Artificial Cornea Restores Vision
DURHAM, N.C. -- A severe allergic reaction to a medication robbed Elma Phifer of her vision two decades ago when she was 39. The reaction scarred her corneas and reduced the ability of her eyes to soothe their damaged surfaces by remaining moist.
She came to rely upon family and friends to help her do many of the activities people with normal vision sometimes take for granted. Now, twenty years and several life milestones later, Elma is able to see again, thanks to advances in ophthalmology research.
Physicians at Duke University Eye Center and Harvard have been monitoring her closely following the implantation of an artificial cornea, or keratoprosthesis, into one of her eyes -- restoring her sight in that eye and ultimately helping her regain much of her independence. Phifer is one of several hundred patients nationwide who have received such artificial corneas, which have revolutionized the treatment and care of patients like her.
"I was blind for twenty years in both my eyes," Phifer says. "A regular cornea wouldn't work because of the severity of damage to my corneas. But now my life is more like normal and I can do more things on my own and finally read the things that I want to read."
While many people with cornea damage are eligible to become candidates for standard human cornea transplants, some cannot tolerate donor tissue. The problem is not necessarily tissue rejection –- although in some cases it is -- but rather progressive growth of blood vessels and scar tissue throughout an implanted natural cornea, according to researchers. The new cornea eventually becomes as opaque as the original.
"The cornea is usually just like a clear window in the eye for people to see through, but sometimes the cornea becomes opacified and people can no longer see," said Natalie Afshari, MD, an ophthalmologist specializing in cornea and refractive care at Duke University Eye Center and one of the few surgeons performing the implantation of artificial corneas in the U.S. "We're able to care for some patients by putting in a prosthetic cornea so that they can see out again, and their doctors can see in."
The development of opacity in the cornea is typically the result of inflammation due to disease. Sometimes it is the result of injuries, like damaging chemicals accidentally introduced into the eye, Afshari added.
The artificial cornea is entirely manmade, but does utilize donated corneal tissue, said Afshari. Available devices include a front and back plate, which would first be attached to a donated cornea and then sewn into the recipient's eye. First, the surgeon cuts a hole from the center of the donated cornea so that the "keratoprosthesis" can be inserted into it.
The next step depends on the artificial cornea model being used, but typically includes connecting a front plate to a back plate with the donor cornea tissue sandwiched in between. The surgeon then removes most of the damaged cornea from the patient's eye so that the new prosthesis can be sewn into place using sutures to connect the donor tissue and keratoprosthesis to the patient's remaining corneal tissue.
"Getting an artificial cornea is not an easy ride for the patient," Afshari warns. "We carefully screen each candidate and educate them about the lifetime commitment involved with the keratoprosthesis. Patients require a lot of follow up to make certain the artificial cornea remains structurally sound and healthy."
Because the artificial cornea is a foreign body, it doesn't "heal" the way a wound would and become a part of the body. There could be complications over time, such as thinning of the tissue surrounding the implant or the development of glaucoma due to preexisting imperfections in the draining mechanics of the eye, according to Afshari.
Infections are always a risk, which is why every patient must adhere to a strict daily regimen of antibiotic eye drops. With regular maintenance – including visits to the ophthalmologist at least every three months (more frequently immediately after surgery) – complications can be kept to a minimum, she said. Because of the intensiveness of the lifetime commitment to follow up, the procedure is rarely performed in children.
Many researchers credit Claes Dohlman, MD, chairman emeritus of ophthalmology at Massachusetts Eye and Ear Infirmary and Harvard Medical School as a "father" of modern cornea science. Dohlman has developed the concept of one such keratoprosthesis for more than forty years.
Despite his advancing age of 82, Dohlman has managed to refine a type of artificial cornea widely known as the Boston keratoprosthesis. He has made more than 300 of the devices himself, but holds no financial interest in the success of the artificial cornea.
"We've been fortunate to see gradual improvement in the use of the keratoprosthesis over the years," Dohlman said. "A series of steps have resulted in good long-term retention and stability, as well as good vision, in patients. We will continue to do research and development in this area so that we can make the devices even safer and less expensive in the future."
Both Afshari and Dohlman agree that their hope is for increased use of keratoprosthesis in the third world.
"Worldwide, corneal blindness is a major problem due to infections, fewer physicians and problems with hygiene," says Afshari.
The major hurdle right now, according to Dohlman, is the cost of the procedure. "The health care system in poor countries cannot afford such devices right now, but in a few decades that situation may be different," he said.
It isn't the cost of the device itself that is the problem, according to Dohlman. Rather, it is the prohibitive cost of the frequent post-operative visits, the travel required, the medications and contact lenses used in follow up with the patients.
For now, however, the devices are becoming more available as more doctors are trained in the procedure and care of the post-operative patient. And for people like Elma Phifer, that has made all the difference.