Spatial and Temporal Changes in Choroid Morphology Associated With Long-Duration Spaceflight.

Purpose: Amid efforts to understand spaceflight associated neuro-ocular syndrome (SANS), uncovering the role of the choroid in its etiology is challenged by the accuracy of image segmentation. The present study extended deep learning-based choroid quantification from optical coherence tomography (OCT) to the characterization of pulsatile and topological changes in the macular plane and investigated changes in response to prolonged microgravity exposure. Methods: We analyzed OCT macular videos and volumes acquired from astronauts before, during, and after long-duration spaceflight. Deep learning models were fine-tuned for choroid segmentation and combined with further image processing toward vascularity quantification. Statistical analysis was performed to determine changes in time-dependent and spatially averaged variables from preflight baseline. Results: For 12 astronauts with a mean age of 47 ± 9 years, there were significant increases in choroid thickness and luminal area (LA) averaged over OCT macular video segments. There was also a significant increase in pulsatile LA. For a subgroup of six astronauts for whom inflight imaging was available, choroid volume, luminal volume, and the choroidal vascularity index over the macular region all increased significantly during spaceflight. Conclusions: The findings suggest that localized choroid pulsatile changes occur following prolonged microgravity exposure. They show that the choroid vessels expand in a manner similar to the choroid layer across the macular region during spaceflight, with a relative increase in the space they occupy. The methods developed provide new tools and avenues for studying and establishing effective countermeasures to risks associated with long-duration spaceflight.