A new study has confirmed that astronauts risk brain and vision abnormalities as a result of spending time in space.
Magnetic resonance imaging (MRI) of the eyes and brains of 27 experienced astronauts revealed optical abnormalities similar to those of intracranial hypertension of unknown cause - a potentially serious condition in which pressure builds within the skull.
The astronauts had been exposed to microgravity, or zero gravity, for an average of 108 days while on space shuttle missions or the International Space Station. Eight of the 27 underwent a second MRI exam after a second space mission that lasted an average of 39 days.
"The MRI findings revealed various combinations of abnormalities following both short- and long-term cumulative exposure to microgravity also seen with idiopathic intracranial hypertension," says Larry A Kramer, of the 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."
Among astronauts with more than 30 days total exposure to microgravity, findings included expansion of the cerebral spinal fluid space surrounding the optic nerve in a third, flattening of the rear of the eyeball in 22 percent, bulging of the optic nerve in 15 percent and changes in the pituitary gland and its connection to the brain in 11 percent.
"Microgravity-induced intracranial hypertension represents a hypothetical risk factor and a potential limitation to long-duration space travel," says Kramer.
William J Tarver, chief of the flight medicine clinic at NASA/Johnson Space Center, acknowledges that visual problems have been observed before in ISS astronauts.
"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," he says.