4. Altered Vision
The upward shift of fluids in microgravity can increase pressure inside the skull, sometimes flattening the eyeball and distorting vision. This phenomenon, called Spaceflight-Associated Neuro-ocular Syndrome (SANS), has affected many astronauts, some of whom require corrective lenses while in orbit. Researchers continue to study SANS to better understand its causes and develop strategies to protect astronaut eyesight on long missions. [Source: BBC]