COMMENTARY

These NASA Docs Keep an Eye on Astronaut Health

Andrew N Wilner, MD; William J. Tarver, MD, MPH; Tyson J. Brunstetter, OD, PhD, MBA

Disclosures

September 26, 2019

This transcript has been edited for clarity.

Andrew N. Wilner, MD: Welcome to Medscape. I'm Dr Andrew Wilner. Today we're going to talk about a very special neuro-ocular syndrome that's affected only a very small population of the world. In fact, this population is otherwise extraordinarily healthy, but they have one thing in common: They are astronauts who have been exposed to microgravity. To speak about this, I'm really thrilled to have two participants from the National Aeronautics and Space Administration (NASA), Dr William Tarver and Dr Tyson Brunstetter. Thank you, gentlemen.

Tyson J. Brunstetter, OD, PhD, MBA: Good morning.

William J. Tarver, MD, MPH: Thank you for inviting us for this. We're excited to speak on it.

Wilner: To set the stage, I remember reading a paper about this in the journal Radiology[1] way back in 2012. Researchers performed MRIs on 27 astronauts and found that when it came to their eyeballs, they actually changed—there were kinks in the optic nerve and all kinds of strange things. In researching this, I found that, sure enough, there are papers everywhere about what is now called spaceflight-associated neuro-ocular syndrome (SANS), which the two of you know a great deal about.

Before we get to SANS, can you first tell us who you are and how you got involved in NASA?

Becoming NASA Doctors

Tarver: I always wanted to be a flight surgeon when I went to medical school. I don't know why. I never met or saw one. I thought, how do you do that?

I graduated medical school and almost didn't finish because I didn't want to get assigned internal medicine; I wanted to be a flight surgeon. So I went into aerospace medicine and occupational medicine, trained and board-certified through the Air Force, where I was for 9 years. Then I actually went into private practice for a little while.

One day, I got a call from NASA. My Air Force friends said, "We need a doc here." I said, "I've got a private practice and I'm enjoying myself." But I came to visit anyway. That's when I learned about a program called the Longitudinal Study of Astronaut Health, where all of the astronauts who've ever been to space get invited back to NASA. I said, "Oh, really? You mean, I can meet Neil Armstrong if I work here? Yes!" I was sold. I came to work here in 2005 and have not regretted it since. I'm living the dream.

Wilner: That's fantastic. Captain Brunstetter, tell us a little about your role in this research.

Brunstetter: As you mentioned, I am an officer in the US Navy. I am detailed here to NASA's Johnson Space Center in Houston, primarily to support the SANS team by acting as Dr Tarver's deputy.

Over the past 20 years, my niche has been mainly in research development, testing, and evaluation. As you can imagine, as an aerospace optometrist, it was in areas of ophthalmologic protection or enhanced visual performance—for example, refractive surgery. More recently, I have also been involved in testing and evaluating expeditionary medical devices used to treat the wounded fighters being evacuated from the battlefield.

I think those are some of the reasons why I've had this incredible opportunity to come here as a detail lead to Johnson. It's been really an answer to my dreams. And I think you're gonna hear the word "dreams" quite a bit today, because you have to pinch yourself when you're here.

My primary duties here are to help with the day-to-day activities and decision-making. I also act as a subject matter expert during actual on-orbit ocular data collections that we perform quite often, probably on average about once a month or so, with the astronauts on board the International Space Station. I also help with the testing certification process of new commercial off-the-shelf devices that we eventually deploy to the International Space Station. And finally, and this is especially important to SANS, I help to develop brand-new medical devices with ultra-small footprints that we can use on board a mission to Mars. And I'm very glad to be here.

Tarver: I'm very glad he's here too. He's the answer to my prayers, not only to my dreams.

Discovering and Defining SANS

Wilner: Has SANS always been the term used to describe this condition?

Tarver: It used to be called "vision impairment intracranial pressure." We changed that name so we could lessen the emphasis on what we were assuming was our problem, which was intracranial pressure. That is still one of the questions today. It's not solved, only hypothetical. We're still trying to get to the core of the intracranial pressure changes that happen with astronauts.

Brunstetter: Another issue with that name is the first two words: vision impairment. In reality, there are no true permanent vision impairments that occur in astronauts, as of today. We don't believe that SANS is a major threat for long-duration spaceflight of approximately 6 months. The real question is, what will occur during a mission to Mars? We don't know what's going to happen. That's why this new small-footprint equipment is so important.

Wilner: When these astronauts return home, I'm sure they get a very thorough physical. It appears that the first case, where something went wrong in the eye, was observed during one of these physicals in 2005. What did that discover?

Tarver: It was the first time in all of our spaceflight history that we had an astronaut return and we noticed disc edema. Prior to that, maybe some things have shown up, but this was the very first case of disc edema post-flight. We thoroughly evaluated it. That individual ended up at Mayo Clinic—we referred them to the best of the best to figure out what's going on—and found mildly elevated intracranial pressure, and really not much else. That was our sentinel case.

Since then, out of, I believe, 78 astronauts who have flown and been fully tested, we have diagnosed 10 cases of disc edema. Our disc edema tends to be very mild compared with what's out there in the world.

Because of this disc edema and that intracranial pressure question, we based all of our initial analysis on the idiopathic intracranial hypertension (IIH) model. Subsequent to that, with all of our detailed analysis, we're finding out that we don't have IIH. For example, the average astronaut is a 40ish years old, very fit male. That does not describe your typical IIH patient. And as we tease out details with an eye evaluation, we find that the eye does not look the same in our SANS condition when you compare it to IIH.

Brunstetter: The main device that we use to measure ocular changes before, during, and after spaceflight is optical coherence tomography (OCT). We're in the process of revamping that definition to take [the diagnosis of SANS] from a subjective test, which is the clinician looking at a photo, and making it more objective using OCT technology. So even though it's currently set at 10 cases out of approximately 78 folks tested, we believe that the number is somewhat different. We know that most everyone has some changes, from the very subtle to the clinically significant. We need to describe it better in the near future.

Wilner: Neurologists and optometrists know that disc edema is a serious thing. In reading the reports, I remember being struck that some of the astronauts had unilateral disc edema. I've never seen that in IIH. That said to me that this is a different animal, although they certainly may be related.

What Happens to the Brain Without Gravity?

Wilner: The other part of this that I found really fascinating was that we believe it's occurring in a setting of sustained low gravity, where you're weightless, and that the brain actually shifts in the skull. As a neurologist, that doesn't really seem like a good thing. Maybe it is, maybe it isn't. But it's certainly different from the norm. What happens to the brain during that process of weightlessness?

Tarver: The International Space Station is an absolutely unique place to work. Because there's no gravity, they are constantly floating for the whole time they're there. And you cannot recreate that on the ground.

We do a special-sequence MRI before they go fly and then once they come back. Dr Donna Roberts analyzes those data and has found that the brain shifts upwards.[2] Well, that shouldn't be a big shocker if they're really floating in space the whole time. One of the challenges with that is that we're wondering how much the flow of cerebrospinal fluid is changed in the microgravity world. Is there a higher reabsorption, a lower outflow? If your brain floats up, it could be compressing the sinuses that are draining the cerebrospinal fluid. That's one of our concerns.

There's so much data coming out lately related to SANS, including reports of ventricular size changes. There's also more MRI data comparing pre-flight with post-flight brain scans. But we need more because now we only do one post-flight MRI. We need MRIs at 6 months and at a year, but getting these is challenging.

Wilner: Send them to Memphis. We'll do them here.

Tarver: Well, there are practical problems surrounding this. When you say "send them to Memphis," it sounds great, but we have trouble just sending them to downtown Houston. Astronauts' time is so valuable and gets eaten up when they get back from flying. Minute by minute, everything counts. One of our challenges is to find an MRI close to us at a quality facility.

Brunstetter: And one that can do it within about 3 days of return.

Tarver: We get our post-flight MRIs pretty quickly, and that is the most precious time for astronauts.

Weighing the Risks to Astronauts' Eyes

Wilner: Let me depart from the science for a moment to talk a little bit about the astronauts. They know this is dangerous work. They're going up in a rocket, there's radiation, and they've come to grips with all of that stuff.

But what about when you tell them, "We don't really know what's going to happen to your eyeballs 10 years from now. Your vision is going to change. You're going to have to wear glasses." I know some of them have had extended refractive changes in their eyes, which is easily correctable, but nonetheless, this is not the same as when they left. Is this a psychological issue for them? How do the astronauts deal with this?

Tarver: One of the astronauts put things in perspective for me a while back. He said, "Doc, I'm worried about a rocket blowing up." So that's worry number one. Something 10 years down the road generally is not priority number one for them.

But they are concerned when they hear about this entity. We try to communicate with them as best we can, but it's complex. It's tough for doctors to understand this, and tougher for other nonphysicians.

What we do see is that if you have half a Doppler shift in your visual acuity and we need different lenses for you, you'll probably get all that back when you return from space. But if it's more than that, then you're going to need a different set of glasses when you come back and you'll need them for the rest of your life, it looks like.

Brunstetter: We're noticing a few different SANS signs that appear to be more or less permanent in some astronauts. If you look at the literature, you'll find MRI images of the flattening globe. It's literally the posterior side of the globe that is flattened, as compared to the rest of the eye. With that, it shifts the fovea, your central vision point, closer to the cornea. That's why these astronauts require a bump in their refractive power. As Dr Tarver mentioned, you may get some rebound on that, but if you have quite a bit of flattening, it's not going to rebound all the way.

We found that that is more or less a permanent situation for many astronauts. As mentioned, if you have to wear these new glasses on the ground after flight, you're probably going to have to wear them long-term. We're seeing this in astronauts who have flown more than 12 years ago.

Another sign would be choroidal folds. The choroid is the vascular bed on the posterior side of the retina, and it can develop ripples when under certain conditions. Think of it like old-school film for cameras, for those people who remember what that is. If you were to take the film, fold it up in your hand, stick it in the camera, and take photos, you would expect them to be distorted when they're developed. That's in theory—what could happen with choroidal folds if they're in just the right spot. There's not so much of a visual impact if they're in the periphery, because your brain will filter it out. But centrally it can cause vision impairment.

But we are finding that those choroidal folds in some astronauts can be permanent. In fact, just last year, we discovered an astronaut who last flew a long-duration spaceflight during Skylab in the 1970s who still has choroidal folds. We don't know how long those choroidal folds have been there; presumably since back then.

We also identified another astronaut who's had choroidal folds for over 5 years. But luckily, like we've said, we have not seen any permanent loss of visual function in any astronauts.

An Astronaut-Operated Eye Clinic

Wilner: You mentioned miniaturization and taking testing equipment up to the International Space Station. In neurology we often say "time is brain." Well, I guess to NASA, "weight is money" when it comes to sending stuff up to the International Space Station. What are the astronauts monitoring and how do they test each other?

Tarver: What's really incredible is that we have a very robust eye-measuring capability on the Space Station. We've got an OCT machine. Eye specialists ask us how we do that. We don't have eye techs constantly using this machine. The astronauts are trained to use the machine and acquire the data on the other astronauts. We come back with excellent OCT data. We have computer-based visual agility testing, fundoscopy, tonometry, Amsler grids, ocular ultrasounds.

Brunstetter: Many of these astronauts are test pilots or engineers; not many of them are physicians. I don't think any of them have been previously trained on how to use a fundoscope or OCT.

They get tremendous training from our folks here on the ground before they fly. And while they're up in orbit, during what we call "eye weeks," when we collect ocular data, we have a remote guider. That person communicates and interacts directly with the astronauts through satellite communication with a short little lag time. And in the same room is a subject matter expert, which could be me or a colleague from the clinic here on campus, whose job is to look at those data in real time and give a thumbs-up or thumbs-down as far as quality. The remote guider works with the astronauts, who do a phenomenal job at all of these things that they have not inherently learned over the course of their entire career. They've learned this 6 months before they've flown, which is amazing.

Wilner: I have a feeling that you can teach an astronaut to do just about anything with proper training. They are good subjects for that.

Dr William Tarver and Captain Tyson Brunstetter from NASA, thank you so much for joining us at Medscape to give this brief introduction to a very complex topic.

For Medscape viewers, if you enjoyed this program, please share it with your colleagues and leave comments below.

This is Dr Andrew Wilner, reporting for Medscape. Thank you.

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