Results from a NASA study show that long-term spaceflight could have a significant impact on the eyes. The study looked at seven astronauts who had spent six continuous months or more in space, on the international space station. All the astronauts were about age 50.
The astronauts all reported some degree of visual symptoms, including blurriness, which was reported by all subjects. The visual symptoms typically began around six weeks into the mission. An in-depth examination of the astronauts’ eyes showed that all had one or more of the following symptoms:
- Flattening of the back of the eyeball (five subjects)
- Folds in the vascular tissue (choroid) behind the retina (five subjects)
- Excess fluid around and presumed swelling of the optic nerve (five subjects)
Researchers speculate that the changes might have been caused by increased intracranial pressure, abnormal flow of spinal fluid around the optic nerve, changes in blood flow, low intraocular pressure, or a combination of factors. In orbit, astronauts experience what is known as microgravity, which can change the distribution and flow of fluids in the body.
Most of the astronauts reported that visual symptoms went away about 6 weeks after returning to earth, while others report symptoms lasting months or years.
Overall, visual changes are seen in about 23% of astronauts on short missions and 48% of astronauts on longer missions. However, it is unknown which changes resulted in visual changes. Although choroidal folds can sometimes be associated with visual symptoms, it is more likely that visual changes were caused by flattening of the eye, which could result in hyperopia, since the lens might be focusing light behind the retina. Researchers also propose that the astronauts may be experiencing presbyopia, which would be more common in astronauts now that their average age has increased.
Visual changes associated with space travel have been speculated since the earliest days. “space anticipation glasses” for improved visual acuity were made for early astronauts. John Glenn and others had them in their space capsule.
These findings are significant for longer trips to Mars or other planets that are being planned for this century. Perhaps these findings will encourage the use of faster continuous-acceleration voyages rather than lower-energy but cheaper “coasting” missions.
If your vision is not as clear as it used to be, you should visit a local ophthalmologist for a comprehensive vision exam.