来自美国的研究提示，航天员特别是年龄相对较大的航天员（如50岁上下）如果在太空停留时间长达或超过6个月，因微重力（microgravity）的作用可使他或她的眼底结构受损，进而损害他或她视功能，如出现视物模糊（their vision to become blurry）等，并且这一影响在航天员返回地面后数年仍可能存在。这一研究结果的意义在于“它告知人们长期处于微重力条件下，人们的视力可能受损，即以后在规划长期的太空旅行（如去火星）时应该认真考虑这一要素”。

Space Travel Might Lead to Eye Trouble: Study

Microgravity could spur blurred vision that could affect astronauts for years after return to Earth

TUESDAY, Nov. 8 (HealthDay News) -- Astronauts who spend six months or more in space may experience changes in the structures in the back of their eyes, causing their vision to become blurry, according to a new study from NASA.

Researchers found these changes may be the result of prolonged exposure to microgravity and could affect plans for trips to Mars or other long-term manned space voyages.

"In astronauts over age 40, like non-astronauts of the same age, the eye's lens may have lost some of its ability to change focus," said study co-author Dr. Thomas Mader, an ophthalmologist with Alaska Native Medical Center, in a journal news release. "In the space program's early days, most astronauts were younger, military test pilots who had excellent vision. Today's astronauts tend to be in their 40s or older. 　This may be one reason we've seen an uptick in vision problems. Also, we suspect many of the younger astronauts were more likely to 'tough out' any problems they experienced, rather than reporting them."

In conducting the study, published in the October issue of the journal Ophthalmology, the researchers examined seven astronauts, all around the age of 50, who spent at least six continuous months in space. The study revealed all seven astronauts experienced blurry vision while on the space station. The changes in their vision began roughly six weeks into their mission and continued long after they returned to Earth.

The researchers also found the astronauts also had at least one change in the tissues, fluids, nerves and other structures in the back of their eye.

Since the visual problems only affected astronauts who spent an extended time in space and none of them had symptoms usually associated with increased intracranial pressure (chronic headache, double vision, or ringing in the ears), the researchers concluded the changes in the astronauts' vision were related to microgravity.

The study authors noted how badly microgravity affects vision varies from person to person. They added that more research is needed to explore why this is the case, or why some astronauts are better suited for extended trips in space.

The researchers pointed out that NASA has acknowledged vision problems among its astronauts on long-term missions and currently provides them with special "space anticipation glasses" to improve their vision. Astronauts also undergo comprehensive eye exams and vision testing.

The U.S. National Aeronautics and Space Administration provides more information on microgravity.

SOURCE: American Academy of Ophthalmology, news release, Nov. 3, 2011