Why Do Astronauts Develop Cataracts?

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Exposure to space radiation mutates genes “p21” & “p57”, causing a decrease in the production of newer fiber cells, ultimately exacerbating the development of cataracts.

Space movies like Interstellar and Gravity make dramatic space travel seem like a plausible reality. However, the only people who get to experience space travel in real life are astronauts. They witness spectacles and heavenly vistas that most humans only dream of. They get to see Earth from a completely different perspective, and float around the endless black canvas we call space.

Among all of their unique experiences, astronauts have also reported witnessing strange flashes of light. These light flashes are actually the result of space radiation. Yes, radiation. The word itself is enough to send shivers down someone’s spine, but adding “space” to it only makes it more daunting and terrifying. Scientists believe that exposure to these strange light flashes (space radiation) is causing the development of cataracts among astronauts.

What are Cataracts?

Cataracts is a disease of the eye caused by the clouding of the eye lens. The eye lens focuses the image (light) on the retina at the back of the eye. On the retina, the light is converted into nerve signals that are then sent to the brain. The brain processes these nerve signals and identifies the image/object in front of our eyes. However, in the case of cataracts, due to clouding, the lens cannot focus a clear image onto the retina, leading to unclear sight or a decrease in vision.

Cataracts and healthy eye detailed structure. - Vector(Tefi)s

Clouded eye lenses in cataracts lead to unclear vision. (Photo Credit: Tefi/ Shutterstock)

Cataracts can affect only one or both eyes, and the eye lens can become clouded for a variety of reasons. The most common cause is aging, but other reasons include trauma and exposure to radiation; sometimes, cataracts are actually incurred from birth! Symptoms of cataracts include blurry vision, light sensitivity, seeing halos around light sources, faded colors, etc.

What are the light flashes that astronauts witness in space?

The first humans to land on the moon, Neil Armstrong and Edwin Aldrin Jr., reported seeing some strange light flashes over the course of their mission. They reported seeing the flashes even with their eyes shut. Strange, right? How can one see something with their eyes closed?

Researchers and scientists over the years have identified the light flashes that Apollo 11 crew members experienced as Space radiation. Before we dive in deeper to Space Radiation, let’s first define what radiation is in general.

In the simplest of terms, radiation is the transmission of energy in the form of waves or sub-atomic particles moving at a high speed. One comes across multiple types of radiation every single daily. The emissions from the sun, commonly known as ultraviolet light, are a kind of radiation. Microwaves in a microwave oven, heat from a stove or a nearby fire, X-rays at the dentist, sound waves from a speaker, etc. are all different types of radiation.

The electromagnetic spectrum - Vector( Polina Kudelkina)S

Radiation is divided into ionizing and non-ionizing radiation. Ionizing radiation is harmful, whereas exposure to non-ionizing radiation does not cause much harm.  (Photo Credit: Polina Kudelkina/ Shutterstock)

Radiation is split into two types: Ionizing and Non-Ionizing Radiation. Ionizing radiation carries energy upwards of 10 eV (1 eV = 1.6022×1019 joules) and is considered harmful. They include α, β, and γ radiation, as well as X-rays and cosmic radiation. Non-ionizing radiation, on the other hand, does not contain enough energy to cause harm; examples include sound waves, microwaves, etc.

Space Radiation

Space radiation is commonly referred to as cosmic radiation. The “cosmic” label comes from the term cosmos, which refers to the universe. All types of radiation found outside Earth’s atmosphere and in space are considered to be cosmic/space radiation. This includes ultraviolet radiation from the sun, radiation trapped in Earth’s magnetic field and galactic cosmic radiation. All three of these are forms of ionizing radiation, and each is more harmful than the last!

space radiation

Among the three types of space radiation, galactic cosmic radiation is the most ionizing and therefore the most harmful, while UV radiation is the least ionizing and easiest to shield against. (Photo Credit: Nasa)

The ionizing radiation found on Earth has energy levels in the neighborhood of 10 eV, whereas the energy levels of space radiation keeps increasing from 107 eV. The most “high-energy” cosmic radiation detected in history had an energy of 3.12 ×  1020 eV. To put this into perspective, 3.12 × 1020 eV is roughly equal to 50 J and the kinetic energy of a baseball traveling at 56 mph.

Energy levels of Earthbound ionizing radiation are still more than enough to cause some serious harm, so one can only imagine what kind of harm ionizing space radiation may cause. Ionizing radiation can pass through substances and also damage/alter them in the process, including human bodies! Ionizing radiation has enough energy to damage the integrity of DNA in living organisms.

But why does it cause cataracts?

How does exposure to space radiation cause cataracts?

The lens of our eye has three main parts: the lens capsule, the lens epithelium (epithelial cells), and fiber cells. The lens fibers or fiber cells form the bulk of the eye lens. These fibers are responsible for keeping the lens clear and functional. Fiber cells are essentially empty cell bodies composed of roughly 30% protein solution. New fiber cells are continuously produced to replace old lens fibers.

The lens epithelium, on the other hand, acts as a covering for the eye lens and is extremely delicate. The epithelial cells, when necessary, discard their internal structures (cell organelles) and transform into new fiber cells.

Exposure to space radiation is believed to mess with the transformation of epithelial cells into fiber cells. To be more specific, exposure to radiation mutates the Fibroblast Growth Factor 2 (FGF-2) gene. The FGF 2 is generally responsible for helping cells respond to stress. However, upon being exposed to radiation, FGF-2 also boosts the activity of two other genes “p21” and “p57”. These genes regulate cell activities like cell division. In the case of our eye lenses, these two genes control the transformation of epithelial cells into fiber cells.

The mutation of the genes  “p21” and “p57” is suspected to cause a decrease in the production of new fiber cells, in addition to leading to the production of abnormal fiber cells. As the availability of new fiber cells decreases, the dead fiber cells eventually clump together and cloud a small portion of the lens. As time progresses, more fiber cells die and the clouded region grows in size, leading to cataracts.

Conclusion

Cataracts are just the tip of the iceberg. Exposure to space radiation can lead to a plethora of different health conditions, including an increased cancer risk in astronauts.

select health effect due to space radiation exposured

Exposure to space radiation can lead to diseases more severe than cataracts in the long run.  (Photo Credit: Creative Commons)

However, a limit to how much radiation exposure you should experience does exist. The exposure limits depend on one’s age, gender and profession. For example, the exposure limits for an astronaut traveling through space are higher than for those working with and around radioactive material. Also, techniques like magnetic shielding, plasma shielding and wearable shielding in the form of space suits for astronauts continue to be improved to decrease the adverse effects of radiation exposure. Considering the effects of space radiation and the lack of proper shielding against it, space travel still seems like a distant dream for human beings!

References

  1. Nasa.gov (Link 1)
  2. Berkeley Lab
  3. Caltech
  4. Nasa.gov (Link 2)
  5. Nasa.gov (Link 3)
The short URL of the present article is: http://sciabc.us/yEbkZ
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About the Author:

Piyush is a mechanical engineer from Mumbai (India) who runs as much as his machines. He’ll always be up to talk about comics, movies, and music. Will meet you annually at the comic-con and daily at the gym.

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