Scientists long have known that extended spaceflight is bad for astronauts' bones and muscles, but new evidence shows it may cause vision problems as well. In a new study, researchers used magnetic resonance imaging (MRI) to study the eyes and brains of 27 astronauts who spent an average of 108 days in space aboard the National Aeronautics and Space Administration (NASA) space shuttles or the International Space Station. The researchers found optical abnormalities similar to those that can occur in patients with intracranial hypertension, a potentially serious condition in which pressure builds up inside the skull. "The MRI findings revealed various combinations of abnormalities following both short- and long-term cumulative exposure to microgravity also seen with ... intracranial hypertension," said study lead author Larry Kramer, a professor of diagnostic and interventional imaging at the University of Texas Medical School. "These changes that occur during exposure to microgravity may help scientists to better understand the mechanisms responsible for intracranial hypertension in non-space-traveling patients," Kramer said. Astronauts long have known that six-month periods aboard the space station can cause bone mineral loss and muscle atrophy. In fact, they exercise rigorously in orbit to avoid the worst of the effects. The new study suggests that spaceflyers' eyes and brains may be at risk as well. "Microgravity-induced intracranial hypertension represents a hypothetical risk factor and a potential limitation to long-duration space travel," Kramer said. NASA medical officials have noted vision changes in some space-station astronauts, though nothing serious enough to ground any spaceflyers. "NASA has placed this problem high on its list of human risks, has initiated a comprehensive program to study its mechanisms and implications, and will continue to closely monitor the situation," said William Tarver, the chief of the flight-medicine clinic at Johnson Space Center in Houston.
