ORBIT & OCULAR ADNEXAE - The Orbit Flashcards
Orbit
What are the bones in the roof of the orbit?
Frontal bone and lesser wing of sphenoid.
What are the bones in the floor of the orbit?
orbital processes of Maxilla, Palatine, Zygomatic bones.
What are the medial wall bones of the orbit?
Medial - MELS.
, frontal process of Maxilla, orbital plate of Ethmoid, Lacrimal and body of the Sphenoid bones.
What are the lateral bones of the orbit?
Zygomatic and greater wing of sphenoid.
How does the sphenoid bone form? How was it made embryologically?
From cartilaginous precursors which ossify.
What are the parts of the sphenoid bone (4)
- Body - contains sella turcica
- Greater wing - contributes to facial skeleton
- Lesser wing - separates anterior and middle cranial fossa
- Pterygoid Process
What are the main structures in the body of the sphenoid? (4)
- Sphenoid sinuses -
- Sella turcica - contains tuberculum sellae (anterior wall), hypophyseal fossa (deepest part where pituitary gland is located), dorsum sellae (posterior wall)
- Chiasmatic groove - sulcus formed by optic chiasm
- Clinoid processes (anterior and posterior) - serve as attachments for tentorium cerebelli
What holes are found within the sphenoid bone (5)
ROSSO
- Optic canal
- SOF
- Foramen rotundum
- Foramen ovale
- Foramen spinosum
What does the greater wing of the sphenoid contribute to in terms of structures? (3)
- Floor of middle cranial fossa
- Lateral wall of the skull
- Lateral wall of orbit.
What does the lesser wing of the sphenoid contribute to in terms of structure? (2)
- Roof of the orbit
- Lateral border of optic canal
What do the pterygoid process contain? (2)
Medial pterygoid plate - supports opening of nasal cavity
Lateral pterygoid plate - site of origin of medial and lateral pterygoid muscles
What does the temporal bone contribute to - the orbit or the skull?
The lower lateral walls of the skull. (does not form the orbit)
What are the 5 components of the temporal bone?
- Squamous
- Zygomatic process
- Tympanic
- Styloid process
- Petromastoid
What does the squamous part of the temporal bone articulate with?
Anteriorly - sphenoid bone
Laterally - parietal bone
Which muscle is connected to the zygomatic process/arch?
The masseter
Which hole does the tympanic part of the temporal bone form?
external auditory meatus of the external ear.
What attaches to the styloid process of the temporal bone?
stylomandibular ligament of TMJ.
What does the petromastoid of the temporal bone contain? (2)
- Mastoid process - site of attachment of sternocleidomastoid
- Mastoid air cells - resovoir of air equalising pressure of middle ear in case of auditory tube dysfunction.
What are the 3 parts of the ethmoid bone?
- Cribiform plate (crista galli –> falx cerberi attachment)
- Perpendicular plate
- Ethmoidal air cells
Which bone contains the supraorbital margin in the orbit?
Frontal bone
Which bones is the infraorbital margin of the orbit formed by?
Zygomatic and maxilla.
What is the volume of the orbit in cm2
30cm3
What is the depth of the orbit in mm
40-50mm
What does the orbital roof separate the orbit from? I.e. cranial structure
The anterior cranial fossa
What structure does the superior orbital rim contain and what structures pass through it
The superior orbital notch - a notch which transmits supraorbital nerve and vessels which supply the forehead.
What structure is the largest part of the medial orbital wall?
The orbital plate of ethmoid - separates orbit from ethmoid sinuses
Where is the frontoethmoidal suture line and what is its clinical significance?
Within the anterior cranial fossa, it Marks approximate level of ethmoidal sinus roof in medial orbital wall-
any dissection above this line should be avoided as it will expose the cranial cavity
Where are the anterior and posterior ethmoidal foramina located?
behind medial orbital rim at junction of medial wall and roof
Where is the lacrimal fossa located? Which bones are involved? What does it contain?
depression in the inferomedial orbital rim formed by ftrontal process of maxillary and lacrimal bone.
Holds the lacrimal sac, tears from the sac drain through the nasolacrimal duct into the nasal cavity.
What is the thickest wall of the orbit?
Lateral wall
What is whitnall’s tubercle? Where is it located?
Small prominence on the orbital surface of the zygomatic bone
Attachment site for the 5 Ls
found on the zygomatic bone, inferior to frontozygomatic suture
What are the attachments to whitnall’s tubercle? (5)
THE 5 Ls
- Lateral rectus check ligament (thickened fascia/sheath over lateral rectus)
- Lateral palpebral ligament (supports tarsal plate with orbital septum by tethering them to lateral margin of orbit)
3.** Lockwood suspensory ligament** (forms hammock inferior to eyeball connecting lateral and medial check ligaments)
4.** Levator aponeurosis** (anterior extension of LPS to tarsal plate, fibrous in nature)
- Lacrimal gland fascia
WHITNALLS TUBERCLE AND LIGAMENT IS NOT THE SAME THING.
Which structure weakens the orbital floor?
inferior orbital fissure
What is the difference between the infraorbital groove and the infraorbital foramen?
A groove on the floor of the orbit that transmits the infraorbital nerve, artery, and vein. The groove continues forward into the maxilla as the infraorbital canal, which ends at the infraorbital foramen.
Which sutures are located in the medial wall of the orbit and what are their roles (2)
- superiorly - frontoethmoidal suture (medial wall articulates with orbital roof) marks point to not breach cranial cavity - can be breached in ethmoid sinus surgery and blunt orbital trauma
- inferiorly - maxillo-ethmoidal suture - prevents hypoglobus during orbital decompression
What is the lamina papyracea?
Paper thin part of medial wall - forms majority of medial wall and facilitates spread of infection (ethmoidal sinusitis –> orbital cellulitis)
Where does whitnall’s ligament attach to?
Lateral orbital wall just above the whitnall’s tubercle.
What bones form the medial margin of the orbit?
- Maxillary process of frontal bone
- Lacrimal crest of frontal process of maxilla.
What epithelium lines the lacrimal sac?
Columnar epithelium.
Cartilage is found on which bone of the orbit?
Frontal bone - the trochlea is situated on superior nasal aspecct of the frontal bone.
