Agnirva Space Premier League - Expedition #30847: Why Astronauts’ Eyes Change in Space: Investigating Fluid Shifts and Vision

When astronauts spend long periods in space, something unexpected can happen—their vision deteriorates. Some return to Earth with blurred sight, flattened eyeballs, or changes in the optic nerve. Scientists needed answers, and thus began one of the most comprehensive human research experiments aboard the International Space Station: Fluid Shifts.

Led by Michael Stenger and a multidisciplinary team, this NASA study looked into how body fluids shift in microgravity and how that affects intracranial pressure (ICP) and visual acuity. Normally, gravity pulls fluids downward. But in orbit, those same fluids redistribute toward the upper body, increasing pressure in the head.

The experiment involved multiple phases, tracking astronauts before, during, and after missions. Advanced imaging, ultrasound, and pressure measurements were used to monitor changes. One key tool was the Lower Body Negative Pressure (LBNP) device, which draws fluids toward the legs, mimicking the effect of gravity.

Findings revealed a strong link between fluid shifts and Spaceflight-Associated Neuro-ocular Syndrome (SANS), a condition affecting vision and brain health. Symptoms included optic disc swelling, choroidal folds, and altered visual acuity. These changes didn’t always reverse after return to Earth, raising long-term health concerns.

Understanding these effects is vital for the future of deep space travel. Mars missions, for example, will require astronauts to spend over a year in microgravity. Managing fluid shifts and protecting vision are now top priorities.

The Fluid Shifts experiment not only enhances astronaut health but also provides insights into similar conditions on Earth, such as intracranial hypertension. Through collaboration across institutions and missions, this research sets the foundation for safer, longer space exploration.

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