People suffering vision loss may one day have new corneas and lenses grown from their own cells, and be spared the invasive transplants required today, according to research papers published in the journal Nature.
A research team said they had managed to engineer corneas from stem cells in the lab, while another regenerated lenses inside the human eye.
"These two studies illustrate the remarkable regenerative and therapeutic potential of stem cells," wrote Julie Daniels of the University College London Institute of Opthalmology, who analyzed the work in a paper also carried by Nature.
To work perfectly, the cornea and lens must be absolutely transparent. Sometimes, due to disease or aging, these become opaque and need to be replaced with a donor or artificial transplant. Such procedures are not foolproof, and in some cases the transplants are rejected by the recipient's body.
Stem cells offer hope as they can be taken from the patient's own body, thereby limiting rejection risk. Stem cells are primitive cells that, as they mature, differentiate into the various specialized cells that make up the different organs.
Until a few years ago, the only way to obtain stem cells was to harvest them from human embryos, a controversial practice as it required the destruction of the embryo.
But now scientists have developed induced pluripotent stem cells, or iPSCs, which are mature cells turned back to an earlier, versatile state from which they can re-diversify.
For the first study, scientists in the United States and China developed a new way to remove and replace damaged eye lenses in people with cataracts. The current surgical method leaves a large incision which can easily become inflamed.
In the new procedure, a team extracted the lens through a much smaller hole than the existing procedure requires, and also left behind many more naturally-occurring, lens-creating stem cells called LECs. These were stimulated into building a new lens.
The method was successful in rabbits and macaques, and later in 12 human children.
"Each year, more than 20 million cataract patients worldwide undergo treatment with less extraction and artificial... implantation," wrote the study authors.
Yet the current procedure "inadvertently destroys the integrity of the lens capsule and the very LECs that hold the regenerative key to lens restoration," they said.
"(W)e have developed a new, minimally invasive surgical method that allows regeneration of a functional lens."
Cataracts are the leading cause of blindness in the world.
Dusko Ilic, a lecturer in stem cell science at King's College London, said the study was "one of the finest achievements in the field of regenerative medicine until now."
For the second paper, researchers in Japan and Cardiff used human iPSCs to create eye cells which they grew into healthy corneas in a lab dish and implanted into rabbits.
This achievement, too, was hailed, though experts pointed out the method remained too expensive and experimental to be a viable treatment just yet.
"Whether either of the reported therapies will lead to cornea or lens transparency that can be maintained in the long term remains uncertain," wrote Daniels.