Humans appear to have true, self-renewing retinal stem cells. Brenda Coles and her colleagues at the University of Toronto minced up eyes donated from deceased people and cultured the cells. They found that about one in 500 cells from the black ring around the iris could divide indefinitely and adopt the full variety of retinal cell types. (Past studies had found retinal stem cells of limited capacity, unable to divide indefinitely and transforming into only a few cell types.) When transplanted into embryonic mice or chicks, the stem cells turned into cells of the type found in that animal at that stage of development. Their next experiment, Coles says, is to transplant the cells into mice with degenerating retinas to see if they restore function and later to figure out how to activate and manipulate them. See the November 2 Proceedings of the National Academy of Sciences USA.