Researchers at the Medical University of South Carolina (MUSC) have explored gravity’s effect on eyesight in a study of astronaut’s vision published in Jama Network Open.

Brain scans before and after spaceflight were compared to explore a condition called spaceflight-associated neuro-ocular syndrome (Sans).

Astronauts who have spent longer in space often return to Earth with altered visual acuity and struggled to distinguish between shapes at a distance.

Findings from a study of 12 astronauts suggested there was an association between intracranial venous congestion and the development of Sans, with blood flow increased and the dural venous sinuses enlarged.

Mark Rosenburg, neurology resident at MUSC Health and researcher on the paper, said: ‘It’s gotten to the point where astronauts actually carry extra pairs of glasses when they go into space. They know that their vision is going to be deteriorating up there and they’ve even started calling them space anticipation glasses. In fact, depending on how you define it, it affects about 70% of astronauts.’