NASA has discovered that 7 out of 10 astronauts returning from the International Space Station have been unable to see clearly, with vision problems that can last for years! As we prepare for multi year Mars missions, scientists are racing to solve this mysterious "space blindness" before it derails humanity's greatest journey. It seems the cause could be as simple as the effects of weightlessness and the distribution of fluids around the body. Thankfully, it seems there are some possible solutions to what could become one of our greatest health challenges as we reach out further among the planets.