A new report from NASA shows that astronauts on extended missions to the International Space Station are suffering seriously blurred vision.
The problem is so extreme that special eyeglasses have been installed on the station to help the afflicted.
One NASA survey says 30% of space shuttle astronauts on missions of two-weeks or less suffered blurred vision, while 60% of those on board the space station for six-months reported diminished sight.
The condition is thought to be caused by an increase of spinal-fluid pressure on the head and eyes during periods of little or no gravity, but the exact cause remains unknown.
NASA is now forced to admit that a multi-year trip to Mars could blind astronauts, and it's treating the problem as one more very large obstacle to a manned Mars mission.
While improvement back on earth is reported by some, many never recover, and fail to re-qualify for subsequent flights.
Read more: http://www.businessinsider.com/findings-show-astronauts-likely-to-go-blind-on-a-trip-to-mars-2011-9#ixzz1YajSrz7H