Scientists in Britain have restored sight to blind mice by transplanting stem cells at a key stage of development into damaged retinas, the journal Nature reports on Thursday. The feat is being hailed as a breakthrough in stem cell technology, which has suffered from many false dawns. Their work focusses on replenishment of rod-like photoreceptor cells on the retina which pick up light and send a signal to the brain via the optic nerve. Photoreceptors are like the pixels in a TV or computer screen, but many times more plentiful