Flattening of the backs of astronauts' eyes may be caused by increased pressure of cerebrospinal fluid in microgravity. Brain scans of Nasa astronauts who have returned to Earth after more than a month in space have revealed potentially serious abnormalities that could jeopardise long-term space missions.
Doctors examined 27 astronauts who had flown long-duration missions with the US space agency and found a pattern of deformities in their eyeballs, optic nerves and pituitary glands that remain unexplained.
The problems are similar to those caused by intracranial hypertension, a rare medical condition that occurs when pressure inside the skull rises and presses on the brain and the backs of the eyes.
Medical crews at Nasa and space agencies in Europe, Russia, Japan and Canada are now screening astronauts before, during and after space missions.
Astronauts who had flown on the Space Shuttle and International Space Station reported changes to eyesight, with some seeing worse and others better.
The proof
Brain scans revealed that seven of the 27 astronauts had a flattening of the back of one or both eyes. By making the eyeball shorter, this made the astronauts more long-sighted, which in some cases reduced or corrected their short-sightedness.
Dr Larry Kramer, who led the study at the University of Texas Health Science Centre in Houston, said the impact on astronauts' eyesight might become “a new limiting factor” to long excursions into space.
His results, published in the journal Radiology , suggested the abnormalities were worse and more frequent in astronauts who spent longer in weightless, or microgravity, conditions.
Kramer said: “Consider the possible impact on proposed manned missions to Mars or even the concept of space tourism. Can risks be eventually mitigated? Can abnormalities detected be completely reversed? The next step is confirming the findings, defining causation and working towards a solution based on solid evidence.” Four of the astronauts had swelling around the optic nerve, which could affect the transmission of signals from the eye to the brain and, in the longer term, cause nerve fibres to die off.
William Tarver, head of flight medicine at Nasa's Johnson Space Centre in Houston, said no astronauts had been ruled out of flying after the findings, which he said were “suspicious but not conclusive of intracranial hypertension.” — © Guardian Newspapers Limited, 2012
