Researchers have long known that astronauts experience significant physical changes during spaceflight. These changes were first seen in test animals that ventured — or, more accurately, were launched — into space before humans. But similar effects also were noted in Mercury astronauts soon thereafter.

To date, most of the research on how spaceflight affects the human body focuses on the muscles, bones, and hearts of astronauts. But many astronauts also report changes in their visual acuity following spaceflight — a condition known as spaceflight-associated neuro-ocular syndrome, or SANS. Astronauts with SANS can develop impaired short-distance vision, experience headaches, and/or see floating blurry spots known as scotomas.

Now, a new study has evaluated how long-term spaceflight is tied to common changes seen within the skulls of astronauts, which impacts both their brains and eyes. The researchers also investigated how these intracranial changes could be related to SANS, uncovering some surprising results. The new findings were published Tuesday in the journal Radiology.

The hazards of long-term spaceflight

To carry out the study, the researchers collected data for 11 astronauts — 10 men and one woman — who lived aboard the International Space Station (ISS) for extended periods of time. On average, the astronauts stayed on the ISS for 171 days, and five of the subjects also had previous spaceflight experience. Before their missions, the astronauts underwent magnetic resonance imaging (MRI) scans that captured preflight brain images. Then, they had additional MRI scans one, 30, 90, 180, and 360 days after their return to Earth.

“We hypothesized from previous MRI studies of the eyes that elevated intracranial pressure during spaceflight could potentially contribute to the changes in vision for astronauts,” Larry Kramer, a professor at the McGovern Medical School at the University of Texas Health Science Center at Houston and lead author of the study, said in a UT Health News statement. “And we wanted to document if there were any changes in the brain that could support this theory.”

By comparing and contrasting the preflight and postflight scans, the researchers found statistically significant changes in several key organs and structures.