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Eye Problems From Space Affect At Least 21 NASA Astronauts
SternisheFan sends this report from Universe Today:
How does microgravity affect your health? One of the chief concerns of NASA astronauts these days is changes to eyesight. Some people come back from long-duration stays in space with what appears to be permanent changes, such as requiring glasses when previously they did not. And the numbers are interesting. A few months after NASA [said] 20% of astronauts may face this problem, a new study points out that 21 U.S. astronauts that have flown on the International Space Station for long flights (which tend to be five to six months) face visual problems. These include "hyperopic shift, scotoma and choroidal folds to cotton wool spots, optic nerve sheath distension, globe flattening and edema of the optic nerve," states the University of Houston, which is collaborating with NASA on a long-term study of astronauts while they're in orbit.
aside from artificial gravity, nothing. No amount of exercise bike pedaling will save your optic nerves from being in zero G too long.
There isn't really any good reason to put people in orbit for 6 months+. Rotate them out every couple of months. Yes we needed data on long-term microgravity effects on the human body. We have them now, zero G does bad things to your body. So don't do it for extended periods.
Fly in the ointment is the expected trip to Mars, which will take 9 months to a year. Fortunately people like Zubrin have developed advanced technologies to deal with this. It's called a rope. Attach the Mars spacecraft to a ballast via a rope (they call it tether) and spin it until you get 1/3rd G. Problem solved.
Obviously orbital habitats either need to be spun-up or contain living quarters located within centerfuges.