Episode 151: Martian Medicine 102
Future Dr. Collins discussed with Dr. Arreaza two common complications of astronauts in a hypothetical travel to Mars: Spaceflight-Associated Neuro-ocular Syndrome and mental illness.
Written by Wendy Collins, MSIV, Ross University School of Medicine. Comments by Hector Arreaza, MD.
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Arreaza: We are back for another episode of Martian Medicine! A couple months ago we published the episode Martian Medicine 101. We talked about radiation and its health risks for astronauts going beyond Low Earth Orbit such as a crew going to Mars. Today, we are going to be covering Martian Medicine 102, where we discuss some more risks from the article “Red risks for a journey to the red planet”. So, let’s just jump into it! The next risk we are going to talk about is Spaceflight-Associated Neuro-ocular Syndrome or SANS.
Wendy: Yes, so this used to be called Vision Impairment Intracranial Pressure because the syndrome affects astronauts' eyes and vision and can appear like idiopathic intracranial hypertension. But the name changed to SANS because is not associated with the classic symptoms of increased intracranial pressure in idiopathic intracranial hypertension such as severe headaches, transient vision obscurations, double vision, and pulsatile tinnitus. Also, it has never induced vision changes that meet the definiti on of vision impairment, as defined by the National Eye Institute. Its name change also reflects that the syndrome can affect the CNS well beyond the retina and optic nerve.
Arreaza: Let’s talk about SANS some more. SANS presents with an array of signs including edema of the optic disc and retinal nerve fiber, and what else?
Wendy: Edema of chorioretinal folds, globe flattening, and refractive error shifts. Flight duration is thought to play a role in the pathogenesis of SANS, as nearly all cases have been diagnosed during or immediately after long-duration spaceflight such as missions of 30 days duration or longer. But signs have been discovered as early as mission day 10. SANS has been studied in ISS crewmembers who are tested with optical coherence tomography (OCT), retinal imaging, visual acuity, a vision symptom questionnaire, Amsler grid, and ocular ultrasound.
Arreaza: About 69% of the US crewmembers on the ISS experience an increase in retinal thickness in at least one eye, indicating the presence of optic disc edema. This can cause an astronaut to experience blind spots and reduced visual function. Fortunately, to date, blind spots are uncommon and have not had an impact on mission performance.
Wendy: And chorioretinal folds if severe enough and located near the fovea, an astronaut can experience visual distortions or reduced visual acuity that cannot be corrected with glasses or contact lenses. Fortunately, and despite a prevalence of 15–20% in long-duration crewmembers, chorioretinal folds have not yet impacted astronauts’ visual performance during or after a mission.
Arreaza: A change in your glasses prescription is due to a change in the distance between the cornea and the fovea, and it occurs in about 16% of crewmembers during long-duration spaceflight. This risk is reduced by giving crewmembers with several pairs of “Space Anticipation Glasses” (or contact lenses). The crewmember can then select the appropriate lenses to correct visual acuity.
Wendy: From a longer-term perspective, SANS presents two main risks to crewmembers: optic disc edema and chorioretinal folds. It is unknown if a multi-year spaceflight like that to Mars will be associated with a higher prevalence, duration, and/or severity of optic disc edema compared to what has been experienced onboard the ISS. Since the retina and optic nerve are part of the CNS, if optic disc edema is severe enough, the crewmember risks a permanent loss of optic nerve and retinal nerve fiber tissue and thus, a permanent loss of visual function. But again, no astronaut has experienced SANS-related permanent vision loss and choroidal folds usually improved post-flight in affected crewmembers.
Arreaza: It is important to understand the pathogenesis of SANS. In microgravity, fluid can distribute uniformly. The fluid that normally pools in your legs due to gravity can now move to your head and cause congestion of the cerebral veins. The pathophysiology of SANS is that CSF outflow can be blocked, which increases intracranial pressure.
Wendy: There can be confounding variables such as exercise, high-sodium dietary intake, and high carbon dioxide levels. It is difficult to know much about SANS because there are not many crewmembers who have completed long-duration spaceflight. There is now enough evidence to state that SANS is not a male-only syndrome. Optical Coherence Tomography (OCT) has been used on the ISS since 2013, and it has allowed NASA to build a database of retinal and optic nerve images to understand SANS better. Research from this has shown that most long-duration astronauts present with some level of optic disc edema.
Arreaza: Now all NASA crewmembers receive pre- and post-flight MRIs of the brain. There is evidence that brain changes structure with longer space flights. For example, the ventricles of the brain enlarge with 2–3 mL of CSF in astronauts. Luckily, there has been no cognitive problems with this. Like with most space health concerns, more research is needed.
Wendy: In summary, SANS is a red risk and top priority to NASA and the human research program. The main concern with SANS is optic disc edema because it could lead to permanent vision impairment. And choroidal folds are also concerning for both short- and long-term flights. But for now, loss of visual acuity is successfully combatted with glasses. Certainly, the more astronauts and flights we take, the more we will learn about SANS.
Wendy: Sorry we took so long on SANS, it’s probably one of my favorites of all the red risk. Now let’s move onto the red risk that includes behavioral health and performance. Future long duration mission in which you are in an isolated and confined space such as a space craft surrounded by an inhospitable environment which humans are not meant to survive could be a problem for the crew’s behavioral and mental health.
Arreaza: This could affect the astronauts and their ability to complete their mission. Typically, astronauts enjoy space and report it is a positive experience. But psychological changes from being in space for a long time will likely be even more challenging.
Wendy: In the past, astronauts have reported ‘hostile’ and ‘irritable’ crew and symptoms of depression.
Arreaza: Stressors to the ISS include long work hours and high workload, and the discomfort of space motion sickness. No one likes vomiting.
Wendy: Being on the ISS, you are close to Earth, and it is easy to communicate with family and friends when needed. Going to Mars there will be communication delay and will make support more difficult. Astronauts on the ISS also have routinely received care packages, which will also not be available to boost morale. Crew members can also change by swapping out astronauts over a certain period, but the crew to Mars will also not have this ability to work with new people.
Arreaza: There are simulation projects to test human resilience. NASA does these kinds of testing at the Johnson Space Center. There is also research in Antarctica that has shown decreased mood and increased stress for scientists in extreme environments. There is also the Mars 500 mission.
Wendy: Yes, the Mars 500 mission was where a crew of 6 went into isolation in Moscow for 520 days to simulate a trip to Mars. The astronauts had to complete behavioral questionnaires weekly. One of the six reported depressive symptoms based on the Beck Depression Inventory. Two crew members who had the highest ratings of stress and exhaustion, also reported conflicts and sleep difficulties. Two crew members reported no adverse behavioral symptoms during the mission.
Wendy: So, I believe we’re done. We’ve covered Radiation, SANS, and behavioral health. I know this topic is probably unique for qWeek, but a lot of what we learn medically from our time in space does have applications to us on Earth. As a medical student advice, I have gotten from others in the field is pursue what you’re passionate about. Aerospace medicine is a growing field for clinicians from all specialties, so there’s no golden path to take. If you are interested more in this field, I highly recommend joining relevant associations specifically AsMA and AMRSO. And if you ever want to discuss aerospace medicine further, feel free to reach out to me at my Ross email!
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Conclusion: Now we conclude episode number 151, “Martian Medicine 102.” Future Dr. Collins explained that ocular issues are a potential problem when astronauts go to Mars, including Spaceflight-Associated Neuro-ocular Syndrome and vision impairments that would require changes in glass prescription, so, don’t forget to take extra pairs of glasses when you go to the red planet. Dr. Arreaza also joined the conversation by talking about the mental health challenges that many astronauts may face as they embark on a long trip to Mars in a secluded spacecraft. We look forward to more information on Martian Medicine as primary care on Mars may look surprisingly similar to primary care on Earth.
This week we thank Hector Arreaza and Wendy Collins. Audio editing by Adrianne Silva.
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References:
- Patel, Z.S., Brunstetter, T.J., Tarver, W.J. et al. Red risks for a journey to the red planet: The highest priority human health risks for a mission to Mars. npj Microgravity 6, 33 (2020). https://doi.org/10.1038/s41526-020-00124-6
- Royalty-free music used for this episode: Space Orbit by Scott Holmes, downloaded on July 20, 2022, from https://freemusicarchive.org/music/Scott_Holmes/.
