By Jacqui Mayhew 

Vision correction  for astronauts who spend a prolonged amount of time in space is a likely consequence of extended exposure to a microgravity environment according to a new NASA-funded study recently published in the journal Ophthalmology. 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/post-mission 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." In an interview with Reuters Health, Alaska Native Medical Center (ANMC) ophthalmologist Dr. Tom Mader, lead author of the study, notes that no astronaut had yet gone blind in five decades of space travel although vision correction  requirements had needed to be addressed.

Mader did say that the results were "something to be concerned about," and could be the result of increased pressure of fluid surrounding the brain. He 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. However, any possible cause is still speculation: "It's very hard for us at this point to define exactly what is causing all of this." Almost 7% of short mission participants and 12% of long mission participants had issues with their long-distance vision while in space, with 11% of short mission participants and 34% of long mission participants reporting "refraction" changes in their corrective lenses thus highlighting the significant vision correction  consequences of extended space travel.

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