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Hanspeter Killer, margaritta montali, Achmed Pircher, Jatta Berberat, Luca Remonda; The optic canal: a bottle neck for cerebrospinal fluid dynamics in normal tension glaucoma?. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2549. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The optic canal is the most narrow and least expandable portion of the subarachnoid space of the optic nerve. The size of its cross section area (OCA) may become a crucial bottel neck for the exchange of cerebrospinal fluid from intracranially to the orbital SAS of the optic nerve. This study on the (OCA) in Caucasian patients with normal-tension glaucoma (NTG) compares the OCA with Caucasian control subjects without known optic nerve (ON) diseases.
Retrospective analysis of computed tomographic (CT) images of the cranium and orbits in 56 NTG patients (21 females and 17 males; 99 of 112 eyes; mean age 67.7±11.1 years). 56 age- and gender matched subjects (mean age: 68.0±11.2 years) without known ON diseases served as controls. The cross sectional area of the orbital opening of the optic canal (OC) was measured in mm2 by using the tool “freehand”. Statistical analysis was performed by using the independent two-tailed t-test.
The mean orbital opening OCA in NTGs measured 14.5±3.5 mm2, (right OCA: 14.4±3.6 mm2, left OCA: 14.5±3.4 mm2) and in controls 18.4±2.6 mm2 (right OCA: 18.4±2.0 mm2, left OCA: 18.1±2.5 mm2). The difference between NTG and controls was statistically significant (p<0.000 for the right OCA, p<0.000 for the left OCA).
Patients with NTG showed a significantly smaller OCA compared to the control group of normals. It has been shown in the literature that in patients with papilloedema the oedama was less pronounced at the side of the smaller OCA. A smaller OCA therefore seems to be protective against a pressure induced optic nerve damage. A smaller OCA however will also influence the CSF dynamics and its transport function as well and might result in a chronic optic nerve damage in NTG patients via a reduced support of nutrition to axons and a lack of CSF clearance.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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