Defining spaceflight associated dry eye syndrome (SADES): Mechanisms, complications, and countermeasures.

There is a high prevalence of dry eye-related symptoms among astronauts during spaceflight. We propose naming this phenomenon: Spaceflight Associated Dry Eye Syndrome (SADES). In this study, we review the potential mechanisms of dry eye in the spaceflight environment, categorizing them into external (radiation, environmental hazards) and microgravity-related (meibum outflow) mechanisms. One key mechanism is that microgravity impedes the secretion of meibum, the primary contributor to the tear film lipid layer. SADES may impact the ocular surface due to the positive feedback loop of inflammation and tear film irregularities. These changes may lead to corneal epithelial defects, keratitis, decreased vision, and an increased potential for corneal thinning and perforation. We discuss available countermeasures to combat SADES, propose a new set of applicable technologies, and review appropriate medications for its prevention and treatment. This topic may be of significant interest to ophthalmologists as many of the established terrestrial mechanisms, diagnosis, and management of dry eye syndrome apply to the extreme environment of spaceflight.