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Editors Selection IGR 8-3

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Comment by Jonathan Crowston on:

20979 Cerebrospinal fluid pressure is decreased in primary open-angle glaucoma, Berdahl JP; Allingham RR; Johnson DH, Ophthalmology, 2008; 115: 763-768

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In current clinical practice, we routinely measure the transcorneal pressure difference and assume that this is an adequate measure of the pressure to which the optic nerve head is exposed. Yet the optic nerve head at the level of the lamina cribrosa is exposed to a pressure gradient that is the difference between intraocular pressure and CSF pressure. Thus, it makes sense that the magnitude of the pressure gradient across the optic nerve head could be increased at lower CSF pressure as well as higher IOP. But is lower CSF pressure a significant risk for glaucoma?

Working within the necessary, but restrictive confines of a retrospective case-control study, Berdahl and co-workers suggest that lower CSF pressure may indeed be a risk factor for glaucoma. Although the authors freely admit the limitations of their study design, it is clear that a prospective study to measure CSF pressure in glaucoma and control patients would be ethically difficult unless a less invasive method than lumbar puncture is developed in the future. Although their data are extremely interesting and suggestive that low CSF pressure is a risk for glaucoma, the results should be interpreted with some caution. In particular the rates of exclusion from the study were extremely high (507/556 potential controls and 88/116 potential POAG were excluded, admittedly with good reason). There were also some differences between the groups with a higher rate of headache in the control group and radiculopathy in the POAG group. Could the apparently lower CSF pressure in POAG be explained by patients with headaches, by chance over-represented in the control group, being more likely to have higher CSF pressure? It seems conceivable that patients with higher CSF pressure could be more prone to headaches severe enough to warrant a lumbar puncture, even without more overt signs of intracranial hypertension that would have led to their exclusion from the study.

Nevertheless, this is very interesting work. Perhaps animal experiments where high IOP is maintained on a background of varied CSF pressure (eg by drugs or a CSF shunt) would aid further in elucidating the important issue raised.

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