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Arthur T Knackerbracket has found the following story:

Extended periods in space have long been known to cause vision problems in astronauts. Now a new study in the journal Radiology suggests that the impact of long-duration space travel is more far-reaching, potentially causing brain volume changes and pituitary gland deformation.

More than half of the crew members on the International Space Station (ISS) have reported changes to their vision following long-duration exposure to the microgravity of space. Postflight evaluation has revealed swelling of the optic nerve, retinal hemorrhage and other ocular structural changes.

Scientists have hypothesized that chronic exposure to elevated intracranial pressure, or pressure inside the head, during spaceflight is a contributing factor to these changes. On Earth, the gravitational field creates a hydrostatic gradient, a pressure of fluid that progressively increases from your head down to your feet while standing or sitting. This pressure gradient is not present in space.

"When you're in microgravity, fluid such as your venous blood no longer pools toward your lower extremities but redistributes headward," said study lead author Larry A. Kramer, M.D., from the University of Texas Health Science Center at Houston. Dr. Kramer further explained, "That movement of fluid toward your head may be one of the mechanisms causing changes we are observing in the eye and intracranial compartment."

To find out more, Dr. Kramer and colleagues performed brain MRI on 11 astronauts, including 10 men and one woman, before they traveled to the ISS. The researchers followed up with MRI studies a day after the astronauts returned, and then at several intervals throughout the ensuing year.

-- submitted from IRC

Journal Reference
Larry A. Kramer, et. al. Intracranial Effects of Microgravity: A Prospective Longitudinal MRI Study, Radiology (DOI: 10.1148/radiol.2020191413)

Original Submission