Living in space can affect the anatomy of your eyeballs
Amongst the many differences experts recorded between astronaut Scott Kelly and his twin brother Mark after the former’s one-year mission to the International Space Station was a thickening of his retina. Structural changes to that part of the eye can affect how people see.
These modifications can lead to far-sightedness, for example, because it disrupts the image that comes into the eye’s photoreceptors. Other astronauts have developed some swelling of the optic nerve, and others came back with folds in the choroid, which is the area rich in blood vessels and connective tissue between the retina and the sclera.