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Brandon Macias, Siva Balasubramanian, Alex S Huang, John H K Liu, Stuart MC Lee, Steven Laurie, Alan Feiveson, Michael B Stenger; Fluid Shift Induced Alterations of the Optic Nerve Head and Peripapillary Choroid Assessed using Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2017;58(8):1312. doi: https://doi.org/.
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More than 50% of International Space Station astronauts demonstrate visual acuity decrements or ocular structural changes during or after spaceflight. The leading hypothesis explaining spaceflight-induced vision impairment is that a cephalad fluid shift leads to altered tissue volume and pressure relationships in the eye and orbit. We hypothesize that reducing venous outflow from the dependent limbs with a venoconstrictive thigh cuff will temporarily reverse or attenuate ocular and cerebral volume changes observed during 15° head-down tilt (HDT).
Twenty normal subjects (12M, 8F) were studied following a 10 min stabilization period, seated, supine, HDT, and HDT with commercially-available thigh cuffs (CUFF) inflated to 60 mm Hg. We quantified Bruch’s membrane to lamina cribrosa (LC) depth in 13 subjects and peripapillary choroidal thickness (PPC) in 19 subjects from enhanced depth imaging optical coherence tomography images. Average PPC was quantified from 1.5 to 3 mm from the center of the ONH along radial B-scans at clock hours 12, 3, 6, and 9. The optic nerve sheath diameter (ONSD) and internal jugular vein cross-sectional area (IJVA) were measured using ultrasound. Mixed-effects linear regression model with repeated measures was used to test for significant PPC, LC, IJVA, and ONSD changes. All data are presented as mean ± standard error.
Compared to seated (377±28 µm) or with CUFF (363±28 µm), LC depth significantly (P<0.01) increased in the supine (395±28 µm) and HDT (384±28 µm) positions. PPC at clock hour 9 significantly (P<0.01) increased from seated (198±16 µm) to HDT (208±16 µm), however CUFF was not significantly different from HDT. In addition, PPC at clock hours 12 and 6 were significantly different between the seated and HDT conditions. IJVA and ONSD increased from the seated (IJVA: 0.15±0.07 cm2 and ONSD: 0.533±0.012 cm) to HDT (IJVA: 1.03±0.07 cm2 and ONSD: 0.581±0.012 cm) posture (P<0.001) but were not affected by CUFF.
Moving from the seated to HDT posture alters LC depth and PPC. These results suggest that HDT, a microgravity analog results in an acute cephalad fluid shift that significantly alters posterior optic nerve head structure. Application of bilateral thigh cuffs inflated to 60 mm Hg for 10 minutes was not sufficient to reverse all these changes to levels measured during the seated posture.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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