title: Finite Element Modeling of Factors Influencing Optic Nerve Head Deformation Due to Intracranial Pressure.
abstract: OBJECTIVE
  Visual impairment and intracranial pressure (VIIP) syndrome is a health concern for long-duration spaceflight, and a proposed risk factor is elevation of intracranial pressure (ICP). Our goal was to use finite element modeling to simulate how elevated ICP and interindividual differences affect tissue deformation within the optic nerve head (ONH).
  
  
  METHODS
  We considered three ICP conditions: the upright and supine position on earth and an elevated ICP assumed to occur in chronic microgravity. Within each condition we used Latin hypercube sampling to consider a range of pressures and ONH tissue mechanical properties, determining the influence of each input on the following outcome measures: peak strains in the prelaminar tissue, lamina cribrosa, and retrolaminar optic nerve. Elevated strains can alter cell phenotype and induce tissue remodeling.
  
  
  RESULTS
  Elevating ICP increased the strains in the retrolaminar optic nerve. Variations in IOP, ICP, and in optic nerve and lamina cribrosa stiffness had the strongest influence on strains within the ONH. We predicted that 5% to 47% of individuals in microgravity would experience peak strains in the retrolaminar optic nerve larger than expected on earth. Having a soft optic nerve or pia mater and elevated ICP were identified as risk factors for these "extreme" strains.
  
  
  CONCLUSIONS
  Intracranial pressure and mechanical properties of the ONH influence the risk for experiencing extreme strains in the retrolaminar optic nerve. These extreme strains may activate mechanosensitive cells that induce tissue remodeling and are a risk factor for the development of VIIP. Future studies must also consider variations in ONH anatomy.
authors.affiliation: Department of Biomedical Engineering Georgia Institute of Technology/Emory University, Atlanta, Georgia, United States.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Feola
authors.affiliation: NASA Glenn Research Center, Cleveland, Ohio, United States.
authors.forename: Jerry G
authors.initials: JG
authors.lastname: Myers
authors.affiliation: Department of Biomedical Engineering Georgia Institute of Technology/Emory University, Atlanta, Georgia, United States.
authors.forename: Julia
authors.initials: J
authors.lastname: Raykin
authors.affiliation: Universities Space Research Association, Houston, Texas, United States.
authors.forename: Lealem
authors.initials: L
authors.lastname: Mulugeta
authors.affiliation: NASA Glenn Research Center, Cleveland, Ohio, United States.
authors.forename: Emily S
authors.initials: ES
authors.lastname: Nelson
authors.affiliation: Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama, United States.
authors.forename: Brian C
authors.initials: BC
authors.lastname: Samuels
authors.affiliation: Department of Biomedical Engineering Georgia Institute of Technology/Emory University, Atlanta, Georgia, United States.
authors.forename: C Ross
authors.initials: CR
authors.lastname: Ethier
mesh_terms: D018450:Disease Progression; D020342:Finite Element Analysis; D005901:Glaucoma / Q000150:complications / Q000473:pathology* / Q000503:physiopathology; D006801:Humans; D019586:Intracranial Hypertension / Q000150:complications / Q000473:pathology* / Q000503:physiopathology; D007427:Intracranial Pressure / Q000502:physiology*; D007429:Intraocular Pressure / Q000502:physiology; D009898:Optic Disk / Q000473:pathology*; D009901:Optic Nerve Diseases / Q000209:etiology / Q000473:pathology* / Q000503:physiopathology; D015203:Reproducibility of Results; D013577:Syndrome