The ocular surface during spaceflight: Post-mission symptom report, extraterrestrial risks, and in-flight therapeutics

Ocular health is critical for overall astronaut health requirements given its essential role for mission performance and safety. The ocular surface is a vital structure to the visual system and is essential for ocular protection and the refraction of light for focused vision. Data from the 2024 NASA Lifetime Surveillance of Astronaut Health identified that Space Shuttle and International Space Station (ISS) astronauts (N = 257) queried during post-flight eye exams reported symptoms of eye irritation (34 %), dry eyes (14 %), and foreign body sensation (21 %). Given these findings, it is critical to understand the risks that the ocular surface faces in the spaceflight environment. This manuscript explores the impact of lunar dust, space radiation, lunar gravity, and microgravity on the astronaut ocular surface. Furthermore, we outline ongoing efforts to minimize associated health risks given our insights into the vision standards, testing procedures, corrective measures, and mitigations designed for the lunar surface and microgravity environments. We further discuss the ophthalmic medications available on space missions to address threats to the ocular surface. We also report personal insights from Dr. Harrison Schmitt, NASA astronaut and Apollo 17 moonwalker, on his experience in space and lunar dust human physiological interactions. Additionally, given the known physiologic changes in microgravity and expectations for partial gravity environments, our review prompted characterization of accelerated aging and gut microbiome on the development of dry eye. We also discuss the potential expansion of ophthalmic imaging capabilities during spaceflight missions and its utility. Addressing these factors is critical to uphold astronauts' ocular health and to ensure the safety of future space missions.