When astronaut Michael Barratt returned to Earth in October 2009, he revealed that something strange had happened during his eight months in microgravity on board the International Space Station: His vision had changed.

Before his sojourn above the Earth, Barratt needed glasses to see at a distance. But once he returned from his mission in space, the astronaut also needed reading glasses to see up-close.

Barratt’s curious case, as well as reports of similar changes from several other astronauts, launched a series of studies on the effects of spaceflight on vision. If humans are to spend any significant time in space, scientists need to know how time spent in the microgravity environment may alter our eyes — and if the changes are permanent.

The cause of the changes Barratt experienced are still unclear, but scientists hypothesize that increased pressure caused by fluid going into astronauts’ heads as a result of being suspended in a microgravity environment could be reshaping their optic nerve — changing the structure of their eyes.

Weightlessness and eyesight

In a study published this week in the journal JAMA Opthalmology, scientists recreated the weightlessness experienced by astronauts in space on 11 people here on Earth in an effort to better understand what effect the environment has on vision. The findings may help develop countermeasures to mitigate the effects of spaceflight on astronauts’ eyes — better preparing them for longer flights in space.

The participants were kept on bedrest for 30 days, with their heads tilted down — a state supposed to simulate the physiological effects of weightlessness in space. Any changes to their optical nerves observed over the course of the study were compared with data collected from 20 astronauts who had spent around 30 days in space from the years 2012 to 2018.

Over the 30-day period, the participants developed significant swelling of their optic nerve at the back of the eye due to a buildup of fluid around the brain. Although the effects were not entirely parallel with those seen in the astronauts, the differences between the two data sets may still provide insight on the phenomenon.

Michael Barratt works in microgravity aboard the International Space Station, wearing his glasses. NASA

Contrary to past theories, the results suggest that increased intracranial pressure, or increased pressure around the brain, as a result of fluid build-up may not be the only cause of vision changes among astronauts. In fact, the Earth-bound participants’ intracranial pressure levels decreased with increased weightlessness.

The results also run contrary to the theory that gender may play a role in changes to vision during spaceflight. In one of the initial studies conducted between 2012 and 2018, NASA noted that half of the astronauts onboard the International Space Station had experienced changes in vision, but none of the female astronauts had developed the same symptoms.

This study, by contrast, involved six men and five women, and the female participants also experienced swelling of their retinas.

The study also found that participants developed more severe symptoms on their right eye versus their left. This reflects the earlier results obtained from the astronauts’ data, suggesting that there may be asymmetry in how each eye is affected.

The results don’t answer the question of how long these effects may last. In Barratt’s case, he reported that his right eye was permanently altered by his time in space, while his left eye returned to its pre-space condition — suggesting some of the effects of weightlessness on the body may remain for years after astronauts come back down to Earth.