TBL29 - Orbit Flashcards
What occupies the anterior portion of the orbit? What does the posterior portion of the orbit contain and what are these structures surrounded by?
1) The eyeball occupies the anterior portion of the orbit
2) The posterior portion contains the optic nerve (CN II) and extraocular muscles, which are surrounded by white fat
How are the medial orbital walls oriented in respect to each other (right & left) and how are the lateral orbital walls oriented in respect to each other? What are the lateral walls formed by and what are the medial walls formed by? What occupy the core of the ethmoid bones and what part of the nasal cavity do the ethmoid bones contribute to?
1) The medial orbital walls are parallel to each other and the lateral walls form a right angle to each other
2) The lateral walls are formed by the thick zygomatic bones and the flat greater wings of the sphenoid bone; and the medial walls are formed mainly by the ethmoid bones
3) Ethmoid cells occupy the core of the ethmoid bones, which also contribute to the lateral walls of the nasal cavity
What is the thin floor of the orbit mainly formed by? What is the floor of the orbit also the roof of? What is the roof of the orbit mainly formed by? What is the roof of the orbit also the floor for?
1) The thin floor of the orbit is formed mainly by the maxilla
2) The floor is also the roof of the maxillary sinus
3) The roof of the orbit is formed mainly by the frontal bone
4) The roof is also the floor of the anterior cranial fossa
What is the optic canal just medial to? What does the inferior orbital fissure demarcate?
1) The optic canal is just medial to the superior orbital fissure
2) The inferior orbital fissure demarcates the floor and lateral wall of the orbit
What is a “blowout” fracture of the orbit and why does exophthalmos often result?
1) Indirect traumatic injury that displaces the orbital walls is called a “blowout” fracture
2) Orbital fractures often result in intra orbital bleeding, which exerts pressure on the eyeball, causing exophthalmos (protrusion of the eyeball)
Why can tumors of the middle cranial fossa cause exophthalmos?
1) Tumors in the orbit produce exophthalmos
2) The easiest entrance to the orbital cavity for a tumor in the middle cranial fossa is through the superior orbital fissure
Recognize the palpebral fissure between the upper and lower eyelids, the palpebral and bulbar conjunctiva, and the superior and inferior conjunctival sacs and fornices.
Look at image
What is conjunctivitis?
Bacterial and viral infections and allergic responses often lead to conjunctivitis —inflammation of the bulbar or palpebral conjunctiva
What is each eyelid strengthened by? What does the levator palpebral muscle attach to? What constitutes the distal part of the levator palpebral muscle, what is this muscle designated as, and what does it attach to?
1) Each eyelid is strengthened by bands of dense connective tissue designated the tarsus
2) The levator palpebral muscle attaches to the dermis of the superior eyelid
3) Smooth muscle, which constitutes the distal part of the levator palpebral, is designated the superior tarsal muscle that attaches to the tarsus
What is the levator palpebral muscle opposed by most of the time and what does it serve as for the superior half of the orbicularis oculi? Define the function of the levator palpebral muscle.
1) The levator palpebral muscle, which is opposed most of the time by gravity, serves as the antagonist of the superior half of the orbicularis oculi
2) The levator palpebrae superioris muscle elevates and retracts the upper eyelid
Where is the lacrimal gland positioned within the orbit? Where does its secretion (lacrimal fluid) spread across and to? What do the puncta drain, what do they drain into, and what does this structure empty onto?
1) The lacrimal gland is positioned superolaterally in the orbit
2) Its secretion (lacrimal fluid) spreads across the eyeball to the medial angle of the eye
3) Puncta (arrows) in the medial aspect of the lower eyelid drain lacrimal fluid into the nasolacrimal duct that empties onto the epithelial surface of the inferior nasal meatus
Recall the course of the presynaptic and postsynaptic parasympathetic fibers that stimulate the secretion of lacrimal fluid.
Facial nerve –> Geniculate ganglion –> Greater petrosal nerve (presynaptic) –> Petrosal foramen of temporal bone –> Middle cranial fossa –> Join with Deep petrosal nerve of carotid plexus to enter the pterygoid canal and form the nerve of the pterygoid canal –> Synapse on pterygopalatine ganglion –> Postsynaptic fiber of greater petrosal nerve travels with the zygomatic nerve of the maxillary nerve through the inferior orbital fissure –> In the orbit the greater petrosal postsynaptic fiber joins the lacrimal nerve, a branch of the ophthalmic nerve (V1), to join the gland
