Automated pupillometry in short-duration human spaceflight

Introduction Quantitative pupillometry, which assesses the pupillary light reflex, is gaining recognition as a potentially rapid, noninvasive, practical, and reliable surrogate marker for intracranial pressure (ICP). Automated pupillometry devices provide virtually immediate quantification of various pupillary parameters which may reflect the structural and functional integrity of wide ranges of intracranial networks involved in the genesis of pupillary responses. This study reports the first use of a commercially available automated pupillometry device in space on the Axiom Mission 2 to the International Space Station (ISS). Methods. The experimental protocol involved data collection from four astronauts of the Axiom Mission 2 before, during, and directly after a short-duration (ten days) mission to the ISS, utilizing the handheld NPi-300 pupillometer (NeurOptics, Irvine, California, United States). Results Several key variables obtained with pupillometry of both the left eye and right eye independently showed an evident increase from baseline (before launch) to when astronauts were in microgravity conditions aboard the ISS, then a reduction to below baseline upon return to 1G on Earth. These variables include pupil size, pupil diameter at peak constriction, percentage of change, constriction velocity, and dilation velocity. Furthermore, disaggregated analysis indicated more extensive changes in pupillary light reflex parameters in the younger astronauts compared to the older astronauts as well as a greater effect on pupillary light reflex parameters in male astronauts compared to female astronauts. Conclusion This study demonstrates that automated pupillometry is a spaceflight-ready technology with significant potential utility in space medicine neuro-monitoring. Pupillometry in human spaceflight could serve as a surrogate physiological measure of fluctuations in ICP and may further our knowledge of Spaceflight Associated Neuro-ocular Syndrome (SANS). Pupillometry may also provide a dynamic and objective method for accurate and timely assessment of neural systems involved in pupillary responses which may further our understanding of SANS, particularly for future planned crewed long-duration missions to the Moon, Mars, and beyond. Due to its simplicity, rapidity, and noninvasiveness, pupillometry may ultimately become a significant component of neurological monitoring and management protocols to protect brain and ocular health during long-duration spaceflight. Additionally, this novel monitoring device can be used in conjunction with existing methods for monitoring neurological and SANS-related changes to potentially create enhanced monitoring protocols.