The long-coveted dream of sending humans to Mars has met a significant obstacle in the form of a mysterious illness causing changes to astronauts’ eyesight, called spaceflight-associated neuro-ocular syndrome (SANS).
Specifically, these changes include swelling in the region where the optic nerve extends to the brain, flattening of the rear of the normally round organ, wrinkles that emerge at the back of the retina, and shifts in the refractive index that change how the eye focuses, according to the Scientific American report published on March 6.
Mysterious eye syndrome with no solution
Despite over a decade of study, researchers are yet to discover what exactly causes SANS in astronauts who spend long periods in the microgravity of space and are therefore unsure how to either prevent or treat it or who might be at the highest risk.
According to Tyson Brunstetter, an aerospace optometrist at the Johnson Space Center in Houston, Texas, who was serving in the US Navy when he first read about the syndrome in 2011, he didn’t think at the time that it would be such a big challenge.
“I said, ‘It’s NASA. They’ll figure it out in six months.’ And yet here I am, part of the team trying to figure out what exactly is going on.”
Eye syndrome’s implications
Because of the potential severity of SANS, as well as the number of astronauts that could be exposed, NASA considers it one of its ‘red risks’ for a Mars mission, other issues including radiation exposure, changes in mental health, and difficulty maintaining adequate nutrition.
That said, not all of the changes associated with the syndrome seem to be permanent, and the majority, even the most severe cases of swelling, resolve after about 12 months back in normal gravity, Brunstetter said. Eyeball flattening and refractive-index shifts might be permanent, but they’re treatable with prescription lenses.
On top of that, NASA equips astronauts with the so-called space-anticipation glasses of varying intensity in case their vision changes during a mission, as so far, no one has had permanent vision loss due to SANS.
Meanwhile, longer missions might present a serious problem because, if the swelling (optic-disc edema) continues, the enlarged blind spot might start to interfere with vision and the choroidal folds (wrinkles) might distort vision like crumpled camera film warps the resulting photograph.
Causes could be many
One of the possible causes of SANS could be the fluid shift that happens in microgravity. On Earth, gravity pulls blood and cerebrospinal fluid towards the ground, while the heart and other muscles push them throughout the body. When there’s no gravity, more fluid than usual pools in the head.
Additionally, an interplay of high CO2 levels, vitamin deficiency, and genetics could have a role, as NASA scientists have observed improvement in patients with four ‘risk alleles’ identified in their genetic setup following vitamin treatment.
And while there’s still no exact answer regarding the causes or treatment for SANS, Scott Smith, a nutritionist at the Johnson Space Center who studies the syndrome, said that researchers will keep hunting for answers, pointing out that “there’s a lot of people out there with ideas.”
Elsewhere, preparations for deep space missions, including those to Mars, are going well in terms of fueling, and aerospace and defense company General Atomics has concluded a test of nuclear fuel for spacecraft in collaboration with the space agency at its Marshall Space Flight Center.
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