Session 6: The Orbit [Complete] Flashcards
What makea up the following of the orbit:
i. Roof
ii. Floor
iii. Lateral wall
Roof: orbital plate of the frontal bone
Floor: orbital plate of the maxilla
Lateral wall: Zygoma and greater wing of sphenoid
What makes up the medial wall of the orbit?
Frontal process of maxilla
Lacrimal bone
Orbital plate of ethmoid bone
Lesser wing of sphenoid
Describe the contents of the Optic canal
Optic nerve (II)
Ophthalmic artery (first branch of the internal carotid artery distal to the cavernous sinus)
Describe the contents of the inferior orbital fissure
V2 [Maxillary nerve] [Specifically the zygomatic nerve which is a branch of V2]
infraorbital vessel
Describe the contents of the superior orbital fissure.
Occulomotor nerve CN3
Trochlear nerve CN4
Abducens CN6
V1 [Ophthalmic nerve/ CN 5]
Opthalmic vein and sympathetic fibres (running with vessels)
In which bones are the foramina of the orbit found?
Optic canal- lesser wing of sphenoid
Superior orbital fissure- between the lesser and greater wings of the sphenoid bone
Inferior orbital fissure- sphenoid bone and maxilla
(posterior wall of the eye too, as the orbital plate of the maxilla runs back! (frontal process of maxlla is one of bones making up medial wall of orbit)
What are the extrinsic muscles of the eye?
The 4 recti muscles
The oblique muscles of the eye
Where is the origin of the 4 recti muscles and where do they insert?
Origin: Common tendinous ring
Insert: Sclera (white of the eye), 5mm behind corneal margin
Describe the nerve supply to rectus muscles
medial, superior and inferior rectus = CN3 (Occulomotor)
lateral rectus muscle = CN6 (Abducens)
What are the names of the 2 oblique muscles of the eye?
inferior oblique muscle and superior oblique muscle
What are the origins of the oblique muscles?
Inferior: orbital surface of maxilla
Superior: body of the sphenoid
What are the insertions of the oblique muscles?
Superior: posterior/superior quadrant of the eye, via trochlea (bony spur in the orbit)
Inferior: posterior/inferior quadrant of the eye
Describe the nerve supply of the oblique muscles
inferior is CN3 (Occulomotor)
superior is CN4 (Trochlear)
What is the origin, insertion and nerve supply of the levator palpebrae superioris (LPS)?
Origin=lesser wing of sphenoid
Insertion= superior tarsal plate and skin of eyelid
Nerve supply= CNIII + Sympathetic nerves to smooth muscle
Why is sympathetic supply of LPS clinically important?
Because in horners syndrome which involves loss of sympathetic ouput to head and neck, there is drooping of the eyelid (=ptosis).
There is also a lack of sweating, constricted pupils and enopthalmos in this condition.
What is the trochlea?
a small bony spur on the medial part of orbit
Describe the isolated contraction of the superior oblique muscle.
down and out *depressor and abductor*
Describe the isolated contraction of the inferior oblique muscle.
up and out *elevator and abductor*
Describe the isolated contraction of the superior and inferior recti.
Superior rectus: elevates and adducts
Inferior rectus: depresses and adducts
Describe the isolated contraction of the lateral and medial rectus muscles.
Lateral rectus muscle: Abducts
Medial rectus muscle: Adducts
How do you test the function of the lateral and medial rectus?
Tracking (moving finger left and right), but remember that version will involve opposite muscle in each eye
How do you test the function of the superior oblique muscle?
They have to adduct that eye, and look down *this removes the effect of the inferior rectus on depression of eye*
How do you test the function of inferior rectus?
you have to abduct the eye and ask them to look down *this removes the effect of the superior oblique on depression of the eye*
How do you test the function of the inferior oblique muscle?
Adduct the eye and look up *removes the effect of superior rectus*
How do you test the function of the superior rectus muscle?
Abduct the eye and look up and up *removes effect of inferior oblique*
Describe the nerves of the orbit
1) Optic nerve [CN2]: provide retinal ganglion cell axons
2) Oculomotor [CN3]: Provides motor fibres to the superior, medial and inferior recti, inferior oblique and to the levator palpebrae superioris. It also provides parasympathetic fibres.
It has 2 rami: The superior branch innervates superior rectus and LPS, and the inferior branch innervates everything else.
Sympathetic nerves from the internal carotid plexus travel with the superior branch of occulomotor to innervate the superior tarsal muscle , which helps maintain opened eyelid (after LPS has opened it)
3) Trochlear [CN4]: Provides motor fibres to superior oblique muscles
4) Abducens [CN6]: Porvides motor fibres to levator rectus
5) Ophthalmic division of trigeminal nerve [CN5]
6) Cilliary ganglion
What are the branches of the ophthalmic division of the trigeminal nerve?
Lacrimal
Frontal [further branches to supratrochlear and supraorbital]
Nasociliary [Further branches to the cilliary ganglion and branches to ethmidal and infratrochlear]
What is the cavernous sinus and where is it located in relation to the orbit?
Describe the order of nerves in the lateral wall of the cavernous sinus and where they enter the orbit.
The cavernous sinus is where the nerves travel, after emerging from the brainstem, just before they’re about to go into the superior and inferior orbital fissure.
It is located postero-medially to the orbit.
So in the order they emerge from the brainstem:
Oculomotor
Trochlear
Abducens (More medially)
Opthalmic branch of trigeminal (V1)
Maxillary branch of the trigeminal (V2).
The oculomotor, trochlear, abducens and V1 then go through the superior orbital fissure.
V2 then goes through the inferior orbital fissure.
Which nerve runs near the internal carotid artery and is thus a bit furhter from the wall of the cavernous sinus?
Abducens CN6
What are the branches of the lacrimal, frontal and nasociliary branches of V1?
Lacrimal (none listed)
Frontal- supratrochlear and supraorbital (which emerges through supraorbital foramen to supply forehea)
Nasociliary- branch to ciliary ganglion, ethmoidal and infratrochlear
Outline the nerves in the preganglionic and post ganglionic parasynpathetic innervation to eye. Which muscle(s) are innervated?
The cilliary ganglion provides parasympathetic fibres.
Preganglionic nerves to cilliary ganglion are supplied from the inferior rami of the the occulomotor nerve
Postganglionic nerves originating from the cilliary ganglion are loctaed in short ciliary nerves which innervate the ciliary muscle and the spinchter pupillae
What does the ophthalmic artery divide into?
central artery of the retina
muscular branches
ciliary arteries
lacrimal artery
supratrochlear artery
supraorbital artery
What do opthalmic veins divide into?
Superior opthalmic veins drain into cavernous sinus (route of infection)
Inferior opthalmic vein drains into the pterygoid plexus
Swelling at the back of the eye (optic disc) is known as? What does it usually indicate?
Swelling of the optic disc is known as papilloedema.
It indicates inreased intracranial pressure
What are the main components which make up the lacrimal system?
Lacrimal gland
Lacrimal sac
Nasolacrimal duct
State the innervation of the lacrimal gland
Parasympathetic secretomotor fibres (CNVII) [Facial] from pterygopalatine ganglion via the zygomaticotemporal nerve (which is a branch of V2)
Also innervated by lacrimal nerves
Where is the lacrimal sac located?
medial canthas of the eye
Where does the nasolacrimal duct drain?
Into the internal meatus of the nose
