Ocular health in outer space and beyond gravity: A minireview

Abstract

Prolonged exposure to microgravity profoundly influences ocular physiology, giving rise to spaceflight-associated neuro-ocular syndrome (SANS), a significant concern for astronauts on long-duration missions. This review consolidates current evidence on ocular adaptations to spaceflight, encompassing pathophysiological mechanisms, diagnostic advances, related ocular conditions, and emerging countermeasures. Literature published between 2000 and 2025 was systematically examined across PubMed, Scopus, and Web of Science, integrating both peer-reviewed studies and technical reports from the National Aeronautics and Space Administration and the European Space Agency. Findings indicate that ocular changes consistent with SANS affect approximately one-third of astronauts, with higher prevalence during missions exceeding six months. Hallmark features include optic disc edema, posterior globe flattening, and mild hyperopic shifts, attributed to cephalad fluid shifts, altered cerebrospinal fluid dynamics, venous congestion, and impaired glymphatic flow. Besides SANS, microgravity predisposes astronauts to dry eye disease, immune-related infections, and radiation-induced cataracts. Recent advances in in-flight optical coherence tomography, optical coherence tomography angiography, and ultrasound have enhanced early detection, while countermeasures such as lower body negative pressure, artificial gravity, and artificial intelligence-driven ocular monitoring show promise. Understanding ocular adaptations to space not only mitigates mission risks but also enriches terrestrial knowledge of intracranial pressure regulation and neuro-ophthalmic health.

Keywords: Spaceflight-associated neuro-ocular syndrome; Microgravity; Intracranial pressure; Ocular health; Astronaut physiology; Space medicine

Core Tip: Vision is mission-critical in human spaceflight. Prolonged exposure to microgravity causes a distinct set of ocular changes known as spaceflight-associated neuro-ocular syndrome. These include optic disc edema, posterior globe flattening, choroidal folds, retinal nerve fiber layer thickening, and hyperopic refractive shifts. Evidence suggests spaceflight-associated neuro-ocular syndrome arises from cephalad fluid shifts, venous congestion, and altered cerebrospinal fluid dynamics rather than raised intracranial pressure alone. Advances in in-flight imaging and artificial intelligence are improving early detection, making ocular health central to safe space exploration and neuro-ophthalmic research.