Orbit
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The orbit is a feature of the face and contains the globe and it's supporting structures, as well as many nerves and vessels.
Gross anatomy
In the adult, the orbit has a volume of approximately 30 mL, of which the globe occupies 6.5 mL. It has a roof, floor, medial and lateral wall. The orbit is open anteriorly where it is bound by the orbital septum, which forms part of the eyelids. Posteriorly, the orbit angles inward such that their apices communicate with the intracranial compartment via the optic canal and superior orbital fissure.
Contents
- globe
- extraocular muscles
-
cranial nerves
- optic nerve (CN II)
- branches of the oculomotor nerve (CN III)
- superior division
- inferior division
- trochlear nerve (CN IV)
- branches of the ophthalmic division of the trigeminal nerve (CN Va)
- branches of the maxillary division of the trigeminal nerve (CN Vb)
- abducens nerve (CN VI)
- autonomic nerves and ganglia
- ciliary ganglion
- sympathetic root to the ciliary ganglion (parasympathetic root travels in the oculomotor nerve)
- arteries
- ophthalmic artery and its branches (ocular and orbital)
- infra-orbital artery
- veins
- superior ophthalmic vein
- inferior ophthalmic vein
- infra-orbital vein
- fat
- lacrimal gland
- fascia bulbi (Tenon's capsule)
Bony margins
The bony margins of the orbits, known as the bony orbit, are composed of seven bones:
- pars orbitalis of the frontal bone
- lacrimal bone
- lamina papyracea of the ethmoid bone
- orbital process of the zygomatic bone
- orbital surface of the maxillary bone
- orbital process of the palatine bone
- greater and lesser wings of the sphenoid bone
The four bones of the medial wall are remembered with this mnemonic.
Spaces
The orbit is divided by the musculofascial cone into 2 separate compartments:
Communications
The orbit communicates posteriorly with the intracranial cavity via the optic canal, through which the optic nerve and ophthalmic artery is transmitted. Immediately inferolateral to the optic canal is the superior orbital fissure, through which most neurovascular structures pass. The infratemporal fossa is accessed via the inferior orbital fissure, which is in direct continuation with the infraorbital foramen, through which the infraorbital nerve exits to supply the skin below the eye (and where it is often damaged by a blow-out fracture).
Medially, small communications with the paranasal sinuses are via the anterior ethmoidal foramen and posterior ethmoidal foramen.
Anteriorly, the supraorbital notch is closed inferiorly by the orbital septum forming a fibrous supraorbital foramen. The nasolacrimal duct drains the nasolacrimal sac via the nasolacrimal foramen.
Nerves of the orbit
There are many nerves within the orbit: see orbital nerve supply.
See also
-<li>greater and lesser wings of the <a href="/articles/sphenoid-bone">sphenoid bone</a>- +<li>
- +<a title="Greater wing" href="/articles/greater-wing-of-sphenoid">greater</a> and <a title="lesser wing of sphenoid" href="/articles/lesser-wing-of-sphenoid">lesser wings</a> of the <a href="/articles/sphenoid-bone">sphenoid bone</a>
-</ul><p>The four bones of the medial wall are remembered with this <a href="/articles/medial-wall-of-the-orbit-mnemonic">mnemonic</a>.</p><h5>Spaces</h5><p>The orbit is divided by the <a title="musculofascial cone" href="/articles/musculofascial-cone">musculofascial cone</a> into 2 separate compartments:</p><ul>- +</ul><p>The four bones of the medial wall are remembered with this <a href="/articles/medial-wall-of-the-orbit-mnemonic">mnemonic</a>.</p><h5>Spaces</h5><p>The orbit is divided by the <a href="/articles/musculofascial-cone">musculofascial cone</a> into 2 separate compartments:</p><ul>
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