Scientists have succeeded in regenerating functional retinal cells in adult mice. Like humans, mice cannot repair damage to their retinas. However, because zebrafish can, researchers created in mice a version of the fish gene responsible for turning Muller glia into retinal cells if eye injury occurs. Researchers found way to prevent the gene’s activity from being blocked as the mice got older. The new interneurons formed connections and reacted normally to signals from light-detecting cells in the retina.