How Is Eyesight Affected In Space?

Comprehending the impact of microgravity on human physiology is crucial for enabling astronauts to withstand the challenging conditions of space travel for extended periods. Extensive research has been conducted over several decades to investigate significant alterations in the skeletal and muscular systems, and diverse countermeasures, such as vigorous physical exercise, are being implemented aboard the International Space Station to preserve physical fitness. However, there is still much that scientists and researchers need to uncover, such as the effects of space travel on the eyes and the brain.

Even during a trip as short as two weeks, vision changes occur for about a one-third of American astronauts. When the trip is longer—say, four to six months—that figure may double. But, before potential solutions can be proposed, scientists first have to understand what's causing these changes.

What happens to your eyes in space?

Gravity on Earth causes natural blood volume to accumulate below the waist, with the heart pumping it back up to areas above the waist, including the eyes. However, when gravity is absent, what happens to this fluid?

The human body possesses an impressive capacity to adapt to changes. Sensors in the upper body detect when excessive fluid is being received, prompting the body to reduce overall blood volume in microgravity. However, this response does not always completely offset fluid shifts, which can manifest in puffy faces among astronauts on the space station. The accumulation of fluid in or around the eyes is also a possibility.

Vision researchers are striving to understand whether chronic fluid shifts towards the head during spaceflight alter the shape of the eye or if fluid accumulates at the back of the eye. Optical coherence tomography, an imaging technique that employs a specialized camera to capture images of the back of the eye, is helping scientists better comprehend the impact of increased fluid accumulation in the tissue there.

The research on eyesight in space

Dr. Steven Laurie leads the Spaceflight Associated Neuro-ocular Syndrome research and notes that vision changes during spaceflight occur more rapidly than they would over the same period on Earth, as observed in astronauts on short-duration Space Shuttle missions. However, the emergence of swelling around the optic nerve at the back of the eye raises concerns since it could cause irreversible long-term vision changes that cannot be remedied with prescription lenses.

Another obstacle for scientists is that a one-size-fits-all treatment approach may not be applicable to all astronauts. Although all astronauts encounter chronic weightlessness, only 70% show early signs of fluid accumulation at the back of the eye, with a mere 15% exhibiting more severe symptoms. When returning to Earth's gravity, these changes may take up to a year to resolve, and some may not revert to their pre-spaceflight state. Men and women are both affected, and either one or both eyes can be impacted.

Dr. Laurie emphasizes that researchers and medical practitioners closely monitor astronauts during and after spaceflight to detect any potential permanent vision changes and continue research efforts to understand the underlying factors contributing to these changes.