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Two Artificial Corneas Promise to Restore Sight

Doctor Joachim Storsberg at the Fraunhofer Institute for Applied Polymer Research has been hard at work developing a couple of artificial corneas to replace diseased or damaged corneas in a patient's eyes.

Artificial corneas that are long-lasting and practical have been sorely needed for some time. Blindness is often caused by corneal diseases, and whilst there are treatments available, they involve a transplant of an intact cornea from a compatible donor. Corneal donors are rare, and compatible corneal donors are rarer still. An artificial cornea that works nearly as well, would save many from unnecessary blindness.

If the scarcity of donor corneas was not bad enough, a sub-group of patients have bodies that cannot tolerate transplanted corneas, attacking the new biological cornea even if it is supposedly compatible. Since there are methods of coating artificial materials that are not feasible for biological ones, this is another reason to look towards artificial materials.

The Fraunhofer institute is based in Germany, so German statistics are what matter to them. In that single country, they are looking at around 7,000 patients with damaged corneas and partial or total blindness, still waiting to be treated.

Dr Storsberg spoke about the research project in some detail. “We are in the process of developing two different types of artificial corneas. One of them can be used as an alternative to a donor cornea in cases where the patient would not tolerate a donor cornea, let alone the issue of donor material shortage.”

“A great many patients suffering from a range of conditions will be able to benefit from our new implant, which we’ve named ArtCornea. We have already registered ArtCornea as a trademark,” reports Storsberg.

The ArtCornea's physical properties are much more important than its trademark name of course. Understanding how it works is critical for further developments in the field.

It is based on a polymer with high water-absorbent properties. Specifically, it uses the polymer polyvinylidene difluoride. It will bond with the fluids of the eye, and is flexible enough to contour to whatever shape is required. A coating on the outside of the cornea prevents fluid leak, and allows tears and eye drops to clean the eye without soaking in. A rough coating on the interior side encourages new tissue growth over the cornea, eventually sealing it permanently in place.


An ArtCornea Implant

The researchers aimed to enlarge the optical surface area of the implant in order to improve light penetration beyond what had previously been possible – a tall order. “Once ArtCornea is in place, it is hardly visible, except perhaps for a few stitches. It’s also easy to implant and doesn’t provoke any immune response,” says Storsberg, keen to promote the merits of the prosthetic.

The second cornea is named ACTO-TexKpro. This complex-sounding prosthetic is actually a variation on the ArtCornea above. The difference here being that the base polyvinylidene difluoride is chemically altered before the prosthetic is assembled. A coating of a biologically reactive molecule, details of which were not available, is bonded onto the polymer. A clear silicon structural framework is then pressed to the inside edge. As a result, the molecule bonds the polymer directly to the eye, but leaves the silicon components completely free to move.

The silicon mesh can surround metal wiring, or a transparent polymer capable of carrying current. This means the cornea can flex and move as instructed, whilst remaining bonded to the eye. As yet, a version with working circuitry has not been tested, though the silicon sheaths work exactly as predicted.

The experiments were carried out in collaboration with Dr. Norbert Nass and Dr. Saadettin Sel, Senior consultant ophthalmologist at Martin-Luther-University Halle-Wittenberg. How well TexKpro and ArtCornea are accepted by clinicians as an additional tool at their disposal was first tested by the doctors in the laboratory thereafter in vivo in several rabbits. After a six month healing process, the implanted prostheses were accepted by the rabbits without irritation, clearly and securely anchored within the eye. Tests carried out following the operation showed that the animals tolerated the artificial cornea well.

Prof. Dr. Norbert Schrage will take charge of human clinical trials that will soon commence at the Eye Clinic Cologne-Merheim, also in Germany. Successful trials will likely see both TexKpro and ArtCornea made available around the world.

References

Artificial cornea gives the gift of vision

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