Life on a space station is very confined. For months on end, astronauts are kept in a structure that's about the size of a football field on the outside and much smaller on the inside. The nearest viewable objects beyond 100 yards are on Earth's surface, 230 miles below. This leaves a lot of distance in which the astronauts generally do not have objects to regularly focus their eyes on.

Does this affect an astronaut's ability to focus on things within that range after returning to Earth? For example, might they have more trouble focusing on distant vehicles or signs while driving on the highway?

Is there anything the astronauts do, or could be doing, to compensate for or prevent such problems?

  • 1
    $\begingroup$ Why can't they focus? $\endgroup$ Commented Jul 17, 2013 at 10:45
  • 2
    $\begingroup$ Without any hard link explaining why the issue exists it will be hard to give examples of how to counteract the issue $\endgroup$
    – user106
    Commented Jul 17, 2013 at 11:26
  • 2
    $\begingroup$ Astronauts seem perfectly capable on focusing on details on the Earth below them, which for all intents and purposes is near infinity, and further than almost anything they will have focused on while earthbound. $\endgroup$
    – Rory Alsop
    Commented Jul 17, 2013 at 12:03
  • 2
    $\begingroup$ There is a large range of distances at which astronauts in space will not likely have things to regularly focus on. From one corner of the solar array to the other is about 120 m (very rough estimate). The ISS is around 370 km above the earth's surface. Between those two distances, it's extremely unlikely that the astronauts will have anything to regularly focus their eyes on, while terrestrial humans very often (e.g. while driving) need to be able to read at those distances. It would be interesting to know if long-term non-exposure to objects at these ranges does affect eyesight. $\endgroup$
    – Iszi
    Commented Jul 17, 2013 at 23:55
  • $\begingroup$ @Iszi Thank you for taking this question further. This is not limited to the ISS. It would apply to a misson to mars as well. For different reasons as I learned. $\endgroup$
    – bastik
    Commented Jul 18, 2013 at 8:23

2 Answers 2


According to ABC News, yes:

But now, as American astronauts spend more and more time in space, they've noticed they're returning to Earth with a surprising malady: They cannot focus their eyes properly after they come home, and for some the problem seems permanent.


A fifth of the astronauts tested showed a flattening of the rear of the eyeball, affecting their ability to focus their eyes. A third showed expansion of the space surrounding the optic nerve that's normally filled with cerebral spinal fluid.

Also according to CNN:

In the past few years, about half of the astronauts aboard the international space station have developed an increasing pressure inside their heads, an intracranial pressure that reshapes their optic nerve, causing a significant shift in the eyesight of male astronauts. Doctors call it papilledema.

Interestingly, only male passengers seem to have been affected:

Female space travelers have not been affected.


Barratt is one of 10 male astronauts, all older than 45, who have not recovered. Barratt returned from a six-month stint aboard the station in October 2009 and has experienced a profound change in his sight.

He used to be nearsighted. But now, the space veteran says he’s eagle-eyed at long distance but needs glasses for reading. There is no treatment and no answers as to why female space flyers are not affected.

Also Aviation Week:

Nineteen ISS astronauts have developed symptoms of impaired vision since the ailment was first recognized in 2005, according to Dr. Christian Otto, a Universities Space Research Association remote medicine specialist who serves as the principal investigator for the NASA-sponsored Prospective Observational Study of Ocular Health.

The study, ultimately involving a dozen closely followed international astronauts, will search for a link between the blurred vision and the long observed shift of fluid from the lower torso to the chests and heads of fliers as they adjust to weightlessness. The fluid shift now appears to affect the eyes as well as the cardiovascular and central nervous systems.

With this in mind, I think we can say that the reduced gravity affects astronaut's vision - not the lack of objects for them to focus on.

  • $\begingroup$ Interesting that it only affects men. However, only about 10% of astronauts historially were women. Maybe with a larger sample size, this might change. $\endgroup$
    – Fezter
    Commented Jul 18, 2013 at 3:59
  • 2
    $\begingroup$ Even more interesting is the fact that a study involving a dozen astronauts found 19 astronauts afflicted with the condition. $\endgroup$
    – dotancohen
    Commented Nov 10, 2013 at 19:21
  • 1
    $\begingroup$ @dotancohen, that would indeed have been very interesting, but that's not what the above statement says. 19 astronauts have developed symptoms of impaired vision since 2005, and a study has been instigated that would closely monitor 12 (possibly different) astronauts. $\endgroup$
    – yoniLavi
    Commented Nov 18, 2015 at 17:27

While astronauts on the ISS have developed eyesight problems, it is for completely different reasons than what you suggest in your question.

The distance of objects that these astronauts focus on is not a problem. In terms of optics, the human eye treats everything past about 20 feet away the exact same, so looking out of the cupola at Earth should give the astronauts plenty of healthy long-distance viewing. In fact, these astronauts don't probably experience anything different than the average white collar worker here on Earth's surface.

However, as mentioned in Undo's answer, the microgravity environment can have very negative effects on astronauts vision, because of the relocation of fluids to the head. Because gravity is not acting like normal to push internal fluids down towards the feet, body fluids have more of a chance to build up in the cranial space. If the fluid movement is strong enough, it can actually physically push against the back of the eyeball, causing it to permanently warp, and ultimately resulting in distorted vision.

  • $\begingroup$ Another potential eye problem with micro gravity might be that particles don't settle but float around. Eyes should become more polluted and exposed to bacteria. I don't know if this has been registered as a real problem though. $\endgroup$
    – LocalFluff
    Commented Mar 12, 2014 at 9:00

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.