The Effect of Microgravity on Lower Eyelid Position in Astronauts

ABSTRACT Background Specific facial changes are known to occur in microgravity. A higher lower eyelid position has been observed during short‐term microgravity but has not been analyzed in astronauts during spaceflight. Purpose To describe the effect of spaceflight on lower eyelid position. Method Images of astronauts captured on Earth and in space were collected from the National Aeronautics and Space Administration online image library. For each astronaut, at least 6 front‐facing portraits (at least 3 captured on Earth and at least 3 in space) were selected. Measurements from the center of the pupil to the lower eyelid margin (margin reflex distance 2 [MRD2]) were determined digitally for each image and compared between Earth and space images using a Wilcoxon signed‐rank test. Additionally, per‐astronaut pooled mean values were descriptively compared with reference values from parabolic flight. Results 115 photographs (52 Earth, 63 space) from 13 astronauts (12 men, 1 woman; mean age 46 ± 7 years, range 35–60) were retrieved from the database. Microgravity induced a mean MRD2 decrease of 1.0 mm ( p < 0.001). Conclusion Spaceflight led to a significant decrease in MRD2. These findings are comparable to those obtained from short‐term microgravity experiments on parabolic flights. Further studies implementing standardized imaging techniques are needed to uncover the mechanism and health implications.