Every year, corneal transplants improve or even restore eyesight for 40,000 people in the United States. But for thousands of others, the operations don’t work. In many of these patients, damage to the cornea—the clear windshield covering the eye—is just too severe for the traditional approach.
Scientists now have grown corneal tissue in laboratory dishes and successfully transplanted it onto the injured eyes of such patients, some of whom couldn’t see beyond a few feet before the operations. This procedure, which uses stem cells in the cornea to replenish worn-out cells, improved sight in most patients.
A team of researchers in Taiwan and another at the University of California, Davis treated people who had at least one damaged cornea. Both teams used snippets of corneal tissue from the healthy eye of the patient or from a living donor. They cultured this tissue with nutrients on a razor-thin sheet of amniotic membrane, which the scientists salvage from placentas after childbirth.
The sheets act as scaffolding on which new corneal cells grow. It takes 2 to 4 weeks for these cells to proliferate into patches up to 3 centimeters in diameter and a few cell layers thick.
The researchers replace the damaged cornea of each patient with this sheet of new tissue, then cover the eye with a porous contact lens that serves as a transparent bandage. The amniotic membrane is later absorbed by cells in the cornea.
The Taiwanese researchers, led by ophthalmologist Ray Jui-Fang Tsai of Chang Gung Memorial Hospital in Taoyuan, report in the July 13 New England Journal of Medicine that the visual acuity in five of their six patients has improved, corrected with eyeglasses, from an average of 20/112 to 20/45 after 15 months. The change restored functional vision. The sixth patient, who was nearly blind in one eye from a chemical burn, recovered 20/200 vision in that eye, a level at which a person can make out the “E” at the top of the eye chart from 20 feet.
The California researchers successfully restored some sight in 10 of 14 patients’ damaged eyes. Roughly 13 months after surgery, 6 of 10 who received a cornea cultured from cells taken from their good eye had improved. Four other patients who received corneas grown from eye cells of a close relative also registered significant gains, says study coauthor R. Rivkah Isseroff, a cell biologist at Davis. Before the operation, these four patients could only distinguish fingers at arm’s length, at best. Afterwards, their corrected vision improved to a range between 20/60 and 20/200, the researchers report in the July Cornea.
No one donating snippets of cornea cells suffered complications in either study. In routine corneal transplants, the deformed or scarred “button” of cornea in the center of the eye is removed and replaced by a matching piece of clear, healthy cornea taken from a dead donor. These patients don’t receive any stem cells, which reside where the cornea meets the white of the eye.
If the recipient harbors adequate homegrown stem cells, the eye gradually accepts the new tissue and regenerates corneal cells. However, if the patient’s eye lacks stem cells, or if immune rejection ensues, then the transplant fails. That happens at least one-fifth of the time, says Timothy P. Fleming, a cell biologist at Washington University School of Medicine in St. Louis.
Both research teams chose patients for whom traditional corneal transplants had failed or who were poor candidates for that surgery.
The new procedure shows promise for people who have caustic burns to their eyes, damage from long-term contact lens abuse, chronic inflammation of the cornea, or Stevens-Johnson disease, which can cause blindness, Tsai says.
The studies suggest that “one could . . . establish a library of cultured [corneal] cells suited to various immune-related needs of recipients,” says Kenneth R. Kenyon of Harvard Medical School in Boston. “This is where the extension of this type of work could go.”