Eyes vote no to space travel
Head scans of astronauts have shown signs of raised intracranial pressure affecting their eyes and pituitary glands, new research has revealed.
Writing in the journal Radiology, University of Texas Medical School, Houston radiologist Larry Kramer MRI scanned 27 spacefarers who had each notched up an average of 108 days in orbit.
The imaging showed signs of small cavities in the pituitary glands of three astronauts, flattening of the backs of the eyeballs in six cases, increased fluid around the optic nerves in nine individuals and bulges in the optic discs inside the eye in four cases.
These are features that would normally characterise increased intracranial pressure and they go some way towards explaining the basis for something that NASA has known for a while: that in the aftermath of exposure to microgravity, astronauts have an above-average chance of experiencing vision problems.
In fact, 30% of short-duration space trippers and 60% of longer-duration orbiters report sight loss symptoms.
The researchers speculate that the changes are caused by fluid shifts that occur inside the head in response to chronic microgravity exposure. Fluid that would normally collect in the tissues of the extremeties under the influence of gravity instead builds up inside the head. This is the same reason that astronauts often characteristically become temporarily puffy-faced in space.
But what is intriguing to NASA is not the 60% who do suffer problems but the 40% who don't. Studying them might reveal why they are relatively protected from the problem and lead to ways to protect those at risk, or identify individuals best suited for longer space missions.
Sending someone to Mars is likely to involve a year in space, so solving problems like this will be critical to the success such missions. In the meantime, NASA are proposing to carry out pre- and post-flight MRI scans of their astronauts on Earth and then monitor them in orbit using ulatrasound scans of their eyes.