Surgeons in New York have performed the first-ever whole-eye transplant in a human.
The accomplishment, announced on Thursday, was being hailed as a breakthrough even though it was far too soon to know if the patient would ever see through his new left eye.
In the six months since the surgery - which was performed during a partial face transplant - the grafted eye has shown important signs of health including well-functioning blood vessels and a promising-looking retina, according to the surgical team at NYU Langone Health.
"The mere fact that we transplanted an eye is a huge step forward, something that for centuries has been thought about, but it's never been performed," said Dr Eduardo Rodriguez, who led the team.
Until now, doctors have only been able to transplant the cornea, the clear front layer of the eye.
The recipient of the eye, Aaron James, was a 46-year-old military veteran from Arkansas, who survived a work-related high-voltage electrical accident that destroyed the left side of his face, his nose, his mouth and his left eye.
The transplant surgery took 21 hours.
Initially, doctors were just planning to include the eyeball as part of the face transplant for cosmetic reasons, Dr Rodriguez told Reuters news agency.
"If some form of vision restoration occurred, it would be wonderful, but... the goal was for us to perform the technical operation," and have the eyeball survive, Dr Rodriquez added.
The transplanted eye is currently not communicating with the brain through the optic nerve, he said, but will continue to be monitored.
Surgeons harvested adult stem cells from the donor's bone marrow and injected them into the optic nerve during the transplant, hoping they would encourage healing of the connection between the donor and recipient optic nerves.
The transplant opens many new possibilities, Dr Rodriguez said, even if sight is not restored in this case.
Other research teams are developing ways to connect nerve networks in the brain to sightless eyes through insertion of electrodes, for example, to allow vision, he said.
"If we can work with other scientists that are working on other methods of restoring vision or restoring images to the visual cortex, I think we're one step closer," Dr Rodriguez said.
Mr James, who retained vision in his right eye following his accident, knew he might not regain vision in the transplanted left eye.
The doctors "never expected it to work at all, and they told me that from the get-go," he said.
"I told them, 'even if I can't see... maybe at least you all can learn something to help the next person.' That's how you get started," he said. "Hopefully this opens up a new path."
Mr James might still regain sight in the transplanted eye, Dr Rodriguez said.
"I don't think anyone can claim that he will see. But by the same token, they can't claim that he will not see," Dr Rodriguez said. "At this point, I think we're pretty happy with the result that we were able to achieve with a very technically demanding operation."
