Long-duration space travel may cause eye and brain changes that affect astronauts’ vision. Scientists refer to this condition as spaceflight-associated neuro-ocular syndrome (SANS).

Researchers previously referred to SANS as visual impairment and intracranial pressure syndrome. Some people also call it space blindness.

This condition involves changes in the eyes and brain during prolonged space travel. These changes may occur due to cerebrospinal fluid in the brain and spine moving toward the head during weightlessness in a microgravity environment.

Although more research is necessary, scientists believe SANS may lead to complications such as short- and long-term vision changes.

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According to the National Aeronautics and Space Administration (NASA), prolonged space travel can cause SANS, a condition that can affect astronauts’ eyesight.

Some people refer to SANS as space blindness, as the condition only affects people who travel in space. However, the condition can vary in severity and does not always result in blindness.

There is no formal definition of SANS, as scientists are continuing to research the condition. According to NASA, researchers do not yet fully understand its long-term health consequences.

NASA states that 70% of space station astronauts experience swelling in the back of the eyes, which may indicate SANS. Other characteristics scientists associate with SANS include the following eye and brain changes.

Eye changes

Weightlessness during space travel can lead to eye changes, including:

  • Choroidal and retinal folds: These are folds or grooves in the eye that may lead to decreased vision.
  • Optic disc edema: This is where one or both optic discs, which are part of the optic nerve in the eye, may become swollen. This could lead to complications, including vision changes.
  • Globe flattening: This is a flattening of the back of the eye, which may contribute to decreased vision.

Brain changes

Structural brain changes that may occur during space travel can also affect eyesight. These include:

  • Upward shifting of the brain: The brain may shift upward inside the skull during weightlessness, causing structural changes that may affect eyesight.
  • Enlargement of ventricular volume: The brain’s ventricles produce and store cerebrospinal fluid. The amount of fluid may increase during space travel, which can affect vision.
  • Changes in the pituitary gland: Prolonged space travel may cause changes in the shape of the pituitary gland, a small gland in the base of the brain. Structural changes in the gland can cause it to press into other areas of the brain, which may result in vision problems.

Researchers do not fully understand the causes of SANS but believe the redistribution of cerebrospinal fluid during weightlessness to be the most likely cause.

Cerebrospinal fluid travels around the hollow spaces of the brain, spinal cord, and meninges, which are layers of tissue that surround the brain and spinal cord. The fluid cushions these organs and structures to protect them from injury and provides nutrients.

On Earth, gravity helps cerebrospinal fluid drain into the venous sinuses and the jugular veins in the neck. In space, astronauts are in a microgravity environment that causes them to become weightless.

During weightlessness, cerebrospinal fluid shifts toward the head rather than down through the body. The body cannot drain or distribute other bodily fluids, including blood and lymphatic fluid, as usual in microgravity.

This fluid shift can cause mild but sustained fluid congestion in the head. This can increase pressure in the area and lead to changes in the eyes and brain. These changes, which are characteristic of SANS, can affect eyesight.

Pressurized cerebrospinal fluid may also become trapped within the optic nerve and sheath in the eye during space travel, which may lead to SANS.

Vision changes due to SANS vary in severity and duration.

Many astronauts only experience SANS, or space blindness, while in space. However, vision changes can be permanent in some astronauts.

Treatment for SANS can include:

  • A reduced workload: Space agencies may assign astronauts with SANS less visually demanding tasks and reduce their workload to help prevent worsening symptoms.
  • Optical corrections: Prescription glasses or contact lenses may help address specific vision problems in astronauts.
  • Medications: A doctor may prescribe medication for SANS, such as anti-inflammatories to reduce inflammation and diuretics to help regulate fluid balance.
  • Vision aids: If an astronaut’s vision remains impaired, visual aids, such as specialized software, magnifiers, and telescopic devices, can help them maintain functionality.
  • Visual and psychological therapy: Visual therapy exercises may help improve some visual functions. Psychological therapy, such as talk therapy or behavioral counseling, may help astronauts manage the mental and emotional effects of SANS.

There are some steps people can take to reduce the risk of space blindness. However, a person may not always be able to prevent the condition.

Current SANS risk-reduction strategies include:

  • Specialized diets: Nutritionists and researchers may help astronauts formulate diets that help address space travel risks, including SANS. Nutritional interventions for astronauts contain properties that may help protect eye tissue from the adverse effects of microgravity.
  • Hydration management: Adequate fluid intake could help minimize the risks of fluid shift toward the head and the eye and brain changes associated with SANS.
  • Exercises: Astronauts may receive specific exercises to perform during space travel to help counteract fluid shifts toward the head.
  • Sleep maintenance: Getting enough high quality sleep may help reduce the risks of SANS.

Researchers are continuing to study and develop possible SANS prevention techniques for future use in space travel, including:

  • Lower body negative pressure (LBNP) devices: Wearable LBNP devices, including gravity suits, may counter fluid shifts within the skull. The suits could help distribute fluids around the body.
  • Intermittent artificial gravity: Scientists may be able to generate artificial gravity in microgravity environments using a short-arm human centrifuge. This machine rapidly spins a person to create a greater force of gravity, which can help fluids move from the head to the rest of the body.
  • Thigh cuffs: Wearing cuffs around the thighs during weightlessness may help capture blood flow in the veins of the lower limbs, reducing venous pressure in the brain.

Cerebrospinal fluid may shift toward the head during prolonged space travel. This may lead to eye and brain changes that can affect an astronaut’s vision. Scientists call this condition spaceflight-associated neuro-ocular syndrome (SANS).

Researchers believe SANS occurs because fluid does not distribute typically throughout the body in a microgravity environment. This can increase pressure in the head and lead to changes that can affect eyesight.

Treatment for SANS includes medication, optical corrections, and visual aids. Risk-reduction strategies include a specialized diet and exercise regime. However, further research is necessary to understand SANS fully.