Spaceflight-Associated Epiphora Mechanisms and Countermeasures

Epiphora, or excessive tearing, is a commonly reported symptom among those with dry eyes in the terrestrial environment. It is therefore not surprising that a higher frequency of epiphora was demonstrated among astronauts onboard both Space Transportation Shuttle and International Space Station missions. In this review paper, we discuss the pathophysiology and mechanisms of epiphora and consider the additional risk factors due to the extreme environments of spaceflight, including microgravity and, to a lesser extent, radiation. We also discuss potential strategies to mitigate spaceflight-associated epiphora.

This review utilized articles related to epiphora and the spaceflight environment from various medical literature databases including Embase, Google Scholar, Web of Science, Grey Literature, PubMed, and reliable secondary sources, such as NASA webpages.

Our search strategy resulted in 94 articles, and 67 articles were relevant to our study.

Spaceflight-associated epiphora has a multifactorial etiology related to both reflex tearing and obstruction of the lacrimal drainage system. Dry eyes are closely associated with epiphora in space as the result of ocular irritation causing reflex tearing. Decreased tear drainage may result from the lack of gravitational assistance and the cephalad fluid shift which may create a functional obstruction of the lacrimal drainage system. While primarily a concern with chronic exposure, radiation may irritate the cornea, cause lacrimal and Meibomian gland atrophy, and disrupt tear film stability. Potential countermeasures include maintaining the tear film, mitigating the cephalad fluid shift, and protecting from radiation. Katsev BD, Lee R, Ong J, Gibson CR, Mader TH, Waisberg E, Lipsky W, Sampige R, Berdahl J. Spaceflight-associated epiphora mechanisms and countermeasures. Aerosp Med Hum Perform. 2026; 97(4):272-278.