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Bones Anatomy

Orbital Anatomy

The orbits are conical or four-sided pyramidal cavities, which open into the midline of the face and travel back into the head. Each consists of a base, an apex and four walls. They protect the eye from injury. The following bones take part in their formation:

  1. Superior margin: frontal bone
  2. Inferior margin: maxilla and zygomatic
  3. Medial margin: frontal, lacrimal and maxilla
  4. Lateral margin: zygomatic and frontal

Orbital volume and dimensions: = 30 cc, 35(Height) x 45(Width) x 45 mm(medial wall depth), globe 25 x 25 mm Bones: (F)rontal, (M)axillary,(Z)ygomatic, (L)acrimal, (E)thmoid, (P)alatine, (S)phenoid

WALL BONES CONTENTS Clinical Correlation
Roof Frontal Lesser wing of sphenoid lacrimal gland fossa trochlea 4mm posterior to margin for superior oblique tendon Supraorbital notch/foramen subperisteal abscess
Medial Wall Maxillary Lacrimal Ethmoid – thinnest Sphenoid lacrimal sac fossa cribiform plate is medial to anterior orbit at the level of fronto-ethmoidal suture Nasoclacrimal duct obstructions./tumors/DCRs Medial wall fractures subperisteal abscess Orbital cellulitis/proptosis from ethmodial extension
Floor Maxillary- second thinnest, thins posteriorly Palatine Zygoma infraorbital foramen inferior oblique origin slopes 20 degrees down suspensory ligament of eyeball subperiosteal abscess blow-out fractures
Lateral Wall Zygomatic bone Greater wing of sphenoid lateral orbital tubercle is 11mm below F-Z suture serves as attachment of check ligament of lateral rectus Tripod fractures Ruptured globes Lateral tarsal strips adjacent to middle cranial fossa, temporal fossa, and pterygopalatine fossa

Clinical Correlations

The medial orbital walls are nearly parallel and are 25 mm apart. The orbit is widest not at its entrance, but 1 cm from the orbital rim. Per the graphic image below, the frontal bone is shown in yellow, maxilla in purple, zygomatic bone in blue, lacrimal bone in green, nasal bone in grey-green (not part of orbit), sphenoid bone in pink, ethmoid bone in brown and palatine bone in light blue. This is a file from Wikimedia Commons, a freely licensed media file repository.

The superior orbital fissure (SOF) measures 22 mm long, separates greater wing of sphenoid from lesser wing of sphenoid, and transmits third, fourth, sixth and V1 and sympathetic fibers. The lateral rectus origin separates into superior and inferior divisions: superior division transmits lacrimal, frontal and trochlear nerves; inferior division transmits superior and inferior divisions of CN III, nasociliary branch of CN V, CN IV, superior ophthalmic vein, and sympathetic nerve plexus.

The inferior orbital fissure (IOF) is ocated between lateral orbital wall and the orbital floor and transmits V2 ( maxillary) and pterygoid nerves arising from pterygopalatine ganglion. The infraorbital nerve (a branch of V2) enters the intraobital groove and infraorbital canal for sensation to lower eyelid, cheek, upper lid, upper teeth.

Holes/Notches/Canals

NASOLACRIMAL CANAL

The nasolacrimal canal is essentially a nasolacrimal duct formed by indentations in the inferior nasal conchae, maxilla, and lacrimal bone. The canal drains into the nasal cavity through the anterior portion of the inferior meatus, which is between the inferior concha and the floor of the nasal cavity. More specifically:

  • Lacrimal sac fossa to the inferior meatus
  • Separates greater wing of sphenoid from lesser wing of sphenoid
  • Transmits third, fourth, sixth and V1 and sympathetic fibers
  • Lateral rectus origin separates into superior and inferior divisions
    • Superior division transmits lacrimal, frontal and trochlear nerves
    • Inferior division transmits superior and inferior divisions of CN III, nasociliary branch of CN V, CN IV, superior ophthalmic vein, and sympathetic nerve plexus
    • Venous system: superior ophthalmic vein
  • Supraorbital foramen/notch
    • transmits blood vessels
    • supraorbital nerve
    • Anterior/posterior ethmoidal foramen: transmits ethmoidal blood vessels and nerve
    • Zygomatic foramen: transmits zygomaticofrontal and zygomaticotemporal nerves, zygomatic artery
    • Nasolacrimal duct (NLD): exits into inferior meatus
    • Infraorbital canal: transmits infraorbital nerve (V2)
  • Ethmoidal foramina
    • anterior ethmoidal artery
    • posterior ethmoidal artery
    • allows infections and neoplasms to enter to orbit from the sinuses
  • Optic canal
    • 8-10 mm long
    • located within the less wing of sphenoid
    • separated from SOF by optic strut
    • transmits to ophthalmic nerve, ophthalmic artery, sympathetic nerves
    • optic foramen is 6.5 mm wide: it may possibly be enlarged in the presence of optic nerve glioma; 1 mm of asymmetry between right and left is abnormal

BEFORE & AFTER

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