The visual problems that affect astronauts on long space missions is related to volume changes in the clear fluid which is found around the brain and spinal cord, say researchers.
According to the study scheduled to be presented at the annual meeting of the Radiological Society of North America (RSNA) on Monday, flight surgeons and scientists at the US space agency NASA said astronauts had blurry vision.
Tests revealed that among several other structural changes, flattening at the back of their eyeballs and inflammation of the head of their optic nerves was the cause of the impairment.
The syndrome, known as visual impairment intracranial pressure (VIIP), was reported in nearly two-thirds of astronauts after long-duration missions aboard the International Space Station (ISS).
"People initially did not know what to make of it, and by 2010 there was growing concern as it became apparent that some of the astronauts had severe structural changes that were not fully reversible upon return to Earth," said study lead author Noam Alperin.
The team led by Dr Alperin, professor at University of Miami's Miller School of Medicine, found that cerebrospinal fluid (CSF) -- the clear fluid that helps cushion the brain and spinal cord while circulating nutrients and removing waste materials -- was the main cause of the syndrome.
"On Earth, the CSF system is built to accommodate these pressure changes but in space, the system is confused by the lack of the posture-related pressure changes," Dr Alperin noted.
The results showed that compared to short-duration astronauts, long-duration astronauts had significantly increased post-flight flattening of their eyeballs and increased optic nerve protrusion.
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