Interdural course of the ophthalmic artery in the optic canal

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In the current neurosurgical and anatomical literature, the intracanalicular segment of the ophthalmic artery (OphA) is usually described to be within the optic nerve dural sheath (ONDS), implying direct contact between the nerve and the artery inside the optic canal. In the present study, the authors sought to clarify the exact relationship between the OphA and ONDS.


Ten cadaveric heads were subjected to endoscopic endonasal and transcranial exposures of the OphA in the optic canal (5 for each approach). The relationship between the OphA and ONDS was assessed. Histological examination of one specimen of the optic nerve and the accompanying OphA was also performed to confirm the relationship with the ONDS.


In all specimens, the OphA coursed between the two layers of the dura (endosteal and meningeal) and was not in direct contact with the optic nerve, except for the first few millimeters of the proximal optic canal before it pierced the ONDS. Upon reaching the orbit, the two layers of the dura separated and allowed the OphA to literally float within the orbital fat. The meningeal dura continued as the ONDS, whereas the endosteal dura became the periorbita.


This study clarifies the interdural course of the OphA within the optic canal. This anatomical nuance has important neurosurgical implications regarding safe exposure and manipulation of the OphA.

ABBREVIATIONS DDR = distal dural ring; DPP = dural piercing point of the OphA; ICA = internal carotid artery; ONDS = optic nerve dural sheath; OphA = ophthalmic artery.

Article Information

Correspondence Mark C. Preul: Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, c/o Neuroscience Publications, Phoenix, AZ.

INCLUDE WHEN CITING Published online January 4, 2019; DOI: 10.3171/2018.6.JNS18856.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.



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    Endoscopic endonasal exposure of the interdural course of the intracanalicular OphA in a cadaveric specimen. A: Exposure of the sella, parasellar ICA, and optic protuberance (prot.) on the right side. Dashed lines demarcate the extents of the bony optic canal corresponding to the medial and lateral vertices of the lateral opticocarotid recess (LOCR). Yellow star marks the region of the medial opticocarotid recess. The location of the DDR is approximated by a white double-headed arrow extended between the medial opticocarotid recess and the medial vertex of the LOCR. B: Dura of the optic nerve (ON) is opened longitudinally (white arrowheads) to expose the origin of the OphA in the subarachnoid space. The OphA pierces the optic nerve dural sheath (ONDS; white arrow) and courses interdurally along the rest of the bony optic canal (dashed double-headed arrow). C: The cut is extended to the orbital apex region and periorbita of the medial orbital wall. Dashed line demarcates the opened annulus of Zinn. Intraorbitally, the OphA is not embedded in dura (black arrow), as the two layers of the dura (endosteal and meningeal) separate. Dashed double-headed arrow indicates the interdural course of the OphA inside the optic canal. Clinoidal segment of the ICA is marked with a white asterisk. D: The intracranial, intracanalicular, and proximal intraorbital course of the OphA is shown. Note the upper (black arrowhead) and lower (white arrowhead) leaflets of the opened ONDS. The interdural segment of the OphA is indicated with a dashed double-headed arrow. E: The meningeal layer of the ONDS is opened to expose the interdural course of the OphA (black arrow). Black and white arrowheads show the leaflets of the opened ONDS. Asterisk designates the proximal intraorbital OphA. All pictures were obtained using a 30° endoscope. PDR = proximal dural ring; rec. = recess; tub. = tubercular. Copyright Barrow Neurological Institute. Published with permission. Figure is available in color online only.

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    Transcranial exposure of the interdural course of the OphA in a cadaveric specimen. A: The ONDS is opened, and the ON is exposed. Note that the fused meningeal and endosteal layers of the dura along the length of the optic canal (solid, bolded double-headed arrows) separate at the point of ON entrance to the orbit. The endosteal layer becomes the periorbita (solid single-headed arrows), whereas the meningeal layer (dashed single-headed arrows) continues as the ONDS. B: The optic nerve is retracted medially to expose the interdural course of the OphA (double-headed arrow). A nerve hook is used to show the free course of the intracranial OphA before it pierces the ONDS. Also note that the OphA pierces the ONDS to freely course in the orbital fat (small black arrow). 1 = meningeal layer; 2 = endosteal layer. C: The interdural course of the OphA is exposed after opening the meningeal layer of the dura. Black arrow shows the intraorbital OphA. D: Following the ONDS (double line) toward the orbit shows that the fused dural layers separate into the periorbita (solid curved arrow) and the true dural sheath of the ON (dashed arrow) in the orbit. Straight black arrow indicates the intraorbital OphA. CN = cranial nerve. Copyright Barrow Neurological Institute. Published with permission. Figure is available in color online only.

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    Cross-sectional photomicrographs of the course of the OphA within the substance of the ONDS. A: Low-magnification photomicrograph showing the ONDS embracing the OphA. B–C: Higher-magnification photomicrographs showing the meningeal layer of the dura (small black arrows) separating the OphA from the ON. H & E. e.d. = endosteal dura; SAS = subarachnoid space. Figure is available in color online only.

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    Snapshots of the original 1887 article by F. Meyer describing (in German) the course of the OphA in the optic canal and its relationship with the ONDS. Upper: Article title page. Lower: Paragraph in which Meyer offers an anatomical description of the OphA course. This text is found in the public domain at Figure is available in color online only.

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    Anteroposterior view (A) of a 3D CT angiogram reconstruction showing an unruptured 8-mm saccular superior hypophyseal artery aneurysm originating from the right side (white arrow) in a 34-year-old woman. Intraoperative view (B) after completed clinoidectomy and unroofing of the optic canal, exposing the DDR (arrow) and the clinoidal segment of the ICA. Gentle depression of the ICA and the optic nerve exposes the origin of the OphA (C, arrowhead). Full exposure of the paraclinoid ICA (D) with clips applied to the aneurysm neck and safe exposure of the OphA. Note the short “tense” intracranial course of the OphA. Postoperative anteroposterior (E) and lateral (F) views of right ICA angiogram. Note the complete exclusion of the aneurysm from the arterial circulation and the preserved OphA (F, arrow). Clin. ICA = clinoidal segment of internal carotid artery. Figure is available in color online only.



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