HNS42 Orbit Flashcards
***Contents of the orbit
- Eyeball
- 1/5 of orbit - Muscles
- Recti x4
- Oblique x2
- Levator palpebrae superioris
- Superior tarsal muscle (Muller’s muscle) - Nerves
- CN2, 3, 4, 6
- CNV1 (Lacrimal, Frontal, Nasociliary)
- CNV2 (Infraorbital, Zygomatic) - Vessels
- Ophthalmic artery and branches (ICA)
- Infraorbital vessels (ECA —> Maxillary)
- Middle meningeal artery and branches (Maxillary)
- Superior + Inferior Ophthalmic vein - Orbital fat, Reticular tissue, Orbital fascia
- Lacrimal gland + Lacrimal sac
Anatomy of eyeball
Anterior segment:
- Conjunctiva (anterior covering Sclera)
- Iris
- Lens (controlled by Ciliary body)
- Pupil
- Cornea
- Anterior chamber (anterior to iris, drainage of aqueous through trabecular meshwork)
- Ciliary body (production of aqueous —> posterior chamber —> anterior chamber)
- Posterior chamber (behind iris)
Posterior segment:
- Vitreous body
- Macula (concentration of cone cells)
- Retina
- Choroid (pack of blood vessels)
- Optic nerve
***Arterial supply of eyeball
Internal carotid artery —> Ophthalmic artery —>
- Retinal artery
- Posterior ciliary arteries (Long + Short)
- Muscular artery —> Anterior ciliary arteries
Anterior segment:
1. Iris + Ciliary body:
—> **Long Posterior ciliary artery (through choroid) anastomose with **Anterior ciliary artery (through extraocular muscles)
—> Minor arterial arcade + Major arterial arcade (trauma: Hyphema)
- Sclera + Conjuntiva + Iris
—> ***Anterior ciliary artery
Posterior segment:
- Retina —> ***Retinal artery (within RNFL Retina Nerve Fibre Layer)
- Choroid —> **Long (anterior to equator)+ **Short Posterior ciliary artery (posterior to equator)
- ***Dual circulation —> Retina and Choroidal circulations are separate circulations
Central retinal artery
- Supply retina
- Pierce Dural sheath of optic nerve 12 mm behind the globe
- Gives off small meningeal branches to supply Pial sheath of optic nerve
**Clinical relevance: **Central retinal artery occlusion
—> Retinal circulation occluded by emboli
—> Choroidal circulation unaffected
—> **Cherry red spot at fovea (unaffected Choroidal circulation) in middle of **Pale retina (occluded Retinal circulation) (oedematous retina due to ischaemia)
Ciliary arteries
Major blood supply of globe
- Long Posterior ciliary artery
- paired arteries that pierce sclera outside the circle of Zinn and travel forward in suprachoroidal space to **Ciliary body
- gives recurrent branches that supply **Choroid anterior to equator and anastomose with Short Posterior ciliary artery - Short Posterior ciliary artery
- 10-20 branches pierce sclera around optic nerve (i.e. at the back)
- anastomotic circle of Zinn supply optic nerve head (Optic disc)
- supply ***Choroid posterior to equator (posterior 2/3 Choroid) - Anterior ciliary artery
- 7 arteries —> 2 for each **rectus muscle except Lateral Rectus (only 1)
- supply **Sclera + **Conjuntiva + **Iris
Anterior segment
- Long Posterior ciliary artery
- Anterior ciliary artery
—> Iris + Ciliary body
- Iris vessels: Non-fenestrated (endothelial tight junctions)
- Ciliary body vessels: ***Fenestrated (NO tight junctions) —> allow production of aqueous humour
- ***Blood aqueous barrier (tight junctions in ciliary epithelium + iris endothelium to prevent substances going into eye)
Posterior segment
- Retina: ***Retinal artery
- 10 layers:
—> Inner 2/3: Central retinal artery
—> Outer 1/3 (beyond Outer Plexiform Layer): Watershed area (diffusion to get nutrients) —> Foveal avascular zone: absent capillaries over fovea (highest concentration of cone cells) —> age-related macular degeneration - Choroid: ***Long + Short Posterior ciliary artery
- Short Posterior ciliary artery: posterior to equator
- Long Posterior ciliary artery: anterior to equator
- **Blood retinal barrier:
- Tight junction between Retinal Pigment Epithelium
- Separate retinal circulation from choroidal circulation —> prevent substances going into eye
***Blood aqueous barrier + Blood retinal barrier
- **Blood aqueous barrier:
- Tight junctions in ciliary epithelium + iris endothelium to prevent substances going into eye
- **Blood retinal barrier:
- Tight junction between RPE (retinal pigment epithelium) of retina
- Separate retinal circulation from choroidal circulation —> prevent substances going into eye
- Immune privileged site: Part of the brain but exposed to outside
***Venous drainage of eye
- Retina: ***Central retinal vein
- Choroid: 4 Vortex veins (2 superior, 2 inferior)
- exit eyeball posterior to equator
- **Superior Vortex veins —> Superior Ophthalmic vein / Cavernous sinus
- **Inferior Vortex veins —> Inferior Ophthalmic venous plexus / Cavernous sinus
- Central retinal vein
- Supraorbital vein
- Facial vein
Clinical relevance:
- Cavernous sinus thrombosis (infection of orbit —> proptosis)
- Central retinal vein occlusion (haemorrhage of retina due to blockage of drainage)
***Orbit
4 walls from 7 bones:
- Ethmoid
- Frontal
- Lacrimal
- Maxillary
- Palatine
- Sphenoid
- Zygomatic
Anatomical space boundary:
- Superior: Anterior cranial fossa
- Inferior: Maxillary sinus
- Medial: Nasal cavity + Ethmoidal air cells
- Lateral: Middle cranial fossa
Superior wall
Triangular shape
Bones:
- Frontal bone (anterior)
- Lesser wing of sphenoid (posterior)
Relations: - Above: —> Frontal lobe + meninges - Below: —> Periorbita, Frontal nerve, Trochlear nerve, LPS, SR, SO, Lacrimal gland
Anterior + Posterior Ethmoidal canals: present at junction of roof + medial wall
Inferior wall / Floor
Triangular shape, Shortest
Bones: 1. Maxillary bone (medial) 2. Zygomatic bone (lateral) 3. Palatine bone (posterior) —> ***Inferior orbital fissure separate posterior part of floor from lateral wall
Infraorbital nerve + vessels:
- Inferior orbital fissure —> groove —> canal —> Infraorbital foramen
Relations: - Below: —> Mamillary + Palatine air sinus - Above: —> Inferior oblique muscle + Rectus muscle + Nerve to Inferior oblique muscle
Clinical relevance:
- Orbital blow-out fracture —> floor fracture —> can damage Infraorbital nerve
Medial wall
Quadrangular shape
Bones:
- Frontal process of maxilla
- Lacrimal bone
- Orbital plate of ethmoid
- Sphenoid body
Lacrimal fossa (Maxilla + Lacrimal bone):
- Anterior lacrimal crest = Maxilla
- Posterior lacrimal crest = Lacrimal bone
Relations: - Medial: —> Anterior, Middle, Posterior Ethmoid sinus —> Middle meatus - Orbital surface related to Superior oblique + Medial rectus: —> Anterior + Posterior ethmoid nerve —> Intratrochlea nerve —> Terminal branch of ophthalmic artery
Lateral wall
Triangular shape
Bones:
- Zygomatic bone (anterior)
- Greater wing of sphenoid (posterior)
Relations: - Lateral: —> Temporal fossa (anterior) —> Middle cranial fossa (posterior) - Medial: —> Lateral Rectus muscle —> Lacrimal nerves + vessels —> Zygomatic nerves and their communication
Apex of orbit
- Superior orbital fissure
- CNV1 (Lacrimal + Frontal)
- CN4 - Inferior orbital fissure
- CNV2 (Zygomatic)
- Infraorbital nerve - Optic canal
- Optic nerve - Annulus of Zinn (origin of most extraocular muscles)
- CN3 (superior + inferior)
- CNV1 (Nasociliary)
- CN6
Thyroid eye disease
Inflammation of ocular muscles —> Enlarged
- Proptosis + Diplopia
- Compress CN2 at apex —> Vision loss
Arterial supply of orbit
Internal carotid artery —> Ophthalmic artery —>
- Anterior + Posterior Ethmoidal artery
- Supratrochlear artery
- Supraorbital artery
- Lacrimal artery
Venous drainage of orbit
Posterior:
- Cavernous sinus + Deep facial vein
Anteromedial:
- Ophthalmic vein
- Angular vein
Anterolateral:
- Superficial temporal vein
***Innervation of orbit
CNV1 —> Medial part:
- Supraorbital nerve
- Supratrochlear nerve
CNV2 —> Lateral + Inferior part:
- Infraorbital nerve
- Zygomatic nerve
Ocular alignment of extraocular muscles
Globe not in parallel with axis of orbit
Synchronous ocular movement is performed by 6 extraocular muscles in each orbit (Rectus x4, Obliques x2)
—> Muscles controlled by brainstem via CN3, 4, 6
Rectus muscle
Pierce Tenon’s capsule —> insert into Sclera in front of equator
Blood supply:
Anterior ciliary artery
- 7 arteries —> 2 for each ***rectus muscle except Lateral rectus (only 1)
1. Medial muscular artery —> Medial, Inferior rectus
2. Lateral muscular artery —> Lateral, Superior rectus
Nerve:
- CN3 —> Medial, Superior, Inferior rectus
- CN6 —> Lateral rectus
(Superior rectus: Complex with Levator palpebrae superioris
—> allow retraction of eyelid when eye elevate
Inferior rectus: Complex with Lower lid retractor)
Superior oblique + Inferior oblique muscles
Blood supply:
- Medial muscular artery: Inferior oblique
- Lateral muscular artery: Superior oblique
Nerve supply:
- CN4: Superior oblique (***Contralateral)
- CN3: Inferior oblique
Inferior oblique: only muscle NOT from Annulus of Zinn, originate from Anterior orbit!!!
Actions of extraocular muscles
Medial rectus: Adduction (向內望)
Lateral rectus: Abduction (向外望)
Superior rectus: Elevation (+ adduction, intorsion)
Inferior rectus: Depression (+ adduction, extorsion)
Superior oblique: Intorsion (向內擰) (+ abduction, depression)
Inferior oblique: Extorsion (向外擰) (+ abduction, elevation)
Suspensory ligament of eyeball
Connect between extraocular muscle
—> allow eyeball to float within orbit
Synchronous eye movement
Brainstem coordinates conjugate eye movement
—> Activate Lateral + Medial rectus on 2 eyeballs
—> Inhibit Antagonist of each eyeball
Fusion reflex ensures images on both retina area similar
—> Brain becomes confused when eyes are focused on different objects
—> Diplopia
Image stabilisation
Images remains stable even if the viewer / subject is moving, rely on:
- Proprioception input
- Vestibular input
- Smooth pursuit eye movement
- Saccadic eye movement
- Higher processing
Eyelids
- Thin fold of skin —> covers and protects eye
- thinnest skin in whole body
- fine row of eyelashes —> protect from dust, foreign body, perspiration - Regularly spread tears, other secretions —> keep eye moist
- Corneal + Menace reflex —> protect eye from foreign body
Anatomy cross section of eyelid
Above lid crease
- Skin
- Orbicularis muscle
- Orbital septum
- Orbital fat (behind orbital septum)
- Levator aponeurosis tendon
- Superior tarsal muscle (innervated by sympathetic NS)
- Conjunctiva
Below lid crease
- Skin
- Orbicularis muscle
- Tarsal plate (maintain shape + secrete oily substance)
- Conjunctiva
Periorbital fat
Upper lid:
- Medial (nasal)
- Preaponeurotic pre-Levator fat pad
- divided by:
—> Medial horn of Levator aponeurosis
—> Lateral fascia on superior oblique muscle
Lower lid:
- Lower medial fat pad
- separated by inferior oblique - Lower central fat pad
- separated by Arcuate expansion of inferior oblique - Lower lateral fat pad
Asian vs Western eyelid
- Fibres vs Fat position
- Created by anterior insertion of Levator aponeurosis
- Attachments prevent descent of orbital fat —> Lid crease
Blood supply of eyelids
- Medial Palpebral artery (from Ophthalmic artery) —> supply medial part
- Lateral Palpebral artery (from Lacrimal artery) —> supply lateral part
Palpebral arteries (from ICA) anastomose with **Facial artery (ECA) and its branch (Zygomatico-temporal artery + Angular artery)
—> at lateral aspect of lid
—> form **Marginal + Peripheral Palpebral arcades
Venous drainage of eyelid
Superior + Inferior Palpebral vein
—> Angular vein + Facial vein etc.
Lacrimal gland + Nasolacrimal duct
Blinking causes tear to travel and distribution of tears over the globe —> Superior + Inferior papilla —> Superior + Inferior canaliculi —> Common canaliculus —> Drain / suck into Lacrimal sac —> Nasolacrimal duct —> Inferior meatus
After this slide is exam-related notes
After this slide is exam-related notes
Anatomy of eyeball
Anterior segment:
- Conjunctiva (anterior covering Sclera)
- Iris
- Lens (controlled by Ciliary body)
- Pupil
- Cornea
- Anterior chamber (anterior to iris, drainage of aqueous through trabecular meshwork)
- Ciliary body (production of aqueous —> posterior chamber —> anterior chamber)
- Posterior chamber (behind iris)
Posterior segment:
- Vitreous body
- Macula (concentration of cone cells)
- Retina
- Choroid (pack of blood vessels)
- Optic nerve
***Blood aqueous barrier + Blood retinal barrier
- **Blood aqueous barrier (前面):
- Tight junctions in ciliary epithelium + iris endothelium to prevent substances going into eye
- **Blood retinal barrier (後面):
- Tight junction between RPE (retinal pigment epithelium) of retina
- Separate retinal circulation from choroidal circulation —> prevent substances going into eye
- Immune privileged site: Part of the brain but exposed to outside
***Arterial supply of eyeball
Internal carotid artery —> Ophthalmic artery —>
- ***Retinal artery
- ***Posterior ciliary arteries (Long + Short)
- Muscular artery —> ***Anterior ciliary arteries
Anterior segment:
1. Iris + Ciliary body:
—> **Long Posterior ciliary artery (through choroid) anastomose with **Anterior ciliary artery (through extraocular muscles)
—> Minor arterial arcade + Major arterial arcade (trauma: Hyphema)
- Extraocular muscles + Sclera + Conjuntiva + Iris
—> ***Anterior ciliary artery
Posterior segment:
- Retina —> ***Retinal artery (within RNFL Retina Nerve Fibre Layer)
- Choroid —> **Long (anterior to equator) + **Short Posterior ciliary artery (posterior to equator)
- ***Dual circulation —> Retina and Choroidal circulations are separate circulations
***Venous drainage of eyeball
- Retina: ***Central retinal vein
- Choroid: 4 Vortex veins (2 superior, 2 inferior)
- exit eyeball posterior to equator
- **Superior Vortex veins —> Superior Ophthalmic vein / Cavernous sinus
- **Inferior Vortex veins —> Inferior Ophthalmic venous plexus / Cavernous sinus
- Central retinal vein
- Supraorbital vein
- Facial vein
Clinical relevance:
- Cavernous sinus thrombosis (infection of orbit —> proptosis)
- Central retinal vein occlusion (haemorrhage of retina due to blockage of drainage)
***Clinical relevance of Blood supply of eyeballs
- Central retinal artery occlusion
**Retinal circulation occluded by emboli
—> Choroidal circulation **unaffected
—> **Cherry red spot at fovea (unaffected Choroidal circulation) in middle of **Pale retina (occluded Retinal circulation) (oedematous retina due to ischaemia) - Hyphema
Damage to iris
—> much bleeding ∵ highly vascularised
—> bleeding fills anterior segment of eye
3. Cavernous sinus thrombosis Severe infection of orbit —> clogged up Cavernous sinus —> Thrombosis —> blood unable to drain —> ↑ Intraorbital pressure —> Proptosis
***Summary of 4 walls of Orbit
Medial wall:
- Frontal process of Maxilla
- Lacrimal bone
- Orbital plate of Ethmoid
- Sphenoid body
Lateral wall:
- Zygomatic bone (anterior)
- Greater wing of Sphenoid (posterior)
Inferior wall:
- Maxillary bone (medial)
- Zygomatic bone (lateral)
- Palatine bone (posterior)
Superior wall:
- Frontal bone (anterior)
- Lesser wing of Sphenoid (posterior)
***Orbital fissure and Optic canal
Superior + Inferior orbital fissure
- separated into 3 segments by ***annulus of Zinn
Superior orbital fissure:
- Superior to annulus of Zinn
1. Lacrimal nerve (CNV1)
2. Frontal nerve (CNV1)
3. CN4 - Inside annulus of Zinn
1. Nasociliary nerve (CNV1)
2. CN3 (superior + inferior branch)
3. CN6
4. Optic canal (but NOT in orbital fissure)
Inferior orbital fissure:
1. Inferior Ophthalmic vein
Arterial supply of Orbit
Internal carotid artery —> Ophthalmic artery —>
- Anterior + Posterior Ethmoidal artery
- Supratrochlear artery
- Supraorbital artery
- Lacrimal artery
Venous drainage of Orbit
Posterior:
- Cavernous sinus + Deep facial vein
Anteromedial:
- Ophthalmic vein
- Angular vein
Anterolateral:
- Superficial temporal vein
***Innervation of Orbit
Vision: CN2
Superior orbit + Upper lids sensation:
- **CNV1
1. Nasociliary nerve —> Anterior + Posterior ethmoidal nerve
2. Frontal nerve —> Supraorbital nerve
3. Lacrimal nerve
Inferior orbit + Lower lids sensation:
- **CNV2
1. Infraorbital nerve
2. Zygomatic nerve
Motor:
- Extraocular muscles: CN3, 4, 6
- Opening of lids: CN3
- Eye closure + Brow movement: CN7
Clinical relevance of Orbit
Blow out fracture:
Fracture in ***orbital floor
—> damage in Infraorbital nerve
—> Infraorbital numbness (∵ nerve damage + compression)
***Movement of Extraocular muscles
Medial rectus: Adduction (向內望)
Lateral rectus: Abduction (向外望)
Superior rectus: Elevation (+ adduction, intorsion)
Inferior rectus: Depression (+ adduction, extorsion)
Superior oblique: Intorsion (向內擰) (+ abduction, depression)
Inferior oblique: Extorsion (向外擰) (+ abduction, elevation)
Innervation of Extraocular muscles
CN3:
- Superior rectus
- Inferior rectus
- Medial rectus
- Inferior oblique
CN4:
- Superior oblique (***Contralateral)
CN6:
- Lateral rectus
Insertion + Origin of Extraocular muscles
Medial rectus:
- Origin: Annulus of Zin
- Insertion: 5.3-5.5mm from Corneal limbus (corneal-scleral junction)
Lateral rectus:
- Origin: Annulus of Zin
- Insertion: 6.9mm from from CL
Superior rectus:
- Origin: Annulus of Zin
- Insertion: 7.7mm from CL
Inferior rectus:
- Origin: Annulus of Zin
- Insertion: 6.5mm from CL
Superior oblique:
- Origin: Annulus of Zin (anatomical), Trochlea (functional)
- Insertion: 12-14mm behind CL (anterior end), 17-19mm behind CL (posterior end)
Inferior oblique:
- **Origin: **Maxilla (From a shallow depression on orbital plate of Maxilla)
- Insertion: Lower + Upper sclera behind equator
Suspensory ligament of eyeball
- Suspend eyeball in orbit
- Connect between EOM
- Help different EOM in place
- act as fulcrum (支點) / pulley as EOM move in orbit
Higher coordination centres for eye movement
Midbrain + Pons —> coordinators for eye movement —> e.g. Activate Lateral + Medial rectus on 2 eyeballs, Inhibit Antagonist of each eyeball 1. Synchronised eye movement 2. Image stabilisation 3. Saccadic eye movement 4. Smooth pursuit eye movement 5. Optokinetic response 6. Other movements
Midbrain / Nerve / Orbital problems that limit the coordination —> Diplopia
Eyelid
- ***Thin fold of skin —> covers and protects eye
- thinnest skin in whole body
- fine row of eyelashes —> protect from dust, foreign body, perspiration - Regularly ***spread tears, other secretions —> keep eye moist
- ***Corneal + Menace reflex —> protect eye from foreign body
Anatomy cross section of Eyelid
Above lid crease
- Skin
- Orbicularis muscle
- Orbital septum
- Orbital fat (behind orbital septum)
- Levator aponeurosis tendon
- Superior tarsal muscle (innervated by sympathetic NS)
- Conjunctiva
Below lid crease
- Skin
- Orbicularis muscle
- Tarsal plate (maintain shape + secrete oily substance)
- Conjunctiva
Asian vs Caucasian eyelid
Asian:
- Lower lid crease
- Smaller tarsal plate
- Lower orbital fat (眼腫腫)
- 50% single lid crease
Caucasian:
- Higher lid crease
- Larger tarsal plate
- Orbital fat above lid crease
- Almost all have double lid crease
Blood supply of eyelids
Artery:
Superior + Inferior **Palpebral arterial arcades
- Anastomosis between Facial artery + **Medial Palpebral (from Ophthalmic artery) + ***Lateral Palpebral (from Lacrimal artery)
Venous:
Superior + Inferior ***Palpebral vein
—> Angular vein + Facial vein etc.
***Supraorbital foramen + Infraorbital foramen
Supraorbital foramen / groove:
- Supraorbital artery (Ophthalmic artery)
- Supraorbital nerve (CNV1) —> upper lid
Infraorbital foramen:
- Infraorbital artery (Maxillary artery)
- Infraorbital nerve (CNV2) —> lower lid
***Lacrimal gland + Meibomian glands
-
**Lacrimal gland:
- in **Lacrimal fossa of Frontal bone (外側上面)
- Produce ***tears (together with other smaller palpebral glands)
- Lubricate eye
Physiology:
Blinking causes tear to travel and distribution of tears over the globe
—> ***Lacrimal sac (內側) pump mechanism while blinking
—> draws tears into it via drainage system
- **Meibomian glands at lid margins —> make **Meibom —> prevent tears from evaporating quickly
***Tears drainage system
Blinking causes tear to travel and distribution of tears over the globe
—> Superior + Inferior **punctum / papilla
—> Superior + Inferior **canaliculus
—> **Common canaliculus
—> Drain / suck into **Lacrimal sac
—> **Nasolacrimal duct
—> **Inferior meatus
Clinical relevance of Nasolacrimal duct
***Dacrocystitis
Blockage of NLD
—> infection of Lacrimal sac
Treatment:
- Drainage surgery to relieve abscess
Definitive treatment:
- Dacryocystorhinostomy (make a connection to nose)
