Much like other parts of the body, parts of the eye can be transplanted. Unfortunately, there are cornea shortages around the world. In order to better this situation, UC Davis’ Dr. Mark Mannis and his multicenter research team conducted 10 years of fieldwork that compared the longevity of corneas from older donors to corneas from younger donors in transplant recipients.
“The study confirmed the fact that older tissue functions just as well as younger tissue,” said Mannis, UC Davis professor, chair of the UC Davis Eye Center and co-principal investigator of the cornea study.
This is the largest corneal study ever done. For 10 years it compared the corneal clarity of donors ages 66 and above to donors under the age of 66. At the five-year mark the success rate of younger tissue to older tissue was the same.
“Whether it was a younger donor or an older donor we saw an 86 percent chance of success,” Mannis said.
At 10 years after the transplants, the results were mostly the same. The only differences were seen at the extreme ends of the study; patients given corneas under the age of 30 had slightly better results while those given corneas over the age of 75 were slightly worse. Those in the 40 to 60 year range had virtually identical results.
“[The cornea is] the front surface of the eye, and is really important for our vision. It functions like the lens of a camera: it does a whole lot for focusing the image correctly on the retina (which is like the film in a camera; where the light gets turned into signals for the brain to interpret). So, to do those things, it has to be very clear and smooth, and have the correct curvature,” said Ken Britten, professor of neurobiology, physiology and behavior, in an email interview.
Due to its location at the very forefront of the eye, it can be subject to damage.
“Anytime you have a body part that’s exposed to the environment it is susceptible to all kinds of injury … Its shape can become deformed or become opaque and the light rays can’t get through. But anything that would either deform the image or block the image from being projected to the back of the retina is a reason to have the cornea replaced,” said Martin Usrey, professor of neurology.
When it is damaged, sight can become severely blurry and things like reading can become nearly impossible. Also, pain or discomfort can be a problem since pain fibers are densely packed in the cornea, according to Usrey.
The donor shortages have origins in many practices doctors use to choose corneas for their patients. Age matching is the process where a doctor tries to match the patient’s age to that of the donor.
“Surgeons were concerned that older donor tissue might not function as well as younger donor tissue,” Mannis said.
Both of these practices are unnecessary according to the study’s findings and create a severe deficit in available corneas.
As one could imagine, corneas are hard to come by since they can only be harvested from deceased donors. The pool of eligible donors also diminishes if they have any disease that could potentially be transferred to the recipient. Older donors are much more common so favoritism toward the rare, young donors diminish the availability for younger transplant recipients who will need their new corneas to last their lifetime.
The U.S. supplies all the corneas for domestic surgeries as well as exporting them for many surgeries abroad. If doctors continue to only depend on younger corneas, there will not be enough to meet the needs of the American public, let alone the world. Thus, these findings have international benefits; they are meant to “debunk some of the myth about what tissue is suitable and to help make tissue more available for transplants all over the world,” Mannis said.
Corneal transplants have been around for over 100 years and it can greatly improve the quality of life of the transplant recipient. They are a very special tissue to replace and are rarely rejected by the recipient’s immune system.
“I think corneal transplants are wonderful … The procedure has restored sight in countless numbers of people,” said Arnie Sillman, emeritus professor in the Department of Neurobiology, Physiology and Behavior.
This study’s findings can even further expand the reach of corneal transplants and sight to more people.
If someone opts to donate their corneas at death, they can have a donor sticker put on their driver’s license. They must also inform their family of their wishes. This is because eye banks need family consent in order to harvest the tissue, whether someone has a donor sticker or not.