Astronauts risk blurred vision after months in space Los Angeles Times

If NASA ever wants to send astronauts to Mars, it first must solve a problem that has nothing to do with rockets or radiation exposure.
A newly discovered eye condition found to erode the vision of some astronauts who have spent months aboard the International Space Station has doctors worried that future explorers could go blind by the end of long missions, such as a multiyear trip to Mars.
Although blindness is the worst-case scenario, the threat of blurred vision is enough that NASA has asked scores of researchers to study the issue and has put special eyeglasses on the space station to help those affected.