SANS (eye & brain changes)
Also: Spaceflight associated neuro-ocular syndrome · VIIP (former name)
Gravity FieldsHostile/Closed EnvironmentNeuro-ophthalmicIn-flightPostflight RecoveryLifetime SurveillanceLEO long-durationMars transit & surfacePublicClinicianResearcher
- About 70% of long-duration crew members show at least one sign of SANS. ◆◆◆◇ Moderate · F
- The cause is not established, and no countermeasure has been validated in flight. LBNP shows promise in short bed-rest studies. ◆◆◇◇ Low · A F
- NASA rates long-term health risk as requiring mitigation even for 6-month ISS missions (4×3), and 4×5 for Mars. ◆◆◆◆ High · E
Proposed certainty (◆ High → ◇ Very low) and evidence-type tags: F flight · A analog · M model/animal · C computational · E expert/operational/standards. AI-proposed, pending reviewer confirmation. How to read the grades.
NASA risk title (verbatim)
Risk of Spaceflight Associated Neuro-ocular Syndrome (SANS)
NASA short title: SANS · HRP element: Human Health Countermeasures (HHC) · Status: Active [current research ongoing] [1]
What it is
Spaceflight associated neuro-ocular syndrome (SANS) is a set of eye and brain findings seen only in people who fly in space. There is no equivalent disease on Earth [1]. Its hallmark signs are swelling of the optic disc, folds in the retina and choroid, flattening of the back of the eye, and a shift toward farsightedness [1].
Current evidence
- About 70% of crew members show one or more hallmark signs [1].
- SANS was first described in detail in 7 astronauts after ISS missions, and postflight questionnaires on vision changes from about 300 more astronauts were analyzed [4].
- The cause is unknown. Leading questions are the headward fluid shift and the role of intracranial pressure (ICP), why some people are affected and others aren’t, and where adaptation turns into disease [1].
- Strict 6° head-down tilt bed rest for 30 days produced optic disc swelling on Earth [5]. That makes it a useful, imperfect ground analog.
- In a 10-person crossover study, nightly lower body negative pressure (LBNP) during 3 days of bed rest reduced the increase in choroid area by 74% [6].
- Brain structure changes after long flights [7]. A link between SANS and brain structure or cognition has not been established [1].
NASA’s risk posture
NASA scores each risk for each design reference mission (DRM) as likelihood × consequence (LxC). Both run from 1 (lowest) to 5 (highest) on the HSRB’s 5×5 matrix [1][3]. Each score comes with a disposition, such as “Accepted”, “Requires Characterization” or “Requires Mitigation”. These ratings were last approved by NASA’s Human System Risk Board (HSRB) in 7/2022 [1].
| Mission | Duration | In-mission (operations) | Long-term health |
|---|---|---|---|
| LEO | Short (under 30 d) | 4x1 · Accepted | 2x2 · Accepted |
| LEO | Long (30 d–1 yr) | 4x3 · Accepted with Monitoring | 4x3 · Requires Mitigation |
| Lunar orbit | Short | 4x1 · Accepted | 2x2 · Accepted |
| Lunar orbit | Long | 4x3 · Accepted with Monitoring | 4x3 · Requires Mitigation |
| Lunar orbit + surface | Short | 4x1 · Accepted | 2x2 · Accepted |
| Lunar orbit + surface | Long | 4x3 · Accepted with Monitoring | 4x3 · Requires Mitigation |
| Mars preparatory | Under 1 yr | 4x3 · Accepted with Monitoring | 4x3 · Requires Mitigation |
| Mars planetary | 730–1,224 d | 4x4 · Requires Mitigation | 4x5 · Requires Mitigation |
Copied from the Human Research Roadmap on 2026-10-14. Ratings change. Check the live record before citing.
Open knowledge gaps
NASA lists 11 knowledge gaps for this risk, 11 of them open as of 2026-10-14 [1]. Each gap ID links to its page on the Human Research Roadmap (HRR).
Show NASA’s gap list (verbatim)
| Gap | NASA gap statement | Status |
|---|---|---|
| SANS-101 | Determine the relationship between fluid shifts (intravascular, interstitial, CSF) and ocular manifestations in astronauts during spaceflight. | Open |
| SANS-102 | Determine the relationship between the fluid shifts-induced ocular changes and fluid shifts in the CNS, including whether elevated intracranial pressure or brain edema play a role. | Open |
| SANS-103 | Determine whether ground-based induced fluid shifts lead to ocular manifestations. | Open |
| SANS-104 | Determine whether ocular manifestations can be induced by fluid shifts in animal models and whether this model can be used for more detailed mechanistic insights. | Open |
| SANS-201 | Determine if altered atmospheric conditions (e.g., elevated ambient CO2, mild hypoxia from exploration atmosphere) has a contributing role in the development of ocular manifestations. | Open |
| SANS-202 | Determine if genetic/metabolic/anatomic dispositions and biomarkers, and sex differences have a contributing role in the development of ocular manifestations. | Open |
| SANS-203 | Determine if radiation has a contributing role in the development of ocular manifestations. | Open |
| SANS-204 | Determine if sleep/glymphatics has a contributing role in the development of ocular manifestations. | Open |
| SANS-304 | Identify and evaluate candidate countermeasure(s) in a space flight analog | Open |
| SANS-403 | Test candidate countermeasure(s) in a space flight environment | Open |
| SANS-501 | Validate/optimize integrated countermeasures in the spaceflight environment | Open |
See also Open questions.
Active countermeasure research
- Clinical surveillance, in place. Since 2009 this has included preflight, in-flight and postflight OCT, ocular ultrasound and fundus imaging, MRI before flight and within 3 days of return, and long-term follow-up about every 3 years [1].
- Countermeasure testing. Remaining gaps cover testing candidate countermeasures in ground analogs and then in flight (SANS-304, SANS-403, SANS-501). HRR lists linked tasks including thigh-cuff and LBNP studies on the ISS and a B-vitamin supplement study [1].
- Mechanism research. Studies cover fluid shifts, direct and non-invasive ICP measurement, CO₂ and mild hypoxia, genetics and B-vitamin metabolism, and sleep and the brain’s waste-clearance (glymphatic) system (gaps SANS-101 to SANS-204) [1].
Project-level detail, including status, investigators and results, is in the NASA Task Book and on each HRR gap page.
Clinical articles
For practical, clinic-facing guidance, see:
Evidence profile
- Overall certainty
- ◆◆◆◇ Moderate (proposed)
- Evidence types
- F · Flight dataA · Terrestrial analogE · Expert / operational / standards
- Literature through
- 2026-10-14
- NASA source
- Human Research Roadmap risk page (last published 05/13/25; read 2026-10-14)
Requirements referenced 3
| Requirement | Title | Plain-language meaning |
|---|---|---|
| [V1 3003] (m) | In-Mission Preventive Health Care | Periodic SANS monitoring; prevention with countermeasures still to be validated. |
| [V1 3018] | Post-Mission Long-Term Monitoring | Longitudinal monitoring for health, injury and the long-term effects of spaceflight. |
| [V2 6004] | Nominal Vehicle/Habitat CO2 | One-hour average ppCO2 no more than 3 mmHg; CO2 is a suspected contributor. |
IDs as published in NASA-STD-3001 Vol. 1 Rev C (2023-09-15) and NASA-STD-3001 Vol. 2 Rev F (2026-07-14). NASA-STD-3001 binds NASA programs; it is not a regulation for commercial flights. Paraphrased. Standards quick reference.
References 8
- NASA Human Research Roadmap. Risk record: “Risk of Spaceflight Associated Neuro-ocular Syndrome (SANS)”. Accessed 2026-10-14. humanresearchroadmap.nasa.gov/Risks/?i=105 NASA E
- NASA Human Research Program. Evidence report for the SANS risk (approved April 7, 2022). humanresearchroadmap.nasa.gov/evidence/reports/SANS%20EB%202… NASA E
- Antonsen EL, et al. Updates to the NASA human system risk management process for space exploration. NPJ Microgravity. 2023;9:72. doi:10.1038/s41526-023-00305-z PMID:37679359 Peer-reviewed E
- Mader TH, et al. Optic disc edema, globe flattening, choroidal folds, and hyperopic shifts observed in astronauts after long-duration space flight. Ophthalmology. 2011;118(10):2058–2069. doi:10.1016/j.ophtha.2011.06.021 PMID:21849212 Peer-reviewed F
- Laurie SS, et al. Optic disc edema after 30 days of strict head-down tilt bed rest. Ophthalmology. 2019;126(3):467–468. doi:10.1016/j.ophtha.2018.09.042 PMID:30308219 Peer-reviewed A
- Hearon CM Jr, et al. Effect of nightly lower body negative pressure on choroid engorgement in a model of spaceflight-associated neuro-ocular syndrome: a randomized crossover trial. JAMA Ophthalmol. 2022;140(1):59–65. doi:10.1001/jamaophthalmol.2021.5200 PMID:34882176 Peer-reviewed A
- Roberts DR, et al. Effects of spaceflight on astronaut brain structure as indicated on MRI. N Engl J Med. 2017;377(18):1746–1753. doi:10.1056/NEJMoa1705129 PMID:29091569 Peer-reviewed F
- Lee AG, et al. Spaceflight associated neuro-ocular syndrome (SANS) and the neuro-ophthalmologic effects of microgravity: a review and an update. NPJ Microgravity. 2020;6:7. doi:10.1038/s41526-020-0097-9 PMID:32047839 Peer-reviewed E
Machine-checked on 2026-10-14: each URL resolved, each DOI's title/journal/year matched via Crossref, and claims were checked against the source text (abstract or full NASA page). Human verification against full text is still required before review. NASA documents are U.S. Government works (public domain) and are summarized with attribution; journal articles are summarized, not reproduced.
Article info
- Authors
- Pending (AI-assisted draft)
- Reviewer
- Pending review
- Last reviewed
- Pending review
- Literature through
- 2026-10-14
- AI-assisted
- Yes (disclosed)
- COI
- Pending
- License
- CC BY-SA 4.0
- Use
- Educational only · Disclaimer
- Cite this version
- Pending first edition