Anatomy Atlas

Orbit

Orbita
Also: Eye socket
Space / regionHigh-yielddraftEENT

Pyramidal bony cavity holding the eyeball, extraocular muscles, nerves and vessels. Its thin floor and medial wall break in blowout fractures, and infection behind the orbital septum is an emergency.

Core anatomy

Location

Paired cavities in the upper face, apex pointing posteromedially toward the optic canal.

Boundaries
roof
Orbital plate of the frontal bone and lesser wing of the sphenoid (anterior cranial fossa above)
floor
Maxilla (with zygomatic and palatine bones) — thin; the maxillary sinus lies below; infraorbital nerve in its groove
medial wall
Ethmoid (lamina papyracea — paper-thin), lacrimal, maxilla, sphenoid; ethmoid sinuses medially
lateral wall
Zygomatic bone and greater wing of the sphenoid — the thickest wall
apex
Optic canal and superior orbital fissure
Contents
  • Eyeball and optic nerve (CN II)
  • Extraocular muscles and levator palpebrae superioris
  • Nerves: CN III, IV, VI, V1 branches (frontal, lacrimal, nasociliary), ciliary ganglion
  • Ophthalmic artery (from the internal carotid) and superior/inferior ophthalmic veins
  • Lacrimal gland (superolateral) and orbital fat
Communications

Optic canal → middle cranial fossa (CN II, ophthalmic artery). Superior orbital fissure (CN III, IV, V1, VI, superior ophthalmic vein) → cavernous sinus (see dural venous sinuses). Inferior orbital fissure → pterygopalatine and infratemporal fossae. Ophthalmic veins are valveless and drain to the cavernous sinus — a route for spreading infection.

Notes

The orbital septum, a fascial sheet from the orbital rim to the tarsal plates, separates the eyelids (preseptal) from the orbit proper (postseptal).

Mentioned in

Generated automatically from links in other entries.

H-pattern test of the extraocular muscles (right eye)The examiner traces an H in front of the patient. For the right eye: looking laterally (temporally) tests the lateral rectus (CN VI); lateral and up tests the superior rectus; lateral and down tests the inferior rectus; looking medially (toward the nose) tests the medial rectus; medial and up tests the inferior oblique; medial and down tests the superior oblique (CN IV). All but the lateral rectus and superior oblique are supplied by CN III.Superior rectusCN IIILateral rectusCN VIInferior rectusCN IIIInferior obliqueCN IIIMedial rectusCN IIISuperior obliqueCN IV← Temporal (patient's right)Nasal (toward the nose) →LR6 · SO4 · all others CN III — examiner's view of the patient's right eye

Swipe sideways to see the whole diagram →

H-pattern test of the extraocular muscles. Examiner's view of the patient's right eye (patient's right = your left). Each end-point is the gaze position that isolates one muscle; gold dots = CN VI and CN IV, red dots = CN III. The obliques are tested with the eye adducted, the superior and inferior recti with it abducted.
Original schematic, created for this atlas.
Anterior view into the right orbit showing the common tendinous ring and origins of the recti, with the oculomotor, trochlear, abducent, frontal, lacrimal and nasociliary nerves at the superior orbital fissure
The orbital apex: the common tendinous ring and the nerves entering through the superior orbital fissure.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 890. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))
Anterior view of the skull showing the frontal bone, orbits with the superior and inferior orbital fissures, nasal cavity, maxillae and mandible
The orbits in the skull from the front.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 190. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))

Clinical correlations

Orbital floor ("blowout") fracture PANCE

Mechanism / lesion

A blunt object larger than the orbit (fist, ball) raises intraorbital pressure, fracturing the thin floor (or medial wall).

Classic presentation

Diplopia on upward gaze (entrapment of inferior rectus), enophthalmos, numbness of the cheek and upper lip (infraorbital nerve), periorbital emphysema after nose blowing. Entrapment in children can trigger the oculocardiac reflex (bradycardia, nausea) — urgent repair.

Orbital vs preseptal (periorbital) cellulitis PANCE

Mechanism / lesion

Orbital cellulitis — infection behind the septum, usually spread from ethmoid sinusitis. Preseptal — eyelid infection in front of the septum.

Classic presentation

Both cause eyelid redness and swelling. Red flags for orbital cellulitis: pain with eye movements, ophthalmoplegia, proptosis, decreased vision, fever. Orbital cellulitis needs CT orbits, IV antibiotics and ophthalmology; complications include abscess and cavernous sinus thrombosis.

Retrobulbar hemorrhage (orbital compartment syndrome)

Mechanism / lesion

Bleeding behind the eye after trauma or surgery compresses the optic nerve and its blood supply.

Classic presentation

Painful proptosis, tense orbit, reduced vision, relative afferent pupillary defect — emergency lateral canthotomy and cantholysis.

High-yield PANCE pearls

  • Blowout fracture: diplopia on upgaze (inferior rectus entrapment), cheek numbness (infraorbital nerve).
  • Pain with eye movement, proptosis, ophthalmoplegia → orbital cellulitis → CT + IV antibiotics.
  • Orbital cellulitis usually spreads from ethmoid sinusitis.
  • Ophthalmic veins → cavernous sinus (valveless) → cavernous sinus thrombosis risk.

Imaging anatomy

X-ray

Waters view may show the "teardrop sign" of a blowout fracture, but CT has replaced it.

CT

CT of the orbits (thin coronal slices) for fractures, muscle entrapment, orbital cellulitis and abscess.

MRI

Optic nerve and orbital apex lesions, orbital tumors.

Ultrasound

Ocular ultrasound for retrobulbar hematoma and globe injury (not if globe rupture is suspected with pressure).

Key views & landmarks
  • CT orbits with coronal reconstructions

Physical exam

Surface landmarks

Orbital rim (supraorbital notch, infraorbital foramen about 1 cm below the rim), medial and lateral canthi.

Palpation

Palpate the rim for step-offs and crepitus; test sensation of the cheek and upper lip (infraorbital nerve).

Strength / function testing

Visual acuity, pupils (relative afferent pupillary defect), extraocular movements and diplopia, proptosis, intraocular pressure.

Self-quiz

Q1.

A 22-year-old is hit in the eye by a baseball. He has double vision when looking up and numbness of the left cheek and upper lip. Which structures are most likely injured?

Show answer

B

An orbital floor blowout fracture can trap the inferior rectus (restricting upgaze) and injure the infraorbital nerve, which runs in the floor, numbing the cheek and upper lip.

Q2.

A 7-year-old with a week of sinusitis has a red, swollen left eyelid, fever, pain when moving the eye, and limited upward gaze. What is the most appropriate next step?

Show answer

C

Pain with eye movement and ophthalmoplegia indicate orbital (postseptal) cellulitis, usually from ethmoid sinusitis. It needs CT orbits (to exclude abscess), IV antibiotics and ophthalmology/ENT involvement.

Q3.

Which orbital wall is the thinnest?

Show answer

C

The lamina papyracea of the ethmoid is paper-thin, which is why ethmoid sinusitis spreads to cause orbital cellulitis. The lateral wall is the thickest; the floor is also thin and fractures in blowout injuries.

Q4.

After facial trauma, a patient has painful proptosis, a tense orbit, reduced vision and a relative afferent pupillary defect. What is the most urgent intervention?

Show answer

A

Retrobulbar hemorrhage (orbital compartment syndrome) compresses the optic nerve and its blood supply. It is an emergency treated with lateral canthotomy and cantholysis to decompress the orbit.

Q5.

Which vessel passes through the optic canal with the optic nerve?

Show answer

B

The optic canal transmits the optic nerve (CN II) and the ophthalmic artery. The superior orbital fissure transmits CN III, IV, V1 and VI with the superior ophthalmic vein.

Flashcards

See also