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 has been found to erode the vision of some astronauts who have spent months aboard the International Space Station. 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. The disorder, similar to a condition called papilledema, is thought to be caused by increased spinal-fluid pressure on the head and eyes due to microgravity, although the exact cause is uncertain. NASA's chief health and medical officer declined to discuss specific cases but acknowledged at least one astronaut never regained normal vision.
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