B O S T O N, July 12, 2000 -- Eye surgeons — and some of their patients — may soon be seeing more light at the end of the tunnel.
In a pioneering technique, two separate research groups announced today they have successfully restored eyesight to patients with severely damaged corneas, using bioengineered tissue grown in a laboratory and then transplanted onto the eye.
The two teams of researchers — one out of Taiwan reporting in the New England Journal of Medicine and the other from University of California at Davis Medical Center reporting in the journal Cornea — announced they used the technique to improve vision in a total of 15 patients.
How to Grow a Cornea
They first took corneal stem cells, or immature cells that have the ability to generate mature cornea cells, and cultivated them in petri dishes to grow replacement corneas. Then they stitched the newly created corneas onto their patients’ eyes. A significant factor in the researchers’ success was growing the corneas on a scaffold of amniotic tissue, also known as afterbirth material.
“The real power of this technique is where it leads us,” says Dr. IvanSchwab, professor of ophthalmology and a co-author of the Cornea study. Schwab says that the cornea may be the next bio-engineered tissue in a list that already includes skin and cartilage, and could someday include the lungs, bladder, and intestines.
The cornea is the clear, dome-shaped surface that covers the eye and allows light to pass through. When it becomes damaged from disease, such as the rare Stevens-Johnson syndrome; an accident, such as a splash of acid to the face; or an infection, it can become scarred and cloudy, impairing vision.
Prior Donors: Corpses
Conventional corneal transplants, which use donated corneas from a corpse, are the most commonly performed transplant surgery, with almost46,000 done last year, according to the Washington D.C.-based Eye Bank Association of America. Eye banks nationwide collect corneas from donors upon their death, often by registries posted on the back of one’s driver’s licenses, and distribute them to needy patients within a few days.
Around 90 percent of these surgeries are successful, but for a handful of patients, even repeated transplants fail.
Those are usually patients who have sustained damage to or lack their crucial “corneal stem cells,” Schwab says. These cells, which lie deep within the cornea, act as “mother cells,” replacing damaged layers of the cornea with fresh cells, much like the skin. (Corneal stem cells are not the same as the controversial fetal stem cells.)
Without a source of stem cells, a transplanted cornea will not be able replenish itself with healthy new corneal cells to sustain clarity.
Promising New Methods
“For years, we didn’t have anything to offer these patients — we’dtransplant a cornea, it would work for a few weeks, then the blindness would return. It’s devastating,” says Dr. Edward Holland,clinical professor of ophthalmology at the University of Cincinnati and director of cornea services at the Cincinnati Eye Institute. “This [research] takes the stem cell procedure to another level, giving us more options to offer [these] patients.
The ultimate goal, says co-author of the study Dr. Rivkah Isseroff, professor of dermatology and director of the Tissue Bioengineering Laboratory at Davis, is to someday create thousands of bio-engineered corneas that can be pulled off-the-shelf to use on all candidates, eliminating the need for donated corneas entirely.
Last year, Japanese researchers reported in the New England Journal of Medicine that they had transplanted less-structured corneal stem cells onto the cornea, improving vision in half of their patients.
But that method poses some possible risk for the donor providing the tissue, explains Dr. Richard Fisher, CornealDisease Program Director for the National Eye Institute at the NationalInstitute of Health, because it requires a larger number of stem cells to be harvested, while the new method needs just a few cells. The institute is also currently conducting similar research, he says.
In the Taiwanese study, led by Dr. Ray Jui-Fang Tsai and colleagues at Chang Gung Memorial Hospital, five of the six patients, who donated cells from their healthy eye, experienced improvement.
In the Davis study, researchers harvested corneal stem cells from either the patient’s own eye or from a donating family member. In thisstudy, vision was restored to 10 of the 14 patients. All four who received cells from a donor showed improvement, and six of the 10 who received cells collected from their “good” eye also showed improvement.
Dr. Schwab concedes that the two studies were performed on small handful of patients, and have yet to be tested for long-term safety and efficacy. “We can’t predict how long these transplants will continue to work,” he said. “The key is longer term follow-up.”
The new procedure is still highly investigational, Isseroff adds, and will not be widely available in the near future. Her laboratory currently is performing additional research.
But some doctors are more optimistic.“I think the clinical acceptability of these operations will blossomexceptionally quickly,” predicted Dr. Roy Chuck, a professor ofophthalmology and surgeon at the University of California, Irvine.