Space is ruining astronauts’ perfect eyesight – this could be why

Alan Martin November 29, 2016

It may seem a fairly obvious statement, but in order to make it to Mars and survive – something that’s already pretty tough – being able to see would be a real advantage. Unfortunately, our evidence from a relatively small body of astronauts who have spent time aboard the International Space Station isn’t looking great on that score: vision tends to deteriorate, and although scientists may be a step closer to figuring out exactly why, preventing the phenomenon is still a pipe dream.

Space is ruining astronauts’ perfect eyesight – this could be why

Around two-thirds of astronauts report a deterioration of their eyesight after a spell in space. How bad a deterioration? Well, John Phillips is a particularly troubling case study. His eyesight went from 20/20 to 20/100 after just six months aboard the ISS 16 years ago. Meanwhile, Scott Kelly returned to Earth back in March this year and has reported needing reading glasses since his return. He was picked for the mission, in part, because of his strong eyesight.

So, what’s going on here? NASA’s working theory was that microgravity was building up pressure inside the astronauts’ skulls, resulting in around two litres of vascular fluid to shift towards the head, putting pressure on both the brain and the back of the eyes. They catchily called this phenomenon “visual impairment intracranial pressure syndrome” (VIIP).

But a team of researchers from the University of Miami has put the ideas to further testing, and have come up with a subtly different answer: it’s cerebrospinal fluid (CSF) rather than vascular fluid that’s responsible, they reckon. Typically, CSF is pretty damned handy: it cushions the brain and spinal cord. It’s used to adapting to different bodily positions, meaning that standing up, sitting down or lying down doesn’t phase it. In space, however, it’s a different story. scott_kelly_eyesight_space

“On earth, the CSF system is built to accommodate these pressure changes, but in space the system is confused by the lack of the posture-related pressure changes,” explained the study’s lead author, Noam Alperin.

To come to this conclusion, Alperin and his team performed high-resolution orbit and brain MRI scans on astronauts before and after seven long-duration stays onboard the ISS. They then compared these to the results from nine astronauts who had only done (comparatively) short-haul space work: travelling to and from the discontinued space shuttle. The results showed that the former group of astronauts had a significantly higher CSF volume, especially around the optic nerves and the cavities in the brain where the fluid is produced.

Dr Alperin says that this kind of change needs to be spotted swiftly to avoid long-term damage. “If the ocular structural deformations are not identified early, astronauts could suffer irreversible damage. As the eye globe becomes more flattened, the astronauts become hyperopic, or farsighted.”

But that’s the thing: because we’ve only just identified this, there’s no prevention or cure for it. Effects are sometimes reduced after returning to Earth – but not always or completely – and we’re talking about the impact of just six months in space. The trip to Mars will be at least six months. Add that to however long humans hang around on Mars, and then another six months to get back, and there’s a serious risk that the impact will be much worse than farsightedness.

If there’s any hope, it may be found in retired astronaut Clayton Anderson, who reported no problems at all upon returning from a five-month spell in space nine years ago. “It appears – from additional NASA studies performed at Johnson Space Center in Houston – that I have a special protein sailing through my body, that does not allow this phenomenon to occur,” he wrote on Quora. NASA is apparently still investigating this.

For now, though, we can add this to the stack of potential medical issues that can affect astronauts. We’ve already learned that they’re four to five times more likely to suffer from cardiovascular disease, and that there’s a high risk of dementia – it’s almost like we weren’t designed to travel beyond our own atmosphere.

Images: NASA and Gordon Wrigley used under Creative Commons