L2: Orbit Flashcards
Roof of orbit
Frontal bone (small contribution from sphenoid bone)
Medial wall of orbit
Maxilla, lacrimal and ethmoid and sphenoid
Floor of orbit
Maxilla (small contributions from zygomatic and palatine bones)
Lateral wall of orbit
Zygomatic bone and greater wing of sphenoid
Clinical: orbital fracture
Fractures within orbit frequently occur within floor and medial wall, however superior and lateral wall fractures also occur
E.g. inferior (floor) fracture - inferior rectus can be dragged leading to patients having upward gaze failure
Layers of eyelid (ant to post)
- Skin
- Subcutaneous tissue
- Orbicularis occuli (voluntary muscle)
- Orbital septum
- Tarsus
- Conjuctiva
Upper and lower eyelid similar except for addition of superior tarsal and levator palpbrae superioris muscles in upper eyelid
Clinical: Racoon eyes
There is a potential space between skin and subcutaneous tissue/within subcutaneous tissue
Base of skull/skull fracture -> blood accumulates in potential space within eyelids
Orbicularis occuli features
Damage
The voluntary muscle of eyelids (palpebrae part) innervated from frontotemporal branch of facial n [VII]
Closes eyelids
Damage to facial n (frontotemporal branch crosses over parotid gland) results in inability to close/blink ipsilateral upper eyelid and lower eyelid droops away
–> assoc w corneal ulcers and spillage of tears
Orbital septum
Deep to palpebrae part of o. occuli It is an extension of periosteum In both upper and lower eyelids - Protects eye - Attaches to tendon of LSP in upper eyelid and attaches to tarsus in lower eyelid
Tarsus
Major support for each eyelid, plates of dense CT, attached medially to ant lacrimal crest of maxilla and laterally to orbital tubercle on zygomatic bone
- Sup tarsus associated w LPS
- Inf tarsus
Muscles associated w raising of eyelid
LPS - somatic muscle of upper eyelid, innervated by [III]
Superior tarsal muscle - collection of smooth muscle fibres (from inf edge of LPS to upper edge of sup tarsus), innervated by post-ganglionic sympathetic fibres from sup cervical ganglion in neck
Clinical: Ptosis (partial and complete)
Complete ptosis: damage to nerve innervating LPS causes eyelid to fully drop
Partial: damage to sympathetic fibres to superior tarsal m or damage to muscle itself (e.g. neck trauma damaging sympathetic cervical ganglion)
Clinical: Horner’s syndrome
Lesion that leads to loss of sympathetic function in head (e.g. trauma, consequence of surgery)
Miosis (pupillary constriction)
Partial ptosis
Anhidrosis (absence of sweating on ipsilateral side)
Conjuctiva
Thin membrane covering post part of eyelid and reflects onto outer surface of eyeball (sclera)
Conjuctiva attaches to eyeball at junction between sclera and cornea
- Membrane forms conjuctival sac when eyelids closed
- Keeps cornea functioning by maintaining moisture
- Highly vascularised
Clinical: conjunctivitis
Bacteria can get in and infect conjunctiva - secretion of immunological factors to try and get rid of bacteria (foreign bodies can get stuck in conjunctiva)
Tarsus glands
Clinical: blockage of gland
Embedded in tarsus, secrete oily substance that increases viscosity of tears and decreases rate of evaporation from surface of eyeball
Blockage of gland/canal = chalazion (swelling, painless)
Sebaceous and sweat glands
Clinical: blockage
Associated with eyelash follicles
Blockage = Hordeolum (stye) - infection
Eyelid blood supply and innervation
Arterial:
Ophthalmic a ( + facial a, superficial temporal a)
Venous: ophthalmic veins
Innervation:
Sensory - V1 (upper), V2 (lower)
Motor - VII (palpebrae of o. occuli), III (LPS), sympathetic fibres (sup tarsal m)
Periosteal layer
Periorbita= periosteum within orbit (post part forms tendinous ring)
When periosteal layer of dura comes into orbit, foramina it came through is sealed to prevent infection from eye entering
Periosteum thickened at every foramen
Orbital septum = where periorbita and periosteum meet and extend downward to eyeball
Structures entering and exiting orbit via optic canal
- Optic n [II]
2. Ophthalmic a
Structures entering and exiting via superior orbital fissure
(Between roof and lateral wall of bony orbit)
- Sup and inf branches of [III]
- [IV]
- [VI]
- Frontal, nasociliary and lacrimal branches of V1
- Sup ophthlamic v
Structures entering and exiting via inferior orbital fissure
(Separates lateral wall from floor of orbit)
- Inferior ophthalmic v (may passs through SOF)
- Infraorbital a and v
- V3 and its zygomatic branch
- Vein communicating pterygoid plexus of veins
Common tendinous ring
Clinical significance
Zinn ring - thickening of periorbita in post part of orbit around optic canal and central part of SOF
4 rectus muscles originate
Optic canal: [II], ophthalmis a
SOF: nasociliary n, [VI], sup and inf divisions of [III]
Narrowing of ring due to inflammation or recti muscle perforation will put pressure on structures in ring
Lacrimal apparatus
Production, movement and drainage of fluid from surface of eyeball
Lacrimal gland, canaliculi, sac, duct
Punta drains tears -> canaliculi -> sac -> nasolacrimal duct
Arterial supply to eyeball
Branches of ophthalmic artery (from int carotid, enters through optic canal)
Central retinal artery supplies optic disc and if there is ophthalmic a clot, patient will be blind
Clinical: Danger triangle
Opthalmic v communicates with facial veins and cavernous sinus
Provides path for spread of infection from outside to inside (mainly superior)
Infection in eye/nose can spread to brain (meningitis potentially)
Ophthalmic veins do have valves so this is not the reason for spread of infection
