How does the human eye see so many colours?

Scientists in Maryland in the United States are exploring what a lab-grown retina can tell us about how we can see millions of colours. Joining Jonathan to explain more about the research is Robert J. Johnston Jr. Associate Professor in the Department of Biology at Johns Hopkins University.Also joining Jonathan for this week's Newsround is Dr. Susan Kelleher, School of Chemical Sciences, DCU & Dr Fergus McAuliffe, Communications and Engagement Manager, iCRAG.