CRISPR, the genome editing tool, has improved eyesight in rats with damaged vision by precisely inserting new DNA into a defective gene, The Guardian reports. Importantly, the study shows that CRISPR can work in the nondividing cells that form most adult tissue. The “unprecedented” finding used a novel pathway to “knock in” the DNA that typically is used to cripple, or knock out, genes, the scientists report online today in Nature. Other researchers caution that the knockin did not have particularly high efficiency, which will make it difficult to apply in humans. But with further improvements, they add, CRISPR may one day be a useful way of adding genes to nondividing cells, for basic research and eventually for gene therapy to treat otherwise incurable diseases like cystic fibrosis and muscular dystrophy.