MRI-derived diffusion parameters in the human optic nerve and its surrounding sheath during head-down tilt.More than half of astronauts present with significant neuro-ophthalmic findings during 6-month missions onboard the International Space Station. 
MRI
In the presented study, diffusion tensor imaging was used to assess changes in diffusivity of the optic nerve and its surrounding sheath during head-down tilt, a ground-based model of microgravity. 
diffusion tensor imaging