When people are sent to space, their bodies are subjected to some pretty extreme forces. How the human body copes with these is obviously of utmost importance, and it seems that researchers might be getting closer to figuring out just how microgravity affects astronauts' vision, as it causes swelling around the highly sensitive optic nerve.
In a recent study, published in JAMA Ophthalmology, researchers looked at the eyes of 15 astronauts who had recently completed around six months in space. They found that on returning to Earth, the tissue around the back of the eye where the optic nerve passes through the skull and into the eye socket looked swollen and inflamed. They suspect that this might be one of the reasons why astronauts experience problems with their vision.
Why this is happening is less clear. The current theory is that it might be something to do with the internal pressure of the eye increasing when in microgravity. They suggest that the body could then be adapting to this new pressure while the astronauts are up there for long periods of time, and that when they then return to Earth, experiencing a rapid change in pressure as a result, the tissue becomes inflamed and irritated.
Worryingly, this isn’t the only way that space travel affects the eyeballs of astronauts. NASA first identified back in 2005 that the eyeballs of their space crew were somehow changing shape until they were permanently flattened. This was eventually found to be due to the liquid that is present in the brain building up in places where it really shouldn’t, putting pressure on the eyes and squishing them.
The problems that astronauts experience with their vision fall under a condition known as visual impairment intracranial pressure syndrome, or VIIP, which also affects the brains of those who undergo space flights. Last year, researchers discovered that in microgravity the brain effectively floats upwards and pushes against the top of the skull, physically changing its structure and shape, and potentially contributing to VIIP.
Far more work still needs to go into understanding how exactly this is affecting the astronauts, though, and as such, NASA has made determining the cause of VIIP a top priority if long-duration space flights and planet colonization are to become a reality.