June 2015
Volume 56, Issue 7
Free
ARVO Annual Meeting Abstract  |   June 2015
Modeling the Effects of Spaceflight on the Posterior Eye in VIIP
Author Affiliations & Notes
  • C Ross Ethier
    Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA
  • Andrew Feola
    Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA
  • Julia Raykin
    Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA
  • Lealem Mulugeta
    Division of Space Life Sciences, Universities Space Research Association, Houston, TX
  • Rudy Gleason
    Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA
  • Jerry G. Myers
    NASA Glenn Research Center, Cleveland, OH
  • Emily S. Nelson
    NASA Glenn Research Center, Cleveland, OH
  • Brian Samuels
    Ophthalmology, University of Alabama Birmingham, Birmingham, AL
  • Footnotes
    Commercial Relationships C Ethier, None; Andrew Feola, None; Julia Raykin, None; Lealem Mulugeta, None; Rudy Gleason, None; Jerry Myers, None; Emily Nelson, None; Brian Samuels, None
  • Footnotes
    Support None
Investigative Ophthalmology & Visual Science June 2015, Vol.56, 4825. doi:
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      C Ross Ethier, Andrew Feola, Julia Raykin, Lealem Mulugeta, Rudy Gleason, Jerry G. Myers, Emily S. Nelson, Brian Samuels; Modeling the Effects of Spaceflight on the Posterior Eye in VIIP. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4825.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract
 
Purpose
 

Visual Impairment and Intracranial Pressure (VIIP) syndrome is a new and significant health concern for long-duration space missions. Its etiology is unknown, but is thought to involve elevated intracranial pressure (ICP) that induces connective tissue changes and remodeling in the posterior eye (Alexander et al. 2012). Here we study the acute biomechanical response of the lamina cribrosa (LC) and optic nerve to elevations in ICP utilizing finite element (FE) modeling.

 
Methods
 

Using the geometry of the posterior eye from previous axisymmetric FE models (Sigal et al. 2004), we added an elongated optic nerve and optic nerve sheath, including the pia and dura. Tissues were modeled as linear-elastic solids. Intraocular pressure and central retinal vessel pressures were set at 15 mmHg and 55 mmHg, respectively. ICP varied from 0 mmHg (suitable for standing on earth) to 30 mmHg (representing severe intracranial hypertension, thought to occur in space flight). We focused on strains and deformations in the LC and optic nerve (within 1 mm of the LC) since we hypothesize that they may contribute to vision loss in VIIP.

 
Results
 

Elevating ICP from 0 to 30 mmHg significantly altered the strain distributions in both the LC and optic nerve (Figure), notably leading to more extreme strain values in both tension and compression. Specifically, the extreme (95th percentile) tensile strains in the LC and optic nerve increased by 2.7- and 3.8-fold, respectively. Similarly, elevation of ICP led to a 2.5- and 3.3-fold increase in extreme (5th percentile) compressive strains in the LC and optic nerve, respectively.

 
Conclusions
 

The elevated ICP thought to occur during spaceflight leads to large acute changes in the biomechanical environment of the LC and optic nerve, and we hypothesize that such changes can activate mechanosensitive cells and invoke tissue remodeling. These simulations provide a foundation for more comprehensive studies of microgravity effects on human vision, e.g. to guide biological studies in which cells and tissues are mechanically loaded in a range relevant for microgravity conditions.  

 
Computed tensile (red) and compressive (blue) strain distributions in the posterior human eye. The upper/lower panels show simulations with ICP=0 mmHg and 30 mmHg, respectively, with the latter assumed to be representative of microgravity conditions. Note that this image focuses on the optic nerve head and that the entire model is not shown.
 
Computed tensile (red) and compressive (blue) strain distributions in the posterior human eye. The upper/lower panels show simulations with ICP=0 mmHg and 30 mmHg, respectively, with the latter assumed to be representative of microgravity conditions. Note that this image focuses on the optic nerve head and that the entire model is not shown.

 
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