We are pleased to bring you a further blog post from our special guest editor, Philip Vukovic – BSc (Melb). Many thanks to Philip for this very informative article.
With prospects of a long-duration spaceflight mission to Mars, it is of vital importance that appropriate countermeasures are developed to prevent Space Associated Neuro-ocular Syndrome (SANS) during spaceflight, and establish if astronauts may develop any long-term health effects.
What is Space Associated Neuro-ocular Syndrome (SANS)?
Space Associated Neuro-ocular Syndrome refers to the changes that occur to the eye and brain during spaceflight. Having first been discovered in 2005, SANS showed similar signs to idiopathic intracranial hypertension (IIH). However, despite some of the similarities between the two, interesting differences were noted, ultimately leading to the distinction.
What is causing SANS?
Current scientific findings suggest that SANS occurs due to the shifting of fluid towards the head as astronauts are exposed to environments of microgravity. The National Aeronautics and Space Administration (NASA) states that exposure to weightlessness results in an upward redistribution of fluid around the brain and a shift of blood from veins toward the head. These physiological changes are currently believed to be the underlying cause surrounding the structural changes seen in the eye and brain. It is important to note however, that SANS is still being intensely studied by NASA (and others), and a single unifying predominant mechanism has yet to be proven.
Changes to the brain and eye
Various physiological and pathological neuro-ophthalmic (brain-eye) changes have been found in astronauts during and following long-duration spaceflight. Some of the structural changes to the brain include ventricular volume enlargement, an upward shift of the brain and pituitary gland shape changes. It has also been documented that astronauts may experience swelling of the nerve as it enters the eye, the development of folds in the retina, flattening of the back of the eye and blurry vision.
The problems associated with SANS and how we can prevent it
NASA has identified a SANS incidence rate of approximately 70% for astronauts travelling to the International Space Station. Due to this high incidence rate, researchers are currently studying ways to prevent and treat SANS during spaceflight, and establish if astronauts may develop any long-term health effects.
SANS poses major problems for long-duration missions. The structural changes that occur to the brain and eye during spaceflight may lead to short-term or long-term alterations in vision, cognitive effects, or other deleterious health effects. As crew will undoubtedly be tasked with carrying out their own cognitively demanding scientific research, vehicle operation and maintenance, and other activities, it is imperative that we develop effective means by which we can mitigate the operational and long-term risks of SANS.
Mader et al. (2011) described the historical, clinical, and imaging findings in seven astronauts after six months of long-duration space flight, and recorded the changes in vision of approximately 300 additional astronauts. The ophthalmic findings included optic disc oedema (n=5), global flattening (n=5), choroidal folds (n=5), nerve fibre layer infarcts (n=3), thickening within the nerve fibre layer on optical coherence tomography (n=6), and decreased near vision (n=6).
With the underlying predominant mechanism yet to be determined, effective treatments for the known problems associated with SANS have not been established. With future manned missions to the International Space Station, Moon, and Mars, specific countermeasures will need to be developed in order to ensure operational success and crew safety.
Further Reading and Information
Lee, A. G., Mader, T. H., Gibson, C. R., Tarver, W., Rabiei, P., Riascos, R. F., … & Brunstetter, T. (2020). Spaceflight associated neuro-ocular syndrome (SANS) and the neuro-ophthalmologic effects of microgravity: a review and an update. npj Microgravity, 6(1), 1-10.
Mader, T. H., Gibson, C. R., Pass, A. F., Kramer, L. A., Lee, A. G., Fogarty, J., … & Polk, J. D. (2011). Optic disc edema, globe flattening, choroidal folds, and hyperopic shifts observed in astronauts after long-duration space flight. Ophthalmology, 118(10), 2058-2069.
Risk of Spaceflight Associated Neuro-ocular Syndrome (SANS) (https://humanresearchroadmap.nasa.gov/risks/risk.aspx?i=105)
NASA – Space Associated Neuro-ocular Syndrome Infographic (https://www.nasa.gov/sites/default/files/atoms/files/sans_infographic-062821-508c_01.pdf)