Scientists believe they have taken a big step forward in their effort to be able to repair damaged nerves.
Optic nerves link the eye to the brain and enable people to see
Researchers at Harvard Medical School say they have had some success trying to regenerate optic nerves in rats.
Writing in the Journal of Neuroscience they said while they were unable to restore sight they achieved three times more regeneration compared to others.
Finding a way to re-grow nerves could lead to cures for a wide range of conditions from blindness to paralysis.
Any injuries that cause damage to nerves tend to be permanent. This is because nerve cells cannot regenerate or repair themselves.
Scientists around the world are working on projects aimed at finding a way to get nerves to re-grow.
One of the reasons nerves are unable to regenerate is that proteins in the outer layer of nerve fibres are programmed to stop re-growth.
Scientists have developed ways to turn these proteins off. However, this has not proved enough to make nerves regenerate.
Dr Larry Benowitz and colleagues tried a two-pronged approach to try to stimulate re-growth.
First, they damaged the lens in the eyes of a group of rats with optic nerve damage. This nerve links the retina to the part of the brain that enables them to see.
Damaging the lens stimulates an immune response - cells travel to the eye and release growth factors to try to repair the damage. This causes nerve fibres to grow into the optic nerve.
Dr Benowitz then used a gene therapy technique to try to boost this growth by injecting a gene designed to turn the proteins that are programmed to stop re-growth off.
"When we combined these two therapies - activating the growth programme in nerve cells and overcoming the inhibitory signalling - we got very dramatic regeneration," said Dr Benowitz.
However, the scientists were unable to get the nerve fibres from the retina and those from the brain to hook up properly.
"It's a mapping problem," said Dr Benowitz. "We have to retain the proper organisation of fibre projections to the brain."
The scientists are now planning further studies to try to overcome this problem.
Kevin Shakesheff, professor of tissue engineering at the University of Nottingham, said scientists were still years away from being able to use these techniques in humans.
"There has been a lot of progress in this area," he told BBC News Online.
"We have taken enough steps forward to indicate we can solve the problem. The science is really exciting.
"However, translating that excitement into clinical applications will take time."