Session 5: Orbit Flashcards
What bones make up the orbit?
- Maxilla
- Lacrimal bone
- Zygomatic bone
- Spheniod bone
- Ethmoid Bone
- Frontal Bone
What makes up the roof of the orbit?
the orbital plate of the frontal bone
What makes up the floor of the orbit?
orbital plate of maxilla
What makes up the lateral wall of the orbit?
- zygoma
- greater wing of the sphenoid
What makes up the medial wall of the orbit?
- Frontal process of maxilla
- Lacrimal bone
- Orbital plate of ethmoid
- Lesser wing of sphenoid
What are the foramina in the orbit?
- optic canal (quite round?)
- inferior orbital fissure
- superior orbital fissure
What passes through the optic canal?
- Optic nerve (II)
- ophthalmic Artery
What passes through the inferior orbital fissure?
- maxillary nerve (V2)
- infraorbital vessles
What passes through the superior orbital fissure?
- ophthalmic nerve (V1)
- oculomotor nerve (III)
- trochlear nerve (IV)
- abducens nerve (VI)
- ophthalmic vessles
- sympathetic fibres
What is a blowout fracture?
- The floor of the orbit can be fractured e.g. squash game injury.
- the eye drops slightly
- causes problems like double vision
- sometimes it has to be surgically fixed
What are the extrinsic eye muscles divided into?
Recti and obliques
What are the 4 recti muscles of the eye?
- superior
- inferior
- medial
- lateral
Where do the recti muscles originate from?
common tendinous ring
Where do the recti muscles insert?
- sclera
- 5mm behind corneal margin
What is the nerve supply to the recti muscles?
- superior, inferior and medial are supplied by CN3 (oculomotor)
- lateral is supplied by CN VI (abducens)
What are the 2 oblique muscles of the eye?
Superior and inferior
Where does the superior oblique originate?
Body of sphenoid (at tendinous ring)
Where does the superior oblique insert?
posterior/superior quadrant via trochlea
Where does the inferior oblique originate?
orbital surface of maxilla
Where does the superior oblique insert?
post/inferior quadrant
What is the nerve supply of the superior oblique?
CNIV (trochlear)
What is the nerve supply of the inferior oblique?
CNIII (oculomotor)
Levator palpebrae superioris (LPS)
- Muscle of upper eyelid
- Origin: Lesser wing of sphenoid
- Insertion: Superior tarsal plate and skin of eyelid
- Nerve supply: III + sympathetic to smooth muscle
What is the muscle of the upper eyelid?
Levator palpebrae superioris (LPS)
trochlea
bony spur in the medial aspect of the orbit
Why is the levator palpebrae clinically important?
- It receives sympathetc innervation
- in Horners Syndrome there is drooping of the eyelid
What eye movement does the contraction of the superior oblique cause?
- away from the midline and down
What eye movement does the contraction of the inferior oblique cause?
out and up
What eye movements do the lateral and medial recti muscles cause?
Medial: adduction towards midline
lateral: abduction away from the midline
What eye movements do the superior and infeior recti cause?
- apart from the elevation / depression they cause adduction and move the eye towards the midline
(BUT: this is re anatomy, not IRL because IRL they do not work in an isolated fashion but together)
How do you test eye muscle (and CN) function?
- lateral and medial rectus: follow finger on horizontal line
- superior oblique: ask the patient to move the eye in and down (this is how you test the trochlear nerve)
Why is following a vertical line not useful for testing the function of the superior and inferior recti muscles?
Because they are not the only ones moving the eye up and down, the obliques do that to. You are not isolating the muscles that way.
-> ask the patient to adduct/abduct the eye to test the function of the superior / inferior ***
optic nerve
- made up of axons from the ganglion cells in the retina
- CNII
Oculomotor Nerve
- CN3
- 2 rami
- motor fibres to: MR, SR, IR, IO & LPS
- parasympathetic fibres
Trochlear nerve
- CNIV
- motor fibres to SO
Abducens nerve
- motor fibres to LR
- CNVI
What are all the nerves of the orbit?
- CNII (optic)
- CNIII (oculomotor)
- CNIV (trochlear)
- CNVI (abducens)
- V1 (ophthalmic, brach of trigeminal): lacrimal and frontal and nasociliary branches
- ciliary ganglion
=> CNs run through the cavernous sinus (not II)
Which nerves run through the cavernous sinus?
- III
- IV
- V1 (ophthalmic)
- V2 (maxillary)
- VI
Which nerve in the cavernous sinus tends to run along the internal carotid artery rather than along the wall?
Abducens (CNVI)
What are the branches of the ophthalmic (V1) nerve?
- lacrimal
- frontal (-> supratrochlear and supraorbital (-> this supplies i.e. forehead))
- nasociliary (-> branch to the ciliary ganglion, ethmoidal, infratrochlear branches)
Ciliary ganglion
- parasympathetic
- preganglionic fibres in inferior ramus of oculomotor
- postganglionic fibres in short ciliary nerves
- sphincter pupillae & ciliary muscle
What are the blood vessles of the orbit?
- ophthalmic artery
- opthalmic vein
Ophthalmic artery
- central artery of the retina
- muscular branches
- ciliary
- lacrimal
- supratrochlear
- supraorbital
Ophthalmic veins
- superior (drains into the cavernous sinus, potential route of infection of the cranial cavity)
- inferior (drains into the pterygoid plexus)
Where is the lacrimal gland?
In the anterolateral superior orbit
What makes up the lacrimal system?
- lacrimal gland
- lacrimal sac (medial canthus of the eye, drains into nose into the inferior meatus of the nose via: )
- nasolacrimal duct
Control of lacrimation
- parasympathetic secretomotor fibres (CNVII) from pterygopalatine ganglion (behind the cheek) via zygomaticotemporal and finally lacrimal nerves
- tears have a protective function (cornea)
What might you suspect if a patient complains of dry eyes?
- problems with the parasympathetic system - no production of tears
