Spaceflight associated neuro-ocular syndrome (SANS): a systematic review, implications for the sans case definition

Background: Astronauts undergoing long-duration space flights (LDSF) often experience a unique set of neuro-ocular findings known as Spaceflight Associated Neuro-ocular Syndrome (SANS). However, the exact mechanisms and the true incidence of SANS remain unclear. This paper aims to review the existing literature on SANS, focusing on its incidence and sequence of findings, and to provide a comprehensive understanding of this condition. Research design and methods: Studies reporting SANS and optic disc edema in astronauts from PubMed, Scopus, and WOS have been collected. Eligible studies were selected based on stringent inclusion criteria. Statistical analysis utilized R software with random effect models for them, and heterogeneity was assessed using I2 and chi-squared tests. Results: Our study includes 19 studies that met the inclusion criteria, which encompassed 294 participants. Included studies revealed that optic disc edema and choroidal folds were highly prevalent, with proportions of 75% and 71%, respectively. Hyperopic shifts (95%CI 0.51, 0.76, I2 = 0%) were also statistically significant, appearing gradually and persisting even after astronauts returned to Earth. Conclusion: This study provides a comprehensive assessment of SANS in astronauts. The study suggests that the current clinical definition of SANS may underestimate its true incidence and proposes the inclusion of quantitative metrics to enhance sensitivity and accuracy in diagnosis.