The orbit Flashcards
What make up the i. roof ii. Floor iii. lateral wall of the orbit
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
contents of Optic canal
Optic nerve (II) Ophthalmic artery (first branch of the internal carotid artery distal to the cavernous sinus)
Contents of inferior orbital fissure
V2, ifraorbital vessel
Superior orbital fissure
Cranial nerve 3, 4 and 6, and V1. Opthalmic vein and sympathetic fibres (running with vessels)
In which bones are the foramina found
Optic canal- lesser wing of sphenoid
Sup. orbital fissure- between the lesser and greater wings of the sphenoid bone
Inf. orbital fissure- sphenoid bone nad 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)
Where is the origin of the 4 recti, where do they insert
origin Common tendinous ring
insert Sclera, 5mm behind corneal margin
Nerve supply to rectus muscles
medial, super and infer = 3
lateral= 6
2 oblique muscles
inferior and superior
origin of oblique muscles
Inferior: orbital surface of maxilla
Superior: body of the sphenoid
Insertion of oblique muscles
Superior: posterior/superior quadrant, via trochlea (bony spur in the orbit!)
Inferior: post/inferior quadrant
Nerve supply of oblique muscles
inferior is 3, superior is 4
Origin, insertion and nerve supply of levator palpebrae superioris (LPS)
Origin=lesser wing of sphenoid
Insertion= superior tarsal plate and skin of eyelid
Nerve supply= III + sympathetic to smooth muscle
Why is synpathetic 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)….. also lack of sweating, constricted pupil and endopthalmos in this condition
What is the trochlea
a small bony spur on the medial part of orbit
Contraction of superior oblique (isolated)
down and out depressor and abductor
Contraction of inferior oblique (isolatesd)
up and out elevator and abductor
Contraction of superior and inferior recti (isolated)
Superior elevatnes and adducts
Inferior depresses and adducts
How to test lateral and medial rectus
Tracking (moving finger left and right), but remember that version will involve opposite muscle in each eye
How to test function of superior oblique
they have to adduct that eye, and look down this removes the effect of the inferior rectus on depression of eye
How to test 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 to test the function of the inferior oblique
Adduct the eye and look up removes the effect of superior rectus
How to test the function of the superior rectus
Abduct the eye and look up and up removes effect of inferior oblique
Nerves of the orbit
Optic (retinal ganglion cell axons)
Oculomotor (2 rami, motor fibres to MR, SR IR, IO and LPS, parasymathetic fibres)…. oculomotor has superior brainch (innervates superior rectus and LPS, and inferior which does everything else. Sympathetic nerves from the internal carotid plexus travel with the superior branch to innervate the superior tarsal muscle , which helps maintain opened eyelid after LPS has opened it)
Trochlear (Motor fibres to SO)
Abducens (motor fibres to LR)
Branches of the opthalmic division of the trigeminal nerve
Lacrimal, frontal and nasociliary
Order of nerves in the lateral wall of the cavernous sinus (this is the area postero-medial to the orbit so it makes sense!)
This is where the nerves travel, after emerging from the brainstem, just before they’re about to go into the superior and inferior orbital fissure!
SO, in the order they emerge from the brainstem!
Oculomotor, trochlear (then more medially), abducens…..
Then opthalmic branch of trigeminal and maxillary branch of the trigeminal….
From here, oculomotor, trochlear, abducens and V1 go through the superior orbital fissure, but 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 cavernus sinus
abducent
Clinical relevance of the nerves in the cavernous sinus
Infection or cavernous sinus thrombosis can lead to problems with these nerves
Branches of the lacrimal, frontal and nasociliary branch of V1
Lacrimal (none listed)
Frontal- supratrochlear and supraorbital (which emerges through supraorbital foramen to supply forehead!!!!!)
Nasociliary- branch to ciliay ganglion, ethmoidal and infratrochlear
Outline the nerves in the preganglionic and post ganglionic parasynpathetic innervation to eye.
Which muscle(s) are innervated
Preganglionic= in the inferior rami of the 3rd cranial nerve
CILIARY GANGLION
Postganglionic= in short ciliary nerves
Innervating the ciliary muscle and the spinchter pupillae
What does the opthalmic artery divide into
central artery of the retina muscular branches ciliary lacrimal supratrochlear supraorbital
What do opthalmic veins divide into
drains back to superior (cavernous sinus)= ROUTE OF INFECTION
inferior (pterygoid plexus)
What does papilloedema show
Its swelling at back of the eye showing inreased intracranial pressure
State the innervation of the lacrimal gland
parasympathetic secretomotor fibres (CNVII) from pterygopalatine ganglion via zygomaticotemporal (which is a branch of V2) and finally lacrimal nerves
Where is the lacrimal sac
medial canthas of the eye
Where does the nasolacrimal duct drain
Into the internal meatus of the nose
Outline the autonomic control of the eyelid….
What is the effect of the following:
- Damage to the oculomotor nerve
- Damage to sympathetic nerves
Both open the eyelid….
CN3 innervates levator palpabrae superioris…. damage to this nerve results in significant ptosis. This is skeletal muscle so has somatic input
Attached to the LPS is the superior tarsal muscle….
this muscle helps the eyelid to remain open once it has been opened by LPS. It is sometimes referred to as the smooth muscle component of LPS. It is innervated by sympathetic fibres and it will cause a slight ptosis if the sympathetic nerves are damaged e.g. in horners syndrome
