The experience of weightlessness is confusing for human bodies. The eyes tell you you're gently bobbing up and down, while your inner ear screams that you're tumbling about, making you nauseous. The fluids in your body, freed from gravity, float upward, causing head congestion. Bones, suddenly useless in holding you up and moving you around, start thinning out. And something strange can happen to your eyeballs: They get squashed, blurring your vision.
About two-thirds of astronauts on the International Space Station report changes in their vision after they come back. Scans show that the backs of their eyeballs somehow get flattened, their retinas wrinkle, and their optic nerves swell after spending a prolonged period of time in microgravity, causing farsightedness. The leading explanation suggests that when bodily fluids rise and pool in astronauts' torsos and heads, they put pressure on the brain and the back of the eye, causing changes in its shape. Scientists don’t know for sure, so they keeping studying astronauts.
They don’t need the astronauts themselves to study vision changes, though, as a new study from researchers in Texas, published Thursday in the Journal of Physiology, shows. A team at UT Southwestern Medical Center instead tested cancer patients who had a device permanently placed in their heads as part of their treatments. The device, known as an Ommaya reservoir, allows doctors to inject medicine into patients’ cerebrospinal fluid or remove extra liquid. For the Texas researchers, the port allowed them to measure intracranial pressure—the force inside the skull that scientists suspect causes structural changes to the eye and optic nerve in microgravity.