Mechanism of Optic Nerve Sheath Fenestration-Reply

Abstract

In Reply. —We appreciate the comments by Bazarian and Burde regarding our article. We certainly acknowledge that this model is simplistic, but it describes a mechanism of action that, for the first time, explains the many, and often paradoxical, findings we see clinically after optic nerve sheath fenestration. The application of Bernoulli's equation to this model illustrates how a filtration mechanism can locally reduce the CSF pressure seen by the optic nerves, while the intracranial pressure remains elevated. In fact, we believe an open fenestration site and elevated intracranial pressure are necessary to maintain filtration. We have observed flattening of chronic total retinal detachments and visual improvement in two cases of morning glory disc syndrome after large window optic nerve sheath fenestrations. In this syndrome, CSF is presumed to reach the subretinal space via the subarachnoid space of the optic nerve. 1 Fenestration of the nerve sheath allows escape of