Here is more from NASA on the effects of microgravity on the eyes. 20% of all astronauts come back from space with visual problems. Slowed venous return creates changes in cerebrospinal fluid pressures. This is why the international space agencies are working with Dr. Zamboni. Please note that many of these optic nerve changes are seen in MS. http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20130000762.pdf