A novel artificial cornea that adheres to eye cells could bring new hope to the estimated 10 million people worldwide who are blind because of corneal damage or disease. The new design should relieve some of the complications–such as tissue rejection–that often accompany corneal transplants or the implantation of existing artificial corneas. The device, which has been extensively tested in rabbits, is expected to be in clinical trials early next year.
Existing artificial corneas are held in place solely by sutures, which leaves patients susceptible to inflammation, infection, and even losing an eye, says John Huang, an assistant professor in the Department of Ophthalmology and Visual Science at the Yale University School of Medicine. “We certainly need a better way to get an artificial cornea in place,” he says.
Today’s implants are large–“just one big piece of plastic,” says Huang–but they have to be, to prevent excess corneal tissue from growing over them and impairing patients’ vision. In the long run, however, their size can be problematic: the difficulty of stitching them into place increases the chance that the surgical wound will reopen or become inflamed, says Huang. The implants are also too big to be stitched directly to eye tissue. Instead, they are built around a layer of corneal tissue extracted from a donor, which acts as a bridge to the recipient’s tissue.
The key to the new implant is a protein-coated polymer developed by researchers at the Fraunhofer Institute, in Postdam, Germany; the group is led by Joachim Storsberg, head of the institute’s medical-polymer research unit. The polymer, which is commercially available, repels water, so it won’t absorb tear-duct secretions that could cause it to swell. It also prohibits cell growth, so natural tissue will not cloud it over.
This is an advantage at the center of the implant, which needs to remain clear. But it would be a disadvantage at the edges, which need to bind to existing corneal tissue. So the outer rim of the cornea is coated with a protein that attracts existing corneal cells. “This special coating allows the implant to firmly connect with the cells [of the natural cornea],” says Storsberg. Although the new implant still has to be sutured into place, that firm connection helps prevent the kind of infection that posed problems in earlier implants. The protein was also chosen for its ability to withstand the thermal sterilization process that the device must go through to meet medical-safety requirements.
And because the German researchers’ polymer prevents cell growth, the implant can be made small enough to be sutured directly to the eye. As a consequence, the layer of donor tissue is unnecessary. This is a “huge advantage,” says Huang. Donor corneal tissue is in short supply, so existing implants end up using tissue of poor quality.