The effect of short-term microgravity and hypergravity on eyelid and brow position

Purpose: Spaceflights induce periocular facial changes which could contribute to ocular conditions which affect astronauts. This study is to validate parabolic flight as a suitable model for studying gravitational facial changes. Methods: Healthy participants (n = 13; 37 ± 10 years) underwent short-term exposure to microgravity and hypergravity during parabolic flight. Facial images were captured and differences in measurements from pupil center to upper and lower eyelid margins (MRD1 and MRD2), and to the inferior and superior eyebrow margin (PTB_i and PTB_s) under normogravity, microgravity, and hypergravity were compared. A repeated measures ANOVA with Bonferroni-Holm corrected post-hoc paired t-test was used for statistical analysis. Results: One hundred and twenty-seven images (44 normal gravity, 43 microgravity, 40 hypergravity) revealed that short-term microgravity induced a mean PTB_i increase of 2.3 mm (p < 0.001) and mean PTB_s increase of 2.4 mm (p < 0.001) while decreasing mean MRD2 by 0.9 mm (p < 0.001) but without change in MRD1 (p = 0.41). Short-term hypergravity did not change PTB_s, PTB_i or MRD2 but reduced mean MRD1 by 0.7 mm (p < 0.01). Conclusions: Short-term microgravity, similar to spaceflight, significantly elevates PTB but not MRD1. It was also shown that MRD2 was reduced. Short-term hypergravity induces significant reductions only in MRD1. Phenomena are likely explicable by co-activation of the muscles raising the eyelid and eyebrow. Comparison to space data suggests that parabolic flight offers a valid model to study periocular facial changes in microgravity.