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Biomechanics of the Optic Nerve Sheath in VIIP SyndromeLong-duration space flight carries the risk of developing Visual Impairment and Intracranial Pressure (VIIP) syndrome, a spectrum of ophthalmic changes including posterior globe flattening, choroidal folds, distension of the optic nerve sheath (ONS), optic nerve kinking and potentially permanent degradation of visual function. The slow onset of VIIP, its chronic nature, and certain clinical features strongly suggest that biomechanical factors acting on the ONS play a role in VIIP. Here we measure several relevant ONS properties needed to model VIIP biomechanics. The ONS (meninges) of fresh porcine eyes (n7) was reflected, the nerve proper was truncated near the sclera, and the meninges were repositioned to create a hollow cylinder of meningeal connective tissue attached to the posterior sclera. The distal end was cannulated, sealed, and pressure clamped (mimicking cerebrospinal fluid [CSF] pressure), while the eye was also cannulated for independent control of intraocular pressure (IOP). The meninges were inflated (CSF pressure cycling 7-50 mmHg) while ONS outer diameter was imaged. In another set of experiments (n4), fluid permeation rate across the meninges was recorded by observing the drainage of an elevated fluid reservoir (30 mmHg) connected to the meninges. The ONS showed behavior typical of soft tissues: viscoelasticity, with hysteresis in early preconditioning cycles and repeatable behavior after 4 cycles, and nonlinear stiffening, particularly at CSF pressures 15 mmHg (Figure). Tangent moduli measured from the loading curve were 372 101, 1199 358, and 2050 379 kPa (mean SEM) at CSF pressures of 7, 15 and 30 mmHg, respectively. Flow rate measurements through the intact meninges at 30mmHg gave a permeability of 1.34 0.46 lmincm2mmHg (mean SEM). The ONS is a tough, strain-stiffening connective tissue that is surprisingly permeable. The latter observation suggests that there could be significant CSF drainage through the ONS into the orbit, likely important for CSF transport in the optic nerve. These experimental measurements, extended to human eyes, are informing computational models of the pathophysiology and biomechanics of the ONS in VIIP syndrome.
Document ID
20150000873
Acquisition Source
Glenn Research Center
Document Type
Presentation
Authors
Ethier, C. Ross
(Georgia Inst. of Tech. Atlanta, GA, United States)
Raykin, Julia
(Georgia Inst. of Tech. Atlanta, GA, United States)
Gleason, Rudy
(Georgia Inst. of Tech. Atlanta, GA, United States)
Mulugeta, Lealem
(Universities Space Research Association Houston, TX, United States)
Myers, Jerry
(NASA Glenn Research Center Cleveland, OH, United States)
Nelson, Emily
(NASA Glenn Research Center Cleveland, OH, United States)
Samuels, Brian C.
(Alabama Univ. Birmingham, AL, United States)
Date Acquired
January 30, 2015
Publication Date
June 11, 2014
Subject Category
Aerospace Medicine
Report/Patent Number
GRC-E-DAA-TN15967
Meeting Information
Meeting: World Congress of Biomechanics
Location: Boston, MA
Country: United States
Start Date: July 6, 2014
End Date: July 11, 2014
Sponsors: World Council of Biomechanics
Funding Number(s)
CONTRACT_GRANT: NNJ11HE31A
WBS: WBS 516724.02.02.10
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
fluid shifts
physiological response
gravitational physiology
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