EurekAlert! notes an accidental discovery: "In a study in rats, neural progenitor cells derived from human fetal stem cells have been shown to protect the vision of animals with degenerative eye disease similar to the kinds of diseases that afflict humans ... The finding that the brain cells protected the cells in the eye was a surprise ... The neural progenitor cells, which arise from stem cells and further differentiate into different types of cells found in the central nervous system, were being tested for their ability to deliver another agent, a growth factor that has been shown to be effective in treating some types of degenerative disease. ... On their own, they were able to support retinal cells and keep them alive. We didn't expect that at all. We've used a number of different cell types from different sources and these have given us the best results we've ever got. ... How the cells act to preserve the deteriorating eye cells remains unknown ... Like all cells, neural progenitor cells do many things and secrete many different types of chemicals that may influence the cells around them."