The Orbit

Situation of the orbit in the skull

Below the anterior cranial fossa, anterior to the middle cranial fossa

Bones contributing to the bony framework of the orbit

Maxilla, zygomatic, frontal, sphenoid, ethmoid, lacrimal, palatine

Bony framework of the orbital rim (base of the orbit)

• Superiorly by the frontal bone

• Medially by the frontal process of the maxilla

• Inferiorly by the zygomatic process of the maxilla, the zygomatic bone

• Laterally by the zygomatic bone, the frontal process of the zygomatic bone and the zygomatic process of the frontal bone

Bony framework of the roof of the orbit

Orbital part of the frontal bone, small contribution of the lesser wing of the sphenoid

Unique features of the roof of the orbit

• Anteromedially: trochlear fovea for the attachment of a pulley for the superior oblique muscle

• Anterolaterally: lacrimal fossa for the orbital part of the lacrimal gland

Bony framework of the medial wall of the orbit

Sphenoid body, orbital plate of ethmoid bone (biggest contributor), frontal process of maxilla, lacrimal bone,

Unique features of the medial wall of the orbit

Anterior and posterior ethmoidal foramina at the junction of the medial and superior wall of the orbit

Lacrimal groove (formed by the lacrimal bone and the frontal process of the maxilla) which contains lacrimal sac

Bony framework of the floor of the orbit

Orbital surface of the maxilla, orbital process of palatine, zygomatic bone

Bony framework of the lateral wall of the orbit

Zygomatic bone, greater wing of sphenoid

Fissures and foramina in the orbit

• Optic canal

• Superior orbital fissure

• Inferior orbital fissure

• Infra-orbital foramen

• Posterior and anterior ethmoidal foramina

• Nasolacrimal canal

• Supraorbital notch/foramen

• Frontal notch/foramen

• Infraorbital groove

• Zygomatico-orbital foramen

Optic canal

• Bounded medially by the body of the sphenoid and laterally by the lesser wing of the sphenoid

• Opens in the middle cranial fossa

• Lets through the optic nerve II and the ophthalmic artery

Superior orbital fissure

• Lateral to the optic canal

• Opens in the middle cranial fossa

• Lets through superior and inferior orbital branches of oculomotor nerve III, trochlear nerve IV, abducent nerve VI, the lacrimal, frontal and nasociliary branches of the ophthalmic nerve V1, superior ophthalmic vein

Inferior orbital fissure

• Separates the lateral wall of the orbit from the floor of the orbit

• Between the greater wing of the sphenoid, the maxilla, palatine, and zygomatic bones

• Allows communication between the orbit and pterygopalatine fossa (post.), infratemporal fossa (middle), and the temporal fossa (posterolaterally)

• Let’s through the maxillary nerve V2 and its zygomatic branch, infraorbital vessels, inferior ophthalmic vein (vein communicating with the pterygoid plexus of veins)

Infraorbital foramen

• The infraorbital groove begins posteriorly, crossing approximately two-thirds of the inferior orbital fissure.

• It continues anteriorly across the orbital floor.

• It becomes the infraorbital canal.

• The canal opens onto the face through the infraorbital foramen.

• It transmits the infraorbital nerve (V2) and vessels.

Anterior ethmoidal foramen

• At the junction of the medial and superior walls

Orbit → ant. ethmoidal foramen → anterior cranial fossa (associated with the ethmoidal cells/region) → nasal cavity

• Lets through anterior ethmoidal nerve (branch of the nasociliary nerve, V1), anterior ethmoidal artery (branch of the ophthalmic artery), anterior ethmoidal vein

Posterior ethmoidal foramen

• At the junction of the superior and medial walls

Orbit → posterior ethmoidal cells associated with the sphenoidal sinus

• Lets though the posterior ethmoidal nerve (branch of the nasociliary nerve, V1), posterior ethmoidal artery (branch of the ophthalmic artery), posterior ethmoidal vein

Lacrimal groove

• Location: Medial wall of the orbit, between the lacrimal bone and frontal process of the maxilla.

• Contents: Lacrimal sac.

• Continuation: Nasolacrimal canal, containing the nasolacrimal duct.

• Communication: Inferior nasal meatus.

Supra-orbital notch

Allows communication with the forehead

Lets through supraorbital nerve and vessels

Supra-orbital notch

Allows communication with the forehead

Lets through supraorbital nerve and vessels

Zygomatico-orbital foramen

1. Zygomaticotemporal pathway

Orbit → Zygomatico-orbital foramen → Zygomaticotemporal canal → Zygomaticotemporal foramen → Temporal fossa.

Transmits the zygomaticotemporal nerve (V2).

2. Zygomaticofacial pathway

Orbit → Zygomatico-orbital foramen → Zygomaticofacial canal → Zygomaticofacial foramen → Face.

Transmits the zygomaticofacial nerve (V2).

Both nerves are branches of the zygomatic nerve, itself originating from the maxillary nerve (V2).