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Editorial Glaucoma The Eye in Space John Berdahl Vance Thompson Vision, Sioux Falls, South Dakota, US L ong-term space travel is one of the most physically taxing experience for the human body. In particular, the rigors of micro gravity can cause decreased vision which is critical for daily activities in space. Current research indicates that an imbalance in between intraocular and intracranial pressure may play an important role. Keywords Glaucoma, IOP, ICP, CSF pressure, Translaminar, Lamina Cribrosa, VIIP Disclosure: John Berdahl has has been a consultant, advisory board member or received research funding from Equinox. This article is a short opinion piece and has not been submitted to external peer reviewers. Open Access: This article is published under the Creative Commons Attribution Noncommercial License, which permits any noncommercial use, distribution, adaptation, and reproduction provided the original author(s) and source are given appropriate credit. Received: June 15, 2016 Published Online: September 26, 2016 Citation: US Ophthalmic Review, 2016;9(2):76–7 Corresponding Author: John Berdahl, Vance Thompson Vision, 1310 W 22nd Street, Sioux Falls, South Dakota, US. E: johnberdahl@gmail.com Support: This work supported by the National Space Biomedical Research Institute through NASA NCC 9-58. The moment the first person steps on Mars will be one of the most unifying and defining moments in human history. Mars is the closest planet to Earth and is 35 million miles away at its closest point and 250 million miles away at its furthest point. A one-way trip to Mars would take 7 months and expose astronauts to incredible stresses on the body. As we all know, the effects of ionizing radiation, bone demineralization, muscle loss, and the psychological impacts of long-term space flight are hard to overstate. Numerous counter measures have been developed so that humans can survive the harshest environment imaginable in an entirely manmade confinement system. A recently described condition, known as VIIP (visual impairment and intracranial pressure [ICP]) poses an immediate risk to astronauts’ vision during long term space flight. As ophthalmologists, we often think of the eye in isolation. We perform cataract surgery, or glaucoma surgery, or retinal surgery and are sub-specialized to millimeters of the body and sometimes sub- specialized to microns. Often times we can lose perspective that the eye is an extension of the body and rarely do we think past 30 mm and how the eye interacts with the brain and the body as a whole. Because we are so focused, we have become tremendous at what we do. Surgeons can do cataract surgeries, and cornea transplants, and orbital surgeries, and retinal surgeries with incredible efficiency, safety, precision, and tremendous outcomes, but through our sub-specialization, we have forgotten many of the things that we were taught in medical school and early anatomy classes. In fact, many ophthalmologists, if asked, would not know that the cerebral spinal fluid bathes the optic nerve all the way to its insertion into the posterior globe. We often think of only the visible portion of the optic nerve, but of course it is actually long connection between the eye and the brain. Perhaps our neuro-ophthalmology colleagues think of the retrolaminar optic nerve frequently, but a glaucoma specialist rarely does, even though their existence is dedicated to the optic nerve. Because of we have focused on the visible and readily studiable portion of the optic nerve, we have not spent adequate resources understanding the interaction between intraocular pressure (IOP) and ICP. Recent studies have shown that the relationship between IOP and ICP may be fundamental in the pathogenesis of glaucoma, and caused by either a high IOP or low ICP. 1,2 For example, if the IOP is normal, but the ICP is low, a pressure differential across the optic nerve head exists and normal tension glaucoma can ensue. Conversely, in ocular hypertension, a patient may have a high IOP, but also a high ICP, and be protected from developing glaucoma despite having high IOP. In idiopathic intracranial hypertension, the ICP becomes higher than the IOP and the optic nerve bows forward and there is axonal transport that is slowed at the level of the lamina cribrosa and you see swelling of the optic nerve head anteriorly. As we understand more about the role that pressure balances play across the optic nerve, new insights into the basic pathophysiology, in addition to new therapeutic targets emerge. This has significant implications for VIIP. VIIP is a syndrome that consists of posterior globe flattening, a hyperopic shift, papilledema, and choroidal folds. This syndrome was not identified until astronauts spent extended periods on the International Space Station. The physiology behind VIIP is likely multifactorial because of the significant fluid shifts and cardiovascular changes in the body during long-term space flight, but it 76 TOUCH ME D ICA L ME D IA