Scientists say they have completely regenerated damaged optic nerves from the eye to the brain in mice.
Damage to the optic nerve is permanent
Experts say the work offers new hope for people with glaucoma, a condition in which raised pressure destroys the optic nerve.
It may also eventually help people with spinal cord and other injuries of the central nervous system, they say.
The research, by Boston's Schepens Eye Research Institute, is published in the Journal of Cell Science.
Lead researcher Dr Dong Feng Chen said: "This is the closest science has come to regenerating so many nerve fibres over a long distance to reach their targets, and to repair a nerve previously considered irreparably damaged."
Many tissues in the body continually renew themselves if injured.
But the optic nerve, along with other tissues of the central nervous system, does not have this ability, so damage is permanent.
Switched off gene
The Schepens team had already discovered that the optic nerve's inability to regenerate was linked to the fact that a key gene called BCL-2 is switched off.
They also believed the regeneration process was blocked by the creation, shortly after birth, of a scar on the brain by specialised glial cells.
These cells have many functions in the brain, one of which is to create this kind of scar tissue.
Potentially the scar puts up a physical as well as molecular barrier to regeneration.
The researchers bred mice in which the BCL-2 gene was always turned on.
They found the animals were able to regenerate optic nerve tissue quickly - but only when they were young, and before their brains had developed the glial scar.
Once the scar had formed, regeneration failed again.
The researchers next bred mice in which not only was the BCL-2 gene turned on, but the ability to produce a glial scar was reduced.
This time even the older animals were able to regenerate damaged optic nerve tissue.
Dr Chen said: "We could see that at least 40% of the optic nerve had been restored, but we believe that an even higher percentage was actually regenerated."
The next step will be to determine whether the regenerated nerves were functional.
The researchers believe the combined BCL-2 and scar prevention technique could work to regenerate other central nervous system tissue - increasing the possibility that spinal cord patients could walk again.
Retired Lieutenant Colonel Robert Read, of the US Department of Defense, said the research had tremendous potential to help wounded service personnel.
"Fifteen percent of all wartime injuries include the eye and those with optic nerve trauma are the most grave," he said.
"Today's medicine has little effective treatment to offer and blindness is often the end result."
Professor Peng Tee Khaw, an expert in glaucoma at Moorfields Eye Hospital, in London, told the BBC News website the research was potentially exciting.
However, he said while a young mouse had to regenerate a damaged nerve across only a few millimetres, for a human the distance could be tens of centimetres.
David Wright, chief executive of the International Glaucoma Association, said treatments for the condition currently focused on trying to prevent further damage to the optic nerve.
"The regeneration of optic nerve fibres has always been considered impossible due to the fundamental difference between these nerves, which are essentially an outgrowth of the brain itself and the other sensory and motor nerve fibres which occur throughout the body," he said.
"This research paper reports what I believe to be the first instance of optic nerve fibre regeneration.
"While it is obviously a long way from research in mice to a technique that may be applicable to people with glaucoma or spinal cord injuries, it certainly holds the promise that further research could lead to a technique that might revolutionise the treatment of people with serious visual impairment or even blindness from glaucoma."