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EW NEWS & OPINION 16 May 2017 by Liz Hillman EyeWorld Staff Writer what Lawley et al., including Dr. Levine as the principal investigator, sought to do. What's more, they also sought to observe the effect of microgravity on central venous pressure as well. Eight volunteers who had chemotherapy ports placed in their head for medical therapy had a nee- dle put through the port to connect to a pressure transducer, which was sutured in place. "For the first time ever we mon- itored beat-by-beat and breath-by- breath and gravity-to-gravity chang- es in intracranial pressure in normal humans—that's pretty ambitious," Dr. Levine said. "To take people and put needles in their heads and wrap them up and use transcranial Dop- pler to measure blood flow and beat- by-beat blood pressure devices and result from cerebrospinal fluid shifts during long-term exposure to micro- gravity environments. In other words, due to the lack of gravity on the ISS, from the standpoint of cerebrospinal fluid, it's as if the astronauts are always lying down, whereas on Earth, humans go from laying down to sitting up according to circadian rhythms. Prolonged intracranial pressure has been associated with flattening of the globe, retinal folds, papilledema, and small hemorrhages, Dr. Levine said. The phenomenon has been dubbed visual impairment/intracra- nial pressure syndrome, according to Lawley et al. 2 Though hypothesized, the possi- ble association between microgravity and elevated intracranial pressure had never been measured. That's intracranial pressure and how it could be impacting vision, as well as a possible remedy. 2 "One of the most important and previously unrecognized problems that we've started to realize in the effects of astronauts on long-du- ration space flights are changes in their vision," said Benjamin Levine, MD, professor of internal medicine/cardiology, University of Texas Southwestern Medical Center, Dallas, and director, Institute for Ex- ercise and Environmental Medicine (jointly operated by UT Southwest- ern and Texas Health Resources), Dallas. "A lot of people have flown in space, but the vast majority for short durations… As we think about the future of manned spaceflight, we're talking predominantly about a mission to Mars, which may be 2 years in duration, so that's a long time." As a cardiologist with a long-standing interest in the effects of gravity on circulation, Dr. Levine said NASA has a good handle on the etiology and mechanisms of most major medical problems caused by spaceflight. While radiation exposure remains what he called "probably the most troublesome and problematic" of factors, the impact of spaceflight on vision, as a some- what newly discovered problem, has seen a lot resources devoted to its research in recent years. "The last thing you want to do is send someone to Mars and have them not be able to see," he said, referencing NASA's goal to send humans to Mars in the 2030s. Research published in 2011 de- scribed the "ophthalmic anomalies" of seven astronauts who experienced long-duration space flight, as well as data from a questionnaire of 300 astronauts. 3 Of the seven astronauts who experienced ophthalmic chang- es after space flight, five were found to have disc edema, five had globe flattening, five had choroidal folds, three had cotton wool spots, six had nerve fiber layer thickening, and six experienced decreased near vision. The questionnaires revealed that about 29% on short-duration flight experienced reduced distance and near visual acuity, while 60% on long-duration flight experienced these visual changes. At this time, Mader et al. 3 hypothesized that optic nerve and ocular changes might Prolonged space travel is recently known to result in visual impairment, and a new study could indicate why I n 2005, John Phillips, PhD, embarked on his second of three NASA space-flight mis- sions. From April to October that year, Dr. Phillips served on the International Space Station (ISS) as NASA's science officer and flight engineer. For 6 months—179 days and 23 minutes—to be precise, Dr. Phillips was in space, according to his NASA profile. At the beginning of this mission, his vision was 20/20, but after returning, it had dropped to 20/100, according to a Washington Post article. 1 In the last decade, there has been a slew of research by the space agency to determine what was happening to astronauts' eyesight in space and how to prevent negative visual effects that seemed to be asso- ciated with prolonged space flight. Most recently, researchers published a study in The Journal of Physiology describing experiments about the effect of microgravity on Researchers pinpoint what might be causing visual deterioration among astronauts Key findings • Contrary to previously held hy- potheses, this study showed that microgravity situations actually reduce intracranial pressure com- pared to the supine position on Earth. • Daily circadian cycles in intracranial pressure experienced on Earth, as a person goes from a seated to supine position, seem to protect the brain and eye, preventing negative ocular pathology. • These cycles don't occur in space at a zero gravity constant, which thus could result in reduced visual acuity and other ocular issues after prolonged periods. • Researchers are testing a negative pressure device that could simulate intracranial pressure cycles and protect astro- nauts' vision. Justin Lawley, PhD, (left), first author of the study and instructor at UT Southwestern Medical Center, with NASA scientists A patient volunteer is monitored during the study Source (all): David Ham/Courtesy NASA and UT Southwestern

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