Transplants using eye tissue from aborted foetuses appear to have improved the sight of two out of four patients involved, say scientists.

It is too early to say whether the improvement will last, but the experts involved are encouraged by the success so far.

The transplants were carried out at the Doheny Eye Institute in Los Angeles.

The patients involved had advanced retinitis pigmentosa, a heriditary disease which causes degeneration of the retina, the layers of cells at the back of the eye that receive light.

The surgery involved inserting two-millimetre squares of foetal tissue to partly replace those lost to the disease.

The secret of the operation, say the researchers, is the implantation of complete chunks of tissue, which maintains vital connections between transplanted retinal cells.

One of the patients, Elisabeth Bryant, who is 63, could see virtually nothing before treatment.

She said: "Now I can see people's eyes, noses and mouths when they are sitting across the room from me."

Caution urged

However, Professor John Greenwood at the Institute of Ophthalmology in London said that it was possible that the improvements might not be genuine.

An effect called the "rescue effect" reacts to any injury or disturbance to the eye by flooding the area with growth factors which may revive damaged or diseased cells.

He said: "Any surgical intervention has the possibility of inducing short-term improvements."

The team now want to use the technique to help people with less advanced retinitis pigmentosa, as they believe the transplants should be more effective if given at an earlier stage.