Glaucoma and Cerebrospinal Fluid Pressure

Abstract

We read with great interest the report by Berdahl et al1Berdahl J.P. Allingham R.R. Johnson D.H. Cerebrospinal fluid pressure is decreased in primary open-angle glaucoma.Ophthalmology. 2008; 115: 763-768Abstract Full Text Full Text PDF PubMed Scopus (312) Google Scholar on cerebrospinal fluid (CSF) pressure in patients with primary open-angle glaucoma (POAG). The authors rightly state that the precise mechanism causing optic nerve damage in POAG remains unknown. In their study, they found that the intracranial pressure (ICP) in patients with POAG was 33% lower than in the control group without POAG and concluded that their findings support the concept that a translaminar pressure difference may result not only from a high intraocular pressure (IOP) but also from reduced ICP, and that the level of ICP may play an important role in the development of glaucomatous optic neuropathy. Lumbar puncture is used routinely to determine the pressure in the subarachnoid space (SAS) surrounding the optic nerve and is based on the assumption that the CSF pressure is the same in all CSF spaces, that is, the ventricles, basal cisterns, spinal cisterns, and SAS. In fact, this assumption is not based on actual measurements in the SAS of the optic nerve, but is merely based on the belief that lumbar pressure and pressure in the SAS of the optic nerve are the same. Because of the complex anatomy of the CSF spaces and the lack of data for the velocity of CSF flow, it is not possible to apply a proper physical formula such as the Navier–Stokes equation to calculate the pressure in a mathematical model. We recently assesed both the dynamics and composition of the CSF in the intracranial CSF spaces and compared these parameters with those in the SAS surrounding the optic nerve in patients with papilledema and in patients with normal-tension glaucoma.2Killer H.E. Jaggi G.P. Flammer J. et al.Cerebrospinal fluid dynamics between the intracranial and the subarachnoid space of the optic nerve Is it always bidirectional?.Brain. 2007; 130: 514-520Crossref PubMed Scopus (183) Google Scholar We demonstrated that the exchange of CSF between the chiasmal cisterns and the SAS around the optic nerve can become severely impaired, leading to optic nerve compartmentation. In addition, we measured the concentration of L-PGDS (β-trace protein) in different CSF spaces and showed that the concentration of this mainly brain-derived protein differs markedly between the spinal CSF and the CSF in the SAS surrounding the optic nerve.3Killer H.E. Jaggi G.P. Flammer J. et al.The optic nerve: a new window into cerebrospinal fluid composition?.Brain. 2006; 129: 1027-1030Crossref PubMed Scopus (116) Google Scholar Thus, the composition of CSF is not homogeneous throughout the central nervous system, and neither is the ICP. We agree that the results published by Berdahl et al1Berdahl J.P. Allingham R.R. Johnson D.H. Cerebrospinal fluid pressure is decreased in primary open-angle glaucoma.Ophthalmology. 2008; 115: 763-768Abstract Full Text Full Text PDF PubMed Scopus (312) Google Scholar are of great interest for the understanding of the biophysical forces at work at the level of the lamina cribrosa. However, we also must keep in mind that a reduced ICP may relate to a difference in both CSF dynamics and CSF composition between the SAS surrounding the optic nerve and the intracranial SAS. We believe that further studies should be performed focusing not only on the ICP with its mechanical forces in patients with glaucoma, but also on the CSF composition in the various CSF spaces in these patients and the possible biochemical effects of differences in composition and dynamics on optic nerve function. Author replyOphthalmologyVol. 115Issue 12PreviewWe appreciate the clear and thoughtful comments presented by Killer et al.1 Although intracranial pressure (ICP) measured by lumbar puncture in the lateral decubitus position may not represent the exact pressure in the retrolaminar subarachnoid space (SAS), it is the best surrogate currently available. Killer et al rightly point out that the anatomy of the SAS is complex and the cerebrospinal fluid (CSF) dynamics are not well understood. To complicate matters further, humans spend considerable time in both vertical and horizontal positions. Full-Text PDF