Eyeworld

EW NEWS & OPINION May 2017 17 the back of the eye might be smaller than expected, "over prolonged periods of time may be sufficient to cause optic remodeling"—a.k.a. damage. "Creative strategies," the study authors wrote, should be devised to help astronauts—and patients on long-term bedrest for that mat- ter—maintain circadian cycles or intracranial pressure. Dr. Levine said they've already been testing a vacu- um (or negative pressure) device to see if it's possible to lower intracra- nial pressure by drawing blood away from the head. "That's probably the best strate- gy that's being tested, I believe, our sleeping sack device," Dr. Levine said, noting that there are also drugs— such as acetazolamide—that can lower cerebrospinal fluid as well, but it's unknown if those will work in this case. "We don't know whether ours will work either, but if what happens in space is a removal of the gravitational gradient and the normal circadian variability of intra- cranial pressure, then reestablishing that should make the problem go away." In addition to astronauts or patients on prolonged bedrest, Dr. Levine said these findings could help patients with traumatic brain injuries as well. "One of the big problems with people who come in with traumatic brain injury is their pressure goes up. We're going to try some very early pilot studies to see if we can use the same kind of device we're developing for the astronauts to lower the intracranial pressure in the hospital," he said. EW References 1. Love S. The mysterious syndrome impairing astronauts' sight. Washington Post. July 9, 2016. Accessed March 8, 2017. 2. Lawley JS, et al. Effect of gravity and micro- gravity on intracranial pressure. J Physiol. 2017. 595:2115–27. 3. Mader TH, et al. Optic disc edema, globe flattening, choroidal folds, and hyperopic shifts observed in astronauts after long-duration space flight. Ophthalmology. 2011;118:2058– 69. Editors' note: Dr. Levine has no finan- cial interests related to his comments. Contact information Levine: Cathy.Frisinger@UTSouthwestern.edu their expired carbon dioxide levels and have them do exercise and CO 2 breathing—people rarely do these kinds of invasive measurements in any space flight experiment, let alone parabolic flight." The researchers conducted several studies to assess changes in intracranial pressure between sitting and lying down, in short-term microgravity situations (about 20 seconds) during parabolic flight, and at a –6-degree head down tilt for 24 hours, a "widely used Earth-based model of prolonged microgravity, the study authors wrote. Participants were also exposed to increased am- bient CO 2 , to simulate that on the ISS, along with a leg press exercise to simulate that which astronauts on the ISS do to prevent muscular atrophy. In contrast to previous hypoth- eses, the researchers found that intracranial pressure is not elevated in zero gravity. "In fact, removing gravity reduced the [intracranial pressure (ICP)] compared to the supine posture," Lawley et al. wrote. The study authors described intra- cranial pressure in zero gravity as at an "equilibrium point between the upright and supine postures" like that on Earth. "Complete removal of gravi- tational gradients (zero gravity of space) does not pathologically ele- vate [intracranial pressure] but does prevent the normal lowering of ICP when standing. Importantly, despite the acute short duration of zero gravity during parabolic flight, we saw no evidence of a progressive rise in ICP due to cephalad fluid shifts with prolonged simulated micro- gravity in HDT portion," according Lawley et al. "Thus, at present, we have no physiological data to sup- port the hypothesis that ICP should be greater than that observed in zero gravity during parabolic flight. The clinical implication of these findings is that the human brain and eye are protected by the daily circadian cy- cles in regional ICPs, without which pathology occurs." Based on the data, higher CO 2 and exercise conditions did not likely contribute to an intracrani- al pressure rise, Lawley et al. also concluded. The study authors said that while the effect of microgravity on the IOP–ICP pressure gradient on 3360 Scherer Drive, Suite B, St. Petersburg, FL 33716 800-637-4346 • Tel: 727-209-2244 • Fax: 727-341-8123 Email: Info@RheinMedical.com • Website: www.RheinMedical.com *Developed In Coordination With Barry S. Seibel, M.D. Botticelli, Madonna of Pomegranate Seibel* Capsulorrhexis Cystotome Forceps ABBH 1377 Rev.A 05-2363 Call 727-209-2244 For More Information. S i d e C lo s ed V i e w T o p D o w n C l o s e d V i e w T o p D ow n Op e n V i e w S i de O p e n V i e w • Unique Viewport Allows Anterior View Through The Tips To See Exactly Where The Jaws Are Grasping. 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