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One of the best parts of spaceflight is the view.
But if you’re on a long journey to Mars, you might
find your eyesight getting worse as you go, thanks to
something called spaceflight-associated neuro-ocular syndrome,
or SANS for short.
I just like to call it space eyes!
The weird thing is, scientists still don’t know
what causes space eyes, or SANS.
We should probably just call it SANS.
That’s what it’s actually called.
And while missing out on awesome views is disappointing,
an astronaut’s health is a much bigger issue.
So before we send people off into the final frontier,
we should probably solve one of the biggest problems of space medicine.
[♪ INTRO]
SANS tends to manifest as blurry vision, but it’s actually an umbrella term
that describes a collection of changes to an astronaut’s eyes and brain.
Inside the eyes, you can get a bunch of symptoms,
like swelling where the optic nerve enters the eye, folding of the retina,
which is the part of the eye that receives images,
or flattening of the back of the eye.
Meanwhile, further inside your head,
the brain might move toward the top of the skull.
The pituitary gland, which regulates a bunch of
hormones in your body, might change shape.
The cerebrospinal fluid that flows around your brain
might get redistributed.
And more.
There’s a lot that might happen, but any one astronaut
can experience none of these changes, or all of them.
And the longer someone is in space, the risk for
developing SANS appears to increase.
Now, the good news is that after most astronauts get back to Earth,
their vision completely recovers.
But the underlying structural changes might stick around for years,
and the effects can be cumulative if they end up going back to space.
For example, one astronaut who did a six-month space flight
came home with folds on his retina.
By the time he went on his next flight nine years later,
the folds were still there, but had lessened dramatically.
But after another six months in space,
those folds had not only come back,
there were even more folds plus some new swelling, too.
All this means that a trip to Mars,
which could take over two years if it’s a round trip,
won’t be easy on the eyes.
So it’s at the top of the list of things space
medicine researchers need to figure out.
Because despite how prevalent SANS is among astronauts,
we don’t actually know very much about it.
In part, that’s because we haven’t been studying it for very long.
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.
I’m talking vision tests, MRIs of the head and eyes, and ultrasounds.
Oh and don’t forget the lumbar punctures.
I’m sure those are super fun!
But some of these tests can even be done during spaceflight,
to see how things are changing in real time.
But as of 2020, roughly 12 astronauts go into space each year.
And that means all these studies have really 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.
Now, one option is parabolic flights with airplanes,
which let passengers experience real microgravity,
but only for roughly 20 seconds at a time.
Another is dry immersion, which simulates microgravity
by submerging subjects in a water tank
covered with stretchy, waterproof fabric.
So, basically the science version of a waterbed.
Except you might have to stay in it for weeks.
Some researchers are even putting donated human eyeballs directly
into a device that mimics the conditions of space to see what happens.
But the most common way to study SANS on Earth
is with head-down tilt bed-rest experiments.
You probably already figured out what this is.
You lie on your back while being tilted by 6 degrees,
so your head is lower than your feet.
Then you just hang out there for months.
If not a full year.
And while you’re hanging out, you can undergo the same testing
that astronauts do, like MRIs, and ultrasounds, and lumbar punctures.
But despite all these research techniques,
scientists still don’t know exactly what causes SANS.
One hypothesis is that it’s related to space
causing the pressure inside your head to increase.
In a microgravity environment, the fluids inside your body
get all redistributed, including inside your skull.
Veins on the surface of your brain can overfill with blood,
and cerebrospinal fluid may have trouble draining out of the brain.
These increase the overall pressure on your brain.
But not every astronaut with SANS has this elevated pressure,
and most that do don’t have the other symptoms
that usually accompany it.
So another hypothesis is that microgravity changes
how the cerebrospinal fluid functions,
specifically how it flows and drains around the optic nerve.
If something gets messed up there, trapping extra fluid in that spot,
it could explain why other parts of the brain
don’t always experience a pressure increase.
There’s also some evidence that there may be
a genetic component to SANS, and that
some people are more at risk than others.
In reality, it could very well be a combination of all of these things,
plus others, which makes it really hard to untangle.
But we do need to untangle it, because right now,
NASA considers SANS a top human spaceflight risk.
New tools are being developed that will allow astronauts
to do more extensive testing in flight,
so that we can get a better idea of how SANS develops
and diagnose astronauts early in that process.
But we also need to know more about prevention and treatment.
Diagnosing an astronaut with SANS while
they’re still in-flight doesn’t help us that much
if there’s nothing we can do about it.
Some research has suggested that
a lower body negative pressure device,
something that surrounds the lower body and pulls
fluid away from the head region, could be helpful for
protecting against or treating SANS.
Other suggested treatments include vitamin B supplements,
and even wearing swim goggles.
Now it’s crucial that we can get SANS figured out,
both because it’s having lasting impacts
on most of our current astronauts,
and because it makes spaceflights longer than a year really problematic.
Once we do figure it out, though, the door will be open
for astronauts to head to Mars, sans vision problems.