NASA-STD-3001 Medical 

Technical Brief

Relevant Technical 

Requirements

Spaceflight 

Associated Neuroocular Syndrome 

(SANS)

OCHMO-MTB-001

NASA-STD-3001 Volume 1, Rev C

[V1 3001] Selection and Recertification

[V1 3002] Pre-Mission Preventive Health Care

[V1 3003] In-Mission Preventive Health Care

[V1 3004] In-Mission Medical Care

[V1 3016] Post-Mission Health Care

[V1 3018] Post-Mission Long-Term Monitoring

[V1 4020] In-Mission Nutrient Intake

[V1 5001] Medical Training

[V1 5002] Crewmember Training

[V1 5003] Crew Medical Officer Medical 

Training

[V1 6008] Crew Health Operations Concept 

Document

[V1 6009] Medical and Crew Health Technical 

Requirements Document

NASA-STD-3001 Volume 2, Rev D

[V2 6001] Trend Analysis of Environmental and 

Suit Data

[V2 6004] Nominal Vehicle/Habitat Carbon 

Dioxide 

[V2 6022] Atmospheric Monitoring and 

Alerting Parameters 

[V2 6107] Nominal Vehicle/Habitat 

Atmospheric Ventilation

[V2 7100] Food Nutrient Composition

[V2 7043] Medical Capability

[V2 7045] Medical Equipment Usability

NASA astronaut Tim Kopra conducts a self-exam as part of 

the Ocular Health investigation on the ISS.

Executive Summary

Spaceflight Associated Neuro-ocular Syndrome 

(SANS) refers to a constellation of ocular findings 

including optic disc edema, posterior globe 

flattening, chorioretinal folds, and hyperopic shifts in 

refractive error observed in astronauts during and 

following long-duration spaceflight. SANS etiology is 

not certain, but altered gravity and fluid shifts 

resulting in venous congestion and intracranial 

pressure elevations are the most likely causes. The 

concerns associated with signs and symptoms of 

SANS are decrements in vision that can affect inflight crew capability and task performance as well 

as long-term eye health risks that could result from 

eye and brain structural changes that develop during 

spaceflight. In this technical brief we discuss the 

pathophysiology, and countermeasures being used 

and studied in order mitigate these risks.
NASA-STD-3001 Technical Brief

OCHMO-MTB-001

Spaceflight Associated Neuro-ocular 

Syndrome (SANS)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Medical Technical Brief is derived from NASA-STD-3001 and NASA medical operations and is 

for reference only. The aim of this Medical Brief is to share clinical knowledge and provide best 

practices, not to deliver direct medical care recommendations or guidance for individuals.

Eye Anatomy

The etiology of SANS is uncertain; one 

theory is that SANS is thought to be a 

result of fluid shifts during gravity 

changes causing increased fluid and 

pressure to the head and eye, leading to 

physiological changes (optic disc edema 

(ODE), globe flattening (GF), and 

chorioretinal folds that can result in 

vision changes (hyperopic vision shifts, 

refractive vision decrements). The main 

concerns of SANS are increased risk of 

vision decrements in-flight, negatively 

affecting crewmember performance and 

risk of irreversible vision decrements 

causing long term vision changes/loss. 

Potential Causes of SANS

• Increased intracranial pressure due to fluid shifts caused by 

microgravity loss of hydrostatic pressure, venous congestion, 

or limited cerebrospinal fluid drainage.

• Nutrition: cyanocobalamin and folate-dependent one carbon 

pathway variability.

• Brain ventricular absorption changes and intracranial 

compartmentalization.

• Impaired sleep which may reduce lymphatic/glymphatic 

clearance from the brain and eye.

Potential Risk Factors

• Space/microgravity environment

• Nutritional changes

• CO2 air pockets

• Repeat flyers

• Increased mission duration and 

severity of SANS signs may increase 

risk for potential in-mission and 

long-term health consequences

• Crowded/small optic nerve head

Idiopathic Intracranial 

Hypertension (IIH) has 

some similar 

characteristics to SANS, 

as both present with 

optic disc edema; 

however, they share 

more differences than 

similarities. Mildly 

elevated ICP caused by 

gravity-induced fluid 

shifts is one hypothesis 

for the potential cause of 

SANS.

Physiology

Image Source: All About Vision

Symptoms of SANS. Image Source: NASA

02/21/2024 2
NASA-STD-3001 Technical Brief

OCHMO-MTB-001

Spaceflight Associated Neuro-ocular 

Syndrome (SANS)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Medical Technical Brief is derived from NASA-STD-3001 and NASA medical operations and is 

for reference only. The aim of this Medical Brief is to share clinical knowledge and provide best 

practices, not to deliver direct medical care recommendations or guidance for individuals.

Optic Disc Edema (ODE) Unilateral or bilateral swelling of the 

intraocular portion of the optic nerve, associated with highest 

risk to crewmember vision. It can be measured by direct 

clinical observation using fundoscopy and photography (see 

right), Optical Coherence Tomography (OCT), and in more 

severe cases, MRI and ultrasound. Images are gathered preflight, in-flight and post-flight, see below for example. 

Percent of crewmembers that present with ocular findings 

of SANS in which data exist. USOS, US Orbital Segment 

ΔTRT, change in global total retinal

The primary concern of SANS is that the changes in 

ocular structure may lead to uncorrectable vision 

changes either during or after a spaceflight mission, 

affecting crew capability/task performance and 

possible long term health decrements..

70% of crew are reported to have one or more signs of SANS and 18% of crewmembers are diagnosed 

with clinically concerning SANS during long duration spaceflight. To date, no crew have reported 

uncorrectable vision changes following spaceflight.

Idiopathic Intracranial hypertension (IIH) is similar to SANS and present with ODE and ICP. Terrestrial IIH 

has different characteristics than SANS and fluid shifts caused by gravity-induced ICP is the leading 

hypothesis for the cause of SANS.

ODE images right: (Top) Pre-flight images of the right and left optic discs. 

(Bottom) Post-flight images of the optic nerve head showing in more detail 

the extent of the edematous optic disc margins and glutting of the superior 

and inferior nerve fiber layer axons. Mader et al. (2011)

Pathophysiology

OCT data is presented in pre- to in-flight 

changes in peripapillary TRT measured by 

OCT. ΔTRT of ±19.4 μm (blue bands) indicates 

the range of normal measurement variability; 

greater than this is the earliest sign of ODE. 

The dark vertical bars represent eyes with 

ODE of Frisen grade of 1, as detected by 

fundoscopy. The orange line represents a 

ΔTRT of 55 μm.

Total Retinal Thickness (TRT) refers to swelling of the optic disc that spills over into the retina next to it, 

causing that retina to thicken. 

02/21/2024 3
NASA-STD-3001 Technical Brief

OCHMO-MTB-001

Spaceflight Associated Neuro-ocular 

Syndrome (SANS)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Medical Technical Brief is derived from NASA-STD-3001 and NASA medical operations and is 

for reference only. The aim of this Medical Brief is to share clinical knowledge and provide best 

practices, not to deliver direct medical care recommendations or guidance for individuals.

Chorioretinal folds (CF) refer to folding of the superficial retinal layers (i.e., retinal folds), retina’s basement 

membrane (i.e., choroidal folds), and/or edges of the optic nerve head (i.e., peripapillary wrinkles). 

Terrestrially they are caused when unusual force is placed on the retina, causing folds. When located near 

the fovea CF can cause distorted or reduced visual acuity. Choroidal folds are present in approximately 25% 

of long-duration crewmembers. Moderate to severe choroidal folds near the fovea have been detected in 

long duration crewmembers. Persistent progressive folds during missions can potentially degrade vision and 

increase risk of debilitating uncorrectable vision defects. To date no permanent losses in vision have been 

detected in any crewmembers. 

Chorioretinal folds are detectable by fundoscopy or 

OCT. Crewmembers are monitored pre-flight, inflight, and post-flight for changes and any associated 

vision decrements. 

Pre-flight (top) and 30 days prior to return (R-30 bottom), 

comparison on OCTwith R-30 showcasing peripapilliary wrinkles, 

choroidal folds, and optic disc edema. Image: HSRB NASA

SANS overview and Clinical Practice Guideline NASA 2020

Laurie et al. determined an increase in TRT of >19.4 μm marks the earliest signs of ODE in SANS. 

SANS Overview and Clinical Practice Guideline, NASA 2020.

Multicolor imaging pre-flight, 30 days prior to returning 

to Earth (R-30), and 4 days after return (R+4). Choroidal 

folds are noted in R-30 and R+4. Possible protrusion of 

optic nerve head is visible at R-30 and R+4. 

Pathophysiology

Frisén scale Describes stages of optic 

disc swelling (grades 0-5). It is the 

standard classification method for 

terrestrial ODE, and is used 

internationally in clinical and research 

practice. Indications for post-flight 

lumbar punctures in SANS cases are: 

>/= Frisen grade ODE as determined by 

fundoscopy, and >/= 55um average 

increase in peripapillary total retinal 

thickness (TRT) in either eye by OCT.

02/21/2024 4
NASA-STD-3001 Technical Brief

OCHMO-MTB-001

Spaceflight Associated Neuro-ocular 

Syndrome (SANS)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Medical Technical Brief is derived from NASA-STD-3001 and NASA medical operations and is 

for reference only. The aim of this Medical Brief is to share clinical knowledge and provide best 

practices, not to deliver direct medical care recommendations or guidance for individuals.

Posterior Globe flattening. Source: J. Ann & E. Kim (2015).

Globe Flattening Posterior globe flattening (GF) refers to shortening of the eye during spaceflight. 

Approximately 25% of long-duration crewmembers experience GF centered at the insertion point of the 

optic nerve into the globe. If severe, this can cause a hyperopic shift in refractive error and vision 

decrements. Globe flattening is usually associated with force pressing on the eye from behind (e.g., 

retrobulbar tumor). Globe flattening is measured pre- and post-flight using an MRI, and in-flight using 

ultrasound (less reliable than terrestrial MRI). Larger GF has been associated with ODE and is being 

monitored to determine vision decrements and associated changes. Long term crewmember health 

monitoring via MRI shows persistent GF has appeared in crewmembers greater than 7 years after flight. 

Hyperopic vision shifts Spaceflight associated alterations in visual acuity have been identified over the past 

40 years. 29% of short duration crewmembers and 60% of long duration crew have reported vision 

degradation. Mader et al. 2011 study showed post-mission shift ranging from +0.5 to +2.0 change in 

diopter measurement. Hyperopic refractive shift changes in visual acuity occur when focal point is adjusted 

due to GF. Vision degradation risk increases the longer you are in space. All crewmembers post-flight vision 

has been correctable to 20/20 or better with updated prescription. Hyperopic changes in refractive error 

occur when the retina's location shifts. Potential causes of hyperopic shift include ODE, GF, choroid 

thickness, and changes to the optical components of the eye. 

Refractive error is a measurement of lens power 

needed to correctly focus light on the retina of the 

eye. Myopia (near-sightedness) occurs when light 

focuses in front of the retina and is corrected with 

‘minus’ lenses, and hyperopia (far-sightedness) is 

when light focuses behind the retina and is 

corrected with ‘plus’ lenses. Myopic patients 

experience blurred distance vision, whereas 

hyperopic patients may experience eyestrain and/or 

blurred near vision if their accommodative system 

(i.e., system that focuses the eye by changing the 

shape of the crystalline lens) is not able to 

compensate for their hyperopic refractive error.

Pathophysiology

Visual acuity shift example. Source: NASA

Source: All About Vision (2022)

02/21/2024 5
NASA-STD-3001 Technical Brief

OCHMO-MTB-001

Spaceflight Associated Neuro-ocular 

Syndrome (SANS)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Medical Technical Brief is derived from NASA-STD-3001 and NASA medical operations and is 

for reference only. The aim of this Medical Brief is to share clinical knowledge and provide best 

practices, not to deliver direct medical care recommendations or guidance for individuals.

Equipment/Diagnostic 

Method Image Example Purpose/Use Schedule

Comprehensive Eye 

Exam

Variety of eye examinations given 

including eye charts, OCT, 

ultrasound, and others to assess eye 

functioning and health

Pre- and post-flight

Fundoscopy Fundoscopy assesses the gross 

structural changes in the optic nerve 

head and retina; detects ODE, CF

Pre-, in-, and postflight 

Optical Coherence 

Tomography (OCT)

OCT is used to assess the retina, 

choroid, and optic nerve head 

anatomy; measures ODE, CF

Pre-, in-, and postflight 

Ultrasound Ultrasound assesses structural 

changes within/posterior to eye; 

measures in-flight globe flattening, 

optic nerve head protrusion, and 

other ocular defects

Pre-, in-, and postflight 

MRI Eye MRI is used to detect structural 

changes in the eye

Pre- and post-flight

Example eye testing 

schedule. Source: NASA

02/21/2024 6

Monitoring & Diagnostics
NASA-STD-3001 Technical Brief

OCHMO-MTB-001

Spaceflight Associated Neuro-ocular 

Syndrome (SANS)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Medical Technical Brief is derived from NASA-STD-3001 and NASA medical operations and is 

for reference only. The aim of this Medical Brief is to share clinical knowledge and provide best 

practices, not to deliver direct medical care recommendations or guidance for individuals.

Equipment/Diagnostic 

Method Image Example Purpose/Use Schedule

Ocular Biometry Measures axial length of the eye. 

Quantifies pre- to post-flight shifts in 

retinal position, correlating with 

shifts in refractive error"

Pre- and post-flight

Visual Acuity Test Visual Acuity Tests and Visual Field 

Tests assess the optical fidelity 

functional state of the eye

Pre-, in-, and postflight 

Visual Field Test Will be deployed 

on future ISS 

mission

Lumbar Puncture Direct measurement of cerebrospinal 

fluid (CSF) pressure. Measures CSF 

accompanying ODE. CSF >18 cm 

considered high normal, CSF > 25cm 

requires treatment

Post-flight

Amsler Grid Pre-, in-, and postflight 

02/21/2024 7

Monitoring & Diagnostics
NASA-STD-3001 Technical Brief

OCHMO-MTB-001

Spaceflight Associated Neuro-ocular 

Syndrome (SANS)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Medical Technical Brief is derived from NASA-STD-3001 and NASA medical operations and is 

for reference only. The aim of this Medical Brief is to share clinical knowledge and provide best 

practices, not to deliver direct medical care recommendations or guidance for individuals.

Equipment Training

SANS is a known risk to spaceflight, therefore monitoring begins at crew selection. Training to operate 

SANS diagnostic devices occurs prior to spaceflight; however, it may be months before this training is 

actually used. Crewmembers are trained to identify SANS symptoms and to use detection and monitoring 

equipment. Crew are trained in SANS equipment: OCT, fundoscope, and ocular ultrasound.

Training Schedule

Pre-flight:

Nominal schedule ocular training begins 2 years before flight. Most pre-flight is hands on training with 

devices prior to flight. Some crewmembers may have more specialized training than others. 

Ocular training includes:

• Fundoscopy – total of 2.5 hours across 2 sessions

• Tonometry – 1.5 hours to one crew designated as SANS specialist

• Ocular ultrasound – 1 hour

• OCT – 2.5 hours across 2 sessions

• First session is within 12 months of launch, second session is within 3 months prior to launch

In-flight:

• Nominal schedule for ‘Eye Weeks’, which consists of 2-3 days (FD 30, 90, and R-30) at a time of 

monitoring and testing including OCT:

• 1 month into mission

• 1 month prior to return

• During 6-month flights, OCT operator tests 3 times FD 30, 90, and R-30

• Additional testing can be performed as clinically indicated at any point during mission

Ground assistance:

On ISS, in-flight crew receive assistance from ground with monitoring equipment.

• Ground based remote guider — person who has trained crew how to use equipment, this person is the 

only person in the room who can speak directly with crew with advice, suggestions, and guidance to 

use equipment.

• Subject Matter Expert (SME) — monitors two displays: 1) cabin view of subject and operator; 2) data to 

review for clinical requirements.

• Biomedical Engineer (BME) — in room and online to interact and guide data collections.

Monitoring & Diagnostics

02/21/2024 8
NASA-STD-3001 Technical Brief

OCHMO-MTB-001

Spaceflight Associated Neuro-ocular 

Syndrome (SANS)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Medical Technical Brief is derived from NASA-STD-3001 and NASA medical operations and is 

for reference only. The aim of this Medical Brief is to share clinical knowledge and provide best 

practices, not to deliver direct medical care recommendations or guidance for individuals.

Medical Evaluation Documents (MED) Volume B – Pre-Flight, In-Flight, and Post-Flight Medical 

Evaluation Requirements for Long-duration ISS Crewmembers

Ocular assessments are performed pre-flight, in-flight, and post-flight, as crewmembers have presented 

with significant changes in ocular structure and function in-flight and post-fight.

Pre-flight In-flight Post-flight

18-21 months prior:

MRI brain and orbits, visual 

acuity (distance and near), 

refraction (manifest and 

cycloplegic), Amsler grid, pupil 

reflexes, extraocular muscle 

balance, biomicroscopy, dialated

fundoscopy, retinal photography, 

tonometry, OCT, optical 

biometry

6-9 months prior: 2-D imaging 

ultrasound

Ocular questionnaire, visual 

acuity, Amsler grid, fundoscopy, 

2-D imaging ultrasound, OCT 

(high-resolution). Threshold 

visual fields (measurement 

equipment being deployed in 

calendar year 2024. Additional 

testing as clinically indicated.

R+1/3 days:

Ocular questionnaire, visual 

acuity, refraction, threshold 

visual fields, Amsler grid, pupil 

reflexes, extraocular muscle 

balance, fundoscopy,retinal

photography, tonometry, OCT, 

Optical biometry, 2-D imaging 

ultrasound, MRI brain and orbits 

– special visual impairment and 

intracranial pressure protocol

Additional testing as clinically 

indicated.

MED B Evaluation

[V1 3003] In Mission Preventive Health CareAll programs shall provide training, in-mission capabilities, and resources to 

monitor physiological and psychosocial well-being and enable delivery of in-mission preventive health care, based on 

epidemiological evidence-based probabilistic risk assessment (PRA), individual crewmember needs, clinical practice 

guidelines, flight surgeon expertise, historical review, mission parameters, and vehicle-derived limitations. These 

analyses consider the needs and limitations of each specific vehicle and design reference mission (DRM) with particular 

attention to parameters such as mission duration, expected return time to Earth, mission route and destination, 

expected radiation profile, concept of operations, and more. In-mission preventive care includes, but is not limited to:

Requirement has 18 bullets, SANS specific information located in bullet m as seen below

m. Spaceflight Associated Neuro-Ocular Syndrome (SANS) periodic monitoring, and prevention with to-be-determined 

countermeasures (to be validated by research in the coming years). 

[V1 3004] In-Mission Medical Care All programs shall provide training, in-mission medical capabilities, and resources to 

diagnose and treat potential medical conditions based on epidemiological evidence-based PRA, individual crewmember 

needs, clinical practice guidelines, flight surgeon expertise, historical review, mission parameters, and vehicle-derived 

limitations. These analyses consider the needs and limitations of each specific vehicle and design reference mission 

(DRM) with particular attention to parameters such as mission duration, expected return time to Earth, mission route 

and destination, expected radiation profile, concept of operations, and more. In-mission capabilities (including hardware 

and software), resources (including consumables), and training to enable in-mission medical care, and behavioral care, 

are to include, but are not limited to: Requirement has 22 bullets, SANS specific information located in bullet g as seen 

below 

g. Capability to provide deployed crewmembers with optical correction (e.g., glasses) with increased levels of power to 

mitigate SANS-induced changes in refractive error. 

From: NASA-STD-3001 Volume 1

02/21/2024 9
NASA-STD-3001 Technical Brief

OCHMO-MTB-001

Spaceflight Associated Neuro-ocular 

Syndrome (SANS)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Medical Technical Brief is derived from NASA-STD-3001 and NASA medical operations and is 

for reference only. The aim of this Medical Brief is to share clinical knowledge and provide best 

practices, not to deliver direct medical care recommendations or guidance for individuals.

Clinical Practice Guideline

Reference Data

Figure 1: SANS Testing Overview

02/21/2024 10
NASA-STD-3001 Technical Brief

OCHMO-MTB-001

Spaceflight Associated Neuro-ocular 

Syndrome (SANS)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Medical Technical Brief is derived from NASA-STD-3001 and NASA medical operations and is 

for reference only. The aim of this Medical Brief is to share clinical knowledge and provide best 

practices, not to deliver direct medical care recommendations or guidance for individuals.

Clinical Practice Guideline

Reference Data

Figure 2: Cerebrospinal Fluid (CSF) Pressure 

Considerations and Guidance

02/21/2024 11
NASA-STD-3001 Technical Brief

OCHMO-MTB-001

Spaceflight Associated Neuro-ocular 

Syndrome (SANS)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Medical Technical Brief is derived from NASA-STD-3001 and NASA medical operations and is 

for reference only. The aim of this Medical Brief is to share clinical knowledge and provide best 

practices, not to deliver direct medical care recommendations or guidance for individuals.

Lower Body Negative Pressure Under consideration as a preventive 

countermeasure for fluid shift effects and SANS. Thigh cuffs may 

reduce fluid shifts and improve venous congestion and ICP changes.

Supplements/Nutrition Crewmembers can be given B vitamins (Bcomplex) in-flight, which are currently being studied for their 

effects on SANS including; affecting homocysteine pathways and 

improving microvascular function and reduce edema. 

Medications No medications are currently proven to mitigate SANS, 

but efforts are ongoing. Potential medications are primarily aimed 

at lowering ICP (e.g., acetazolamide, which reduces ICP in 

terrestrial IIH patients).

Space Anticipation Glasses Used to help crewmembers with inflight vision changes due to hyperopic shifts. All crew fly with at 

least 3 pairs of prescription lenses of varying power to help 

compensate for vision decrements in-flight. 

“All CSF pressures ≥ 25 cm H2O require special consideration 

by the Astronaut Medical Board (AMB)/ Multilateral Space 

Medicine Board (MSMB) to pursue continued flight status. 

Final waiver approval is the authority of the NASA Chief 

Health and Medical Officer (CHMO).” NASA HSRB 2022

Ong, Tarver, Brunstetter, Mader, Gibson, & Mason (2023)

Countermeasures & Treatment

02/21/2024 12
NASA-STD-3001 Technical Brief

OCHMO-MTB-001

Spaceflight Associated Neuro-ocular 

Syndrome (SANS)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Medical Technical Brief is derived from NASA-STD-3001 and NASA medical operations and is 

for reference only. The aim of this Medical Brief is to share clinical knowledge and provide best 

practices, not to deliver direct medical care recommendations or guidance for individuals.

Elevated Intracranial Pressure 

The pathogenesis of SANS ODE is unknown. Terrestrially, the significance of ICP on SANS remains unclear. 

However, based on the collection of SANS pathophysiology (i.e., ODE, chorioretinal folds, globe flattening, 

and hyperopic shifts), it is reasonable to hypothesize that ICP may be mildly elevated in SANS, but ICP 

measures have not been made during spaceflight so no definite in-flight conclusions can be made. 

• Treatment of spaceflight-associated elevated ICP in an astronaut will occur on a case-by-case basis since 

we do not yet have adequate experience to give clear and well-tested treatments. Generally, post-flight 

CSFOP ≥25 cm H2O should be given treatment consideration, particularly in the presence of new-onset 

optic disc edema and/or scotoma.

• For more serious cases of suspected ICP, lumbar punctures are given. Indications for post-flight lumbar 

punctures in SANS cases have 2 requirements: ≥ 1 Frisen grade ODE in either eye, as determined by 

fundoscopy, and/or ≥ 55 μm average increase in peripapillary TRT in either eye, as determined by OCT. 

Medication Usage Side Effects

Diamox Interfering with the sodium pump in the ciliary body, reducing 

the osmolality of aqueous humor, lowering the osmotic 

gradient and, thereby, aqueous volume. This reduces IOP and 

improves optic perfusion pressure.

Nausea, fatigue, 

diarrhea, vomiting, 

paresthesia, and 

decreased intraocular 

pressure

Topamax Inhibits choroid plexus carbonic anhydrase, leading to 

decreased CSF secretion and the consequent control of 

intracranial pressure.

Vision disturbances, 

dizziness, drowsiness, 

confusion, speech and 

memory issues

11B HSD-1 Intracellular enzyme converts inactive cortisone to active 

cortisol, reduces CSF secretion.

Under study

GLP-1 agonist Gut peptide with diuretic effect reducing NA+ re-absorption in 

renal proximal tubule, increasing NA+ water excretion 

contributing to possible reduction in CSF production.

Nausea

Lumbar puncture consists of a needle inserted into the 

space between two lumbar bones (vertebrae) to 

remove a sample of cerebrospinal fluid. A lumbar 

puncture is performed to determine if the pressure of 

the CSF is elevated.

Countermeasures & Treatment

Medications are currently being considered as a countermeasure to SANS. Of these medications, 

acetazolamide (Diamox) is the only one available onboard the ISS, but side effects limit the scenarios 

where it may be considered. Other potential SANS medications are listed below.

02/21/2024 13
NASA-STD-3001 Technical Brief

OCHMO-MTB-001

Spaceflight Associated Neuro-ocular 

Syndrome (SANS)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Medical Technical Brief is derived from NASA-STD-3001 and NASA medical operations and is 

for reference only. The aim of this Medical Brief is to share clinical knowledge and provide best 

practices, not to deliver direct medical care recommendations or guidance for individuals.

Title Source

Optic disc edema, globe flattening, choroidal folds, and hyperopic shifts observed 

in astronauts after long-duration space flight (2011)

Ophthalmology

DOI: 10.1016/j.ophtha.2011.06.021

Optic disc edema in an astronaut after repeat long-duration space flight (2013) Journal of Neuro-Ophthalmology

DOI: 10.1097/WNO.0b013e31829b41a6

Association of Structural Changes in the Brain and Retina After Long-Duration 

Spaceflight (2021)

JAMA Ophthalmology

DOI: 10.1001/jamaophthalmol.2021.1400

Changes in the Optic Nerve Head and Choroid Over 1 Year of Spaceflight (2021) JAMA Ophthalmology

DOI: 10.1001/jamaophthalmol.2021.0931

Ocular Deformations in Spaceflight-Associated Neuro-Ocular Syndrome and 

Idiopathic Intracranial Hypertension (2023)

Investigative Ophthalmology & Visual 

Science 

DOI: 10.1167/iovs.64.3.32

MRI-based quantification of posterior ocular globe flattening during 60 days of 

strict 6° head-down tilt bed rest with and without daily centrifugation (2022)

Journal of Applied Physiology

DOI: 0.1152/japplphysiol.00082.2022

Identification of Factors Associated With the Development of Optic Disc Edema 

During Spaceflight (2022)

JAMA Ophthalmology

DOI: 10.1001/jamaophthalmol.2022.4396

Noninvasive indicators of intracranial pressure before, during, and after longduration spaceflight (2022)Journal of Applied Physiology

DOI: 10.1152/japplphysiol.00625.2021

Changes in Optic Nerve Head and Retinal Morphology During Spaceflight and 

Acute Fluid Shift Reversal (2022)

Journal of Applied Physiology

DOI: 10.1001/jamaophthalmol.2022.1946

Cerebrovascular Effects of Lower Body Negative Pressure at 3T MRI: Implications 

for Long-Duration Space Travel (2022)

Journal of Magnetic Resonance Imaging

DOI: 10.1002/jmri.28102

Optic disc edema and chorioretinal folds develop during strict 6° head-down tilt 

bed rest with or without artificial gravity (2021)

Physiological Reports

DOI: 10.14814/phy2.14977

Lower body negative pressure reduces jugular and portal vein volumes and 

counteracts the elevation of middle cerebral vein velocity during long-duration 

spaceflight (2021)

Journal of Applied Physiology

DOI: 10.1152/japplphysiol.00231.2021

Intraocular pressure and choroidal thickness respond differently to lower body 

negative pressure during spaceflight (2021)

Journal of Applied Physiology

DOI: 10.1152/japplphysiol.01040.2020

Association of Structural Changes in the Brain and Retina After Long-Duration 

Spaceflight (2021)

JAMA Ophthalmology

DOI: 10.1001/jamaophthalmol.2021.1400

Mechanical countermeasures to headward fluid shifts (2021) Journal of Applied Physiology

DOI: 10.1152/japplphysiol.00863.2020

Effects of head-down tilt bed rest plus elevated CO2 on cognitive performance 

(2021)

Journal of Applied Physiology

DOI: 10.1152/japplphysiol.00865.2020

Literature Review

02/21/2024 14
NASA-STD-3001 Technical Brief

OCHMO-MTB-001

Spaceflight Associated Neuro-ocular 

Syndrome (SANS)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Medical Technical Brief is derived from NASA-STD-3001 and NASA medical operations and is 

for reference only. The aim of this Medical Brief is to share clinical knowledge and provide best 

practices, not to deliver direct medical care recommendations or guidance for individuals.

Back-Up

02/21/2024 15
NASA-STD-3001 Technical Brief

OCHMO-MTB-001

Spaceflight Associated Neuro-ocular 

Syndrome (SANS)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Medical Technical Brief is derived from NASA-STD-3001 and NASA medical operations and is 

for reference only. The aim of this Medical Brief is to share clinical knowledge and provide best 

practices, not to deliver direct medical care recommendations or guidance for individuals.

NASA-STD-3001 Volume 1 Revision C

[V1 3001] Selection and Recertification Crewmembers shall be medically and psychologically selected 

and annually recertified following the guidance in OCHMO-STD-100.1A, NASA Astronaut Medical 

Standards Selection and Annual Recertification.

[V1 3002] Pre-Mission Preventive Health Care Pre-mission preventive strategies shall be used to reduce 

in-mission and long-term health medical risks including, but not limited to: (see NASA-STD-3001 Volume 1 

Rev C for full technical requirement).

[V1 3003] In-Mission Preventive Health Care All programs shall provide training, in-mission capabilities, 

and resources to monitor physiological and psychosocial well-being and enable delivery of in-mission 

preventive health care, based on epidemiological evidence-based probabilistic risk assessment (PRA), 

individual crewmember needs, clinical practice guidelines, flight surgeon expertise, historical review, 

mission parameters, and vehicle-derived limitations. These analyses consider the needs and limitations of 

each specific vehicle and design reference mission (DRM) with particular attention to parameters such as 

mission duration, expected return time to Earth, mission route and destination, expected radiation profile, 

concept of operations, and more. In-mission preventive care includes, but is not limited to: (see NASASTD-3001, Volume 1 Rev C for full standard).

[V1 3004] In-Mission Medical Care All programs shall provide training, in-mission medical capabilities, 

and resources to diagnose and treat potential medical conditions based on epidemiological evidencebased PRA, individual crewmember needs, clinical practice guidelines, flight surgeon expertise, historical 

review, mission parameters, and vehicle-derived limitations. These analyses consider the needs and 

limitations of each specific vehicle and design reference mission (DRM) with particular attention to 

parameters such as mission duration, expected return time to Earth, mission route and destination, 

expected radiation profile, concept of operations, and more. In-mission capabilities (including hardware 

and software), resources (including consumables), and training to enable in-mission medical care, and 

behavioral care, are to include, but are not limited to: (see NASA-STD-3001, Volume 1 Rev C for full 

standard).

[V1 3016] Post-Mission Health Care Post-mission health care shall be provided to minimize occurrence of 

deconditioning-related illness or injury, including but not limited to: (see NASA-STD-3001, Volume 1 Rev C 

for full standard).

[V1 3018] Post-Mission Long-Term Monitoring Crewmembers returning from spaceflight shall be 

monitored longitudinally for health, behavioral health, and well-being parameters in a standardized 

manner.

[V1 4020] In-Mission Nutrient Intake Programs shall provide each crewmember with 100% of their

calculated nutrient and energy requirements, based on an individual’s age, sex, body mass (kg), height 

(m), and an appropriate activity factor.

[V1 5001] Medical Training Medical training shall be provided to crewmembers, flight surgeons

(FSs), mission control support staff, and other ground support personnel (GSP).

Referenced Technical Requirements

View the current versions of NASA-STD3001 Volume 1 & Volume 2 on the 

OCHMO Standards website

02/21/2024 16
NASA-STD-3001 Technical Brief

OCHMO-MTB-001

Spaceflight Associated Neuro-ocular 

Syndrome (SANS)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Medical Technical Brief is derived from NASA-STD-3001 and NASA medical operations and is 

for reference only. The aim of this Medical Brief is to share clinical knowledge and provide best 

practices, not to deliver direct medical care recommendations or guidance for individuals.

NASA-STD-3001 Volume 1 Revision C

[V1 5002] Crewmember Training Beginning with the crewmember candidate year, general medical 

training, including but not limited to, first aid, cardiopulmonary resuscitation (CPR), altitude physiological 

training, carbon dioxide exposure training, familiarization with medical issues, procedures of spaceflight, 

psychological training, toxicology, medical equipment, and supervised physical conditioning training shall 

be provided to the astronaut corps.

[V1 5003] Crew Medical Officer Medical Training Crewmembers who have received a mission assignment 

as a Crew Medical Officer (CMO) shall be provided with detailed and specific medical training, including 

but not limited to, health issues, space physiology, behavioral health, medical procedures, medical 

equipment, toxicology, and countermeasures.

[V1 6008] Crew Health Operations Concept Document The program(s) shall develop a crew health 

concept of operations document to define the medical and health care concepts during all phases of the 

spaceflight program.

[V1 6009] Medical and Crew Health Technical Requirements Document

NASA-STD-3001 Volume 2 Revision D

[V2 6001] Trend Analysis of Environmental and Suit Data The system shall provide environmental and 

suit monitoring data in formats compatible with performing temporal trend analyses.

[V2 6004] Nominal Vehicle/Habitat Carbon Dioxide The system shall limit the average one-hour CO2 

partial pressure (ppCO2) in the habitable volume to no more than 3mmHg.

[V2 6022] Atmospheric Monitoring and Alerting Parameters The system shall alert the crew locally and 

remotely when atmospheric parameters, including atmospheric pressure, humidity, temperature, ppO2, 

and ppCO2 are outside safe limits.

[V2 6107] Nominal Vehicle/Habitat Atmospheric Ventilation The system shall maintain a ventilation rate 

within the internal atmosphere that is sufficient to provide circulation that prevents CO2 and thermal 

pockets from forming, except during suited operations, toxic cabin events, or when the crew is not 

inhabiting the vehicle.

[V2 7100] Food Nutrient Composition The system shall provide a food system with a diet including the 

nutrient composition that is indicated in the Dietary Reference Intake (DRI) values as recommended by the 

National Institutes of Health, with the exception of those adjusted for spaceflight as noted in Table 7.1-2—

Nutrient Guidelines for Spaceflight.

[V2 7043] Medical Capability A medical system shall be provided to the crew to meet the medical 

requirements of NASA-STD-3001, Volume 1.

[V2 7045] Medical Equipment Usability Medical equipment shall be usable by non-physician 

crewmembers in the event that a physician crewmember is not present or is the one who requires 

medical treatment.

Referenced Technical Requirements

View the current versions of NASA-STD3001 Volume 1 & Volume 2 on the 

OCHMO Standards website

02/21/2024 17
NASA-STD-3001 Technical Brief

OCHMO-MTB-001

Spaceflight Associated Neuro-ocular 

Syndrome (SANS)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Medical Technical Brief is derived from NASA-STD-3001 and NASA medical operations and is 

for reference only. The aim of this Medical Brief is to share clinical knowledge and provide best 

practices, not to deliver direct medical care recommendations or guidance for individuals.

References

1. Mader, T.H., et al. (2011). Optic disc edema, globe flattening, choroidal folds, and hyperopic shifts 

observed in astronauts after long-duration space flight. Opthamology, 118(10): 2058-2069.

2. Mader, T.H., et al. (2013).Optic disc edema in an astronaut after repeat long-duration space flight. 

Journal of Neuro-opthamology, 33(3):249-55.

3. Ong, J., et al. (2023). Spaceflight associated neuro-ocular syndrome: proposed pathogenesis, terrestrial 

analogues, and emerging countermeasures. British Journal of Opthamology, 107(7): 895-900.

4. J. Ann & E. Kim. (2015). Assessment of Posterior Globe Flattening: Two-Dimensional versus ThreeDimensional T2-Weighted Imaging. Investigative Magnetic Resonance Imaging, 19: 178-185.

5. Laurie, S.S., et al. (2022). Evidence Report: Risk of Spaceflight Associated Neuro-ocular Syndrome 

(SANS). NASA Human Research Program: Human Health Countermeasures Element. 

https://humanresearchroadmap.nasa.gov/evidence/reports/SANS%20EB%202022%20FINAL_8-15-

22.pdf

6. Marshall-Goebel, K., et al. (2019). Assessment of Jugular Venous Blood Flow Stasis and Thrombosis 

During Spaceflight. JAMA Cardiology, 2(11): e1915011.

7. Macias, B., et al. (2021). Changes in the Optic Nerve Head and Choroid Over 1 Year of Spaceflight. JAMA 

Ophthalmology, 139(6): 663-667.

8. Thompson, M., Brunstetter, T., Hart, S., and Tarver, B. (2020). Spaceflight Associated Neuro-ocular 

Syndrome (SANS): Overview & Clinical Practice Guideline. Internal NASA Document.

9. Mark Rosenburg. (2022). Mars University: R&D, Countermeasures to Improve SANS, Vision, and Human 

Spaceflight. https://www.youtube.com/watch?v=yHBOY78v2ko

10. Rosenberg, M.J., et al. (2021). Comparison of Dural Venous Sinus Volumes Before and After Flight in 

Astronauts With and Without Spaceflight Associated Neureo-ocular Syndrome. JAMA Network Open, 

4(10): e2131465.

11. ON AIR with CAPT Tyson J. Brunstetter and Dr. William J. Tarver – Part II. 

https://www.youtube.com/watch?v=jvc58Y6bN3s

12. Agarwal, P. (2022). Understanding spaceflight-associated neuro-ocular syndrome (SANS): what do we 

know? https://www.eyenews.uk.com/features/ophthalmology/post/understanding-spaceflightassociated-neuro-ocular-syndrome-sans-what-do-we-know

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