Orbit (anatomy)

Source: Wikipedia, the free encyclopedia.
(Redirected from
Orbital bone
)
This article is about the anatomical space that contains the eye. For other uses, see Orbit (disambiguation) and Orbita (disambiguation).
Orbit
inferior rectus muscles; supraorbital foramen shown above the eye, and inferior orbital fissure inferolaterally.
Details
Identifiers
Latinorbita
MeSHD009915
TA98A02.1.00.067
TA2469
FMA53074
Anatomical terminology]

In

cranial nerves II, III, IV, V, and VI, blood vessels, fat, the lacrimal gland with its sac and duct, the eyelids, medial and lateral palpebral ligaments, cheek ligaments, the suspensory ligament, septum, ciliary ganglion and short ciliary nerves
.

Structure

3D model of orbit with surrounding bones

The orbits are conical or four-sided pyramidal cavities, which open into the midline of the face and point back into the head. Each consists of a base, an apex and four walls.[4]

Openings

There are two important

into the brain
or other deep facial structures.

The

zygomatic orbital foramen
.

Bony walls

Maxillary bone
aqua = Palatine bone
red = Sphenoid bone

teal = Nasal bone
(illustrated but not part of the orbit)

The bony walls of the orbital canal in humans do not derive from a single bone, but a mosaic of seven

orbital process, is formed by the frontal bone.[6]

The roof (superior wall) is formed primarily by the orbital plate frontal bone, and also the lesser wing of sphenoid near the apex of the orbit. The orbital surface presents medially by trochlear fovea and laterally by lacrimal fossa.[7]

The floor (inferior wall) is formed by the orbital surface of maxilla, the orbital surface of zygomatic bone and the minute orbital process of palatine bone. Medially, near the orbital margin, is located the groove for nasolacrimal duct. Near the middle of the floor, located infraorbital groove, which leads to the infraorbital foramen. The floor is separated from the lateral wall by inferior orbital fissure, which connects the orbit to pterygopalatine and infratemporal fossa.

The medial wall is formed primarily by the orbital plate of

ethmoid, as well as contributions from the frontal process of maxilla, the lacrimal bone, and a small part of the body of the sphenoid. It is the thinnest wall of the orbit, evidenced by pneumatized ethmoidal cells.[7]

The lateral wall is formed by the frontal process of zygomatic and more posteriorly by the orbital plate of the greater wing of sphenoid. The bones meet at the zygomaticosphenoid suture. The lateral wall is the thickest wall of the orbit, important because it is the most exposed surface, highly vulnerable to blunt force trauma.

Borders

The base, orbital margin, which opens in the face, has four borders. The following bones take part in their formation:

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

Function

The orbit holds and protects the eyes.

Eye movement

Main article: Eye movement

The movement of the eye is controlled by six distinct extraocular muscles, a

inferior oblique. The superior ophthalmic vein is a sigmoidal vessel along the superior margin of the orbital canal that drains deoxygenated blood from surrounding musculature. The ophthalmic artery is a crucial structure in the orbit, as it is often the only source of collateral blood to the brain in cases of large internal carotid infarcts, as it is a collateral pathway to the circle of Willis. In addition, there is the optic canal, which contains the optic nerve, or cranial nerve II, and is formed entirely by the lesser wing of the sphenoid, separated from the supraorbital fissure by the optic strut. Injury to any one of these structures by infection, trauma or neoplasm can cause temporary or permanent visual dysfunction, and even blindness if not promptly corrected.[8] The orbits also protect the eye from mechanical injury.[4]

Clinical significance

In the orbit, the surrounding fascia allows for smooth rotation and protects the orbital contents. If excessive tissue accumulates behind the ocular globe, the eye can protrude, or become exophthalmic.[4]

Tear system:
a. tear gland / lacrimal gland,
b. superior lacrimal punctum,
c. superior lacrimal canal,
d. tear sac / lacrimal sac,
e. inferior lacrimal punctum,
f. inferior lacrimal canal,
g. nasolacrimal canal

Enlargement of the lacrimal gland, located superotemporally within the orbit, produces protrusion of the eye inferiorly and medially (away from the location of the lacrimal gland). Lacrimal gland may be enlarged from inflammation (e.g. sarcoid) or neoplasm (e.g. lymphoma or adenoid cystic carcinoma).[9]

Tumors (e.g. glioma and meningioma of the optic nerve) within the cone formed by the horizontal rectus muscles produce axial protrusion (bulging forward) of the eye.

Graves disease may also cause axial protrusion of the eye, known as Graves' ophthalmopathy, due to buildup of extracellular matrix proteins and fibrosis in the rectus muscles. Development of Graves' ophthalmopathy may be independent of thyroid function.[10]

Additional images

  • Orbita
    Orbita
  • Medial wall of left orbit
    Medial wall of left orbit
  • Dissection showing origins of right ocular muscles, and nerves entering by the superior orbital fissure
    Dissection showing origins of right ocular muscles, and nerves entering by the superior orbital fissure
  • Lateral orbit nerves
    Lateral orbit nerves
  • Orbital cavity
    Orbital cavity

References

  1. ^ "Orbit – Definition and More from the Free Merriam-Webster Dictionary". Retrieved 2010-03-26.
  2. ^ Orbit at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
  3. ISBN 978-0-7817-6855-9
    .
  4. ^
    Encyclopædia Britannica 2006 Ultimate Reference Suite DVD
    2009
  5. S2CID 43317074
    .
  6. PMID 25665284
    .
  7. ^
    ISBN 978-07817-7525-0
    .
  8. S2CID 5567574
    .
  9. ISBN 9780721601878
    .
  10. PMID 12064074
    .

External links

Wikimedia Commons has media related to Orbit (anatomy).
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