So here, unfortunately, is another hurdle in MANkind's dreams of long duration space flight. It turns out there are serious vision problems in astronauts that don't go away when they return to earth. Strangely enough these problems don't seem to affect women!
Anyway, at this point I'd normally say rather than making big elaborate spacecraft with spinning sections to provide gravity and heavy radiation shielding, we should just genetically re-engineer humans. But I recently read the short story "People of Sand and Slag" which describes a dystopian future where this has been done. Unfortunately the people(?) of the future have lost their humanity in more ways than one.
So maybe that's not the best idea. Hibernation anyone?