Unless you happen to practice in Houston, you’re unlikely to have an astronaut in your chair anytime soon. But researchers are learning more about what they subject themselves to in the harsh environs of a long-term space mission. The work may help us better understand ocular injuries and other aspects of pathophysiology.
More than half of these individuals return to Earth with neuro-ocular changes that can affect their visual acuity, including choroidal folds, optic disc edema, cotton wool spots and hyperopic shifts. Looking further into the association between eye changes and long durations in space, a new study found that astronauts who returned from a six-month mission had consistent inward displacement of the globe at the optic nerve, which only partially resolved one year after returning to Earth.
The investigators developed an automated system that segmented the ocular globe based on MRI images and then compared the posterior globe shape to its preflight form, allowing for a detailed quantification of structural changes and a better understanding of neuro-ocular syndrome.
The study included 10 astronauts who participated in missions on the International Space Station. Participants were scanned 508 days before the flight and again at days one, 30, 90, 180 and 360 post-flight.
The majority of astronauts showed inward displacements of the posterior globe at all timepoints, with the exception of one subject who showed a significant outward displacement of the right eye at day 180. This was the only observation out of 79 to show such a displacement, the researchers noted.
The mean globe volumetric displacement was 9.88mm3 on the first day of assessment after the mission, 9mm3 at day 30, 6.53mm3 at day 90, 4.45mm3 at day 180 and 7.21mm3 at day 360.
More pronounced globe flattening has been observed in similar studies; however, those observations lacked quantitative measures and were subjective in nature, the researchers noted.
“Coupling future research MRIs with other ocular measures will help us understand future cases of outward globe displacement, should they arise,” the study authors wrote in their paper.
Sater SH, Sass AM, Rohr JJ, et al. Automated MRI-based quantification of posterior ocular globe flattening and recovery after long-duration spaceflight. Eye. January 29, 2021. [Epub ahead of print].