Last Published:  07/31/19 10:05:30 AM (Central)
Responsible Element: Human Health Countermeasures (HHC)
Status: Open

Initial State:

Limited data are available to definitively establish the underlying etiological mechanisms and contributing risk factors for SANS. Current efforts include crew data mining and occupational surveillance activities as well as terrestrial and in-flight studies to characterize these aspects. The leading hypothesis is that SANS is caused by increased intracranial pressure resulting from a cephalad (headward) fluid shift resulting from microgravity exposure and elevated CO2 levels. Microgravity-induced cephalad fluid shift is known to occur but has not been fully quantified. The degree of cephalad fluid shift (and cerebral venous drainage) is hypothesized to vary based on individual levels of vascular compliance, which can be influenced by environmental and/or individual risk factors that are, as yet, insufficiently understood.


The spectrum of SANS signs and symptoms spans a range from mild (choroidal folds, globe flattening, and change in refraction) to more clinically significant (optic disc edema, scotomas, and visual field changes such as an enlarged blind spot). These observations suggest that SANS signs and symptoms develop along a clinical continuum, and if discovered early could be mitigated with the application of suitable countermeasures to minimize long-term health concerns. Successful countermeasure development is dependent on a thorough understanding of the cause and progression of this syndrome, including the identification of the most prevalent environmental and individual risk factors that contribute to its onset. Since etiology and risk factors are inextricably linked and are studied together, this gap addresses both aspects concurrently. The primary research goal is to understand the cause and progression of SANS and the risk factors that most significantly influence its development. 

Target for closure:
Establish the etiology of SANS development and the impact of the hypothesized risk factors (as determined by the RCAP) to direct and focus countermeasure development.


Interim steps:

  1. Define the time course of in-flight and postflight changes to ocular structure and function as compared to a preflight baseline (20%)
  2. Quantify the time course and relative change in preflight, in-flight, and postflight intracranial pressure (20%)
  3. Characterize the degree of spaceflight-induced cephalad fluid shift and establish whether a correlation exists between individual degrees of vascular and/or spinal compliance and changes in ocular structure and function (15%)    
  4. Define the correlation, if one exists, between in-flight and postflight ocular structure and function changes and central nervous system structure and function changes. (10%)
  5. Characterize the relative contributions of the following hypothesized risk factors to the development of SANS:  (25%) 
    1. Duration of microgravity exposure (cumulative, multiple, and single)
    2. Environmental CO2 levels
    3. Diet (specifically sodium consumption)
    4. Individual anatomy
    5. Genetic predisposition
    6. Effects of medications used by crewmembers pre-, in-, and postflight
    7. Effects of exercise 
    8. Other predisposing health parameters
  6. As interim steps progress and major questions are answered, update the SANS Evidence Report to reflect and integrate the current state of knowledge. (5%)
  7. Target closure will be recommended by a SANS advisory panel (i.e. the Research and Clinical Advisory Panel) following a review of the collective results of ground and in-flight studies and data mining efforts. Closure will be indicated by an advisory panel recommendation that identifies which risk factors and etiology mechanisms to target during countermeasure development efforts. (5%)

 Research Approach:

The rVIIP project considers the SANS 1 knowledge gap to be its highest priority and, as such, current research efforts are predominately directed at this gap. Much of the planned work in SANS research plan cross-informs both etiology and risk factors. As progress is made on one interim stage, the other stages are informed. Activities to-date have included retrospective data mining, prospective occupational surveillance, and flight and ground studies to identify the numerous aspects of SANS outlined above. Importantly, many questions regarding etiology and risk factors can only be answered using actual space flight exposure. As such, preflight, in-flight, and postflight crew testing is planned and required to close this gap.  Space Medicine Operations Division (i.e. non HRP) funded and managed tasks not covered by the SANS Research Plan include in-flight monitoring of visual health as part of the Medical Requirements Integration Document (MRID) mandated testing.


Target for Closure
No Target for Closure available.
Risk Risk of Spaceflight Associated Neuro-ocular Syndrome (SANS)
You are here! Gap SANS1: We do not know the etiological mechanisms and contributing risk factors for ocular structural and functional changes seen in-flight and postflight.

No Documentation Available