AstroOphthalmology: Basic and Pathophysiological Concepts of Space-Induced Ocular Changes

Long-duration space missions pose a considerable risk to eye health, and visual dysfunction is recognized as a primary health concern for astronauts. Hence, we have developed a series of review reports to study the effects of space on the eye, called AstroOphthalmology (including Basics, Ocular Anterior Segment, Ocular Posterior Segment). This report serves as the first report of our series, and integrates the current insights into the pathophysiological consequences of the space environment on the eye. The two key space-specific stressors include microgravity and cosmic radiation. Both stressors are the interconnected pathways of oxidative stress and mitochondrial dysfunction, which inflict damage on cellular components and disrupt the function of essential ocular tissues. Microgravity triggers a cephalad fluid shift, which leads to vascular congestion, changes in hemodynamics, and increased intracranial pressure. The aforementioned changes are considered to be culprits in the onset of spaceflight-associated neuro-ocular syndrome (SANS). Exposure to galactic cosmic radiation and solar particle events presents a substantial risk for the formation of cataracts, retinal cotton-wool spots, and optic neuropathy. This review indicates that ocular damage during spaceflight is influenced by multiple factors, resulting from the synergistic interaction of fluid shifts and radiation. In addition to pathophysiology, we summarize the current in-flight evaluations such as optical coherence tomography and fundoscopy. Future research should focus on assessing combined countermeasures and establishing predictive biomarkers to mitigate these risks, which is imperative for the success of future lunar and Martian missions.