While browsing Snopes’s Glurge Gallery, I came across the last e-mail from Laurel Clark, one of the deceased Columbia astronauts. ( http://www.snopes.com/glurge/laurel.htm ) Among other things, she notes:
What is the cause of this loss of near vision? My guess would be a change in the shape of the eyeball due to conditions aboard an orbiting shuttle–say, it not being as flattened due to gravity as it normally would be, or it being filled with more fluid than usual due to the absence of earth gravity, or due to air pressure differences aboard the shuttle (do they keep it at one atmosphere?)–but I’ve never heard of such a thing before. Anyone know the actual cause?
Last I heard, the shuttle was normally kept at one atmosphere pressure for crew comfort, about 15 lbs/in
On spacewalks, the astronauts involved decompress to about 3 lbs/in for their spacesuits, which are not at 1 atmosphere. This can, in very rare circumstances, affect vision, but it doesn’t sound like what you’re talking about.
Fluid balances do change in orbit, but I’m not aware how fluid buildup in the head would change vision.
It is also possible that she was experiencing the normal presbyopia of aging and on that trip it had simply gotten to the point where it was bothersome, either through sheer coincidence or because she was required to do considerable close-vision work.
It is my understanding that under normal gravity, body fluids tend to pool somewhat in the lower parts of the body (which is why it isn’t terribly comfortable to hang upside down for a long time) - in the absence of this influence, body fluids are going to distribute themselves differently and this might result in a larger fluid volume inside the eyeball.
A larger eyeball means that the lens will tend to be focusing images at a point that falls short of the retina (short sightedness), but that condition is the opposite of what is apparently being reported.