Turns out that long stints in outer space affect levels of cerebrospinal fluid. That explains why many astronauts who had 20/20 vision before space missions needed glasses upon return, according to a paper presented this week.
Noam Alperin's research team scanned the brains and eyeballs of seven astronauts prior to longer missions onboard the International Space Station. They compared those scans with nine astronauts who had short missions. The difference in cerebrospinal fluid (CSF) was significant:
The results showed that, compared to short-duration astronauts, long-duration astronauts had significantly increased post-flight flattening of their eyeballs and increased optic nerve protrusion. Long-duration astronauts also had significantly greater post-flight increases in orbital CSF volume, or the CSF around the optic nerves within the bony cavity of the skull that holds the eye, and ventricular CSF volume–volume in the cavities of the brain where CSF is produced. The large post-spaceflight ocular changes observed in ISS crew members were associated with greater increases in intraorbital and intracranial CSF volume.
• Study finds cause of visual impairment in astronauts (EurekAlert via Mental Floss)