Men experience greater eye changes from spaceflight, while brain differences between sexes are subtle

A new study into how spaceflight impacts the human brain and eyes revealed notable sex differences in brain fluid shifts, with female astronauts showing a greater reduction in fluid around the uppermost part of the brain than their male counterparts.

Led by Rachael D. Seidler, Ph.D., director of the University of Florida’s Astraeus Space Institute and professor of applied physiology and kinesiology, the study analyzed data from astronauts to determine how factors such as sex, age and body metrics relate to structural brain and eye changes after space travel. The findings, published in August in npj Microgravity, provide key information for protecting astronaut health on long-duration missions to the moon and Mars.

This is one of the first studies to look at sex differences in the physiological response to spaceflight.

“The data on sex differences in response to spaceflight are scant, given the historically low number of female astronauts,” Seidler said. “Our dataset was still only approximately one-quarter females, but since the overall dataset was fairly large we were able to examine sex differences.”

In addition to changes in fluid around the brain, the team also found that a form of eye compression, a hallmark of Spaceflight Associated Neuro-ocular Syndrome known as globe flattening, was the most consistent eye change among crew members.

“By far the most prevalent sign of eye changes that we observed was globe flattening, suggesting that this should be the primary monitoring target for ocular health,” Seidler said. “Interestingly, eye changes were more prevalent in males than females.” 

Globe flattening, when the back of the eyeball becomes slightly indented or pushed inward,  might sound minor, but it can have significant effects on vision and raise concerns for long-duration space missions.

Surprisingly, there was no strong link between brain structural changes and eye changes, suggesting that the effects on the eyes and brain may arise from distinct mechanisms rather than shared physiological causes.

The research underscores UF’s growing leadership in space health science. Through the Astraeus Space Institute, Seidler leads multidisciplinary collaborations that connect neuroscience, physiology and space research to advance human performance and safety in spaceflight.

“We used UF's HiPerGator computing cluster for our analyses in this study, enabling us to analyze our data at high speeds,” Seidler said.

Read the full study in npj Microgravity.