British firm reported early success with procedure that repairs damaged retina Treatment involves growing billions of ‘progenitor’ stem cells in a laboratory Have the ability to transform themselves into other types of cell There is no cure for retinitis pigmentosa, which slowly constricts vision By STEPHEN ADAMS FOR THE MAIL ON SUNDAY PUBLISHED: 20:44 EDT, 13 April 2019 | UPDATED: 02:58 EDT, 14 April 2019 Victims...