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Spaceflight-associated neuro-ocular syndrome (SANS) - or, as we like to call it, space eyes - is a set of changes to an astronaut’s eyes and brain that can manifest as blurry vision. We don’t know what causes it, but it’s a big issue in space medicine. The good news is that after most astronauts get back to Earth, their vision completely recovers. But the risk for developing SANS increases with longer space journeys, like a trip to Mars, which could take over two years if it’s a round trip.
NASA has known about vision issues in astronauts since the late 80s, but studies describing this specific set of symptoms weren’t produced until 2011. Since then, researchers have been doing a bunch of different kinds of tests both right before and after spaceflight missions. To study SANS without spaceflight, researchers are using parabolic flights with airplanes, dry immersion, and even putting donated human eyeballs directly into a device that mimics the conditions of space.
However, with only 12 astronauts going into space each year, these studies have small sample sizes and it takes a while to get enough data to draw any conclusions. So, figuring out ways to study SANS that don’t require spaceflight is critical. Studying Space Adaptation Syndrome (SANS) on Earth is commonly done with head-down tilt bed-rest experiments. In this experiment, the person lies on their back with their head lower than their feet, tilted at 6 degrees. They then spend months, sometimes even a full year, undergoing tests such as MRIs, ultrasounds, and lumbar punctures. While scientists have yet to figure out the exact cause of SANS, some hypothesize it is related to increased pressure inside the head due to fluid redistribution in a microgravity environment. Another hypothesis suggests that microgravity affects the flow and drainage of cerebrospinal fluid around the optic nerve. Additionally, there may be a genetic component to SANS.
It is important to investigate the cause of SANS in order to prevent and treat it. New tools are being developed to allow astronauts to do more extensive testing in flight. Lower body negative pressure devices, vitamin B supplements, and even wearing swim goggles have been suggested as treatments.
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