Spatial and temporal changes in choroid morphology associated with long-duration spaceflight

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 extends deep learning-based choroid quantification from optical coherence tomography (OCT) to the characterization of pulsatile and topological changes in the macular plane and investigates changes in response to prolonged microgravity exposure. 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 towards vascularity quantification. Statistical analysis was performed to determine changes in time-dependent and spatially averaged variables from preflight baseline. 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 6 astronauts for which inflight imaging was available, choroid volume, luminal volume and choroid vascularity index over the macular region all increased significantly during spaceflight. 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.