SGW - eye 2 Flashcards
what is an orbital blow-out fracture?
direct impact to the orbit e.g. fist / ball causing sudden increase in INTRA-ORBITAL pressure
what does the rapid rise in intra-orbital pressure from orbital blow-out fracture cause?
rapid rise in pressure is transmitted through the walls of the orbit
with inferior, thin wall (floor) and maybe medial often fracturing
orbital rim remains intact
what happens as the floor of the orbit fractures?
contents of the orbit e.g. ORBITAL FAT can prolapse through into the MAXILLARY SINUS
extra-ocular muscles (R III muscles) can also become trapped
how would the eye appear in an orbital blow-out fracture?
- sunken from some of the contents of the orbit (orbital fat + extra-ocular muscles) displaced
- eye cannot be elevated due to trapping of inferior rectus
why can an orbital blow-out fracture lead to reduced sensation over the cheek?
due to damage of infra-orbital branch of maxillary (V2) - which exits just below the orbit through infra-orbital foramen
why might suturing orbital blow-out fracture wounds be difficult?
any injury involving area near the medial angle of eye (angular vein) could involve injury to the lacrimal canaliculi and nasolacrimal duct
describe drainage of the lacrimal gland
lacrimal gland –> sweeped across eyes by eyelids –> lacrimal puncta –> lacrimal canaliculi –> lacrimal sac –> nasolacrimal duct –> inferior meatus –> choanae –> nasopharynx –> oesophagus –> stomach
where does angular vein receive blood from? drains to?
from the superior, inferior palpebral, external nasal, and INFRAORBITAL veins.
It drains into the superior ophthalmic vein at angular vein and forms an important connection with the cavernous sinus
what happens if wound is repaired without consideration for the lacrimal drainage system immediately beneath, then what can happen?
the injured ducts can become stenosed as they heal
pt could be left with long-term problems with the excessive tearing (no draining of lacrimal gland secretions)
and recurrent conjunctivitis (dirt particles not drained) due to impedance of tear drainage
how should wounds through medial angle of eye be dealt with?
referred to a specialist
treatment may involve microsurgery and placing a stent through the canniculi / duct to ensure it remains patent as the wound heals
function of superior rectus?
eye up and out
out because of position of the muscle attachment, so naturally pull out - from orbital apex to limbus
superior oblique function?
abducts, depresses and internally rotates the eye
(down and in, intort)
(orbital apex –> lateral of superior rectus)
inferior oblique function?
extorsion (external rotation); elevation; abduction
(eye up and in - in to ABduct, therefore, without it = down and out)
(orbital apex –> inferior to lateral rectus)
medial and lateral rectus function?
medial = moves eye medially lateral = moves eye laterally
inferior rectus function?
eye down and out (eye sits in orbit pointing out, attachment from orbital apex to limbus)
muscles for eye to look directly down?
superior oblique
inferior rectus
muscles for eye to look directly up?
inferior oblique
superior rectus
how do you test for action of superior oblique?
move eye medially first - SO becomes dominant muscle (in the plane of the muscle) then direct eye down to contract SO (CN IV)
how do you test for action of inferior oblique?
direct pupil medially (in plane of IO)
contraction of IO pulls eye up
(so medial then up) - test CN III
what is the orbicularis oculi?
sphincter muscle surrounding the palpebral fissure
what happens upon contraction of orbicularis oculi?
tears are swept across the eye form the lateral part to the medial - allows for lubrication of the eye and removal of potential foreign bodies
what can damage to orbicularis muscle lead to?
compromise the ability to close the eye and thus affect the ability to lubricate and protect the eye
what can weakness in orbicularis muscle lead to?
can cause lower eyelid to fall away from the eye
allow pooling of tears in the inferior fornix (pocket of conjunctiva), creating an environment for potential infection
what can paralysis of orbicularis oculi result in?
lack of protection of the cornea - can lead to cornea dry out and may subsequently ulcerate
function of the choroid?
thin CT filled with blood vessels, between sclera and retina
provide oxygen and nutrients to the eye
where is the blind spot found? what does it contain?
nasal (medial) side of fundus (macula)
optic nerve and central retinal artery
(ophthalmic artery travels within orbit, BUT central retinal artery travels within the optic disc to supply the eyeball)
what can blockage of the central retina artery lead to?
blockage secondary to thrombosis BEFORE central artery divides into smaller branches within retina = instant, painless loss of vision
due to ischaemia (end artery) - blocks tissue distal to site of blockage
ONLY artery to supply retina (neural + pigmented layers)
how does facial vein connected to cavernous sinus?
inferior ophthalmic vein –> angular vein (joining with SUPERIOR OPHTHALMIC VEIN) –> cavernous sinus
or
facial vein –> superior ophthalmic vein –> cavernous sinus
how does blood drain within the facial vein?
can flow in both directions (valveless) - usually drains inferiorly due to gravity
potential to drain into cavernous sinus (superiorly)
blood clots can pass into intracranial venous system
why might a lesion of the ophthalmic division of trigeminal nerve be dangerous to the eye?
ophthalmic division provides sensation to the conjunctiva and cornea
therefore cornea becomes insensitive to touch in damage to nerve
dust etc. not felt, can lead to corneal injury, scarring / ulceration
what is a cause of damage to ophthalmic nerve (V1)?
reactivation of varicella zoster (herpes) virus from previous chicken pox infection
if involves ophthalmic nerve can be sight threatening (dermatomes) - can cause blindness
rash involving skin CAN also affect CORNEA and CONJUNCTIVA - causing inflammation
which vein drains cornea and conjunctiva?
S+I ophthalmic veins
describe the corneal reflex
test orbicularis oculi (CN VII):
touch –> ophthalmic sensory afferent (V1) –> trigeminal sensory nucleus –> facial motor nucleus –> CN VII facial motor efferent –> eye shuts (blink) orbicularis oculi
(muscles of facial expression via stylomastoid foramen, 5 terminal branches in parotid gland, through parotid sheath)
test corneal reflex - why test the cornea?
most sensitive (most receptors of ophthalmic) cotton wool test
causes of abducens nerve palsy?
trauma, stroke, brain tumour, inflammation, infection
