▲ Astronauts photographed on Earth (a) and in space (b)
It is widely known that when astronauts leave Earth and enter a microgravity environment, their faces puff up and the area around their eyes changes shape.
Now, research findings indicate that actual changes occur in space where the lower eyelid rises, making the eyes appear smaller.
An international research team, including Western Sydney University in Australia and Saarland University Medical Center in Germany, announced on August 24 in the international journal Eye & ENT Research that they analyzed photographs of 13 astronauts taken on Earth and in space, confirming a consistent upward shift of the lower eyelid in space.
The research team stated that these changes appear rapidly during spaceflight and may persist over the long term, adding that further research is needed to determine how these changes affect eye health and other factors during long-duration space missions.
Considering long-term exploration missions to the Moon or Mars, understanding the physical changes caused by spaceflight and their impact on health is becoming increasingly important.
The research team noted that while various physical changes have been observed in microgravity environments, and an elevation of the lower eyelid position has been observed in short-term microgravity environments, analyses targeting astronauts during active spaceflight had not been conducted until now.
The research team collected and analyzed 115 photographs (52 taken on Earth and 63 taken in space) of 13 astronauts (12 men, 1 woman) captured on Earth and in space from the National Aeronautics and Space Administration (NASA) online image archive.
The average age of the subjects was 46 (ranging from 35 to 60 years old). For each astronaut, at least three frontal photographs each from Earth and space were secured, and the distance from the center of the cornea to the margin of the lower eyelid (MRD2) was compared.
The analysis revealed that when moving from Earth to space, the average MRD2 decreased from 4.9 mm to 3.9 mm, confirming a statistically significant level of change.
The research team explained that a smaller MRD2 means the margin of the lower eyelid moves closer to the center of the eye, resulting in a "reverse ptosis" where the lower eyelid shifts upward.
They added that the decrease in MRD2 was observed in all 13 individuals, with 8 of them (62%) showing a reduction of 1 mm or greater, noting that clinically, a decrease in MRD2 exceeding 1 mm is considered a significant change.
The research team stated that an elevation of the lower eyelid is also observed in parabolic flight experiments that create short periods of weightlessness using aircraft, suggesting that these changes may occur immediately upon exposure to microgravity rather than developing slowly during long-duration spaceflight.
Fluid shifts occurring in space were suggested as the cause of these changes.
When entering a microgravity environment, about 2 liters of body fluid shift toward the head, causing the face to swell, which can push the lower eyelid upward.
Additionally, while gravity on Earth pulls facial tissues such as skin, muscles, and tendons downward toward the jaw, this force disappears in microgravity, raising the possibility that the elastic recoil of tissues alters the position of facial structures and contributes to the elevation of the lower eyelid.
The research team noted that the position of the lower eyelid goes beyond simple facial shape changes and has the potential to affect corneal status, visual field, and visual acuity, stating that more standardized research is needed to examine the impact of these changes on health during long-duration spaceflight.
They added that this study provides a new starting point for research into the relationship between long-duration spaceflight and eye health, and that understanding these changes could be crucial for protecting the eye health of astronauts on long-term exploration missions to destinations like the Moon or Mars in the future.
(Photo courtesy of Eye & ENT Research, provided by Timon Ax et al., Yonhap News)
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