It’s the dream of many a little boy or girl – to one day become an astronaut and gaze upon our beautiful blue planet not from the earth, but from outer space. However, unless you were a particularly sensible, well-researched child, you may not be aware of the profound effects that space flight can have on the human body. Extensive and ongoing research by NASA and other authorities have found that extended durations spent with your head in the stars can actually result in:
- An increased risk of neurodegenerative diseases
- Alterations to your sense of smell and taste
- A drop in red blood cell count
- Loss of muscle mass and bone density
- A compromised immune system
There is also an observation delightfully described as “puffy face” and “bird legs”, which refers to swelling of the face and a decrease in leg circumference of up to 30%, thanks to microgravity causing a shift in body fluid distribution.
As we don’t have hundreds of astronauts taking to the stars every month, it took some time to identify the effects of space flight on the human visual system. Now NASA researchers use the term “space-associated neuro-ocular syndrome” (SANS) to refer to the vision changes astronauts experience while on mission.
What is Space-Associated Neuro-Ocular Syndrome?
SANS refers to a collection of changes to the visual system after a prolonged time spent in space, typically on missions longer than a month. Understanding SANS and how to manage it is considered to be of significant concern as astronauts depend on their vision to carry out their tasks (as most of us do), and space missions are expected to be extended for even longer durations in the future.
Currently, we don’t fully understand exactly what causes SANS. The research so far points to a combination of contributing factors, such as a shift in fluid distribution upwards to the head due to changes in gravity, inflammation, increased levels of carbon dioxide, genetics, and radiation exposure. Around 70% of astronauts appear affected by SANS with most cases occurring in older men compared to females or younger males.
So far, it’s been observed that SANS can result in a swelling and thickening of various structures in the eyeball, including the retina (the tissue that senses incoming light) and the choroid (the tissue that supports the retina’s oxygen and metabolic requirements). Swelling of these structures can lead to a wavy distortion in the vision as the usually smooth layers become wrinkled. Another effect of SANS is a lengthways flattening of the eyeball, also described as a shortened axial length. This results in a far-sighted shift, which is what’s likely to be responsible for the reported difficulties in vision. Astronauts experiencing this far-sighted shift in their vision will find their near reading sight becomes blurrier, though this can easily be corrected with appropriate reading glasses (assuming the astronaut thought to pre-emptively pack reading glasses in their suitcase!).
Upon return to earth, studies noted that these structural changes to the eyes persisted for up to a year. At the moment there is insufficient data to understand the long-term effects of space flight on the eyes and whether it’s associated with an increased risk of eye problems further down the road. NASA is also still investigating what countermeasures might be effective at reducing SANS but so far has not come up with much. Studies looking at various options such as wearing cuffs on the thighs or negative pressure suits to encourage body fluid to stay where it’s supposed to, wearing swimming goggles, and reducing carbon dioxide levels, have not concluded that these demonstrate any significant effect.
A Little Detour: Laser Vision Correction for Astronauts
In September 2007, NASA changed its policy to permit aspiring astronauts to correct their vision with PRK or LASIK in order to meet the 20/20 vision requirements. To be considered (beyond the required master’s degree in science, engineering, technology, or mathematics, minimum 2 years of relevant professional experience, at least 1000 hours piloting a jet… the prerequisite list goes on), candidates who have had refractive surgery must have had their procedure performed at least a year ago and not suffer any visual side effects such as glare or haloes.
So, which is better, PRK or LASIK? Both techniques have pros and cons. PRK (photorefractive keratectomy), involves removing the superficial layer of cells from the cornea, reshaping the deeper tissues with a laser, and then allowing the superficial cells to regenerate. By changing the curvature of the cornea, the passage of light is modified so as to focus on a sharp point on the retina, providing clear vision.
The downtime for the PRK procedure for those in military service is around 3 months before being permitted to return to the job, which is a fairly long time for those in this line of work. On the other hand, LASIK (laser assisted in situ keratomileusis) involves the formation of a hinged corneal flap, which is later replaced once the laser has done its reshaping. This means the recovery time is much faster, but there were concerns about how secure this corneal flap would be when faced with minor trauma (it would be awkward to have this flap dislocate while in outer space and just watch it floating away, wouldn’t it?). However, rigorous testing by the US military determined that LASIK is a safe option for those in military service, a decision that was later adopted by NASA for its astronaut program.
Bespectacled astronauts-to-be can therefore rejoice; you now have the chance to apply for the space program (assuming you meet the master’s degree, piloting experience, right body measures…etc)!
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