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.