Scientists have been able to restore sight in partially blind rats using a new technique which has been described as a breakthrough for genetic engineering.
The technique may even be capable of extending the human lifespan by slowing down aging, it is claimed.
Researchers at Salk Institute in San Diego, California have discovered how to insert strands of DNA into non-dividing cells - for example in the heart, brain and liver.
The experiment was done on rats with retinitis pigmentosa, which affects one in 4,000 people and causes blindness.
After a few weeks, the rats showed a response to light in tests.
This new technique is called homology-independent targeted integration (HITI), and is based on an earlier method called the CRISPR-Cas9 system.
A researcher said: "We are very excited by the technology we discovered because it’s something that could not be done before."
Another professor warned that the method "does not quite reach the level as hyped in the press release" but added that it is "indeed rather important."