Córnea Artificial Ofrece Mejores Resultados para Infantes, Algunos son Pacientes CiegosContributed by: Anonymous · Views: 1,423
Contributed by: Anonymous · November 14, 2006 @ 09:58 AM MST · Views: 1,423
Artificial Cornea Offers Better Results for Infants, Some Blind PatientsNew Plastic Device Cuts Down on Repeat Surgeries, Infections, and Improves Vision
Infants and adults who are blind due to a cloudy or damaged cornea are seeing some remarkable results thanks to a new version of an artificial implant that takes the place of the cornea, the clear covering of the eye that serves as our window on the world.
The results of operations involving the first infants and children in the world to receive the device, performed by physicians at the University of Rochester Eye Institute and a colleague at Johns Hopkins University, are being announced at the annual meeting of the American Academy of Ophthalmology in Las Vegas.
The results, though based on a small number of patients, point to a new option for dramatically improving the vision of a group of people for whom traditional cornea transplants usually fail. The new work, supported in part by Research to Prevent Blindness, mirrors similar success in adult patients that was reported by the Rochester team this summer.
The latest study involved a plastic device known as the Boston Keratoprosthesis, an artificial cornea used by just a few doctors in the world to treat children who can’t see because their corneas are opaque. Usually the cornea serves as a clear window, but in some children, it’s as if a dark, opaque shade has been pulled over that window due to conditions like glaucoma, congenital anomalies, or previous cornea surgeries.
In Las Vegas, Rochester doctors showed that the Boston device seems to be very effective in infants and children from six weeks to 13 years old, restoring vision and putting an end to long cycles of eye operations that dog many patients who have needed a cornea transplant.
The study included 17 children who collectively had been through more than 100 surgical procedures, including 39 traditional cornea transplants that had failed, before the latest implant. In the new study, two of the children received another type of artificial implant that failed, while 15 received the Boston device. All 15 of those children recovered some vision, sometimes remarkably so, and none had an infection or a problem with the implant. In the seven cases where the child was 4 years old or older and could explain to some degree how much he or she could see, every child could at least see fingers held at an arm’s length, and some children improved to 20/30 vision.
“Finally, we seem to have a method in hand to improve the vision of these children, many of whom have endured several surgeries that have failed,” said James Aquavella, M.D., the University of Rochester ophthalmologist who is pioneering the use of the implant and who operated on most of the children in the study.
“These are children for whom, until now, there really has not been a good option. While this study is somewhat small and these children need to be followed for more time, we have decided that for now this is the treatment of choice for children who have corneas that are cloudy or opaque. It’s either do this, or do nothing,” he added.
Aquavella is discussing the work at the Cornea Society meeting in Las Vegas, while pediatric ophthalmologist Matthew Gearinger, M.D., of the Eye Institute is presenting at AAO. The study overall included 23 separate procedures on 17 patients; most of the procedures were performed by Aquavella in Rochester, while four were done by Esen K. Akpek, M.D., of the Wilmer Eye Institute at Johns Hopkins University.
The work addresses vision problems in some of the toughest-to-treat children. Oftentimes, in addition to needing a new cornea, these children require treatment for other ongoing conditions like glaucoma, cataracts, and retinopathy. And in children, successful transplants can be more difficult to perform than in adults.
“The vibrancy of a child’s immune system has been one of the main reasons why cornea transplants haven’t worked well in children,” said Gearinger. “The risk of rejection is huge, and it just goes up with every subsequent operation. But with the plastic implant, these kids are looking great.
“The timing is crucial, because if a child hasn’t seen out of an eye for a few years, and then suddenly vision in the eye is fixed, the brain doesn’t know what to do with that information,” Gearinger added. “If the brain has been deprived of vision at an early age, it’s permanently affected, no matter how well the eye is focused later on. That’s why it’s crucial to intervene early on.”
So far in Rochester, approximately 25 infants and children have been outfitted with the Boston device since 2003, including children from France and the United Kingdom whose families sought out Aquavella for treatment. The youngest child to receive the implant was 5 weeks old.
Along with his work in children, Aquavella has implanted the device in more than 100 adults from around the nation in the last three years and is now performing about one or two of the procedures each week.
Earlier this year, in a publication in Cornea: The Journal of Cornea and External Disease, Aquavella evaluated results of the Boston device in adults compared to an older device. In his study, a group of 25 patients who have received the plastic device since 2003 had no infections in the first year after surgery, and not a single one has needed to undergo another operation due to complications. This is in marked contrast to a group of 31 patients whom he also operated on, using a different technology, nearly 30 years ago. That group underwent a total of 51 additional operations to fix problems such as the implant popping out of the eye, and about one in three patients had a subsequent eye infection.
“The change is absolutely dramatic,” said Aquavella. “Thirty years ago, our hope was that after the operation, patients could see well enough to see some movement and care for themselves for a few years. That was considered success. Now many of our patients are out driving cars, riding horses, and leading active lives, and several have near-normal vision soon after the operation.”
While natural corneas from donors continue to be the main source for transplants, such tissue can trigger a variety of problems, including rejection by the immune system as well as difficulties such as scarring from infections or out-of-control growth of blood vessels. For years doctors have worked to develop an artificial cornea, known as a keratoprosthesis or a “K-Pro,” that bypasses some of the problems that come about with natural tissue.
Aquavella himself stopped doing procedures with artificial implants for several years because of the poor results and high rates of complication. Meanwhile, Aquavella’s former mentor, Claes Dohlman, M.D., of the Massachusetts Eye and Ear Infirmary, was evaluating new types of designs, eventually devoting decades to the project. When Dohlman unveiled a new design a few years ago, Aquavella tried it in several patients.
“Immediately we noticed an enormous difference,” said Aquavella, one of the world’s leading corneal surgeons. “After traditional cornea transplant surgery, usually it takes a year or 18 months for the patient to see well. With this device, within the first week or so, the patient will see as well as they’re ever going to see. While astigmatism often limits the quality of vision with traditional corneal transplant, this new device produces no astigmatism and a clearer image.”
Aquavella evaluated the recent progress in an unusual study, with himself serving as the common point as he compared the outcomes of 31 patients who received artificial corneas in procedures he performed from 1975 to 1981, to the outcomes of 25 patients who received the newer implant from 2003 to 2005. About half the patients in each group eventually recovered vision of 20/200 or better, with the newer group experiencing far fewer complications and infections. In both groups, though, Aquavella said the quality of the patient’s eyesight was often limited by other deficiencies in the eye.
The partnership between Aquavella and Dohlman stretches back nearly half a century. Aquavella was the first doctor in the nation to serve a fellowship focused specifically in cornea surgery, in the early 1960s; he served under Dohlman, a leading figure in corneal science. The two physicians have worked together since, with Dohlman developing better artificial corneas, and Aquavella doing cornea transplants on thousands of patients. Together the pair has logged more than 100 years treating patients blinded by severe cornea disease or injury and creating new ways to treat them.
Among the efforts has been a series of designs for artificial corneas, which in adults are primarily for patients whose previous transplants using traditional tissue have failed, oftentimes because of rejection by the immune system.
Dohlman’s latest implant, the Boston Keratoprosthesis used in the recent studies of infants and adults, is about the size of a contact lens and is sewn into the patient’s eyeball with a piece of donor tissue to hold the implant in place, like a washer. The device is made of a newer type of plastic that allows nutrients to enter the eye more quickly than previous designs. The latest procedure also includes a large contact lens placed over the cornea to help protect it from inflammation and scarring. After the procedure patients use antibiotic eye drops each day for the rest of their lives to prevent infection.
The current procedure is less invasive and cumbersome than some other efforts to implant artificial corneas. In the procedure carried out by Aquavella and other surgeons 30 years ago, physicians would remove a piece of leg bone from the patient and place the bone over the eye to help it heal and to protect it. And in another procedure still common today, physicians enshroud the implant in a patient’s tooth socket, stash the mix in the patient’s cheek for a few months to encourage the growth of new tissue – all in an effort to help a patient’s body accept the new device– and then implant the whole structure in the patient’s eye
Traditional corneas still constitute the great majority of transplants, with approximately 40,000 performed in the United States each year. About half the patients need a new cornea because of complications after cataract surgery, while others have conditions like severe eye infections, severely misshapen corneas, or congenital causes like glaucoma that have damaged the cornea. Aquavella said the advent of a trouble-free artificial cornea or K-Pro is good news for those patients.
“In the past, people have thought that keratoprosthesis, or an artificial cornea, was only for patients who were in disastrous circumstances, who couldn’t receive a cornea the traditional way,” Aquavella said. “Now, because of improvements in materials and in surgical technique, this should be the first choice for some patients.”
In addition to Aquavella, Gearinger and Akpek, others taking part in the research include Rochester doctors Ying Qian, M.D.; Gregory J. McCormick, M.D.; and Jayachandra Reddy Palakuru, M.D.
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