Biomaterial Database

A model for the mechanism of optic nerve sheath fenestration. 1990

S R Seiff, and L Shah

Department of Ophthalmology, University of California, San Francisco 94143.

The mechanism by which optic nerve sheath fenestration relieves papilledema associated with increased intracranial pressure has not been clearly defined. A model was constructed to determine if the induction of fluid flow along the nerve sheath and through the fenestration could account for a reduction in pressure around the optic nerve, as might be expected according to Bernoulli's equation of fluid dynamics. The model states that as the velocity of a fluid increases, the pressure it exerts decreases. The model simulated fluid spaces corresponding to the intracranial vault, chiasm, and optic nerves. The unfenestrated model showed direct transmission of elevated intracranial pressure to the nerves, consistent with the production of papilledema. When one nerve was fenestrated, fluid flow along the nerve was initiated and pressure in that nerve sheath dropped substantially. In addition, pressure in the unfenestrated sheath dropped due to fluid communication across the chiasm. These lower intrasheath pressures were consistent with the bilateral resolution of papilledema after unilateral fenestration. The reduced intrasheath pressures persisted even when the intracranial pressure was again elevated to pathologic levels as long as active fluid flow continued along the nerve sheaths. Thus, induction of cerebrospinal fluid flow along the optic nerve sheath by fenestration appears to locally reduce the pressure around the optic nerve, in spite of persistently elevated intracranial pressure. This is in accordance with what would be predicted by Bernoulli's equation.

UI	MeSH Term	Description	Entries
D007427	Intracranial Pressure	Pressure within the cranial cavity. It is influenced by brain mass, the circulatory system, CSF dynamics, and skull rigidity.	Intracerebral Pressure,Subarachnoid Pressure,Intracerebral Pressures,Intracranial Pressures,Pressure, Intracerebral,Pressure, Intracranial,Pressure, Subarachnoid,Pressures, Intracerebral,Pressures, Intracranial,Pressures, Subarachnoid,Subarachnoid Pressures
D008954	Models, Biological	Theoretical representations that simulate the behavior or activity of biological processes or diseases. For disease models in living animals, DISEASE MODELS, ANIMAL is available. Biological models include the use of mathematical equations, computers, and other electronic equipment.	Biological Model,Biological Models,Model, Biological,Models, Biologic,Biologic Model,Biologic Models,Model, Biologic
D009186	Myelin Sheath	The lipid-rich sheath surrounding AXONS in both the CENTRAL NERVOUS SYSTEMS and PERIPHERAL NERVOUS SYSTEM. The myelin sheath is an electrical insulator and allows faster and more energetically efficient conduction of impulses. The sheath is formed by the cell membranes of glial cells (SCHWANN CELLS in the peripheral and OLIGODENDROGLIA in the central nervous system). Deterioration of the sheath in DEMYELINATING DISEASES is a serious clinical problem.	Myelin,Myelin Sheaths,Sheath, Myelin,Sheaths, Myelin
D009900	Optic Nerve	The 2nd cranial nerve which conveys visual information from the RETINA to the brain. The nerve carries the axons of the RETINAL GANGLION CELLS which sort at the OPTIC CHIASM and continue via the OPTIC TRACTS to the brain. The largest projection is to the lateral geniculate nuclei; other targets include the SUPERIOR COLLICULI and the SUPRACHIASMATIC NUCLEI. Though known as the second cranial nerve, it is considered part of the CENTRAL NERVOUS SYSTEM.	Cranial Nerve II,Second Cranial Nerve,Nervus Opticus,Cranial Nerve, Second,Cranial Nerves, Second,Nerve, Optic,Nerve, Second Cranial,Nerves, Optic,Nerves, Second Cranial,Optic Nerves,Second Cranial Nerves
D010211	Papilledema	Swelling of the OPTIC DISK, usually in association with increased intracranial pressure, characterized by hyperemia, blurring of the disk margins, microhemorrhages, blind spot enlargement, and engorgement of retinal veins. Chronic papilledema may cause OPTIC ATROPHY and visual loss. (Miller et al., Clinical Neuro-Ophthalmology, 4th ed, p175)	Choked Disk,Edema of the Optic Disc,Edema of the Optic Disk,Optic Disc Edema,Optic Disk Edema,Optic Papilla Edema,Papillitis, Optic,Decreased Intraocular Pressure-Associated Papilledema,Increased Intracranial Pressure-Associated Papilledema,Optic Nerve Papillitis,Papilledema Associated with Decreased Intraocular Pressure,Papilledema Associated with Increased Intracranial Pressure,Papillitis,Retinal Edema,Choked Disks,Decreased Intraocular Pressure Associated Papilledema,Disk, Choked,Edema, Optic Disc,Edema, Optic Disk,Edema, Optic Papilla,Edema, Retinal,Edemas, Optic Disc,Edemas, Optic Disk,Edemas, Retinal,Increased Intracranial Pressure Associated Papilledema,Optic Papillitis,Papillitis, Optic Nerve,Retinal Edemas
D002555	Cerebrospinal Fluid	A watery fluid that is continuously produced in the CHOROID PLEXUS and circulates around the surface of the BRAIN; SPINAL CORD; and in the CEREBRAL VENTRICLES.	Cerebro Spinal Fluid,Cerebro Spinal Fluids,Cerebrospinal Fluids,Fluid, Cerebro Spinal,Fluid, Cerebrospinal,Fluids, Cerebro Spinal,Fluids, Cerebrospinal,Spinal Fluid, Cerebro,Spinal Fluids, Cerebro