Orbit (anatomy)

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Orbit
Eye orbit anatomy anterior2.jpg
Diagram of eye with surrounding superior, oblique, medial and inferior rectus muscles; supraorbital foramen shown above the eye, and inferior orbital fissure inferolaterally.
Details
Identifiers
Latin Orbita
MeSH D009915
TA A02.1.00.067
FMA 53074
Anatomical terminology

In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. Anatomical term created by Gerard of Cremona. [1] "Orbit" can refer to the bony socket, [2] or it can also be used to imply the contents. [3] In the adult human, the volume of the orbit is 30 millilitres (1.06 imp fl oz; 1.01 US fl oz), of which the eye occupies 6.5 ml (0.23 imp fl oz; 0.22 US fl oz). [4] The orbital contents comprise the eye, the orbital and retrobulbar fascia, extraocular muscles, cranial nerves II, III, IV, V, and VI, blood vessels, fat, the lacrimal gland with its sac and nasolacrimal duct, the eyelids, medial and lateral palpebral ligaments, check ligaments, the suspensory ligament, septum, ciliary ganglion and short ciliary nerves.

Anatomy The study of the structure of organisms and their parts

Anatomy is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science which deals with the structural organization of living things. It is an old science, having its beginnings in prehistoric times. Anatomy is inherently tied to developmental biology, embryology, comparative anatomy, evolutionary biology, and phylogeny, as these are the processes by which anatomy is generated over immediate (embryology) and long (evolution) timescales. Anatomy and physiology, which study (respectively) the structure and function of organisms and their parts, make a natural pair of related disciplines, and they are often studied together. Human anatomy is one of the essential basic sciences that are applied in medicine.

Human eye mammalian eye; part of the visual organ of the human body, and move using a system of six muscles

The human eye is an organ that reacts to light and allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth. The human eye can differentiate between about 10 million colors and is possibly capable of detecting a single photon. The eye is part of the sensory nervous system.

Accessory visual structures

Accessory visual structures are the adnexa of the eye, including the eyebrow, eyelids, and lacrimal apparatus.

Contents

Structure

3D model of Orbit with surrounding bones Orbit of the Face, STL file processed 1.0.0.stl
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. [5]

Openings

There are two important foramina, or windows, two important fissures, or grooves, and one canal surrounding the globe in the orbit. There is a supraorbital foramen, an infraorbital foramen, a superior orbital fissure, an inferior orbital fissure and the optic canal, each of which contains structures that are crucial to normal eye functioning. The supraorbital foramen contains the supraorbital nerve, the first division of the trigeminal nerve or V1 and lies just lateral to the frontal sinus. The infraorbital foramen contains the second division of the trigeminal nerve, the infraorbital nerve or V2, and sits on the anterior wall of the maxillary sinus. Both foramina are crucial as potential pathways for cancer and infections of the orbit to spread into the brain or other deep facial structures.

In anatomy, a foramen is any opening. Foramina inside the body of humans and other animals typically allow muscles, nerves, arteries, veins, or other structures to connect one part of the body with another.

In anatomy, a fissure is a groove, natural division, deep furrow, elongated cleft, or tear in various parts of the body also generally called a sulcus, or in the brain a sulcus.

Canal Man-made channel for water

Canals, or navigations, are human-made channels, or artificial waterways, for water conveyance, or to service water transport vehicles.

The optic canal contains the optic nerve (cranial nerve II) and the ophthalmic artery, and sits at the junction of the sphenoid sinus with the ethmoid air cells, superomedial and posterior to structures at the orbital apex. It provides a pathway between the orbital contents and the middle cranial fossa. The superior orbital fissure lies just lateral and inferior to the optic canal, and is formed at the junction of the lesser and greater wing of the sphenoid bone. It is a major pathway for intracranial communication, containing cranial nerves III, IV, VI which control eye movement via the extraocular muscles, and the ophthalmic branches of cranial nerve V, or V1. The second division of the trigeminal nerve enters the skull base at the foramen rotundum, or V2. The inferior orbital fissure lies inferior and lateral to the ocular globe at the lateral wall of the maxillary sinus. It is not as important in function, though it does contain a few branches of the maxillary nerve and the infraorbital artery and vein. [6] Other minor structures in the orbit include the anterior and posterior ethmoidal foramen and zygomatic orbital foramen.

Optic canal

The optic foramen is the opening to the optic canal. The canal is located in the sphenoid bone; it is bounded medially by the body of the sphenoid and laterally by the lesser wing of the sphenoid.

Optic nerve paired nerve that transmits visual information from the retina to the brain

The optic nerve, also known as cranial nerve II, or simply as CN II, is a paired nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived from optic stalks during the seventh week of development and is composed of retinal ganglion cell axons and glial cells; it extends from the optic disc to the optic chiasma and continues as the optic tract to the lateral geniculate nucleus, pretectal nuclei, and superior colliculus.

Ophthalmic artery

The ophthalmic artery (OA) is the first branch of the internal carotid artery distal to the cavernous sinus. Branches of the OA supply all the structures in the orbit as well as some structures in the nose, face and meninges. Occlusion of the OA or its branches can produce sight-threatening conditions.

Bony walls

The seven bones that form the orbit:
yellow = Frontal bone
green = Lacrimal bone
brown = Ethmoid bone
blue = Zygomatic bone
purple = Maxillary bone
aqua = Palatine bone
red = Sphenoid bone

teal = Nasal bone (illustrated but not part of the orbit) Orbital bones.png
The seven bones that form the orbit:
yellow = Frontal bone
green = Lacrimal bone
brown = Ethmoid bone
blue = Zygomatic bone
purple = 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 embryologically distinct structures: the zygomatic bone laterally, the sphenoid bone, with its lesser wing forming the optic canal and its greater wing forming the lateral posterior portion of the bony orbital process, the maxillary bone inferiorly and medially which, along with the lacrimal and ethmoid bones, forms the medial wall of the orbital canal. The ethmoid air cells are extremely thin, and form a structure known as the lamina papyracea, the most delicate bony structure in the skull, and one of the most commonly fractured bones in orbital trauma. The lacrimal bone also contains the nasolacrimal duct. The superior bony margin of the orbital rim, otherwise known as the orbital process, is formed by the frontal bone. [7]

Embryology branch of biology studying prenatal biology

Embryology is the branch of biology that studies the prenatal development of gametes, fertilization, and development of embryos and fetuses. Additionally, embryology encompasses the study of congenital disorders that occur before birth, known as teratology.

Zygomatic bone facial bone

In the human skull, the zygomatic bone is a paired irregular bone which articulates with the maxilla, the temporal bone, the sphenoid bone and the frontal bone. It is situated at the upper and lateral part of the face and forms the prominence of the cheek, part of the lateral wall and floor of the orbit, and parts of the temporal fossa and the infratemporal fossa. It presents a malar and a temporal surface; four processes, and four borders.

Sphenoid bone unpaired bone situated at the front middle of the skull in front of the temporal bone and basilar part of the occipital bone

The sphenoid bone is an unpaired bone of the neurocranium. It is situated in the middle of the skull towards the front, in front of the temporal bone and the basilar part of the occipital bone. The sphenoid bone is one of the seven bones that articulate to form the orbit. Its shape somewhat resembles that of a butterfly or bat with its wings extended.

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. [8]

Frontal bone Bone in the human skull

The frontal bone is a bone in the human skull. The bone consists of two portions. These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bony part of the forehead, part of the bony orbital cavity holding the eye, and part of the bony part of the nose respectively. The name comes from the Latin word frons.

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. [8]

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

  1. Superior margin: frontal bone and sphenoid
  2. Inferior margin: maxillary bone, palatine and zygomatic
  3. Medial margin: ethmoid, lacrimal bone, sphenoid (body of) and maxilla
  4. Lateral margin: zygomatic and sphenoid (greater wing)

Function

The orbit holds and protects the eye.

Eye movement

The movement of the eye is controlled by six distinct extraocular muscles, a superior, an inferior, a medial and a lateral rectus, as well as a superior and an 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. [9] The orbits also protect the eye from mechanical injury. [5]

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. [5]

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 Tear system.svg
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). [10]

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. [11]

Additional images

Related Research Articles

Articles related to anatomy include:

Maxilla upper jawbone formed from the fusion of two maxillary bones; includes the frontal portion of the palate of the mouth

The maxilla in animals is the upper fixed bone of the jaw formed from the fusion of two maxillary bones. The upper jaw includes the hard palate in the front of the mouth. The two maxillary bones are fused at the intermaxillary suture, forming the anterior nasal spine. This is similar to the mandible, which is also a fusion of two mandibular bones at the mandibular symphysis. The mandible is the movable part of the jaw.

Superior orbital fissure

The superior orbital fissure is a foramen in the skull, although strictly it is more of a cleft, lying between the lesser and greater wings of the sphenoid bone.

Orbital part of frontal bone

The orbital or horizontal part of the frontal bone consists of two thin triangular plates, the orbital plates, which form the vaults of the orbits, and are separated from one another by a median gap, the ethmoidal notch.

Cavernous sinus

The cavernous sinus within the human head, is one of the dural venous sinuses creating a cavity called the lateral sellar compartment bordered by the temporal bone of the skull and the sphenoid bone, lateral to the sella turcica.

Maxillary nerve

The maxillary nerve (CN V2) is one of the three branches or divisions of the trigeminal nerve, the fifth (V) cranial nerve. It comprises the principal functions of sensation from the maxillary, nasal cavity, sinuses, the palate and subsequently that of the mid-face, and is intermediate, both in position and size, between the ophthalmic nerve and the mandibular nerve.

Ophthalmic nerve sensory nerve

The ophthalmic nerve is the first branch of the trigeminal nerve. The ophthalmic nerve is a sensory nerve mostly carrying general somatic afferent fibers that transmit sensory information to the CNS from structures of the eyeball, the skin of the upper face and anterior scalp, the lining of the upper part of the nasal cavity and air cells, and the meninges of the anterior cranial fossa. Some of ophthalmic nerve branches also convey parasympathetic fibers.

Supraorbital foramen

The supraorbital foramen, is a bony elongated opening located above the orbit and under the forehead. The supraorbital foramen lies directly under the eyebrow. Sometimes this foramen is incomplete and is then known as the supraorbital notch.

Greater wing of sphenoid bone

The greater wing of the sphenoid bone, or alisphenoid, is a bony process of the sphenoid bone; there is one on each side, extending from the side of the body of the sphenoid and curving upward, laterally, and backward.

Lesser wing of sphenoid bone The bone that is situated in the orbit on either side of the presphenoid; it generally forms a part of the sphenoid in the adult, and may be independent in the young

The lesser wings of the sphenoid or orbito-sphenoids are two thin triangular plates, which arise from the upper and anterior parts of the body, and, projecting lateralward, end in sharp points [Fig. 1].

Inferior orbital fissure

The medial wall and the floor of the orbit are separated posteriorly by the inferior orbital fissure which transmits the zygomatic branch of the maxillary nerve and the ascending branches from the pterygopalatine ganglion. The infraorbital vessels are found in the inferior orbital fissure, and travel down the infraorbital groove into the infraorbital canal and exit through the infraorbital foramen. Inferior division of ophthalmic vein passes through the inferior orbital fissure.

Infraorbital foramen Foramen (round hole) in maxilla

In human anatomy, the infraorbital foramen is an opening in the maxillary bone of the skull located below the infraorbital margin of the orbit. It transmits the infraorbital artery and vein, and the infraorbital nerve, a branch of the maxillary nerve. It is typically 6.10 to 10.9 mm from the infraorbital margin.

Squamous part of the frontal bone

There are two surfaces of the squamous part of the frontal bone: the external surface, and the internal surface.

Middle cranial fossa

The middle cranial fossa, deeper than the anterior cranial fossa, is narrow medially and widens laterally to the sides of the skull. It is separated from the posterior fossa by the clivus and the petrous crest.

Anterior cranial fossa houses the projecting frontal lobes of the brain

The anterior cranial fossa is a depression in the floor of the cranial base which houses the projecting frontal lobes of the brain. It is formed by the orbital plates of the frontal, the cribriform plate of the ethmoid, and the small wings and front part of the body of the sphenoid; it is limited behind by the posterior borders of the small wings of the sphenoid and by the anterior margin of the chiasmatic groove. The lesser wings of the sphenoid separate the anterior and middle fossae.

Infratemporal fossa

The infratemporal fossa is an irregularly shaped cavity, situated below and medial to the zygomatic arch. It is not fully enclosed by bone in all directions, and it contains superficial muscles that are visible during dissection after removing skin and fascia: namely, the lower part of the temporalis muscle, the lateral pterygoid, and the medial pterygoid.

Le Fort fracture of skull

A Le Fort fracture of the skull is a classic transfacial fracture of the midface, involving the maxillary bone and surrounding structures in either a horizontal, pyramidal or transverse direction. The hallmark of Lefort fractures is traumatic pterygomaxillary separation, which signifies fractures between the pterygoid plates, horseshoe shaped bony protuberances which extend from the inferior margin of the maxilla, and the maxillary sinuses. Continuity of this structure is a keystone for stability of the midface, involvement of which impacts surgical management of trauma victims, as it requires fixation to a horizontal bar of the frontal bone. The pterygoid plates lie posterior to the upper dental row, or alveolar ridge, when viewing the face from an anterior view. The fractures are named after French surgeon René Le Fort (1869–1951), who discovered the fracture patterns by examining crush injuries in cadavers.

Outline of human anatomy Overview of and topical guide to human anatomy

The following outline is provided as an overview of and topical guide to human anatomy:

References

  1. Arráez-Aybar, Luis-A. "Toledo School of Translators and their influence on anatomical terminology". Annals of Anatomy - Anatomischer Anzeiger. 198: 21–33. doi:10.1016/j.aanat.2014.12.003.
  2. "Orbit – Definition and More from the Free Merriam-Webster Dictionary" . Retrieved 2010-03-26.
  3. Orbit at the US National Library of Medicine Medical Subject Headings (MeSH)
  4. Tasman, W.; Jaeger, E. A., eds. (2007). "Embryology and Anatomy of the Orbit and Lacrimal System". Duane's Ophthalmology. Lippincott Williams & Wilkins. ISBN   978-0-7817-6855-9.
  5. 1 2 3 "eye, human."Encyclopædia Britannica from Encyclopædia Britannica 2006 Ultimate Reference Suite DVD 2009
  6. Mehta, M. P.; Perry, J. D. (2015). "Medial orbital wall landmarks in three different North American populations". Orbit. 34 (2): 72–8. doi:10.3109/01676830.2014.997394. PMID   25804299.
  7. Bertelli, E; Regoli, M (2014). "Branching of the foramen rotundum. A rare variation of the sphenoid". Italian Journal of Anatomy and Embryology. 119 (2): 148–53. PMID   25665284.
  8. 1 2 Moore, Keith L. (2010). Clinically Oriented Anatomy (6th ed.). Lippincott Williams & Wilkins. ISBN   978-07817-7525-0.
  9. Ference, E. H.; Smith, S. S.; Conley, D; Chandra, R. K. (2015). "Surgical anatomy and variations of the infraorbital nerve". The Laryngoscope. 125 (6): 1296–300. doi:10.1002/lary.25089. PMID   25992806.
  10. Kumar, V.; Abbas, A. K.; Fausto, N. (2005). Robbins and Cotran Pathologic Basis of Disease (Seventh ed.). Philadelphia: Elsevier Saunders. p. 1423.
  11. Hatton, M. P.; Rubin, P. A. (2002). "The pathophysiology of thyroid-associated ophthalmopathy". Ophthalmol Clin North Am. 15 (1): 113–119. doi:10.1016/S0896-1549(01)00004-9. PMID   12064074.