Background/aim: Vascularisation of the distal, namely intracranial and intracanalicular parts of the optic nerve have not been explained in conventional textbooks of anatomy, while there have been explanations of proximal, that is intraorbital segment. The aim of this research was to study the pattern of arterial supply of the intracranial and intracanalicular part (the distal part) of human optic nerve.
Methods: The optic nerve and the ophthalmic artery (OA), predominately in their intracranial and intracanalicular parts, were investigated in 25 human specimens by three different methods: macroscopic, stereomicroscopic, and histological observations. Mixture with 10% of India ink and gelatin was injected through the intracranial part of the internal carotid artery, and the most proximal part of the OA. Each optic canal specimen was fixed in formaldehyde and finally paraffin embedded, sectioned, and stained with Masson trichrome, Azan, Toluidin blue, and Van Gieson methods.
Results: OA passed through the optic canal within the dural sheath of the optic nerve. In 44% of our specimens the OA was on the inferomedial side of the optic nerve at the entrance point to the optic canal. OA left the optic canal at its lateral border in the apex of the orbit in 72% of our specimens. The intracanalicular portion of the optic nerve receives arterial blood principally from the intracanalicular part of OA. OA gives one (72% of the specimens) to two branches that supply the intracanalicular part of the optic nerve. Each branch pierces the dura mater from below and then supplies the nerve through the pia mater. These arteries then terminate in a pial vascular network of continuous transverse centripetal arterioles and capillaries that surround each optic nerve. The rich anastomoses with branches of superior hypophyseal artery, from the cranial cavity, which take part in the optic nerve vascularization in its hole length, was observed. There were no intraaxial vessels in the intracranial and intracanalicular parts of the nerve in our specimens.
Conclusion: These anatomical data offer important informations for understanding the variety of the pathology in the region of optic canal and orbito-cranial junction, and is also useful for designing operative strategies. This report indicates the delicacy and vulnerability of the intracranial and intracanalicular capillary network to traumatic disruption.