The lack of gravity in space can have many different effects on the body, including on the visual system. Many astronauts have reported temporary and permanent changes in their vision upon returning from a trip to space.
Dr. Marc Ellman of the Southwest Eye Institute was a guest at the Association of Space Explorers XXXII Planetary Congress at Space Center Houston in October of 2019, where he had the opportunity to meet many space explorers during the largest gathering of astronauts and cosmonauts in the world.
One astronaut he met was Michael Lopez-Alegria, originally of Madrid Spain, who explained a permanent visual loss he experienced after his time at the International Space Station. Lopez-Alegria who now lives in Washington, DC, performed ten spacewalks in his career including the second longest duration spacewalk of all time.
“The only lasting effect is about 1.5 diopter farsighted shift in 7 months on orbit,” Lopez-Alegria told Dr. Ellman. “I think the overall shift may not have been any more than what would have occurred naturally, but the time scale certainly seems accelerated.”
Visual Impairment Intracranial Pressure Syndrome
NASA identified the problem as Visual Impairment Intracranial Pressure Syndrome (VIIP), which is now knowns as Space-Associated Neuro-Ocular Syndrome (SANS). This syndrome affects 80% of astronauts on long-duration missions in space. Interestingly, many astronauts suffer from visual changes that are irreversible even after returning to Earth.
Though studies are still being conducted, researchers believe that the visual problems are a result of increased pressure in the skull related to near absence of gravity (microgravity). When you are on Earth, the force of gravity exerts pressure on you. When you travel to space, there is almost no gravity there. Since your body has evolved with gravity as a constant presence, living in a state without significant gravity for a prolonged period comes with numerous health issues such as muscle atrophy and bone loss. Additionally, changes in fluid patterns result in increased pressure in the cerebrospinal fluid inside your skull (intracranial pressure). This fluid can work its way down to the sheath around the optic nerves behind your eyes, causing swelling of the optic nerve in your eye and visual changes.
In one study, researchers used magnetic resonance imaging (MRI) to examine the eyes of 27 astronauts who spent about 108 days in space. The results showed ocular abnormalities that are similar to those that occur to patients with intracranial hypertension, a condition where pressure builds up in the head. The results indicated that 33% of the astronauts showed an expansion of the cerebrospinal fluid space that surrounds the optic nerves, 15% had a bulging optic nerve, and 22% showed flattening of the back of their eyeballs.
Artificial Gravity
Scientists are working on ways to decrease the effects of the lack of gravity on the human body. They feel that artificial gravity may be the solution. A team of researchers from the Japan Aerospace Exploration Agency (JAXA), together with professors and members from the University of Arkansas for Medical Sciences, examined changes in ocular tissues of mice. They divided the mice into two groups. One group was put in ambient microgravity condition (similar to space) and the other group in artificial gravity state (similar to Earth). The researchers found that those mice in the microgravity condition suffered damage to the blood vessels that are responsible for the regulation of fluid pressure within the eyes.
In July of 2019 NASA published a statement titled “Risk of Spaceflight Associated Neuro-Ocular Syndrome (SANS)” in which they wrote “Given that the microgravity environment causes cephalad fluid shift in astronauts, there is a probability that astronauts will have intracranial pressure changes to some degree, and if left untreated, could lead to vision alterations and potentially other deleterious health effects.”
Scientists will continue to investigate the health and vision effects of space travel in humans, especially as space agencies work toward longer missions including the possible travel to and habitation of other planets such as Mars.
