For the first time researchers have successfully repaired the damaged retina. The technique restored vision in mice that had been genetically programmed to mimic various forms of human vision loss. Writing in this week's edition of the journal Nature, UCL's Rachel Pearson, Jane Sowden and colleagues collected cells from the developing retina of a donor animal and injected them into an adult recipient. By labelling the donor cells with a glowing green protein borrowed from a jellyfish the researchers were able to chart the progress of the injected cells. After three weeks they had migrated to a region of the retina called the outer nuclear layer and turned into photoreceptors, the rods which convert light into electrical signals that the brain can understand. Shining a light into the eye caused the pupil to constrict, proving that the new cells had correctly wired themselves up. The other eye, which had been left unrepaired as a control, didn't respond to light, proving that the injected cells must be responsible for the effect. Other researchers have previously tried to achieve this feat using stem cells, but without success; the critical breakthrough in this study was the time at which the donor cells were harvested, which was just as the rods were beginning to form. These cells seem to intuitively know how to integrate themselves into the retina in the correct location. "This study proves, for the first time, that repair of the mammalian retina is possible. Now we just need to find a way to produce the cells needed to do it", says study author Jane Sowden.