Astronaut EyesNASA has already reported on astronauts experiencing bone and muscle loss due to the weightlessness of space.  Now the first study of returning space travelers’ eyes may suggest that extended amounts of time in orbit can take a serious toll on vision, the long-term effects of which aren’t yet clear.

Of the more than 300 astronauts in the U.S. space program who were enrolled in the study, nearly 50 percent of those on missions six months or longer reported experiencing new problems with their vision.  The most common complaint was a loss of the ability to see objects up close while they were in space and for some time after returning to Earth.

The researchers also performed physical examinations on seven astronauts who reported vision problems after returning from six month trips in space. They found a handful of signs of eye stress in all of them, including an accumulation of fluid around the optic nerve, early signs of changes to the vessels that supply blood to the retina and shortening of the eyeball.

Dr. Tom Mader, an ophthalmologist at the Alaska Native Medical Center in Anchorage, who led the study said:

People have been flying in space for 50 years and nobody has gone blind yet.  But it’s still something to be concerned about… It’s very hard for us at this point to define exactly what is causing all of this.”

Mader went on to speculate that less gravity in outer space may increase the pressure of the fluid surrounding the brain by not allowing this fluid to properly drain back into the body. However, the exact mechanism remains unclear.

David Robertson, who runs the Center for Space Physiology and Medicine at Vanderbilt University Medical Center in Nashville, was somewhat surprised by the extent of the eye changes.

Robertson did add that astronauts experience swelling in the face in space, which has been chronicled by in-flight pictures. He went on to say:

There are more changes in the eyes that I might have expected, but I would imagine that the increased headward movement of fluid during travel in space, together with the puffiness of the face and facial tissues likely also affects the eye.”

While these results aren’t exactly “out of this world,” it certainly is something to keep an eye on.