Repeat Space Missions Do Not Appear to Worsen Eye or Brain Structural Changes: JAMA
A case series published in the Journal of the American Medical Association has found that a single repeat exposure to spaceflight or head-down tilt bed rest (HDTBR) was not associated with greater structural changes in the eyes or brain compared with initial exposure. The findings suggest that individual astronauts tend to experience similar physiological changes across subsequent missions rather than progressively larger effects. However, it remains unclear whether repeated exposures may lead to cumulative long-term functional consequences. These results may help the space medicine community better predict health changes in astronauts undertaking multiple spaceflight missions, though further research is needed to assess long-term risks.
Crewmembers on long-duration spaceflight missions are at risk of developing mild to moderate optic disc oedema and ventricular volume expansion. The effect of repeated exposures on ocular and brain tissues is unknown and needs to be better understood for astronauts flying multiple missions.
A study was done to evaluate whether a second exposure to spaceflight or a spaceflight analogue is associated with larger changes in optic disc oedema or brain ventricular volume expansion. Peripapillary total retinal thickness (TRT) extending from the Bruch membrane opening to 250 µm was quantified using optical coherence tomography imaging before and during spaceflight or the spaceflight analogue head-down tilt bed rest (HDTBR). Magnetic resonance imaging was performed before and after spaceflight or HDTBR to quantify changes in brain volumetrics. Included were astronauts and participants in HDTBR from the International Space Station or the German Aerospace Centre:envihab facility. Study data were analysed from November to December 2025.
Two spaceflight missions of approximately 6 months or 2 HDTBR campaigns of 30 to 60 days in duration were considered for this study. The change in TRT (∆TRT) from preflight/pre-HDTBR to approximately 30 days before return to Earth or 30 days into HDTBR, and the change in lateral ventricular volume (∆LVV) from preexposure to postexposure. Data were analyzed to determine if repeat exposure to spaceflight or HDTBR augmented the magnitude of change from the first exposure to the second.
Findings of this case series show that a single repeat exposure to HDTBR or spaceflight did not appear to be associated with an increase in the magnitude of change in ocular or brain structures. Whether these exposures are additive in causing increased long-term functional changes remains unknown. These findings may be used by the space medicine community to guide the prediction of changes that might occur in those who undertake multiple spaceflight missions.
Carter KJ, Smith JD, Huang AS, et al. Repeat Exposures to Spaceflight or Bed Rest and Spaceflight-Associated Neuro-Ocular Syndrome Findings. JAMA Ophthalmol. Published online June 18, 2026. doi:10.1001/jamaophthalmol.2026.2140
