Orbit Flashcards
What are the dimensions of the orbit?
45-55mm ant-post
35mm sup -inf
40mm med to lat
Volume 30ml
Describe the features of the orbital rim
Acrus marginalis Attachment of orbital septum Anterior "boundary" of orbit Incomplete circle Discontinuous at fossa for lacrimal sac
How many bones make up the orbit?
7 bones
Which bones make up the boney orbit?
Roof: frontal and lesser wing of sphenoid
Medial wall: maxillary, lacrimal, ethmoid and sphenoid
Floor: maxillary, zygomatic, palatine
Lateral wall: greater wing of sphenoid, frontal
Which sinuses surround the orbit?
Frontal sinus
Ethmoidal sinus
Maxillary sinus
Sinus infections can tract into orbit
How does the orbit relate to the intracranial space?
Via the orbital apex
Orbital canal
Superior orbital fissure into cavernous sinus
What are the lymphatics of the orbit?
None
What lies within the orbit?
Globe Optic nerve Extraocular muscles Vessels Nerves Lacrimal gland Orbital fat Periosteum
What is the first branch of the internal carotid artery within the cavernous sinus?
Ophthalmic artery
Within which bones do the optic canal, superior orbital fissure and inferior orbital fissure sit?
Optic canal: sphenoid
Superior orbital fissure: bound by lesser +greater wound of the sphenoid
Inferior orbital fissure: bound by greater wing of sphenoid, zygomatic, maxilla and palatine bone
Which muscles originate at the orbital apex?
All extraocular muscles except the inferior oblique
What travels through the optic canal?
Optic nerve
Ophthalmic artery
Sympathetic fibres
What travels through the superior orbital fissure?
CN III superior and inferior divisions
CN IV
CN VI
CN V branches (lacrimal V1, frontal V1, nasociliary V1)
Superior ophthalmic vein
Anastomosis of orbital branch of MMA and recurrent branch of lacrimal artery
What travels through the inferior orbital fissure?
CN V branches (infraorbital V2, zygomatic V2)
Parasympathetics to lacrimal gland
Inferior ophthalmic vein
Where is the ciliary ganglion found in the orbit?
Lateral to ophthalmic nerve
Hanging off oculomotor nerve
How do sympathetic and parasympathetic nerves enter the orbit?
Sympathetic: synapse in superior cervical ganglion
Ascends along ICA and enter orbit on ophthalmic artery. Pass through ciliary ganglion without synapse
Parasympathetic: Originate in Edinger westphal. Travel through CN III. Synapse in ciliary ganglion
What are the actions of the autonomic nervous system on the orbit?
Sympathetic: Dilate pupil and lift eyelid via Muller’s muscle
Parasympathetic: constrict pupil and causes accommodation
What are the vessels of the orbit?
Internal carotid artery Ophthalmic artery Central retinal artery Short posterior ciliary artery Long posterior ciliary artery Anterior ciliary artery Great circle of iris
What is the venous supply of the orbit?
Superior and inferior ophthalmic vein, drains into cavernous sinus and pterygoid plexus
No valves
Blood flows back from eye into the meninges
What lies in the suprorbital foramen?
Supraorbital nerve and artery
What lies in the infraorbital canal
Infraorbital nerve and artery
What travels through the anterior ethmoid foramen?
Anterior ethmoidal nerve and artery
What travels through the posterior ethmoidal foramen?
Posterior ethmoidal nerve and artery
What travels through the trochlear fossa?
Trochlea of superior oblique
Why is it relevant that the visual axis and orbital axis are not aligned?
The extraocular muscles are at work even to keep the eye facing straight ahead
Orbital axis is 23 degrees nasal to visual axis
What are the three nerves for the motor supply of the orbit?
Oculomotor
Trochlear
Abducens
What is the sensory nerve supply of the orbit?
Trigeminal nerve V1 and V2
Optic nerve
What is the autonomic supply of the orbit?
Sympathetic -superior cervical ganglion Parasympathetic -ciliary ganglion -pterygopalatine ganglion
Describe the course of the occulomotor nerve
Arises in anterior midbrain
Pierces dura on lateral side of posterior clinoid process
Travels anteriorly along lateral wall of cavernous sinus
Divides into smaller superior oculomotor division and larger inferior oculomotor division at cavernous sinus
Enters through superior orbital fissure within tendinous ring
Travels near posterior communicating artery
What does the superior division of the oculomotor nerve supply?
Superior rectus
Levator palpebrae superioris
What does the inferior division of the oculomotor nerve supply?
Medial rectus
Inferior rectus
Inferior oblique
Branch to inferior oblique also supplies parasympathetic fibres to ciliary ganglion
Describe the course of the trochlear nerve?
Arises in midbrain and exits posterior surface below inferior colliculus
Decussates to contralateral side
Pierces dura below free border of tentoroum cerebelli, close to posterior clinoid process
Travels anteriorly in lateral wall of cavernous sinus
Enters through superior orbital fissure and enters superior oblique
Describe the course of the abducens
Emerges below pons and medulla
Pierces arachnoid and dura lateral to dorsum sella of sphenoid bone
Travels anteriorly within cavernous sinus inferolateral to internal cartoid artery
Enters through superior orbital fissure within tendinous ring
Enters lateral rectus
Describe the course of the trigeminal nerve in the orbit
Brainstem in posterior cranial fossa
Large sensory root and a small motor root
Sensory root bodies lie in trigeminal ganglion
3 branches emerge from anterolateral surface of the ganglion
Describe the course of the ophthalmic nerve V1
Superior and smallest branch of trigeminal
Arises from anteromedial surface of trigeminal ganglion
Passes anteriorly to enter lateral wall of cavernous sinus
Splits into 3 branches in the cavernous sinus; lacrimal, facial, nasociliary
Describe the course of the lacrimal nerve
Enters orbit through lateral superior orbital fissure superolateral to frontal and trochlear nerves
Enters outside the tendinous ring
Courses anteriorly along upper border of lateral rectus
Innervates the lacrimal gland, conjunctiva and lateral skin of the upper eyelid
Receives a branch from zygomaticotemporal nerve with parasympathetic fibres
Describe the course of the frontal nerve in the orbit
Largest branch of V1
Enters superior orbital fissure
Passes beneath orbital roof along upper surface of levator palpebrae superioris
Midway along orbit divides into supraorbital and supratrochlear nerve
What does the supraorbital nerve innervate?
Leaves orbit via supraorbital notch
Innervates skin and conjunctiva of lateral upper eyelid, skin of forehead posteriorly to scalp vertex and frontal sinus mucosa
What does the supratrochlear nerve innervate?
Pierces orbital septum and turns upwards deep to orbicularis
Supplies skin and conjunctiva of medial upper eyelid and medial forehead skin
Describe the course of the nasociliary nerve
Enters orbit via medial superior orbital fissure
Within tendinous ring
Crosses optic nerve with ophthalmic artery to reach medial orbital wall
Passes forward on upper border of medial rectus muscle
Divides into anterior ethmoidal nerve and infratrochlear nerve
What does the anterior ethmoidal nerve supply?
Passes through anterior ethmoidal foramen
Supplies anterior ethmoidal air cells
Enters nasal cavity via crista galli and enters nasal cavity
Supplies nasal mucosa via internal nasal nerves and skin of nasal tip via external nasal nerve
What does the infratrochlear nerve supply?
Travels along border of medial rectus
Joined by branch of supratrochlear nerve
Passes beneath trochlea and pierces orbital septum
Supplies lacrimal sac, conjunctiva, medial skin of upper and lower lids
Where do the long ciliary nerves come from?
Nasociliary nerve
Which branch of the nasociliary nerve is sometimes missing?
Posterior ethmoidal nerve
Describe the course of the maxillary nerve
Enters lower part of lateral wall of cavernous sinus
Enters pterygopalatine fossa via foramen rotundum. Gives off zygomatic nerve.
Enters orbita via inferior orbital fissure
Continues as infraorbital nerve
Exits via infraorbital foramen
2 branches connect to pterygopalatine ganglion within pteryopalatine fossa
What does the maxillary nerve V2 innervate?
Conjunctiva and skin of lower eyelid, cheek, upper lip and nasal ala
Describe the course of the zygomatic nerve (branch of maxillary V2)
Enters orbit via inferior orbital fissure
Passes anteriorly along lateral orbital wall
Divides into zygomaticotemporal and zygomaticofacial nerves
Zygomaticotemporal: lateral skin of forehead
Zygomaticofacial: cheek skin
How does the sympathetic nerve supply reach the orbit?
Originates in superior cervical ganglion
Travels via internal carotid plexus
Pass uninterrupted through the ciliary ganglion
Enter eye via long and short ciliary nerves-> dilate iris
Innervates Muller’s muscle and lacrimal gland (via greater petrosal nerve)
How does parasympathetic supply reach the orbit?
Arises from Edinger-Westphaal nucleus of oculomotor nerve
Fibres reach ciliary ganglion via branch to inferior oblique from the oculomotor nerve
Enters eyeball via short ciliary nerves - accomodation and pupil constriction
Also arises in lacrimatory nucleus of facial nerve
Travels to pterygoid ganglion via nervus intermedius and greater petrosal nerve
Fibres hitchhike along zygomaticotemporal nerve (V2) to increase lacrimation via lacrimal nerve
What is the contents of the tendinous ring?
One canal, several orbital nerves in one annulus Optic canal Superior div. occulomotor nerve Nasociliary nerve Inferior division occulomotor nerve Abducens nerve
Which nerves pass through superior orbital fissure?
Lacrimal Frontal Trochlear Superior division of oculomotor Abducens Nasociliary Inferior division of oculomotor
What is the common origin of rectus muscles?
Annulus of Zinn
Superior orbital fissure
Forms muscle cone
Where do the nerves pierce the rectus muscles?
Middle and posterior 1/3 of muscle
Except lateral rectus +inferior oblique where nerve enters halfway along
Origin
Insertion
Size
Superior rectus
Origin: annulus of Zinn and dural sheath of optic nerve
Inserts: 7.7mm behind limbus onto sclera
Size: 42mm length 9mm width
Relations of superior rectus
Superior: levator palpebrae superioris (2 muscles connected by a band of connective tissue), frontal nerve, roof or orbir
Inferior: optic nerve, ophthalmic artery, nasociliary nerve, tendon of SO crosses
Lateral: lacrimal artery and nerve
Nerve supply superior rectus
Occulomotor CN3
Superior division (only rectus muscle to be supplied by superior division)
Nerve also ascends to supply levator palpebrae superioris
Blood supply superior rectus
Lateral muscular branch of ophthalmic artery
Actions of superior rectus
Elevates (strongest in abduction)
Adducts
Intorts
Origin
Insertion
Size
Inferior rectus
Origin: annulus of zinn
Insertion: 6.5mm from limbus
Length: 40mm Width 9mm
Which muscles are attached to the suspensory ligament?
Inferior rectus is attached to fascial sheath of inferior oblique, which is then attached to suspensory ligament
This sheath is attached to lower eyelid
Relations of inferior rectus
Superior: oculomotor nerve, optic nerve, orbital fat and eyeball
Inferior: infraorbital nerve and vessel and maxillary sinus. Inferior oblique is inferior at point of piercing the eyeball
Nerve supply inferior rectus
Oculmotor
Inferior division
Blood supply inferior rectus
Medial muscular branch of ophthalmic artery
Action inferior rectus
Depresses (strongest at abduction)
Adducts
Extorts
Origin
Insertion
Size
Medial rectus
Origin: annulus of Zinn and dural sheath of optic nerve( so pain when optic nerve inflammed)
Inserts: 5.5mm from limbus
Largest and thickest but not longest muscle- length 40mm width 10mm
relations of medial rectus
Superior: superior oblique, nasociliary nerve, ophthalmic artery
Inferior: floor of orbit
Lateral: central orbital fat and optic nerve
Nerve supply medial rectus
Oculomotor nerve
Inferior division
Blood supply medial rectus
Medial muscular branch of ophthalmic artery
Action of medial rectus
Adduction
Origin
insertion
Size
Lateral rectus
O: annulus of Zinn and greater wing of sphenoid
I: 6.9mm from limbus via tendon 8.8mm long
Length: 48mm
Relations of lateral rectus
Sup: lacrimal nerve and artery
Inf: Inferior oblique tendon and floor of orbit
Medial: abducens nerve, ciliary ganglion, ophthalmic artery and nerve to IO
Lateral: lacrimal gland
Nerve supply lateral rectus
Abducens
Inserts in the middle of the muscle
Blood supply lateral rectus
Muscular branch of ophthalmic artery
Lacrimal artery
Action of lateral rectus
Abduction
Origin
Insertion
Size
Superior oblique
O: Lesser wing of sphenoid just medial to optic canal and tendinous ring
Gives rise to a rounded tendon
Tendon travels through a trochlea of fibrocartilage which is attached to the trochlea fossa/frontal bone
After passing through trochlea tendon passes down and backwards laterally (55 degrees)
Travels below superior rectus and inserts behind equator of the eyeball laterally
Insertion length 11mm.
Relations of superior oblique
Superior: roof of orbit and supratrochlear nerve. SR lies above after piercing eyeball fascial sheath
Inferior: OPhthalmic artery and branches, nasociliary nerve
Nerve supply superior oblique
Trochlea nerve
Enters superior surface of muscle close to the origin
Blood supply superior oblique
Superior muscular branch of ophthalmic artery
Action superior oblique
Intorsion
Depression
Abduction
Origin
Insertion
Inferior oblique
O: maxilla bone/floor of orbit lateral to nasolacrimal canal
Passes laterally, posteriorly and superiorly
I: posterior lateral aspect of eyeball behind equator (near macula)
Relations
Inferior oblique
Sup: inferior rectus + eyeball
Inferior: floor of orbit and infraorbital nerve and vessel
Nerve supply inferior oblique
Occulomotor
Enters muscle at midpoint
Blood supply inferior oblique
Infraorbital artery and medial muscular branch of ophthalmic artery
Action inferior oblique
Extorsion
Elevates
Abducts
How does the center of rotation of the eyeball remain constant in relation to the orbital pyramid?
Pulleys act as mechanical origins of rectus muscles
Pulleys are rings of collagen 2mm around the EOM
Elastic fibres in and around pulleys provide extensibility
Eye movements become smooth
Describe the embryology of the occular muscles
Prechordal and paraxial mesoderm
7 weeks: 4 recti differentiate
8 weeks: Levator palpebrae superioris differentiates from SR
3 months: levator palpebrae superioris grows laterally on higher plane
Posterior recession of the tendon from the limbus occurs. Tendons reach adult location between 18 months and 2 years
Why are ocular muscles resistant to dystrophy?
Unique gene expression
Embryonic and cardiac muscle proteins +high enzyme levels lead to improved calcium homeostasis and reduced oxidative stress. These muscles are resistant to many forms of muscular dystrophy
Describe the histology of EOM
2 compartments (global layer and orbital layer)
Global layer is located adjacent to globe in rectus muscles and in the centre core of oblique muscles. Contains one MIF and 3 SIFs. Controls oculorotatory tension
Orbital layer contains 80% SIF and 20% MIFs. Does not insert onto eyeball but onto connective tissue pulleys. Controls pulling direction
What is the difference between multiple innervated fibres and single innervated fibres
SIF: fast, twitch generating, resembling skeletal muscle fibres
MIF: do not conduct action potentials
What are the rules of eye muscles and movements?
Recti: adduct (except lateral rectus)
Obliques: abduct and vertically oppose
Superiors: Intort
Inferiors: extort
What are the possible pathologies within the brain, cranial nerves, NMJ and muscles that affect ocular movements?
Brain: primary strabismus syndromes (esotropia, exotropia)-> most common
CN: palsies
NMJ: Myasthenia gravis
Muscles: thyroid eye disease
What is the fascial sheath of the globe called and what ligament does it form?
Tenon’s capsule
Expansions of medial and lateral recti form check ligaments
Inferiorly, thickening of the IR and IO form the suspensory ligament of lockwood
How can medial and lateral rectus be used surgically to elevate or depress the eye?
When displaced vertically can have some elevation or depression
What are the two different fibres present in the superior oblique?
20% anterior intorting fibres
80% posterior depressing fibres
Important surgically
Describe EOM fibres
Long, run length of the muscle
Nuceli are underneath plasma membrane
Contain myofibrils
Epimysium covers the muscle, endomysium covers individual nerve fibre
What do the check ligaments do and why are they special?
Support globe during eye movement
Dense collagenous bridge
Run between distal 3rd of medial/lateral recti and periosteum of orbital wall
Nil smooth muscle or innervation in check ligament
What does the suspensory ligament of lockwood do?
Runs from sheaths of inferior rectus and inferior oblique to the orbital margin
Supports globe like a hammock
If intact when eye is fractured, eye will not sag
How does the orbital fascial system vary from anterior to posterior?
Well developed anteriorly around the globe
Poorly developed posteriorly near apex
Describe what happens to the connective tissue around the globe during a blowout fracture
Connective tissue is pushed through a boney wall defect entrapping intraocular muscles
Which imaging is best for differentiating intraconal and extraconal structures?
T1 weighted MRI
Describe the rectus muscle connective tissue sleeves in tenons capsule
Connective tissue surround recti, attached to orbital walls
Contains smooth muscle cells
Listing’s law (optic orientation)
How do we know that the ocular connective tissue system has well defined planes?
Tumours grow within tissue planes
intraconal or extraconal
Where do the fibrous septa of the eye run?
From the levator superioris and superior rectus to the periorbita of the roof
Medial and lateral check ligamanets connect horizontal rectus muscles to the periorbita
Arcuate expansion of ligament of Lockwood from inferior globe to orbital floor
Band from inferior oblique to medial check ligament
What is the extraconal space bound by?
Periorbita of orbital wall externally
Fibrous sheaths envelope extraocular muscles with intermuscular membrane internally
Closed anteriorly by the orbital septum and tarsal plates of the eyelids
Levator aponeurosis lies in extraconal space
Small recess containing orbital fat under the levator
What is the intraconal space bound by?
The cone of muscles and intermuscular septum Fascia bulbi (tenons) which is attached at the limbus and is continuous in the space for the optic nerve and dura
Where is the pre aponeurotic space?
The aponeurosis of LPS and trochlea inferiorly
Orbital septum in front
Periorbita above
Contains pre aponeurotic fat pad
What is the clinical significance of the apertures of the orbital connective tissue system?
Blood pus or fat may pass from extra conal space to the deep strata of eyelids
How does the orbital connective tissue system change with age?
Prolapses of fatty tissue subconjunctivaly and inferiorly as the tissue gets more lax
Describe the ocular connective tissue in front of the equator of the globe
IOM within their sheaths Intermuscular membrane Fibrous septa present Suspensory ligament of Lockwood Medial and lateral check ligaments present
Describe the ocular connective tissue at the equator of the globe
Ligament of Lockwood still present
Medial and lateral ligaments of horizontal muscles no longer present
Describe the ocular connective tissue posterior 1/3 of the globe
No longer suspensory ligament or pulley suspensory system
No longer muscular sleeves
Describe the ocular connective tissue at globe apex
Intraconal and extraconoal zones are confluent
No intermuscular membrane
How does extraconal haemorrhage differ from intraconal haemorrhage?
Extraconal: blood spreads to lid and subconjunctival spaces. Lids become dark
Intraconal: proptosis, immobility and compression of optic nerve +/- blindness
What happens to the volume of the orbit when the eye is removed?
It decreases around 6-7ml
Why do we inject anaesthetic via subtenons just posterior to the globe?
Retrobulbar initially, but these could cause globe rupture and brain stem anaesthesia
Peribulbar put the anaesthesia in the extraconal space but required a greater volume and carried a risk of optic nerve perforation
Access to the orbit is now down inferolaterally
