September 3, 2011
Eyes May Be Damaged By Prolonged Space Travel
Astronauts who spend a prolonged amount of time in space could experience problems with their eyesight, a new NASA-funded study has discovered.
As part of the study, a team of 17 researchers observed the eyes of seven astronauts and reviewed post-flight questionnaires of 300 more, half of whom had served on missions that lasted at least six months.
They measured several different factors, including refractive changes, pressure, orbital MRI, and visual acuity, and discovered that five of the seven astronauts experienced "a hyperopic shift +0.50 diopters (D) between pre/postmission spherical equivalent refraction in 1 or both eyes," as well as "globe flattening on MRI."
Furthermore, 29% of the 150 short-mission astronauts and 60% of the long-mission astronauts whose questionnaires they reviewed had "experienced a degradation in distant and near visual acuity. Some of these vision changes remain unresolved years after flight."
They concluded by hypothesizing that these changes that occurred in the optic nerve and ocular of the astronauts could be the result of "cephalad fluid shifts brought about by prolonged microgravity exposure." If so, it would mean that the eye would be affected by the weightlessness of space in much the same way that bones and muscles are, Adam Marcus of Reuters Health reports.
Their findings have been published in the journal Ophthalmology.
In an interview with Marcus, Alaska Native Medical Center (ANMC) ophthalmologist Dr. Tom Made, lead author of the study, notes that no astronaut had yet gone blind in five decades of space travel. However, he did say that the results were "something to be concerned about," and could be the result of increased pressure of fluid surrounding the brain.
Mader also pointed out that it was possible that the loss of gravity would cause a spike in the pressure around the optic nerve, or that low-gravity environments could cause vision problems by lowering the pressure in the eye. At this point, however, any possible cause is speculation, for as Mader told Reuters, "It's very hard for us at this point to define exactly what is causing all of this."
According to Marcus, at least one of the astronauts directly observed by researchers still displayed physical eye changes more than five years after returning to Earth. Furthermore, they found that 6.6% of short mission participants and 12% of long mission participants had issues with their long-distance vision while in space, and 11% of short mission participants and 34% of long mission participants reported "refraction" changes in their corrective lenses.
NASA is currently conducting follow-up studies, according to Reuters Health. Among the research the U.S. space agency is involved with is careful pre- and post-mission vision and eye anatomy tests, as well as an analysis of astronauts onboard the International Space Station (ISS).
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