Learning Objective: Learners will be able to describe the anatomy, contents, and clinical relevance of the bony orbit, including its borders, openings, neurovascular structures, and implications of orbital fractures.
Borders and Anatomical Relations
- Roof (superior wall): frontal bone, lesser wing of sphenoid → separates orbit from anterior cranial fossa.
- Floor (inferior wall): maxilla, palatine, zygomatic → separates orbit from maxillary sinus.
- Medial wall: ethmoid, maxilla, lacrimal, sphenoid → separates orbit from ethmoid sinus.
- Lateral wall: zygomatic, greater wing of sphenoid.
- Apex: optic canal/foramen.
- Base: orbital rim, opening to face.
Contents
- Extraocular muscles: move the eyeball and the superior eyelid.
- Eyelids: cover the anterior orbit.
- Nerves: optic (CN II), oculomotor (III), trochlear (IV), trigeminal (V), abducens (VI).
- Blood vessels: ophthalmic artery, superior and inferior ophthalmic veins.
- Orbital fat: cushions the eye and stabilizes muscles.
Pathways into the Orbit
- Optic canal: optic nerve, ophthalmic artery.
- Superior orbital fissure: lacrimal, frontal, trochlear (IV), oculomotor (III), nasociliary, abducens (VI), superior ophthalmic vein.
- Inferior orbital fissure: zygomatic branch of the maxillary nerve, inferior ophthalmic vein, and sympathetic nerves.
- Nasolacrimal canal: drains tears to the nasal cavity.
- Supraorbital foramen & infraorbital canal: carry small neurovascular structures.
Clinical Relevance
- Orbital rim fracture: fracture of rim bones (maxilla, zygomatic, frontal).
- Blowout fracture: herniation of orbital contents through weak medial/inferior walls (into ethmoid/maxillary sinuses).
- Signs: raised intraorbital pressure → exophthalmos; possible hemorrhage into neighboring sinuses.
