WASHINGTON — Older corneas seem to transplant as well as younger ones, says a major new study that promises to expand the age of cornea donation to 75.
It may sound surprising. After all, when it comes to most types of transplants, younger organs and tissue are more coveted.
But U.S. government-funded researchers randomly assigned cornea recipients to get either younger or older tissue and found the corneas of both groups survived just as well five years later. The study is published Tuesday in the journal Ophthalmology.
“There was a bias against older tissue,” said Dr. Jonathan Lass of University Hospitals Case Medical Center in Cleveland, one of the study's authors. “This is going to change our view of that.”
The cornea is the clear covering for the front of the eye, important for helping it focus light. More than 39,000 corneal transplants were performed last year, according to the Eye Bank Association of America.
Enough corneas have been available so far for those seeking transplants in the United States. But specialists say there are international shortages, and eye banks fear U.S. supplies will tighten as a result of tougher Food and Drug Administration donor-safety rules that began last summer, increasing interest in using older donors where possible.
Eye banks typically set the age limit for cornea donors at 65, or even younger, although age is not the most important criterion. Donors must be in good health and free of various infections, and the corneas must contain enough of a particular cell type – endothelial – that is responsible for keeping it clear, not cloudy.
To see whether age mattered, the National Eye Institute funded the new work at 80 U.S. medical centres. Researchers recruited about 1,000 people in their 60s and 70s who needed new corneas because of two conditions that destroyed their own – a swelling known as Fuch's dystrophy and a complication of cataract surgery – that together account for almost half of corneal transplants.
Participants were divided into two groups, getting corneas either from donors ages 12 to 65 or from those 66 to 75. Then researchers tracked how often the transplant failed through rejection or turning cloudy. Five years later, 86 per cent of both groups still had successful transplants.
There are two caveats:
• The researchers tested only people 60 and older with conditions that put them at medium risk of transplant failure. About 20 per cent of corneal transplants, however, are in younger adults whose transplants seldom fail. The study does not address whether a 20-year-old would be okay with a 75-year-old cornea.
• Also, Dr. Lass led a closer look at the fate of those endothelial cells responsible for preventing corneas from turning cloudy. The average 30-year-old has about one million of those cells on his or her cornea, but they die off at a rate of about half a per cent a year, he said. For unknown reasons, transplanted corneas rapidly lose more than half their endothelial cells before the density plateaus.
Older transplanted corneas did lose slightly more endothelial cells than did those from younger donors, but the difference was not statistically significant. Nor was there any difference in cloudiness, Lass said. Still, the researchers will continue to track these patients for five more years to see whether the cell loss eventually makes a practical difference.
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