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Editors Selection IGR 13-4
Clinical Forms of Glaucoma: Cerebrospinal fluid space in NTG
Comment by Franz Grehn on:
50611 Orbital Cerebrospinal Fluid Space in Glaucoma: The Beijing iCOP Study, Wang N; Xie X; Yang D et al., Ophthalmology, 2012; 119: 2065-2073.e1
The mechanisms of optic nerve (ON) damage in normal-tension glaucoma (NTG) is still poorly understood. A new hypothesis inves- tigates the pressure gradient between the intraocular compartment (represented by IOP) and the optic nerve tissue pressure, in particular the cerebrospinal fluid (CSF) pressure in the optic nerve subarachnoidal space. Previous studies have found that CSF pressure as measured in the spinal compartment is lower in NTG. The present study by Wang and coworkers used MRI 3 TESLA technology to measure the optic nerve subarachnoidal space width (ONSASW) behind the globe as a surrogate for orbital CSF pressure in NTG patients as compared to POAG patients and normal subjects.
The ONSASW was significantly narrower in the three orbital locations where ON diameter and ONSASW was measured at three, nine, and 15 mm behind the globe. NTG had a 20-30% narrower subarachnoid space of the ON, with a significant (p < 0.05) reduction even when adjusted for glaucoma damage or the reduced thickness of the ON in glaucoma.
Reduced subarachnoidal space in the retrobulbar ON may be a valuable surrogate for estimating the retrobulbar CSF pressure in the optic nerve subarachnoidal space of normal-tension glaucoma patients
Reduced subarachnoidal space in the retrobulbar ON may be a valuable surrogate for estimating the retrobulbar CSF pressure in the optic nerve subarachnoidal space of normal-tension glaucoma patients. Low CSF pressure may compromise the retrograde axoplasmic flow transporting survival signals to the ganglion cell bodies over a steep uphill pressure step within the laminar region. With obvious thinning of the lamina cribrosa in advanced glaucomatous cupping not only the pressure difference between the IOP and the retrobulbar ON tissue pressure but also the increased steepness within the compressed laminar transition zone may be a detrimental factor.
In summary, the paper gives valuable data on the new approach to measure the optic nerve thickness and the subarachnoidal space to pick up a possible risk factor for development or progression of normal tension glaucoma.
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