Astronauts who spend more than a month in space are at risk of potentially serious damage to their eyes and brain, a new study suggests.
A team led by Larry Kramer of the University of Texas Health Science Center conducted magnetic resonance imaging (MRI) scans on 27 NASA astronauts who each spent at least 30 days in orbit. The findings appear in the journal Radiology.
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According to The Guardian, the researchers found a pattern of deformities in the crew's eyeballs, optic nerves and pituitary glands. The complications are similar to those associated with intracranial hypertension, a rare medical condition in which excess pressure builds up within the skull.
Nine of the astronauts studied showed expansion of the space surrounding the optic nerve that's normally filled with cerebrospinal fluid, six displayed flattening at the back of their eyeballs, and four had a bulging optical nerve, the BBC reported.
Three of them displayed changes to their pituitary gland – which is located between the optic nerves and secretes hormones that regulate functions including growth, sex organs and the thyroid gland – and its connection to the brain.
The changes may be explained by the absence of gravity in space, ABC News suggested:
"On Earth, the human body is attuned to gravity, with the heart pumping to keep fluids from pooling in the legs. In weightlessness, the body keeps forcing fluids upward – even though there's no gravity to pull them down. So most astronauts report a feeling of fullness in the head."
Some of the effects are reversible, but some seem to translate into permanent changes in astronauts' eyesight, the head of NASA's Astronaut Office, Peggy Whitson, told ABC. Spacefarers have reported problems focusing their eyes, finding themselves in need of glasses having previously enjoyed 20/20 vision. A few have reportedly been advised against flying in space or piloting aeroplanes.
This latest study raises particular questions as to the safety of longer-term space missions such a flight to Mars, which would likely involve astronauts spending more than a year in space, the BBC said.
William J. Tarver, head of the flight medecine clinic at NASA's Johnson Space Center, said the space agency was aware of the problem and had placed it "high on its list of human risks," Space.com reported. Its specialists are looking into the symptoms, which remain unexplained, Tarver said.
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