implantation of kera rings provides the best preconditions for an additional treatment: corneal cross-linking
Corneal transplantation
In case of a severe disease of the cornea, the graft of a donor cornea (corneal transplantation, keratoplasty) is often the only possibility to regain a useful eyesight.
Until a few years ago, the transplantation of the cornea was performed, as a rule, in its entirety (so-called perforating keratoplasty). Today, we can use more modern and gentler procedures, which allow us to replace only the diseased layers of the cornea. The unaltered healthy parts are kept intact. In many cases, this leads to a marked reduction of risk as well as to faster recovery of visual acuity.
In DALK (= deep anterior lamellar keratoplasty) the outer layers of the cornea are replaced. The innermost corneal layer (endothelium) can thus be preserved and rejection reactions hardly ever occur anymore. This procedure is applied mainly in case of strong deformations of the cornea (so called keratoconus) and in case of corneal scars.
In DMEK (= Descemet membrane endothelial keratoplasty) only the innermost layer of the cornea is exchanged, the outer 99% remain unchanged. Rejection reactions and deformations of the graft are much rarer with this procedure. No sutures are necessary and the healing phase is markedly shortened in comparison to the older procedures. This surgical technique is applied in diseases of the innermost corneal layer (Fuchs’ endothelial dystrophy).
Recently, the possibility of the implantation of an artificial cornea (keratoprosthesis) has also been introduced, to be used in very severe cases (e.g. after acid burns). The Boston-Keratoprosthesis is applied in cases that were previously deemed to be untreatable.
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