Every year, in Germany alone, around 7000 people wait for a new cornea to save their eyesight. But donor corneas are in short supply. In an EU project, researchers have developed an artificial cornea which is to be clinically tested in early 2008.
A patient whose cornea is damaged through a congenital malformation, hereditary disease or corrosion is at risk of going blind. One solution is to implant a donor cornea. The central part of the natural cornea is removed in a circular fashion, and the new cornea is inserted and sutured in place. A vast number of patients are affected: every year, 40,000 people in Europe alone hope for a donor often in vain. Many attempts have therefore been made at producing artificial corneas, so far with little success. This is due to the conflicting requirements imposed on the material: While it has to grow firmly into the natural tissue at the edge, it must allow no cells to deposit themselves at the center of the cornea, as this impairs the patient’s vision.
Working with other colleagues in the EU-funded CORNEA project, research scientists at the Fraunhofer Institute for Applied Polymer Research IAP in Potsdam and the Department of Ophthalmology at the University Hospital of Regensburg have found a solution. “Our artificial corneas are based on a commercially available polymer which absorbs no water and allows no cells to grow on it,” says IAP project manager Dr. Joachim Storsberg. “Once our partner Dr. Schmidt Intraokularlinsen GmbH has suitably shaped the polymers, we selectively coat the implants: We lay masks on them and apply a special protein to the edge of the cornea, which the cells of the natural cornea can latch onto. In this way, the cornea implant can firmly connect with the natural part of the cornea, while the center remains free of cells and therefore clear.” What is special about this protein is that it can survive the later thermal sterilization of the artificial cornea without being damaged, as it does not have the three-dimensional structure typical of large proteins. Such a structure would be destroyed during the sterilization process, leading to changes in the material’s properties. The optical front part of the implant is coated with a hydrophilic polymer, so that it is constantly moistened with tear fluid.
Researchers in Dr. Karin Kobuch’s working group at Regensburg University Hospital have already tested these corneas in the laboratory and found that their cells graft very well at the edge and cease growing where the coating stops. The optical center of the implant thus remains clear. The first implants have already been tested in rabbits’ eyes with promising results. If further tests are successful, the technology will be tried on humans in 2008.