L42 - Orbit Flashcards
Define the bones that form the medial wall of the orbit?
Medial wall:
a. Frontal process of Maxilla
b. Lacrimal bone
c. Orbital plate of ethmoid
d. Body of sphenoid
Bones that form the Inferior wall of orbit?
a. Medial part: Maxillary bone
b. Lateral part: Zygomatic bone
c. Posterior part: Palatine bone
Bones that form the Lateral wall of orbit?
a. Anterior part: zygomatic bone
b. Posterior part: Greater wing of sphenoid
Bones that form the Superior wall of orbit?
a. Anterior part: Frontal bone
b. Posterior part: Lesser wing of sphenoid
Define the divisions of the orbital fissure?
- Divided into the superior and inferior orbital fissure
- Separated into 3 segments by the annulus of Zinn
Which part of the orbit is most prone to blowout fracture?
posteromedial aspect of orbital floor (thin)
where infraorbital nerve passes through infraorbital foramen
Which bone forms the orbital fissure?
Sphenoid bone
Superior orbital fissure: Extraconal (outside annulus of Zinn) content?
Lacrimal nerve (V1)
Frontal nerve (V1): Supraorbital nerve Supratrochlear nerve
Trochlear nerve (CN IV): superior oblique muscle
Superior ophthalmic vein
Intraconal (inside annulus of Zinn) superior orbital fissure content?
Nasociliary nerve (V1): branches:
- Infratrochlear nerve
- Long ciliary nerves
- Short ciliary nerves
Abducens nerve (CN VI): lateral rectus muscle
Oculomotor nerve (CN III): Superior division Inferior division
Describe the origins of the Long and Short ciliary nerves?
Long ciliary nerves (postsynaptic/postganglionic sympathetic fibers from superior cervical ganglion)
Short ciliary nerves (postsynaptic parasympathetic fibers from oculomotor nerve, synapse at ciliary ganglion)
The optic nerve passes through the superior orbital fissure inside the annulus of Zinn. T or F?
False
Inside annulus of Zinn but passes outside the sup. orbital fissure through optic canal
Content of the Inferior orbital fissure?
Inferior ophthalmic vein
Maxillary nerve (V2) and branches:
- Zygomaticotemporal nerve
- Zygomaticofacial nerve
- Infraorbital nerve
Which nerve passing through the orbital fissures cause numbness that radiate to teeth when damaged?
Infraorbital nerve (through inferior orbital fissure)
Define the sensory nerve supply of the orbit?
Optic nerve: for vision
V1: superior orbital sensation, Upper eyelids
- Nasociliary n.
- Ant + post. Ethmoid,
- Frontal n.,
- Supraorbital n.
- Lacrimal n.
V2: inferior orbital sensation, lower eyelids
- Infraorbital nerve,
- zygomatic n.
Motor supply of the orbit?
- CN III, IV, VI for Extraocular muscles
- CN III: opening of eyelids (levator palpebrae superioris)
- CN VII: for eye closure and brow movement.
Define the blood supply to the anterior segment of the eyeball?
- Iris + ciliary body:
Long Post ciliary artery (runs through the choroid) anastomose with Ant. Ciliary Artery (runs to anterior segment through extraocular muscles). - Forms major and minor arterial circles on the iris
Define what is supplied by the Long posterior ciliary artery?
Recurrent branches supply the choroid anterior to equator
Anastomose with Anterior ciliary artery and Short Posterior Ciliary artery
Define what is supplied by short posterior ciliary artery?
Supply choroid posterior to equator + Optic disc
Define what is supplied by Anterior ciliary artery?
7 arteries, 2 for each rectus muscle except Lateral Rectus (only 1)
Supply sclera, conjunctiva, iris
Define the posterior arterial supply of the eyeball?
Retina: Central Retinal artery (runs along optic nerve)
Fovea avascular zone = no capillaries over fovea
Choroid:
- Short posterior ciliary artery (anastomose with long posterior ciliary a.)
What forms the blood retinal barrier?
Tight junctions of the Retinal Pigmented epithelium
Separate choroidal and blood circulation = immune privileged site
Venous drainage of eyeball?
Retina: Central retinal vein
Choroid: 4 vortex veins (2 on each side) Exit eyeball posterior to equator
- Superior Vortex + central retinal vein»_space; superior Ophthalmic vein»_space; supraorbital vein + facial v.
- Inferior vortex vein»_space; inf. Ophthalmic v.»_space; Ophthalmic v/pterygoid venous plexus/Cavernous sinus
Define Hyphema
bleeding that fills the anterior segment of the eye
Explain why Central retinal artery occlusion results in a Cherry red spot?
When the retinal circulation is occluded by a emboli, the choroidal circulation is unaffected
whole retina is pale because of a lack of retinal circulation. But the thinnest part at the fovea shows through as a “cherry red spot” of the underlying choroidal ciruclation
List the cavities located around the orbit?
Superior = Anterior cranial fossa Medial = Nasal cavity and ethmoid air cells Inferior = Maxillary sinus Postero-Lateral = Middle cranial fossa
Define the sinuses that lie medial to the orbit?
Anterior, middle and posterior ethmoid sinus
Middle meatus
List the nerves and arteries that pierce the medial orbit wall
Ant. and post. ethmoid nerve
Infratrochlear n.
Terminal branch of opthalmic artery
List the sinuses that lie inferior to the orbit?
Maxillary and palatine sinus
List the vessels and nerves that are found on the lateral wall of the orbit?
Lacrimal nerve and vessels
Zygomatic nerves and branches
List the structures found at the superior wall of the orbit?
Periorbital fat Frontal nerve Trochlear nerve Levator Palpebrae superioris Superior rectus Superior oblique Lacrimal gland
List the veins that drain the orbit?
Superior = Supratrochlear and Supra-orbital veins
Medial = Opthalmic and angular v.
Lateral = Superficial temporal v.
Compare the action of the Superior and inferior oblique muscles?
obliques act opposite to their names + abduct
Superior oblique: Intorsion, Depression , Abduction
Inferior oblique:
Extorsion, Elevation , Abduction
List the actions of all the rectus musces?
MR - Adduction
SR - Elevation, Adduction, Intorsion
LR - abduction
IR - Depression, Adduction, Extortion
Role of suspensory ligaments of eyeball?
suspends the eyeball of the orbital space
Act as fulcrum/ pulleys for extraocular muscles
Function of eyelids?
- eyelashes to protect from dust, foreign body, and perspiration
- To regularly spread tears and other secretions to keep the eye moist
- Blink and menace reflex protect the eye from foreign body
Compare asian with caucasion eyelids?
Asian:
Lower lid crease
Smaller tarsal plate (cartilage)
Lower orbital fat
50% people have single lid crease
Blood supply of eyelids?
Marginal and Peripheral/ Superior and inferior palpebral arterial arcades
= anastomosis between the facial artery and branches + medial and lateral palpebral arteries
Define the nerves that provide sensation to parts of the eyelids?
Superior eyelid = Supraorbtal and Supratrochlear
Inferior eyelid = Infraorbital nerve
Venous drainage of eyelids?
Superior and inferior palpebral veins
Branches of the facial vein: angular, anterior facial (medial)
Superficial temporal vein (lateral)
Supraorbital and Supratrochlear veins (superior)
Drainage of tears?
Superior and inferior puntum > Upper and Lower Lacrimal canaliculus > Common canaliculus > Lacrimal sac > Nasolacrimal duct > Opening of nasolacrimal duct into Inferior nasal meatus
What maintains tears from quickly evapourating?
Meibomian glands at the lid margin makes meibom to prevent tears from quickly evaporating
Pathogenesis of Dacrocystitis?
Dacrocystitis occurs when the Nasolacrimal duct is blocked. Bacteria infect
