The Ocular Surface–Gut Axis in Spaceflight: Implications of Intestinal Changes in Microgravity on Tear Film Physiology

Abstract

With increasing space exploration, there is a rising need to evaluate the impact of spaceflight on astronauts’ health, including the effects of space-associated hazards such as microgravity. Astronauts’ reports of experienced symptoms upon spaceflight include a notable prevalence of dry eye disease (DED). Hence, there is a pressing need to understand the pathogenesis and mechanism behind space-associated DED onset, which will subsequently guide the development of necessary therapies to reduce dry eye symptoms among astronauts. One critical effect of spaceflight includes alterations to the gut microbiome. On Earth, the prior literature has established the presence of an ocular surface–gut axis and the potential role of gut dysbiosis in DED onset. Meanwhile, the literature about astronauts’ health underscores the presence of space-associated gut microbiome composition alterations and the presence of DED separately. Therefore, in this opinion article, we review and present the current literature regarding the ocular surface–gut axis on Earth and regarding potential translations to spaceflight. We present the view that, based on the existing literature, the ocular surface–gut axis may be a critical mechanism for the pathogenesis of DED in space, and this axis needs to be further explored in the context of identifying ways to reduce astronauts’ experiences of DED during spaceflight.