If your favorite astronaut returns from space wearing horn-rim glasses and funny stockings, don’t be too disappointed. It’s all part of the job. And there’s a logical explanation.

Among the challenges astronauts face during their stints on the International Space Station, farsightedness is fairly common. Hence the horn-rims. But it may be that those funny stockings can reduce the need for them.

“About three quarters of ISS astronauts experience changes in the structure and function of their eyes during and/or after their mission,” says Michael Stenger of Wyle Science Technology and Engineering Group. “And some of these changes in some of the astronauts do not correct themselves after the mission.”

Stenger is one of the principal investigators of an International Space Station experiment with a very long name that we’ll call “Fluid Shifts Study” for short. It’s investigating vision problems in space.

During space travel, the fluids of the body shift toward the head and even move across blood vessel and cell membranes differently than they do on Earth. Scientists hypothesize that this headward shift of blood and other fluids causes increased pressure in the brain, pushing on the back of the eye and causing it to change shape. The retina swells and the entire eye slightly flattens, resulting in farsightedness -- and maybe those glasses. 

Stenger and his colleagues seek to fully characterize these changes and investigate ways to prevent them.

“We want to know exactly how much fluid shifts and how it redistributes in the body. How does it move in or out of cells and blood vessels? How do the fluid shifts affect fluid pressure in the head, changes in vision, and eye structures?Those are the kinds of questions we’ll answer. We expect to find individualized responses to the headward fluid shift that correlate to vision changes.”

To find the answers, they’ll take measurements of 10 astronauts’ saliva, urine, and blood at different points in their missions. Other details collected will be their intracranial pressure, intraocular pressure, ocular structure, blood pressure, and heart rate, in addition to ultrasound measurements of their fluid shifts.

Another aim of this study is to find out whether the Russian Chibis suit (also known as the lower body negative pressure suit, or funny stockings) can help keep the bodies’ fluids where they need to be.

“The Russian cosmonauts use the Chibis suit during the last 3 weeks of their missions as part of their preparation for re-entry.It’s really just a pair of semi-rigid leggings that seal at the waist. A vacuum can be applied to reduce the pressure in the device, which acts to trap fluid in the lower body.”

The researchers will take cardio, cerebrovascular, and ocular measurements on the test subjects before and during 25 mmHg of vacuum in the Chibis.

“If it turns out that lower body negative pressure helps reverse fluid shifts and prevent the visual symptoms, it may indicate that crew members should use the Chibis earlier and more often on long missions. We’ve seen some promising results in our first subjects.” 

Stenger and company will also be looking at other things that might exacerbate vision problems on the space station.

“For example, we may find that an exercise that’s good for bone or muscle is bad for elevated intracranial pressure.”

Space travel veterans Scott Kelly from NASA and Mikhail Kornienko from Roscosmos are the first test subjects for this study. They will spend nearly a year aboard the station, twice as long as a typical crew member. They’re having measurements taken for the Fluid Shifts Study early in their flight, at its mid-point, and about 45 days before they return.

Here’s hoping they come back in style—no horn-rims and hosiery required.

For more from the international space station, go to www.nasa.gov/station

For news from the always fluid world of science, visit science.nasa.gov.