Astronauts' Eyelids Rise in Microgravity... Why Eyes Appear Smaller in Space

First Confirmation Based on Analysis of 115 NASA Photos
MRD2 Value Shortens from 4.9 mm on Earth to 3.9 mm in Space
Possible Impact on Cornea, Field of Vision, and Eyesight Suggested

A new study has found that when astronauts travel into space, their lower eyelids move upward, making their eyes appear smaller.

NASA astronaut's eyes photographed from Earth (a) and space (b). Eye & ENT Research

According to a report by Yonhap News on August 24, an international research team including Western Sydney University in Australia and Saarland University Medical Center in Germany published these findings in the international journal 'Eye & ENT Research.' While it was already known that the face tends to swell in near-weightless environments, this is the first time changes around the eyes of astronauts in flight have been specifically examined.

The researchers analyzed photographs of astronauts. They collected 115 images of 13 astronauts from NASA's online image archives. Of these, 12 were male and one was female, with an average age of 46 years. There were 52 photos taken on Earth and 63 taken in space, and for each individual, at least three frontal photos from both environments were analyzed.

The key measurement was 'MRD2,' which refers to the distance from the center of the cornea to the edge of the lower eyelid. A shorter MRD2 value means the lower eyelid is pushed upward and moves closer to the pupil.

The analysis showed that the average MRD2 was 4.9 mm on Earth but decreased to 3.9 mm in space—a statistically significant difference. All 13 astronauts showed this directional change; for eight of them, the reduction was greater than 1 mm. In clinical settings, a decrease exceeding 1 mm is considered significant.

The research team named this phenomenon 'reverse ptosis.' Usually, 'ptosis' refers to a drooping of the eyelid, but in this case, the lower lid moves upward. The team noted, "We observed a consistent increase in lower eyelid position—i.e., a reduction in MRD2—that had not been previously noticed." The same phenomenon was observed during parabolic flights, which create temporary weightlessness by rapidly descending an aircraft. This suggests the change may begin immediately after gravity disappears, rather than gradually over a long mission.

A photo to help understand the article, showing an astronaut floating in space. NASA

There are two main explanations for why this occurs. The first involves body fluids: when gravity lessens, about 2 liters of bodily fluid shift toward the head, causing the face to swell and potentially pushing up the lower eyelid. The second explanation concerns the balance of forces on facial tissues: on Earth, gravity pulls the skin, muscles, and tendons downward toward the chin, but in space, this force disappears, allowing the tissues' elastic recoil to move them back toward their natural position.

The researchers concluded that this change cannot be dismissed as merely cosmetic. The position of the lower eyelid can affect the cornea, field of vision, and even eyesight. Although it has been reported that about one in three astronauts experience dry eyes, the study was not specifically designed to verify a direct link between these phenomena. The researchers also noted limitations due to analyzing publicity photos after the fact—some included smiling or tilted heads—and needing to correct results based on average corneal diameter rather than individual measurements.

The growing importance of these questions is due to missions to the Moon and Mars. As long-duration stays in space become more realistic, understanding the physical changes in astronauts’ bodies is increasingly necessary. The research team stated, "Further studies under standardized conditions are needed to confirm how long-term spaceflight affects eye health," adding that the present findings are expected to serve as a starting point.

This content was produced with the assistance of AI translation services.