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- Sarah Ferreira
The orbits of a human skull is the space in which the eye and it’s appendages are located. The two orbits in the human skull are conical “holes” that opens into the midline of the face and point back into the head. Each orbit includes an apex, four walls and a base. The functions of these orbits is firstly to keep the eye “safe” from any mechanical injury and secondly to supply an entrance for the optic nerve(that transports visual information from the eye’s retina to the vision centers in the brain through electrical impulses) to the brain. A thorough understanding of the anatomy of the orbits of the human skull is very important to any doctor in order to comprehend any disorders that patients might experience that are related to the eye socket itself, as well as to understand the surgical management of this region in the human skull.
2.The orbit of the skull
2.1The general location of the orbits in the human skull:
The orbit in the human skull lies anterior to the temporal fossa (laterally) and anterior to the middle cranial fossa (medially). It’s also situated superior to the maxillary air sinus, lateral to the nasal space as well as below the anterior cranial fossa.
2.2The shape of the orbit of the skull:
The shape of the orbit in the human skull looks like a pyramid that has four distinctive sides (“walls”), but as one moves posterior, it becomes three sided( toward the apex). The most posterior portion of the pyramid shaped orbit is the apex (of the orbit) and it’s positioned at the craniofacial junction. ( The apex is also where the optic canal (that contains the central retina vein, ophthalmic artery, symphathetic nerve and optic nerve) opens into the posterior part of the orbit and it forms the tip of this pyramid shaped “cavity” or structure.)
2.3The bones of the orbit of the skull and their bone classification:
There are seven bones that make up the orbit namely the:
1)The Maxillary bone(that is also classified an irregular bone)
2)The orbital plate of the Frontal bone(that is also classified as an irregular bone)
3)The Zygomatic bone(that is also classified as a flat bone)
4)The Ethmoidal bone(that is also classified as an irregular bone)
5)The Lacrimal bone(that is also classified as a flat bone)
6) The Palative bone (that is also classified as an irregular bone)
7) The Sphenoid bone (that is also classified as an irregular bone)
All of the above mentioned bones also form part of the human skull. The orbit also contains fissures and fossae where various blood vessels and nerves pass through.
2.4The walls of the orbit
The orbit as mentioned earlier consist of four sides or “walls”. The facial and cranial bones that forms the structure of the orbits also forms these four walls. The walls of the orbit of the skull are as follows:
1)The superior wall/ “roof”
2)The lateral wall
3)The inferior wall/ “floor”
4)The medial wall.
3Introduction to the bones of the orbit and the orbital walls that they form:
The superior margin and most of the roof of the orbit are formed by the frontal bones of the orbital plate. The inferomedial margin and the floor of the orbit is also formed by the maxilla bone. The anterior part of the lateral wall and the inferolateral margin of the orbit is also formed by the zygomatic bone. Much of the medial wall of the orbit is also formed by the lateral mass of the ethmoid bone. There are also a number of ways in which the sphenoid bone contributes to the structure of the orbit: Firstly, the lateral wall posterior to the Zygomatic bone is constituted by the greater wing of the sphenoid bone and secondly the posterior margin of the roof (or superior wall) is formed by the lesser wing of the sphenoid bone.Thirdly the optic canal (that provide a passage for the optic canal and the optic nerve into the orbital space) which is in the apex of the orbit, is also framed by the roots of the lesser wing of the sphenoid bone.( This”roots” of the lesser wing also connects it to the body of the sphenoid bone.)
The medial wall of the orbit( that is between the frontal process of the maxilla and the lateral mass of the ethmoid is completed by the small, curved , lacrimal bone. The posterior angle of the floor or inferior wall is completed by the orbital process of the palatine bone that is insinuated behind the maxilla and underneath the ethmoid bone.
3.1The superior wall or “roof”
The lesser wing of the sphenoid bone constitutes/forms the posterior margin of the superior wall and also surrounds the optic canal( that “ac” as a channel for the optic nerve and ophthalmic artery). Thus the optic canal is situated posteriorly in the wing of the sphenoid bone that is smaller i.e. the lesser wing and this canal also communicates with the middle cranial fossa. (A fossa is a hollow or a shallow depression.)
The superior margin of the bony cavity that contains the human eyeball are formed by the orbital plate of the frontal bone and this bone forms almost everything of the superior wall of the orbit except the posterior extremity of the superior wall. This specific part (the posterior extremity) is formed by the lesser wing of the sphenoid bone. The superior orbital fissure is also situated posteriorly between the greater wing of the sphenoid bone and the lesser wing of the sphenoid bone. (This fissure also communicates with the middle cranial fossa and also provides a passage for the frontal nerve, lacrimal nerve, oculomotor nerve, trochlear nerve, abducent nerve, nasociliary nerve and lastly the superior ophthalmic vein). A fossa for the lacrimal gland is made by the roof that rises laterally above the level of the rim of the orbit.
The superior orbitals margin’s contour is laterally sharp and medially round. The supraorbital notch also leads from the orbit onto the face at the point of transition. On the frontal bones maxillary process, a small trochlear fossa that is in the anterior medial angle of the orbit gives an attachment to the trochlea.
3.2The Medial wall
The medial wall consists of 4 bones namely: the sphenoid bone, ethmoid bone, lacrimal bone and maxillary bone. Thus the frontal process of the maxilla largely constitutes the medial margin of the orbit. The shorter maxillary process of the frontal bone are also met by the rising of the frontal process of the maxilla. The maxilla itself contributes little more than the rim to the medial orbital wall.
The lacrimal bone, that has an irregular shape, articulates vertically with the frontal process of the maxilla within the orbit. The lacrimal sac’s fossa are framed or formed by both of these bones.
The bony nasolacrimal canal is also continuous with the fossa which also proceed into the inferior nasal meatus below( that is the gap(space) covered by the inferior nasal concha.
Posteriorly the fossa is bounded by a vertical ridge (that is named the lacrimal crest) and from this the orbital surface of the lacrimal bone increases posteriorly to meet the lateral mass of the ethmoid bone.
The upper part of the nasal cavity are separated from the orbit by the lateral mass of the ethmoid bone.
The lateral mass of the ethmoid is pneumatized extensively by the ethmoid air cells and in many skulls this gives the medial wall the appearance or likeness of an unviolated honeycomb.
The thinnest part of the wall is the lamina papyracea which means a “layer as thin as paper”
The frontoethmoidal suture is where the medial wall and the roof of the orbit mets. Across this boundary, the ethmoid air cells of the lateral mass extend upward into the overlying frontal bone.The anterior and posterior ethmoidal foramina open out of the orbit along the suture line into canals that pass horizontally between adjacent air cells. The first leads onto the upper surface of the cribriform plate, the second into the posterior ethmoidal and sphenoid air sinuses.
3.3The Lateral wall
The Zygomatic bone forms the lateral margin and wall of the orbit and the greater wing of the sphenoid bone, completes this lateral wall
The greater wing of the sphenoid also does not articulate with the lesser wing of the sphenoid or the maxilla bone and because of this there is two gaps posteriorly.
The first “gap” is the superior orbital fissure that is located between the lateral wall and the superior wall and the second”gap” is the inferior orbital fissure that located between the floor( also called the inferior wall ) and the lateral wall. These 2 fissures converge in the apex of the orbit of the skull that is just lateral to he optic canal.
The inferior orbital fissure is roughly in line with the zygomatico-orbital foramen that opens in the orbital surface of the zygomatic bone.h
This Zygomatic orbital foramen can be doubled or multiple or it may be so hidden as to be virtually missed by the human eye.
3.4The floor or inferior wall
The maxilla(medially) and the Zygomatic bone(laterally) forms the inferior margin of the orbit that is also named the floor. The floor is also the shortest of all the orbit’s walls)
The whole of the orbit floor is also virtually formed by the maxilla bone and the Zygomatic bone.
The maxilla bone constitutes almost all of the surface of the floor except the extreme lateral angle.The roof of the maxillary air sinus is also formed by the bone of the floor that is very thin.
The floor is completed in front of the apex by the small orbital process of the palatine bone.The inferior orbital fissure is left by the prominent infraorbital groove and this prominent infraorbital groove runs directly forward on the surface of the maxilla.This groove (halfway across the floor of the orbit) becomes continuous with the infraorbital canal( thus the infraorbital groove (and canal) is located in the inferior wall of the orbit and in the maxilla’s orbital plate and it “transfer” the blood vessels and the infraorbital nerve) , which eventually ends in the infraorbital foramen ( on the anterior surface of the maxilla below the orbital margin.
4The neurovascular portals in the orbit’s walls and in the apex( some of them ( the nerves and arteries that go through passages in the orbit and apex) are discussed below.):
From the middle cranial fossa the optic canal opens directly into the apex of the orbit. The ophthalmic branch of the internal carotid artery as well as the optic nerve(that’s covered by all meningeal layers) goes through the optic canal. Between the orbit and the middle cranial fossa the main passageway is the superior orbital fissure.
4.2The Medial wall
The anterior and posterior ethmoidal branches of the nasociliary nerve are transmitted by the anterior and posterior ethmoidel foramina. Corresponding branches of the ophthalmic artery and veins draining to the superior ophthalmic vein also accompanies them.
The supraorbital nerve and vessels are transmitted by the supraorbital notch( or foramen) onto the forehead. The supraorbital nerve is the larger extension of the frontal nerve and the artery is from the ophthalmic artery.
The infraorbital and zygomatic nerves and vessels are “transferred” by the inferior orbital fissure.
The infraorbital nerve and vessels are carried from the inferior orbital fissure to the infra orbital foramen(through this foramen they appear onto the face) , by the infraorbital canal and the infraorbital groove.
The zygomatic orbital foramen transmits the zygomatic vessels and the zygomatic nerves into the zygomaric bone( this happens beyond the lateral end of the inferior orbital fissure)
The Zygomatoc facial foramen is the passageway through which the zygomatico facial nerve and vessel appear on to the head. It may happen that there are two foramens rather than one and this is not unusual. The zygomaticotemporal foramen is also the passageway through which the zygomaticotemporal nerve and vessels emerge into the temporal fossa.
Picture of the orbits
5Possible clinical application in Radiography
In Radiography(orbital Radiogrpahy) injury to they eye or trauma to the eye are detected by orbital x rays. ( Orbital x-rays are x-ray images of the left and right eye sockets in the human skull. It also includes the frontal sinuses and maxillary sinuses). Orbital x-rays are also used to detect changes in the structure of the eye, which may lead to various diseases, as well as to detect foreign bodies in the eye that a opthalmoscope( that’s an instrument that detect foreign bodies in the eye) cannot “spot”
In the Radiography department there is going to be patients who have fractures and diseases of the orbitals. Some of the fractures encountered could be a fracture of the zygomatic arch, displacement of the zygomatico-frontal suture, infraorbital fractures, etc. It will be expected of every qualified Radiographer to take orbital x-ray images of these patients orbitals. To be able to do this a Radiographer must be familiar with complex anatomy of the orbits in the skull and it associated soft tissue . For example if a patients that’s been in a car accident has fractured his orbitals and this resulted in a fracture of the zygomatic arch, then it would be expected of a radiographer to know where this zygomatic arch is located in order to take an orbital x-ray image of that area. A Radiographer must also have sufficient knowledge to be able take an orbital x ray image in the correct angle or to discern when to take several x-rays (from different angles) in order to show the fracture to the zygomatic arch more clearly.
It may happen in serious emergency cases that the Radiographer must firstly look for any damage on the patients face(before he/she can take an x-ray) , and if this radiographer doesn’t know where the facial bones or orbital bones is located then it wouldn’t help taking an image of the wrong facial bone, because that would be of no usage to the doctors seeing the orbital x-rays, because they want to see the fracture in order to make a diagnosis. A doctor may also ask a radiographer if she can see anything abnormal on the x-ray and then again this radiographer must be able to identify the bones and the location of the fractures. Thus it is very important for a radiographer to know where the orbitals lie and of what bones it consists.
From the above mentioned research I conclude that it is very necessary for a radiographer to know the orbits of the eye in order to take valuable x-ray orbital images of this area. The orbitals of the human skull is also of utmost importance , because of the fact that it contains the eye, ( a vital organ that is used in almost every activity of a human being ex. from reading the newspaper to crossing the street) and thus patients that has any damage to this area need to be helped swiftly before a minor orbital injury could proceed to a life threatening injury and results in the patient losing his eye. A Radiographer also pays an important role in “helping” these patients and must know the anatomy of the orbits in order to supply the doctors with the needed medical information that would help doctors to make a diagnosis.
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