Scientists believe that the humble garden vegetable spinach may provide a possible treatment for some forms of blindness.

Scientists are now working on a technique to extract light-absorbing pigments from the vegetable and add them to nerve cells in the retina. They have stressed that the technique would restore only limited vision in people suffering from colour blindness.

The researchers also believe that it could provide a more effective alternative to electronic retinal implants that are also being developed.

Degenerative diseases of the retina such as retinitis pigmentosa and macular degeneration are among the most common forms of blindness in developed countries. These diseases affect rods and cones, the photoreceptor cells at the back of the retina, but the nerve cells in front of them usually remain intact.

The new technique works by taking advantage of plants' ability to generate an electrical impulse when struck by light, part of the process of photosynthesis.

The researchers isolated the relevant proteins from spinach, and inserted them into the membranes of fatty spheres called lipsomes, which are used to deliver drugs to cells. They found the voltage generated when the liposomes were exposed to light was high enough to make a nerve cell fire.

The modified liposomes were then added to the membranes of eye cancer cells and the cells were found to respond to light. However, much more work is needed to determine whether the technique will actually work when tried on patients.

Scientists are also unsure about the quality of vision that could be restored from stimulating nerve cells alone, as, in normal circumstances, there is a sigificant amount of visual processing that occurs between the photoreceptors and the nerve cells.

"In a normal photoreceptor, a whole series of reactions is needed to amplify the light signal," The BBC quoted Professor Alan Bird, of Moorfields Eye Hospital in London as saying to New Scientist.

"We welcome any new scientific advances in the understanding and treatment of eye conditions. Hopefully in years to come they will lead to medical solutions for many eye diseases. In the meantime over a 100 people a day start to lose their sight in the UK and many of them can be helped with aids and adaptations," added Matthew Athey, of the Royal National Institute for the Blind.