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May 1991

Mechanism of Optic Nerve Sheath Fenestration

Arch Ophthalmol. 1991;109(5):613. doi:10.1001/archopht.1991.01080050019007

To the Editor.  —We were interested to learn of the model developed by Seiff and Shah1 to explain the mechanism by which fenestration of the optic nerve sheath might relieve papilledema due to raised intracranial pressure. We have been working on various animal models to explain the same process. Seiff and Shah note that increased flow around the optic nerve following sheath fenestration will result in decreased cerebrospinal fluid (CSF) pressure locally, according to Bernoulli's equation. A condition of Bernoulli's equation, however, is that the fluid be in streamline flow. Such a condition does not exist in primates as a consequence of adhesions in the subarachnoid space, especially in the area of the optic canal.2,3 These adhesions make the amount of CSF communication between the intracranial space and the two optic nerves highly variable between species and individuals. Because such adhesions have not been found in subprimates, we

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