Puzzling Syndrome Impairing Astronauts Sight? Space–Associated Neuro-Ocular Syndrome

Shib Sankar Roy, PhD Research Scholar

Program Manager, Vision Science Academy, London, U.K.

Vision Science Academy Exclusive

Unusual Visual changes during long duration space flights?

The long-term health effects of space travel are still being closely watched and researched. According to reviews, astronauts may endure mild eye puffiness. ⁽¹⁾

The human body is exposed to a number of dangers and physiological changes during long-duration spaceflight, including increased radiation exposure, bone density loss, skeletal muscle atrophy, and eyesight impairments. Venous blood shift, structural alterations to the brain, and cerebrospinal fluid shift are all related changes. The flattening of the rear of the eye, the development of folds over the retina, and other core globular alterations.

Space–Associated Neuro-Ocular Syndrome (SANS) is a particular neuro-ocular condition of space travel that has no equivalent on Earth. Future manned lunar/Martian missions and/or colonisation missions could be hampered by SANS. ⁽²⁾ The basic aetiology of SANS is still hotly contested and not fully understood. Cephalic fluid shift, vascular and lymphatic obstruction, inflammation, ischaemia, and environmental variables are a few of the potential processes.

In patients who developed SANS, no evidence of long-term irreversible vision loss has been found. NASA has previously noted changes to the eyeball during brief spaceflight (less than two weeks), such as hyperopic shift. The choroidal and retinal folds, cotton wool patches, optic disc oedema, optic nerve sheath distension, and globe flattening are further constellations of SANS-identifying symptoms.

When compared to upright postures on earth, entering weightlessness induces an immediate and persistent fluid shift towards the head that increases the amount of blood and fluid filling in the brain and central nervous system. Astronauts are unable to “stand up” and periodically unload cerebral structures because of the lack of gravitational stress, which causes mild but persistent cephalad fluid congestion. We and others have hypothesised that this cephalad fluid congestion is an initiating and driving factor in the development of SANS. ⁽³⁾

Visual scotomas, worsening distant vision, headaches, and reduced near-visual acuity are all symptoms. Self-reported SANS-related symptoms on board the International Space Station correlated with spaceflight time in a dose-dependent manner, with 23% reporting near-sightedness disturbances after short-duration space flight and up to 47% reporting similar symptoms after long-duration space flight.

Epilogue:

• As spaceflight duration increases, SANS causes structural and occasionally residual changes in vision.
• NASA has continued to pay attention to and conduct research into this issue, but its scope has been somewhat constrained by the small number of spaceflight-related human cases that have been studied.
• No crew member has yet reported having permanent vision loss following the trip, despite the fact that various ocular anatomical changes from SANS, including as globe flattening, choroidal folds, and hyperopia shifts, may last for years after the voyage.

References:

1. Yang JW, Song QY, Zhang MX, Ai JL, Wang F, Kan GH, Wu B, Zhu SQ. Spaceflight-associated neuro-ocular syndrome: a review of potential pathogenesis and intervention. International Journal of Ophthalmology. 2022;15(2):336.
2. AGARWAL P. Understanding spaceflight-associated neuro-ocular syndrome (SANS): what do we know?.
3. Wojcik P, Batliwala S, Rowsey T, Galdamez LA, Lee AG. Spaceflight-Associated Neuro-ocular Syndrome (SANS): a review of proposed mechanisms and analogs. Expert Review of Ophthalmology. 2020 Jul 3;15(4):249-58.