Spaceflight-associated neuro-ocular syndrome: potential etiologies and connections to the glymphatic system

The etiology of spaceflight-associated neuro-ocular syndrome (SANS) is a developing field of research, with many current hypotheses receiving varying degrees of support. This syndrome affects ∼70% of astronauts both during and after long-duration space missions, resulting in impaired near vision and visual scotomas (blind spots). In this article, three prominent risk factors for SANS including zero gravity conditions, extraterrestrial hypercapnic environments, and individual genetic predisposition are described. These risk factors are then compared and their pathophysiological pathways are divided into five current hypotheses for the development of SANS. Finally, glymphatic system impairment is explored as a potential mutual end point for these pathways in the development of SANS.