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ATLANTA -- Doyle Stulting, MD, PhD, corneal specialist at Emory Eye Center, will perform the first artificial corneal transplant in the U.S. this week using a new device developed in Australia by Argus Biomedical. Both Emory Eye Center and the Cincinnati Eye Institute have been chosen as the first U.S. sites to use the new synthetic keratoprosthesis (artificial corneal device).
The cornea is the clear window at the front of the eye, providing physical protection to the eye and part of the eye's focusing power required for sight. When the cornea becomes diseased or scarred, the passage of light is impaired, thereby limiting vision.
Synthetic keratoprostheses have been around since the 19th century when a physician named Heusser was the first to place a glass implant in a human patient -- it was retained for some three months. Since then, with the success of many corneal transplants from donor corneas, attention has diverted from keratoprosthesis research. After the realization that not all patients are successfully treated with natural corneal transplants, more emphasis was placed on developing an artificial cornea material.
Various materials have been studied over the last few decades, including poly glyceryl methacrylate and poly methyl methacrylate (PMMA). AlphaCor differs from previous keratoprostheses because of its unique design and biocompatible material, which were developed during thirteen years of research. Although it has been approved by the FDA, the long-term success of AlphaCor has not been fully determined since it is such a new product. Several patients outside of the United States have retained the device for more than two years.
Patients with the new device have had outcomes varying from a slight improvement in vision to regaining the ability to read. The visual potential of the grafted eye depends upon the health of all parts of the eye. If a patient also has glaucoma or retinal problems, his or her vision would still be limited, even if the graft worked perfectly.
AlphaCor is a biocompatible, flexible one-piece artificial cornea designed to replace a scarred or diseased native cornea in patients unsuitable for a corneal graft using human donor tissue. It is a small, flexible plastic disc.
The central part of the disc is clear and acts like a lens, just like the natural cornea. The rim of AlphaCor (the skirt) resembles a sponge and acts to secure the device into place by allowing the patient's own tissue to grow into it and hold it in place.
"This device provides new hope for patients who have been unsuccessful with previous surgical procedures," says Dr. Stulting. The transparent artificial cornea should provide a refractive power similar to that of the human cornea.
The AlphaCor keratoprosthesis is implanted in two stages. In the first stage, the AlphaCor is inserted into the cornea through a small incision at the top of the eye, which is stitched at the end of the operation. At the end of the operation, a flap of tissue from the conjunctiva (outer layer of the "white" of the eye) is used to cover the surface of the front of the eye. This means that the eye does not look normal after the operation, but the conjunctival flap is important because it allows the AlphaCor to heal into place under the protection of this natural bandage.
After three months, the second stage of the operation, a relatively minor one, is performed. At this time, tissue covering the AlphaCor at the front of the eye is removed to allow light to enter. The colored part of the eye (iris) may appear smaller and look blue-gray, because some of the existing cornea will be covered by the white skirt of the AlphaCor. The white of the eye may seem to have larger blood vessels than a normal eye.
"While the long history of synthetic keratoprostheses has not always offered success for all patients, this new device offers advantages that other prostheses do not," says Thomas M. Aaberg, MD, director of the Emory Eye Center. "We are pleased to have been chosen as one of two sites in the country to begin performing this surgery. Our selection is due to the expertise of Dr. Stulting."
"AlphaCor may be the answer for patients who have exhausted other possibilities for restoring their sight," Dr. Stulting says. "This surgery has been performed successfully in Australia for some time now. It is important to remember that the new device will not provide a instant, dramatic restoration of vision. Even after the second stage of the operation, the visual outcome is dependent on several other factors including the overall health of that patient's eye. Nevertheless, this is an exciting new product with great potential," he says.