Visual impairment due to intracranial pressure information
STS-41 crewmembers conduct Detailed Supplementary Objective (DSO) 472, Intraocular Pressure on the middeck of Discovery, Orbiter Vehicle (OV) 103. Mission Specialist (MS) William M. Shepherd rests his head on the stowed treadmill while Pilot Robert D. Cabana, holding Shepherd's eye open, prepares to measure Shepherd's intraocular pressure using a tonometer (in his right hand).
Spaceflight-associated neuro-ocular syndrome (SANS),[1] previously called spaceflight-induced visual impairment,[2] is hypothesized to be a result of increased intracranial pressure (ICP), although, experiments directly measuring ICP in parabolic flight have shown ICP to be in normal physiological ranges during acute weightless exposure.[3] The study of visual changes and ICP in astronauts on long-duration flights is a relatively recent topic of interest to space medicine professionals. Although reported signs and symptoms have not appeared to be severe enough to cause blindness in the near term, long term consequences of chronically elevated intracranial pressure are unknown.[4]
NASA has reported that fifteen long-duration male astronauts (45–55 years of age) have experienced confirmed visual and anatomical changes during or after long-duration flights.[5] Optic disc edema, globe flattening, choroidal folds, hyperopic shifts and an increased intracranial pressure have been documented in these astronauts. Some individuals experienced transient changes post-flight while others have reported persistent changes with varying degrees of severity.[6]
Although the exact cause is not known, it is suspected that microgravity-induced fluid shift towards the head and comparable physiological changes play a significant role in these changes.[6] Other contributing factors may include pockets of increased carbon dioxide (CO2) and an increase in sodium intake. It seems unlikely that resistive or aerobic exercise are contributing factors, but they may be potential countermeasures to reduce intraocular pressure (IOP) or ICP in-flight.[5]
^Martin Paez, Yosbelkys; Mudie, L. I.; Subramanian, P. S. (2020). "Spaceflight Associated Neuro-Ocular Syndrome (SANS): A Systematic Review and Future Directions". Eye and Brain. 12: 105–117. doi:10.2147/EB.S234076. PMC 7585261. PMID 33117025.
^Chang, Kenneth (27 January 2014). "Beings Not Made for Space". The New York Times. Retrieved 2014-01-27.
^Lawley, Justin S.; Petersen, Lonnie G.; Howden, Erin J.; Sarma, Satyam; Cornwell, William K.; Zhang, Rong; Whitworth, Louis A.; Williams, Michael A.; Levine, Benjamin D. (2017-03-15). "Effect of gravity and microgravity on intracranial pressure: Gravity on intracranial pressure". The Journal of Physiology. 595 (6): 2115–2127. doi:10.1113/JP273557. PMC 5350445. PMID 28092926.
^Cite error: The named reference 5-5 was invoked but never defined (see the help page).
^ abOtto, C.; Alexander, DJ; Gibson, CR; Hamilton, DR; Lee, SMC; Mader, TH; Oubre, CM; Pass, AF; Platts, SH; Scott, JM; Smith, SM; Stenger, MB; Westby, CM; Zanello, SB (12 July 2012). "Evidence Report: Risk of spaceflight-induced intracranial hypertension and vision alterations" (PDF). Human Research Program: Human Health Countermeasures Element.
^ ab"The Visual Impairment Intracranial Pressure Summit Report" (PDF). NASA. p. 17. Archived from the original (PDF) on 11 February 2015. Retrieved 13 June 2012.
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