Dr. Michael Barratt (second from the left in the above photo) is a Mission Specialist astronaut for NASA whose expertise is in space medicine. He was originally nearsighted and needed glasses to see distant objects, while his close-up vision was fine (apparently, you do not have to have 20-20 eyesight to be a Mission Specialist). After several months in space, his vision altered permanently so that he can now see far objects perfectly but needs reading glasses.
This change resulted from a condition called papilledema, which is a swelling of the optic disk in the eye. It affects a large percentage of male astronauts. Essentially, weightlessness alters the shape of the eye. In Barratt's case, his optic nerves became flattened and his retinas developed folds in them. Sometimes the change is temporary; often it is not. Since it can lead to blindness, it is of major concern to NASA, especially if NASA ever gets its funding back to commence long-term
manned (or womanned)
space exploration, including missions to other planets.
For some unknown reason, no female in space has ever developed papilledema.
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