Association of Space Flight With Problems of the Brain and Eyes

Abstract

Space flight-associated neuroocular syndrome (SANS), characterized by increased optic nerve sheath diameter (ONSD) and globe flattening, is detected in some astronauts. 1 Because inflight cerebrospinal fluid (CSF) pressure measurement is excessively invasive, it is not realistic to conduct. We estimated CSF pressure (p CSF) during space flight based on published reports 2 and found that SANS was not caused mainly by increased p CSF but rather by brain upward shift (BUS), recently demonstrated in postflight astronauts. 3 Our findings suggest that eyes are portals into effects on the brain during space flight.

Spaceflight associated neuro-ocular syndrome (SANS) and the neuro-ophthalmologic effects of microgravity: a review and an update

“…27 This spectrum of potential mechanisms emphasizes the possible multifaceted origin of the unusual neuro-ophthalmic findings in SANS. 1,5,[20][21][22]27 Initially, due to the moderately elevated ICP measurements in some astronauts, SANS was termed the visual impairment and intracranial pressure (VIIP) syndrome. However, over time the role of elevated ICP as the sole mechanism for the findings has come into question and the name was changed from VIIP to SANS to reflect the uncertainty about the pathogenesis and the possible multifactorial etiology for the findings.…”

“…1,21,22 Shinojima recently offered an alternate compartmentalization theory which proposes that during LDSF the optic nerve and globe may be retracted posteriorly as a result of brain upward shift and resultant uplifting of the optic chiasm during and after LDSF. 27 They propose that this posterior "pull" on the optic nerve and globe compresses the CSF within the optic nerves leading to localized pressure elevation and expansion. 27 This spectrum of potential mechanisms emphasizes the possible multifaceted origin of the unusual neuro-ophthalmic findings in SANS.…”

“…27 They propose that this posterior "pull" on the optic nerve and globe compresses the CSF within the optic nerves leading to localized pressure elevation and expansion. 27 This spectrum of potential mechanisms emphasizes the possible multifaceted origin of the unusual neuro-ophthalmic findings in SANS. 1,5,[20][21][22]27 Initially, due to the moderately elevated ICP measurements in some astronauts, SANS was termed the visual impairment and intracranial pressure (VIIP) syndrome.…”

Spaceflight-Associated Brain White Matter Microstructural Changes and Intracranial Fluid Redistribution

“…In addition, the preflight to postflight FW shift we observed in this study complements our previous report of spaceflight-associated regional brain gray matter changes 1 and the report of CSF compartment changes 2 in astronauts, highlighting the link between fluid shifts and brain morphology alterations with spaceflight. Given the potential effect of brain positional alterations on the optic system, such as an upward repositioning of the optic nerves and globe flattening, 2,22 fluid shifts and upward brain displacement with spaceflight are important to study. The mechanisms underlying spaceflight-associated neuro-ocular syndrome, a concern that has affected about onethird of long-duration astronauts, 23 Interestingly, irrespective of the flight duration and cumulative days in space, astronauts with a greater number of missions showed FW decreases (as opposed to increases in more novice flyers) in the anterior, medial portion of the brain.…”

Long‐duration spaceflight alters estimated intracranial pressure and cerebral blood velocity

“…SANS has been reported to include the development of optic disc oedema, choroidal folds, globe flattening and/or hyperopic visual shifts during long-duration spaceflight, with a potential major risk of visual changes in future human spaceflight (Lee et al 2018). Many hypotheses have been proposed for the mechanisms causing them (Zhang & Hargens, 2014;Lee et al 2018;Shinojima et al 2018). Also, related to SANS, several studies have been conducted, such as investigations of ophthalmological and orbital changes (Kramer et al 2012), cerebrospinal fluid flow and production rates (Kramer et al 2015), ventricular volume (Van Ombergen et al 2019), and brain structure (Roberts et al 2017;Lee et al 2019).…”