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Table of contents
Principles of the Orbit

The orbit is the bony socket that holds the eye and its associated structures


Anatomy

Orbital openings

Orbital openings and their contents.

Optic foramen

  • Found on the lesser wing of the sphenoid bone
  • Transmits the optic nerve and the ophthalmic artery

Superior orbital fissure

  • Lies between the greater and lesser wings of the sphenoid bone
  • Contains: Superior ophthalmic vein, lacrimal (CNV1) and frontal nerves (CNV1) and CN4
    • The structures within the superior orbital fissure and the common tendinous ring are: CN3, CN6, and nasociliary nerve (CNV1)

Inferior orbital fissure

  • Lies between the maxilla and the greater wing of the sphenoid
  • Contains: infraorbital(CNV2) and zygomatic nerves(CNV2), and the inferior ophthalmic vein

Retrobulbar anesthesia affects all the nerves within the common tendinous ring (annulus of Zinn)


Bones of the Orbit

Bones

Roof

  • Frontal
  • Lesser wing of the sphenoid

Medial wall

  • Maxillary
  • Lacrimal
  • Sphenoid
  • Ethmoid

Floor

  • Zygomatic
  • Maxillary
  • Palatine

Lateral wall

  • Zygomatic
  • Greater wing of the sphenoid.

Bones of the orbit. By OpenStax College, CC BY 3.0 .

The medial wall is the weakest. It has a thin transparent membrane called the lamina papyracea through which infection can easily spread. This is how ethmoid cellulitis can lead to orbital cellulitis.


Clinical Manifestations

The eyeball can sit abnormally in the socket and this is the hallmark of orbital disease.

A Hertel exophthalmometer, used to measure the protrusion of the globe in the orbit. By Drahreg01, CC BY-SA 3.0.


Exophthalmos

  • Axial proptosis (straight out) indicates a lesion within the tendinous ring such as optic nerve glioma and cavernous haemangioma.
  • Non-axial proptosis (protrusion at an angle) indicates a lesion outside the tendinous ring such as the lacrimal gland
  • Pseudoproptosis is the false appearance of proptosis and is typically due to facial anatomy.

Proptosis is the protrusion of any organ whereas exophthalmos is proptosis of the eye. The terms are used interchangeably in ophthalmology.
A Hertel exophthalmometer can be used to measure the degree of proptosis. >20mm indicates proptosis and any difference between the eyes should be investigated further


Enophthalmos

Enophthalmos is the opposite of exophthalmos

  • Can be congenital as a result of atrophy of the ocular contents
  • Psuedoenophthalmos can be seen in a small eye (microphthalmos), ptosis or proptosis of the fellow eye.

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