PurposeThe development of neuro-ophthalmic symptoms during long-duration spaceflight presents major risks to astronauts and their missions. 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.MethodsWe 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 OCT data.ResultsFor 13 astronauts with a mean age of 47 ± 9 years, there were significant increases in choroid thickness (CT) and luminal area (LA) of 14 ± 25 μm (P = 0.01) and 0.11 ± 0.2 mm2(P = 0.009) and no significant change in choroid vascularity index (CVI) averaged over OCT macular video segments. There was no significant change in the amplitude of pulsatile CT fluctuation (ΔCT), but significant increases in both pulsatile LA (ΔLA) and CVI (ΔCVI) of 0.077 ± 0.14 mm2(P = 0.009) and 0.03 ± 0.06 (P = 0.01), respectively. For a subgroup of 6 astronauts for which inflight imaging was available, choroid volume, luminal volume and CVI over the macular region all increased significantly during spaceflight with the greatest differences reached at 90 days following launch.ConclusionsThe findings show that localized choroid pulsatile changes occur following prolonged microgravity exposure. They suggest that the choroid vessels expand in a manner similar to the choroid layer across the macular region during spaceflight, accompanied by 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.
