Following the advent of the space station, it’s been observed and demonstrated that exposure to weightlessness may have some deleterious effects on human health. The human body is too adjusted to the gravitational conditions on Earth, and as such extended periods of weightlessness cause various physiological systems to change and atrophy. Astronauts on-board the International Space Station battle nausea, and vertigo or headaches are on a day to day basis, however their biggest problem is muscle atrophy, which forces them to exercise constantly to diminish some of the effects.
Also, another serious weightlessness physiological symptom is vision deterioration. Previous NASA surveys which interviewed over 300 astronauts post-prelongued space missions (more than six months) revealed that half of all astronauts involved in orbital missions since 1989 complained about changes in near- and far-sightedness. One of 4 astronauts who flew missions of less than 6 months also reported eye problems.
Older crew members, aged over 40, are more predisposed to vision deficiencies, which first start after around six weeks of weightlessness exposure, and go on to continue even months after returning back to Earth. NASA has been aware of this problem for decades now, and for the past few years it has even issued reading glasses to all of the astronauts that serve long-term space missions.
Recently, the National Aeronautic and Space Administration performed a more indepth examination of this serious hazard, as the agency conducted a clinical evaluation which involved studying seven astronauts, all of whom were aged around 50 and had spent at least six continuous months in space.
Five of the 7 astronauts in the study complained of lost visual acuity beginning several months into their long-duration flights, and all 7 showed evidence of pathological processes undercutting their vision after their missions. Several abnormalities have been revealed, including the flattening of the back of the eyeball, folds in the vascular tissue behind the retina and excess fluid around and presumed swelling of the optic nerve.
“If the choroid gets damaged, you may get insufficient or altered blood flow to the photoreceptors, leading to detachment of the retina, leakage of fluid under the retina, or damage to the visual cells,” said Michael F. Marmor, MD, professor of ophthalmology at the Stanford University School of Medicine in California, who was not involved with the study.
The results are currently impacting plans for long-duration manned space voyages, such as a trip to Mars, explained the team including ophthalmologists Dr Thomas H Mader, of Alaska Native Medical Center, and Dr Andrew G Lee, of The Methodist Hospital, in Houston, Texas. Their findings have been reported in the October issue of Ophthalmology.
NASA is constantly developing technology, aided by data provided by studies such as the present one, which tries to counter the various worrisome effects zero gravity has on the human body. Regarding the eye problem in particular, astronauts are now required to routinely undergo pre- and postflight magnetic resonance imaging of their head and eyes, along with dilated fundus exams with photography of the macula and optic nerve, to provide intraocular pressures measurements.
“It is just a question of getting more data,” Dr. Mader said. “Recent long-duration missions have made these changes more pronounced, and improved technologies have served to better analyze these findings.”
Until artificial gravity can finally become functional, astronauts will have to pay for the best views in their lives.
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Copyright 2011 ZME Science
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