Why astronauts get blurry vision in space

Space changes people in surprising ways. One of the most puzzling shifts that astronauts have experience on long missions is blurry vision.

Many found themselves needing stronger reading glasses the longer they stayed aboard the International Space Station. Researchers began to investigate and found a pattern. The astronauts’ eyes were changing shape.

Optic discs – where the optic nerve connects to the eye – were swelling. Eventually, these symptoms were grouped under one name: Space-Associated Neuro-Ocular Syndrome, or SANS.

Microgravity messes with astronaut vision

Scientists began digging deeper into what causes these eye problems. The key issue appears to be the effect of microgravity.

In space, fluids in the body shift upward toward the head. Blood and cerebrospinal fluid don’t settle as they do on Earth. This headward fluid shift is now thought to be one of the main reasons behind SANS.

To test how this works, researchers launched the Thigh Cuff investigation. The study explores whether wearing snug cuffs around the upper thighs can redirect fluid away from the head.

If effective, these cuffs could offer a simple, noninvasive way to prevent vision problems in space. And not just in orbit – this approach could also help patients on Earth who experience fluid buildup due to illness or extended bed rest.

Eye data from 300 astronauts

From 2015 through 2020, a project called Fluid Shifts documented how blood drains from the brain differently in space.

Around the same time, the Vision Impairment and Intracranial Pressure (VIIP) study tested whether increased brain fluid pressure played a role in SANS.

To get answers, scientists used clinical eye exams – both with and without dilation – as well as imaging of the retina, optic nerve, and surrounding blood vessels.

Noninvasive scans helped measure the thickness of different eye structures. They also collected MRI data and surveyed nearly 300 astronauts about how their vision changed during missions.

Understanding astronaut vision issues

In a paper published from this research, scientists noted that these tools have improved the understanding of SANS. They also discussed a new idea: a head-mounted virtual reality device that could someday assess SANS in real time using multiple types of data.

Another research group looked into the optic nerve sheath. They discovered that measuring its diameter might be a reliable way to track vision changes during space travel.

The team also urged fellow scientists to standardize how these tests are done to make future studies easier to compare and repeat.

One astronaut’s unusual vision case

One study focused on a single astronaut who experienced more severe symptoms than most after a six-month mission.

In this case, the symptoms began to improve mid-mission – possibly due to two factors: vitamin B supplements and a drop in cabin carbon dioxide levels after some crew members left the station.

“While a single case does not allow researchers to determine cause and effect, the magnitude of the improvements suggest this individual may be more affected by environmental conditions,” said the researchers.

They noted that this may have been the first attempt to mitigate SANS with inflight B vitamin supplementation.

Is eye tissue softer in space?

Another study, SANSORI, which was led by the Canadian Space Agency, used Optical Coherence Tomography to explore whether softer eye tissue might be part of the problem. On Earth, a loss of tissue stiffness is linked to aging and diseases like glaucoma or myopia.

Scientists found that long stays in space affected the stiffness of tissues around the eyeball. That change might help explain why eyes start to lose their shape during spaceflight.

The results could also help doctors better understand vision problems in older adults here on Earth.

Genes, mice, and artificial gravity

Meanwhile, researchers in Japan ran the MHU-8 experiment. They looked at how space travel affects gene expression in mice.

After the mice returned to Earth, the team found changes in their optic nerves and retinas.

Interestingly, the experts also tested whether artificial gravity might reduce these changes – and it did. This raises the possibility of using rotating habitats or other tools to simulate gravity during future missions.

Protecting vision in space

SANS is still being studied, but every experiment brings scientists closer to understanding how space affects the human body – and how to protect it.

The hope is that one day, astronauts headed to the Moon or Mars won’t have to worry about vision loss. And the same discoveries may help people on Earth too.

Information for this article was obtained from a NASA press release.

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