Upon their return from the International Space Station, numerous astronauts have observed an unforeseen consequence of their mission: a modification in their visual acuity.
This phenomenon, impacting approximately 70% of astronauts engaged in extended duration missions, has prompted NASA scientists to delve into the underlying mechanisms responsible for the effects of weightlessness on human vision.
Dr. Sarah Johnson was the first to encounter this phenomenon during her six-month tenure aboard the ISS. She documented that text that was discernible prior to launch became indistinct.
Dr. Johnson’s experience is not isolated, as astronauts frequently report challenges in reading, blurred distance vision, and other visual alterations that can persist for several years after their return to Earth.
Currently, the condition is recognized as Spaceflight Associated Neuro-ocular Syndrome (SANS) and has emerged as a significant health concern for extended space missions. Unlike motion sickness or muscle weakness, which are transient upon return to Earth, the visual alterations can be permanent.
The primary cause of SANS is hypothesized to be microgravity. On Earth, gravity consistently exerts downward force on fluids within our bodies. In space, these fluids redistribute, resulting in facial edema and elevated intracranial pressure.
Elevated pressure can flatten the back of the eyeball and cause swelling of the optic nerve. These findings have significant implications for Mars missions, which can last from two to three years.
Robert’s team at NASA is developing several countermeasures, including specialized contact lenses, medications to reduce intracranial pressure, and exercise protocols that may aid in maintaining normal circulation.
They are also testing a device called the Visual Impairment Intracranial Pressure (VIIP) chamber, which can simulate Earth-like pressure conditions for the eyes.
Although concerning, this research benefits all of humanity. Scientists are gaining new insights into how pressure affects vision, which may potentially aid in treating conditions such as glaucoma and intracranial hypertension.
Understanding how our bodies adapt to space remains crucial. As we push the boundaries of our bodies further through longer-duration spaceflight, we inevitably uncover more challenges.
Research into solutions will continue at NASA and on board the International Space Station so that, hopefully, when we finally embark on a human trip to Mars, we can at least perceive clearly the accomplishments we have achieved.
According to NASA, As astronauts embarked on extended missions of six months or more aboard the International Space Station, they began to observe alterations in their visual acuity. Notably, many astronauts discovered that, as their missions progressed, they required stronger reading glasses. Researchers investigating this phenomenon identified swelling in the optic disc, the point of entry for the optic nerve into the retina, and flattening of the eye’s shape. These symptoms collectively came to be known as Space-Associated Neuro-Ocular Syndrome (SANS).
Microgravity induces a redistribution of blood and cerebrospinal fluid towards the head, leading to studies suggesting that these fluid shifts may be a contributing factor to Space Anemia (SANS). A current investigation, titled “Thigh Cuff,” investigates whether tight leg cuffs alter the circulation of fluids within the body, particularly in the ocular region and cardiovascular system. If this is the case, the cuffs could serve as a mitigating measure against the challenges associated with fluid shifts, including SANS. A straightforward and user-friendly device capable of counteracting the upward displacement of body fluids could potentially safeguard astronauts during future missions to the Moon and Mars. Additionally, these cuffs could be employed to address conditions on Earth that result in fluid accumulation in the head or upper body, such as prolonged bed rest and certain medical conditions.
The Fluid Shifts investigation, conducted from 2015 to 2020, was the inaugural study to elucidate alterations in cerebral blood drainage patterns during microgravity. Vision Impairment and Intracranial Pressure (VIIP) commenced testing the potential role of these fluid shifts and concomitant elevation of intracranial pressure in the pathogenesis of Space Anesthesia-Induced Nausea and Vomiting (SANS). This research employed a diverse range of modalities, including clinical examinations with and without dilation, retinal and associated vascular and neural imaging, noninvasive imaging techniques to assess retinal structural thickness, and magnetic resonance imaging of the ocular and optic nerve. Furthermore, approximately 300 astronauts completed questionnaires to document visual alterations experienced during their missions.
In a seminal publication from the research, scientists expounded upon the enhanced comprehension of SANS achieved through these imaging techniques. The authors synthesized emerging research on the development of a head-mounted virtual reality display capable of conducting multimodal, noninvasive assessments to facilitate the diagnosis of SANS.
Another research study indicated that measuring the optic nerve sheath diameter holds promise as a method for identifying and quantifying ocular and visual alterations during spaceflight. The study also proposes recommendations for standardizing imaging equipment, measurement protocols, and other aspects of study design.
A separate study reported on an astronaut who experienced more severe than average changes following a six-month spaceflight, along with certain factors that may have contributed to these changes. Researchers also observed a positive improvement in the individual’s symptoms, which may have been attributed to B vitamin supplementation and reduced cabin carbon dioxide levels following the departure of some crew members. Although a single case does not permit researchers to establish a causal relationship, the extent of the improvements suggests that this individual may be more susceptible to environmental conditions such as carbon dioxide. This may have represented the initial attempt to mitigate SANS through in-flight B vitamin supplementation.
A CSA (Canadian Space Agency) investigation employed an imaging technique known as Optical Coherence Tomography to assess whether the reduced stiffness of eye tissue is a contributing factor to Space-Related Neurodegenerative Syndrome (SANS). On Earth, alterations in the tissue stiffness surrounding the eyeball have been linked to aging and conditions such as glaucoma and myopia. The researchers discovered that prolonged spaceflight impacted the mechanical properties of eye tissues, potentially contributing to the development of SANS. This finding enhances our comprehension of ocular changes during spaceflight and in aging patients on Earth.
Genetic Changes and Artificial Gravity: Advancements in Vision Research
The Japan Aerospace Exploration Agency’s (JAXA) MHU-8 investigation, which delved into the effects of spaceflight on DNA and gene expression in mice, unveiled significant alterations in the optic nerve and retinal tissue. Notably, researchers discovered that artificial gravity exhibited the potential to mitigate these changes, potentially serving as a countermeasure for future space missions.
These findings, along with other pertinent studies, hold the promise of revolutionizing vision research. By harnessing these discoveries, researchers can effectively prevent, diagnose, and treat vision impairments among crew members and individuals on Earth.