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.
Certainly there needs to be more research into the subject. Could the issues be simulated with rats? Perhaps rats that are already being used for other experiments?
Why do we have to perpetuate the myth of "microgravity"? Astronauts in Earth orbit are experiencing pretty much the same gravity as the rest of us. What is different for them is that they are weightless because there is nothing to prevent their continuous free-fall.
I do think that Zero-G is just as good of a term.
Zero-G is complete bollocks rather inaccurate too, but possibly less offensive than microgravity.
Geezer, I note you have a "thing" about this :-) Don't you think we should embrace the concepts of General Relativity and say that a force due to accelerated motion is just as much a real force as that produced in any other way (e.g centrifugal force) and, likewise, the cancellation of gravity by being in free-fall can also be considered as "Zero-G". I sense you were taught the evils of ever using the phrase "centrifugal force" at school (as was I), but I don't think it is beyond people's imagination to understand the basic concepts of GR and to be taught that this force is (in every sense) a real force for the person experiencing it. In fact, it may be more educational than the convoluted denial of its existence. graham.d, Wed, 21st Mar 2012
How did you guess that?!?
I would agree that "microgravity" is the wrong term for the gravity experienced in LEO. According to the wikipedia page above, the gravity in LEO is about 9 m/s2, hardly "micro".
I suppose the main difference between the basketball player and the astronaut is that for the astronaut, the frame of reference (international space station) is falling at the same rate they are falling, and thus they have zero acceleration with respect to their reference frame. Not even any extra wind resistance.
I am guessing you have a specific meaning for LEO Clifford. If you were aboard a Low Earth Orbiting satellite then you would experience no gravity (except some very slight tidal force) providing, as the name suggests, it was in a stable orbit. From the frame of someone on the earth the satellite would be experiencing 9m/s/s as that would be the centripetal acceleration due to the earth's gravity. graham.d, Thu, 22nd Mar 2012
I am all with Geezer, get rid of the confusing nonsense such as micro gravity. It really just confuses things! Free-fall would be a much better description? Aaron_Thomas, Fri, 23rd Mar 2012
It's all a bit horses for courses - Geezer; I think is correct. But the term free-fall whilst understood by some - will always have public connotations of hitting something at the end (I know orbits decay - but that's not the point). For the great unwashed gravity is what stops us floating off - and those pictures of guys in the ISS seem to be just floating off; therefore they are in zero gravity. Dumbing down is a terrible thing - but sometimes it does make things easier. My favourite explanation is that they are constantly falling towards earth and always missing imatfaal, Fri, 23rd Mar 2012
Well, I really don't know many non-scientists who bother to try to understand the idea that centifugal force (for example) is not a "real" force so that the term should never be used. It is my opinion that they are actually right and more in tune the the concepts of GR. It is right to explain the mechanisms and how it comes about as viewed from a stationary frame of reference, but it is also true if something looks like a force and feels like a force, then it is a force, and there is nothing to stop it having a convenient name.
After beating a dead horse into the ground... perhaps it is time to get back to the original topic of eye problems related to travelling in space, and changes in CSF, with the conclusion that these eye and pituitary problems are due to the Zero-G environment aboard the spacecraft.
This horse is not dead - it's just resting :-)