8. Orbit anatomy & pathology Flashcards
name the boundaries of the orbital cavity
- roof: frontal bone and lesser wing of sphenoid - floor: maxilla and zygomatic bone - medial wall: maxilla, lacrimal, ethmoid and sphenoid - lateral wall: zygomatic bone and greater wing of sphenoid
which parts of orbital cavity are the weakest and why
medial wall and floor due to presence of paranasal air sinuses: maxillary and ethmoid
which structure in the eyelid acts as a barrier to infection
- ORBITAL SEPTUM: thin sheet of fibrous tissue originating from orbital rim, blends with tendon of LPS and tarsal plates - separates intra-orbital contents from eyelid fat and obicularis oculi muscle - prevents spread of infection from pre-septal space to post-septal orbital cavity
which muscles act to open and close the eyelid and how are these innervated
Close: orbicularis oculi (palpebral part for light closure, orbital part for forceful closure) - facial n. Open: levator palpebrae superioris - occulomotor n. superior tarsal - SNS of occulomotor n.
describe the production of tears
i. lacrimal glands in superolateral orbit fossa secrete lacrimal fluid (controlled by PNS of facial n: greater petrosal n… pterygopalatine ganglion… CN Va) ii. fluid enters conjunctival sac through lacrimal ducts and passes into lacrimal lac at medial angle of eye iii. drains through lacrimal punctum and lacrimal canaliculus into lacrimal sac iv. passes via nasolacrimal duct into nasal cavity
what are the conjunctivae and where are these found
- transparent mucous membrane that produces mucus and tears - covers the sclera, extending up to edge of cornea and reflecting onto inner surface of upper and lower eyelids - highly vascularised
what is the main arterial supply and venous drainage of the orbit content
- arterial supply: ophthalmic a. (1st branch of ICA) - venous drainage: superior and inferior ophthalmic vv. (into facial v., cavernous sinus and pterygoid plexus
describe the innervation of the eye
- special sensory: optic n. - general sensory: trigeminal n. (CN Va) - motor: mainly occulomotor n. but also trochlear and abducens nn.
which openings allow passage of vessels into the orbit
- optic canal: optic n. and ophthalmic a.
- superior orbital fissure: occulomotor n. trochlear n., abducens n. and superior ophthalmic v.
- inferior orbital fissure: inferior ophthalmic v., maxillary n. (CN Vb) and sympathetic nn.
which condition is this and describe the associated signs/symptoms
orbital blowout fracture - ‘tear drop’ sign and accumulation of blood in maxillary sinus
symptoms:
- painful periorbital swelling/bruising
- impaired vision/double vision (esp. on vertical gaze)
- anaesthesia over affected cheek, upper teeth and gums (caused by damage to infraorbital n which runs along orbital floor to infraorbital fissure)
why can a P with orbital blow out fracture often not look up
i. retropulsion of eye ball causes sudden increase intra-orbital pressure…
ii. fractures floor of orbit…
iii. orbital contents and blood prolapses into underlying maxillary sinus…
iv. fracture site can entrap structures, e.g. sof tissue, inferior rectus and inferior oblique
what are the 2 types of periorbital cellulitis and explain which is more severe
- pre-septal - localised to eyelid by orbital septum
- post-septal - deep inside orbital cavity so can cause complications, eg
- abscess formation
- spread of infection intracranially via ophthalmic vv which drain to cavernous sinus, pterygoid venous plexus and facial vv
name these 2 conditions - how will they present differently
- meibomian cyst (painless) - infection and inflammation of meibomian glands
- styes (painful) - infection and inflammation of eyelash follicles
infection often caused by Staph.
which condition is this
conjunctivitis: highly contagious infection and inflammation of conjunctiva causing BV dilation
which condition is this
subconjunctival haemorrhage (often spontaneous and resolves with time)
