Over the past decade, NASA flight surgeons and scientists complain about visual impairment after long-duration space missions. The astronauts said they had blurry vision along with a suite of physical changes. Recently, a team of researchers say they have found the answer.

No One Knew What Caused The Problem

The syndrome gave astronauts a flattening at the back of their eyeballs and inflammation at the head of the optic nerve. Lead author, Noam Alperin, from the University of Miami, said: "People initially didn't know what to make of it, and by 2010 there was growing concern as it became apparent that some of the astronauts had severe structural changes that were not fully reversible upon return to Earth."

Cerebrospinal Fluid Could Be The Source Of The Problem

Prof Alperin started to look at a possible source of the problem - the cerebrospinal fluid (CSF). This helps cushion the brain and spinal cord while circulating nutrients and removing waste materials, and accommodates significant changes in hydrostatic pressures, such as when a person rises from a lying to sitting or standing position. "On earth, the CSF system is built to accommodate these pressure changes, but in space the system is confused by the lack of the posture-related pressure changes," Prof Alperin said.

Astronauts Could Suffer 'Irreversible' Damage

Prof Alperin's team performed high-resolution MRI scans before and shortly after lengthy space missions for seven astronauts. The results showed that astronauts on long-duration had significantly greater post-flight increases in the volume of CSF within the bony cavity of the skull that holds the eye.

"If the ocular structural deformations are not identified early, astronauts could suffer irreversible damage, as the eye globe becomes more flattened, the astronauts become hyperopic, or far-sighted," Alperin said.

Prof Alperin received a $600,000 grant from Nasa to study this further.