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Heather Moss, Jafar Arash Mehr, Hamed Hatami-Marbini; Effect of posterior optic nerve and sheath boundary conditions on globe deformation in high intracranial pressure (ICP) states. Invest. Ophthalmol. Vis. Sci. 2019;60(9):5228. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
High ICP is a consequence of neurological and neurosurgical diseases such as idiopathic intracranial hypertension and brain tumors. Ophthalmic changes associated with high ICP, including mechanical effects of broad flattening of the posterior globe (GF) and local peripapillary deformation (PD), may have application towards diagnosis and monitoring of these diseases. Recent numerical analysis suggests that posterior optic nerve boundary conditions may be relevant in clinical observations of ocular deformations in space associated neuro-ocular syndrome, which shares some features with terrestrial high ICP states. Therefore, we sought to study the mechanical effects of posterior optic nerve and sheath boundary condition on the relationships between ICP, GF & PD using numerical models.
A numerical mechanical model of the posterior globe, optic nerve and optic nerve sheath with loads of intraocular pressure and ICP was created and solved using finite element analysis (ANSYS, Ansys Inc.). The parameters of the model were tuned so that model predictions of GF and PD with a load of high ICP matched a magnetic resonance image of an eye of a human with high ICP. The posterior constraints on the optic nerve (ON) and sheath (S) were modeled using spring constants (KON, KS). These were manipulated to represent combinations of slack posterior fixations (K=low) and stiff posterior fixations (K=high). Model predications of GF and PD for different posterior fixation conditions were compared.
The FEA model with a load of high ICP was successfully tuned so that outcome matched a globe in a high ICP state as characterized using MRI. Globe flattening was most influenced by KS and was most pronounced when KS was high (i.e. stiff). Peripapillary deformation was most influenced by KON, and was most pronounced when this was high (i.e. stiff) regardless of KS.
Based on our numerical models of posterior globe, optic nerve and optic nerve sheath biomechanics in high ICP states, we hypothesize that posterior optic nerve and sheath fixation in the orbit impact degree of flattening of the globe and peripapillary deformation resulting from high ICP. The nature of posterior optic nerve and sheath fixation may need to be accounted for when developing globe shape measurements as markers for ICP.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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