Bones and Structure of the Orbit
- Shaped like a quadrangular pyramidal cavern in the upper face, with a superficial base (orbital margin) and a deep, posteromedial apex
- Orbital margin:
- Superior margin: frontal bone
- Medial margin: frontal process of the maxilla
- Inferior margin: zygomatic process of the maxilla and zygomatic bone
- Lateral margin: zygomatic process of the frontal bone and frontal process of the zygomatic bone
- Apex: optic foramen
- Orbital margin:
- Walls: covered with periosteum (periorbita)
- Superior (roof): orbital part of the frontal and lesser wing of the sphenoid
- Medial: orbital plate of ethmoid bone, body of sphenoid bone, frontal bone, lacrimal bone, and maxilla
- Inferior (floor): orbital surface of the maxilla, zygomatic bone, and palatine bone
- Lateral: greater wing of sphenoid, orbital plate of frontal bone, and frontal process of zygomatic bone
- Important openings: optic foramen or canal, anterior and posterior ethmoidal foramina, superior and inferior orbital fissures, infraorbital groove, and supraorbital notch
The right orbit and the 7 bones that make up its walls: frontal (red), maxilla (orange), lacrimal (green), ethmoid (purple), sphenoid (yellow), palatine (dark orange), and zygomatic (blue)
Image: “Illustration from Anatomy & Physiology” by OpenStax College. License: CC-BY-3.0
The left orbit, featuring its many openings: optic foramen, ethmoidal foramina, superior and inferior orbital fissures, infraorbital groove, and supraorbital notch
Image: “An illustration from the 1909 American edition of Sobotta’s anatomy” by Dr. Johannes Sobotta. License: Public Domain
| Location | Contents | |
|---|---|---|
| Optic foramen or canal | Apex, bordered by the body and lesser wing of the sphenoid |
|
| Ethmoidal foramina |
| Anterior and posterior ethmoidal veins, arteries, and nerves |
| Superior orbital fissure | Between the greater and lesser wings of the sphenoid bone | Inside the common tendinous ring:
|
| Inferior orbital fissure |
|
|
| Infraorbital foramen | Middle of the orbital floor (maxilla) | Exit of the infraorbital vein, artery, and nerve |
| Supraorbital notch or foramen | Superior margin of the orbit (frontal bone) | Exit of the supraorbital vein, artery, and nerve |
Mnemonic 1
To help memorize the bones that make up the orbit, remember: Many Friendly Zebras Enjoy Lazy Summer Picnics
- Many: Maxilla
- Friendly: Frontal bone
- Zebras: Zygomatic bone
- Enjoy: Ethmoid bone
- Lazy: Lacrimal bone
- Summer: Sphenoid bone
- Picnics: Palatine bone
Extraocular Muscles
| Muscle | Origin | Insertion | Irrigation | Innervation | Function |
|---|---|---|---|---|---|
| Medial rectus | Annulus of Zinn (common tendinous ring) | Anterior, medial surface of the eye | Inferior muscular branch of ophthalmic artery | Inferior branch of oculomotor nerve (CN III) | Adduction |
| Lateral rectus | Anterior, lateral surface of the eye | Lacrimal artery | Abducens nerve (CN VI) | Abduction | |
| Inferior rectus | Anterior, inferior surface of the eye | Inferior muscular branch of ophthalmic artery and the infraorbital branch of the maxillary artery | Inferior branch of oculomotor nerve (CN III) | Depression, extorsion, and adduction. In abduction: only depresses | |
| Superior rectus | Anterior, superior surface of the eye | Superior muscular branch of ophthalmic artery | Superior branch of the oculomotor nerve (CN III) | Elevation, intorsion, and adduction. In abduction: only elevates | |
| Superior oblique | Lesser wing of sphenoid, medial to optic canal | Posterior, superior, lateral surface of the eye | Superior muscular branch of the ophthalmic artery | Trochlear nerve (CN IV) | Intorsion, depression, and abduction |
| Inferior oblique | Lateral to the lacrimal groove (maxilla) | Posterior, inferior, lateral surface of the eye | Inferior branch of the ophthalmic artery and infraorbital artery | Inferior branch of oculomotor nerve (CN III) | Extorsion, elevation, and abduction |
| Levator palpebrae superioris | Lesser wing of the sphenoid, above the optic canal | Tarsal plate of upper eyelid | Supraorbital branch of the ophthalmic artery | Superior branch of oculomotor nerve (CN III). Sympathetic fibers innervate the smooth muscle fibers on the inferior surface of this muscle. | Retracting and elevating the eyelid |
Origin and insertions of the extraocular muscles. Note that the four rectus muscles originate from a common tendinous ring (the obliques do not) and the location of the trochlea for the superior oblique.
Image: “Extraocular Muscles” by OpenStax College. License: CC BY 3.0
Eye movements for each extraocular muscle
Image by Lecturio.
Eye movements for each extraocular muscle. Note the synergistic movements of the superior rectus and oblique, as well as the inferior rectus and oblique muscles.
Image: “Version 8.25” by OpenStax. License: CC BY 4.0, edited by Lecturio.
Mnemonic 2
To help memorize the innervation of the extraocular muscles, remember: LR6, SO4, 3
- Lateral rectus innervated by the abducens nerve (CN VI)
- Superior oblique innervated by the trochlear nerve (CN IV)
- The remaining extraocular muscles are innervated by the oculomotor nerve (CN III)
Mnemonic 3
To help memorize the actions of the muscles, remember: RAD
Recti are Adductors, except the lateral rectus.
Lacrimal Apparatus
- Lacrimal gland:
- Serous; releases aqueous layer of tear fluid directly onto the eyeball
- Minimizes friction, protects and cleans the eye (“tear film”)
- Located on upper lateral aspect of orbit, drains via lacrimal ducts to the superior conjunctival fornix
- Innervated by parasympathetic fibers of the facial nerve (VII) via the pterygopalatine ganglion
- Tears:
- Isotonic solution
- Contains bactericidal enzymes (lysozyme and lactoferrin), immunoglobulin A, and lipocalin
- Tarsal or Meibomian glands:
- Sebaceous glands; produce meibum, which decreases evaporation of the tear film
- Located within tarsal plate of eyelids (within the superior eyelid) with orifices at the rim of the marginal zone of the conjunctiva
- Tear drainage system—consists of:
- Lacrimal canaliculi
- Lacrimal sac: dilated portion of the nasolacrimal duct
- Nasolacrimal duct: drains into the inferior nasal meatus
Clinicopathologic Correlations
| Nerve palsy | Causes | Symptoms involving affected eye |
|---|---|---|
| Oculomotor (CN III) |
|
|
| Trochlear (CN IV) |
| Eye is up and in |
| Abducens (CN VI) |
| Eye directed medially |
- Orbital and preseptal cellulitis: possible complications to paranasal sinusitis or trauma to the eye orbit. Patients may present with fever, malaise, proptosis ophthalmoplegia, toxic shock, and impaired vision.
- Orbital fractures: fractures to the eye sockets are classified as orbital rim fractures, direct orbital floor fracture, and blowout fractures. These fractures can present with blurry, decreased, or double vision, and black-and-blue bruising around the eyes.
- Dacryoadenitis: an inflammation of the lacrimal glands commonly due to a bacterial or viral infection. May present as swelling of the outer portion of the upper lid, with redness and tenderness, pain in the area of swelling, excess tearing, and swelling of the preauricular lymph nodes.
- Sjögren’s syndrome: an autoimmune disease that affects the moisture-producing glands of the body. Primary symptoms are dry mouth and dry eyes.
- Strabismus: a condition characterized by a misalignment of the eyes. If left untreated throughout childhood, strabismus may result in amblyopia or loss of depth perception.
- Blepharitis: one of the most common ocular conditions; characterized by inflammation, scaling, reddening, and crusting of the eyelid. May also present with a burning, itching, or grainy sensation
