Given that all life evolved in the presence of the Earth’s gravity, it is unsurprising that removing that element has some curious effects on our physiology*. Our bodies compensate for fluids being pulled downwards; our bones actually grow stronger from the normal stresses put on them by exercise; and is the definition of physical strength not one’s ability to counteract the force of gravity on objects? Toss us into space and we find our bones become brittle, our muscles atrophy from disuse, and our circulatory functions are thrown in disarray—causing headaches, stuffy noses, and puffy faces. Now we can officially add “loss of eyesight” to that list of space maladies.
As mentioned above, it’s not an entirely new idea to researchers. In fact, not knowing what weightlessness would do to the human body kept all sorts of agency doctors awake at night. Watch this clip of John Glenn reminiscing over all the contingencies they planned for before his historic orbital flight:
Glenn came home safe, and the zero-g eyeball issue was largely forgotten. Until it began to creep up again. It’s unsure when the first case was experienced (as opposed to the first reported case in 2005), as it has been largely hidden to researchers by worried astronauts—who upon returning to Earth, find their vision returned to normal. No harm, no foul, right? Well, apparently it’s not that simple, and in some cases full visual acuity was not regained. A major problem.
Since that first astronaut stepped forward**, others have joined him/her in reporting their visual problems. What followed was a battery of surveys, studies, and the Visual Impairment Intracranial Pressure Summit in 2011 that have all together pinpointed the likely cause to be a buildup in cerebrospinal fluid placing pressure on the backs of the eyes—a process detailed wonderfully in this report by Karina Marshall-Bowman. Called papilledema, it often occurs as a result of a tumor or inflammation in the brain or surrounding regions. You can see the result in the photo included in the comic: the optic nerve is pushing into the eye, creating a “bump” in the center. This pressure can cause permanent vision impairment and even blindness in worst-case scenarios. So it’s clear that before we can send astronauts on long journeys to other planets, something has to be done to mitigate this effect.
So what can be done? Treatment is unclear as in most cases, you relieve the pressure by treating the underlying cause. Microgravity induced increases in intracranial pressure are extremely unique, and its pathology isn’t completely understood. Bowman states that ICP (intracranial pressure, not the clowns) on Earth usually presents with more severe symptoms, leading her to believe there may be other contributing factors. One possible secondary factor she brings up is the high concentration of CO2 present in spacecraft, which increases cerebral blood flow. Another is that the initial fluid shift upon entering microgravity (where all fluids move upwards, sometimes called “Puffy-face chicken-legs syndrome”) somehow preventing the later egress of fluid from the cerebral cavity—even after the rest of the fluids have regained equilibrium.
Corroborating on the hypothesis for the Guardian is Volker Daman, head of the Crew Medical Support Office at the European Space Agency.
“We don’t know if it’s due to microgravity, launch stresses or landing, or a higher production of cerebral fluid, or reduced resorption of that fluid in orbit,” Dr Damann said. “In some crew we have some astronauts that have changes while others have none. Some have severe changes, others don’t. Some have it in both eyes, others not. We are looking for what could be the smoking gun but we don’t know the answer yet.”
Coincidentally, in the comic, I argue that the smoking gun has been found—intracranial pressure is distorting the eyes of astronauts, causing vision impairment—it’s the trigger finger they’re looking for. For now scientists can only continue to study the condition and hope a solution presents itself before we’re ready to send people on the nearly year-long journey to Mars. Luckily, I think we’ll have time, but that’s a whole other conversation.
*Granted there are functions that operate regardless of orientation. Humans are able to eat and digest in any position, though hanging upside-down brings on symptoms similar to those experienced in weightless environs.
**I suspect some of this is also due to NASA’s loosening of visual criteria. Where it was once required that all astronauts had 20/20 vision, advancements in laser eye surgery have caused them to rethink this policy. Video game mogul and Ultima franchise creator Richard “Lord British” Garriot spoke at the Moth about his NASA childhood and how his imperfect vision drove him to become one of the first citizen astronauts.