Orbital Foramina, Ducts, Canals, and Fissures
The optic foramen is the entry point to the optic canal, which leads from the middle cranial fossa to the apex of the orbit (see Fig 1-1). The optic canal is directed forward, laterally, and somewhat downward and conducts the optic nerve, the ophthalmic artery, and sympathetic fibers from the carotid plexus. The optic canal passes through the lesser wing of the sphenoid bone.
The supraorbital foramen (which, in some individuals, is a notch instead of a foramen) is located at the medial third of the superior margin of the orbit. It transmits blood vessels and the supraorbital nerve, which is an extension of the frontal nerve, a branch of the ophthalmic division (V1) of cranial nerve V (CN V, the trigeminal nerve). The anterior ethmoidal foramen is located at the frontoethmoidal suture and transmits the anterior ethmoidal vessels and nerve. The posterior ethmoidal foramen lies at the junction of the roof and the medial wall of the orbit and transmits the posterior ethmoidal vessels and nerve through the frontal bone (see Fig 1-3). The zygomaticotemporal and zygomaticofacial foramina lie in the portion of the lateral orbital wall formed by the zygomatic bone and transmit vessels and branches of the zygomatic nerve (see Fig 1-5).
The nasolacrimal duct travels inferiorly from the lacrimal sac fossa into the inferior meatus of the nose (see Figs 1-4, 1-40).
The infraorbital canal continues anteriorly from the infraorbital groove and exits 4 mm below the inferior orbital margin. From there it transmits the infraorbital nerve, a branch of V2 (the maxillary division of CN V) (see Fig 1-1).
The superior orbital fissure (Fig 1-6; see also Fig 1-1) is located between the greater and lesser wings of the sphenoid bone and lies lateral to and partly above and below the optic foramen. It is approximately 22 mm long and is spanned by the tendinous ring formed by the common origin of the rectus muscles (annulus of Zinn). Above the ring, the superior orbital fissure transmits the following structures (Fig 1-7):
lacrimal nerve of CN V1
frontal nerve of CN V1
CN IV (trochlear nerve)
superior ophthalmic vein
Within the ring or between the heads of the rectus muscle are the following (see Fig 1-7):
superior and inferior divisions of CN III (the oculomotor nerve)
nasociliary branch of CN V1, which also carries the postganglionic sympathetic fibers en route to the ciliary ganglion
CN VI (the abducens nerve)
Figure 1-6 Axial computed tomography scan of the orbits. The superior orbital fissure (SOF) passes above and below the plane of the optic canal (OC) and is commonly mistaken for the OC. The OC lies in the same plane as the anterior clinoid processes (AClin) and may be cut obliquely in scans so that the entire canal length does not always appear.
(Courtesy of William R. Katowitz, MD.)
A, Anterior view of the right orbital apex showing the distribution of the nerves as they enter through the superior orbital fissure and optic canal. This view also shows the annulus of Zinn, the fibrous ring formed by the origin of the 4 rectus muscles. B, Top view of the left orbit. AZ, annulus of Zinn; CG, ciliary ganglion; CS, cavernous sinus; ICA, internal carotid artery; IRM, inferior rectus muscle; LA, levator aponeurosis; LG, lacrimal gland; LM, levator muscle; LRM, lateral rectus muscle; Man., mandibular nerve; Max., maxillary nerve; MRM, medial rectus muscle; ON, optic nerve; Oph., ophthalmic nerve; SG, sphenopalatine ganglion; SOM, superior oblique muscle; SOT, superior oblique tendon; SOV, superior ophthalmic vein; SRM, superior rectus muscle; STL, superior transverse ligament; T, trochlea; TG, trigeminal (gasserian) ganglion; VV, vortex veins; 1, infratrochlear nerve; 2, supraorbital nerve and artery; 3, supratrochlear nerve; 4, anterior ethmoid nerve and artery; 5, lacrimal nerve and artery; 6, posterior ethmoid artery; 7, frontal nerve; 8, long ciliary nerves; 9, branch of CN III to medial rectus muscle; 10, nasociliary nerve; 11, CN IV; 12, ophthalmic (orbital) artery; 13, superior ramus of CN III; 14, CN VI; 15, ophthalmic artery, origin; 16, anterior ciliary artery; 17, vidian nerve; 18, inferior ramus of CN III; 19, sensory branches from ciliary ganglion to nasociliary nerve; 20, motor (parasympathetic) nerve to ciliary ganglion from nerve to inferior oblique muscle; 21, branch of CN III to inferior rectus muscle; 22, short ciliary nerves; 23, zygomatic nerve; 24, posterior ciliary arteries; 25, zygomaticofacial nerve; 26, nerve to inferior oblique muscle; 27, zygomaticotemporal nerve; 28, lacrimal secretory nerve; 29, lacrimal artery and nerve terminal branches.
(Part A illustration by Cyndie C.H. Wooley. Part B reproduced from Stewart WB, ed. Ophthalmic Plastic and Reconstructive Surgery. 4th ed. San Francisco: American Academy of Ophthalmology Manuals Program; 1984.)
The course of the inferior ophthalmic vein is variable, and it can travel within or below the ring as it exits the orbit.
The inferior orbital fissure lies just below the superior fissure, between the lateral wall and the floor of the orbit, providing access to the pterygopalatine and inferotemporal fossae (see Fig 1-1). Therefore, it is close to the foramen rotundum and the pterygoid canal. The inferior orbital fissure transmits the infraorbital and zygomatic branches of CN V2, an orbital nerve from the pterygopalatine ganglion, and the inferior ophthalmic vein. The inferior ophthalmic vein connects with the pterygoid plexus before draining into the cavernous sinus.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.