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INTRODUCTION: Spaceflight-associated neuro-ocular syndrome (SANS) is a health risk for astronauts manifesting as hyperopic shifts in refractive error, globe flattening, choroidal fold formation, and/or optic disc edema. The pathophysiology behind these phenomena is thought to be due to microgravity-induced intracranial fluid shifts. Examining the specific alterations in ophthalmic measures like refractive error (RE) and axial length (AL), may provide insights into the mechanisms of SANS, especially as some clinical manifestations persist after return to Earth. METHODS: Data were obtained retrospectively from medical records of NASA astronauts associated with short-duration Space Shuttle (STS) missions or long-duration International Space Station (ISS) missions. RE and AL data collected closest to launch and landing for 535 STS and 85 ISS astronauts were included. Each astronaut's RE was converted into angular data (i.e. rectangular vector components converting sphere, cylinder, and axis). Individual values for vision correction were represented as three vectors that represent the spherical component of vision correction (V1) and the magnitude of astigmatism in two predefined directions (V2 and V3). Data were analyzed by linear mixed effects models. RESULTS: Significant hyperopic RE shifts occurred in ISS astronauts (+0.15D, p<0.0001) but not in STS astronauts. ISS astronauts experienced significant decreases in AL (-0.122mm, n=55, p=0.0012), while no STS AL pre-flight data were available for comparison. Similar decreases in AL were observed between sexes (Male: -0.122mm, n=39 missions, p=<0.0001; Female: -0.116 mm, n=16 missions, p=0.0299), with equivalent results (p=0.9736). Eye laterality did not significantly affect decreases in AL (Right: -0.100mm, n=55, p=0.0339; Left: -0.137mm, n=55, p=0.0010), (overall p=0.4745). Finally, novice and veteran flyers showed similar changes in AL (Veteran: -0.079mm, n=207, p=0.0006; Novice: -0.175mm, n=185, p=0.0372), with magnitudes not being significantly different (p=0.2597). DISCUSSION: Notably, AL consistently decreased across sex, eye laterality, and astronaut flying experience, countering previous work suggesting certain biases. Additionally, significant hyperopic RE shifts occurred in ISS astronauts and were primarily spherical, suggesting that globe flattening may be the primary mechanism of RE changes in SANS. Continued research is critical as NASA and other organizations prepare for future long-duration missions. Learning Objectives 1. Further characterize the contribution of axial length and refractive shifts related to visual impairment following spaceflight given the various microgravity-induced ocular perturbations that contribute to SANS. 2. Learn how axial length/refractive error changes in SANS do not appear to have a predilection for sex, eye laterality, or astronaut flier experience. [ABSTRACT FROM AUTHOR]

INTRODUCTION: Spaceflight Associated Neuro-ocular Syndrome (SANS) is a condition that negatively impacts crew eyesight and ocular health and is defined by four primary ocular signs: optic disc edema, chorioretinal folds, hyperopic refractive error shift, and globe flattening. Exact pathogenesis and relationships between signs remain poorly understood. METHODS: Data were collected from U.S. astronauts utilizing diagnostic modalities at pre-, in-, and post-flight time points. This dataset was assessed for associations and relationships across a variety of variables including disc edema, chorioretinal folds, MRI/US globe flattening, refractive error, sex, laterality, and prevalence of SANS using Fisher's exact t-test. RESULTS: Global analysis determined that 58% of subjects (n=260) demonstrated signs of SANS. From the subset diagnosed with SANS, cycloplegic refractive error was significantly associated with optic disc edema and chorioretinal folds (p = 0.001 and p = 0.0029, respectively). Males were more affected than females (p = 0.005). The association of disc edema and chorioretinal folds was statistically significant (p < 0.0001). There was no difference in prevalence of SANS regarding eye laterality (p = 1.00), regardless of sex (M(n=409 eyes)/F(n=90 eyes) p = 0.869 vs 0.766 respectively). DISCUSSION: SANS signs showed a variable distribution. Some individuals had no signs, while others displayed multiple. Given limitations, it is difficult to ascertain whether this is due to differences in sex seen prior to missions or due to changes during missions, as females were noted to have statistically significantly less total number of flights and flight mission time than males. Learning Objectives 1. The audience will be able to describe current Spaceflight Associated Neuro-ocular Syndrome (SANS) findings, significance, and countermeasures. 2. The audience will be able identify and appreciate relationships and associations between individual variables related to spaceflight associated neuro-ocular syndrome, with an understanding that there are significant difficulties and limitations when performing spaceflight related ocular measurements and analysis. [ABSTRACT FROM AUTHOR]

Posterior globe flattening has been well-documented in astronauts both during and after long-duration space flight (LDSF) and has been observed as early as 10 days into a mission on the International Space Station. Globe flattening (GF) is thought to be caused by the disc centred anterior forces created by elevated volume and/or pressure within the optic nerve sheath (ONS). This might be the result of increased intracranial pressure, increased intraorbital ONS pressure from compartmentalisation or a combination of these mechanisms. We report posterior GF in three astronauts that has persisted for 7 years or more following their return from LDSFs suggesting that permanent scleral remodelling may have occurred. [ABSTRACT FROM AUTHOR]