CorpusHuman Anatomy
SkeletalRegion

Bony orbit

Orbita

Also known as: orbit, eye socket, orbital cavity

A pyramidal bony socket formed by seven bones that houses and protects the eyeball, extraocular muscles, nerves, vessels and lacrimal gland.

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Overview

Bones forming each orbit7
Volume≈30 mL
Angle between lateral walls≈90°

Each orbit is a four-sided pyramid with its base (orbital opening) facing anteriorly and its apex at the optic canal, posteromedially. The medial walls are nearly parallel, while the lateral walls diverge at ≈90° to each other. Its volume is ≈30 mL, of which the eyeball occupies about one-fifth.

Roof: orbital plate of the frontal bone and lesser wing of the sphenoid (separates the orbit from the anterior cranial fossa). Floor: maxilla (mainly), zygomatic and palatine bones; traversed by the infraorbital groove and canal. Medial wall: frontal process of the maxilla, lacrimal bone, orbital plate of the ethmoid (lamina papyracea) and body of the sphenoid — the thinnest wall. Lateral wall: zygomatic bone and greater wing of the sphenoid — the thickest and strongest wall, but also the least protected anteriorly (lateral rim is set back, increasing peripheral vision).

Openings: the optic canal (CN II, ophthalmic artery), the superior orbital fissure, the inferior orbital fissure (maxillary nerve branches — infraorbital and zygomatic nerves, infraorbital vessels, inferior ophthalmic vein connections to the pterygoid plexus), the supraorbital notch/foramen, the infraorbital foramen, the anterior and posterior ethmoidal foramina, the nasolacrimal canal and the zygomatic foramina.

Location

Either side of the root of the nose, below the anterior cranial fossa and above the maxillary sinus.

Parts & subdivisions

  1. Roof
    Frontal bone (orbital plate) and lesser wing of sphenoid.
  2. Floor
    Maxilla, zygomatic and palatine bones — commonly fractured in blow-out injuries.
  3. Medial wall
    Maxilla (frontal process), lacrimal, ethmoid (lamina papyracea), sphenoid body — thinnest.
  4. Lateral wall
    Zygomatic bone and greater wing of sphenoid — strongest.
  5. Optic canal
    Optic nerve and ophthalmic artery.
  6. Superior orbital fissure
    CN III, IV, V1, VI and superior ophthalmic vein.
  7. Inferior orbital fissure
    Infraorbital and zygomatic nerves (V2), infraorbital vessels, emissary veins to the pterygoid plexus.

Function

  • Protects the eyeball and its accessory structures
  • Provides attachment for the extraocular muscles (common tendinous ring at the apex)
  • Transmits nerves and vessels to the eye and face

Clinical significance

Orbital blow-out fracture

A blunt object larger than the orbital rim (fist, ball) raises intraorbital pressure, fracturing the thin floor (or medial wall). Inferior rectus may be entrapped → restricted upward gaze and diplopia; enophthalmos; infraorbital nerve damage → numbness of the cheek and upper lip; "teardrop sign" on imaging.

Mnemonics

Seven bones of the orbit

"Many Friendly Zebras Enjoy Lazy Summer Picnics": Maxilla, Frontal, Zygomatic, Ethmoid, Lacrimal, Sphenoid, Palatine.

Compiled from standard anatomy and physiology references — see the Skeletal System sources. For education only; not medical advice.