H&N 5 Flashcards
what is at the apex of the orbit?
foramen= optic canal
in addition to the optic canal, what permits passage of nerves into the orbit?
superior and inferior orbital fissures
protective mechanisms of front of eye?
lacrimal gland
eyelids
via which 2 muscles does movement of eyelids occur?
orbicularis oculi
levator palpebrae superioris
function of orbit?
affords protection of eyeball and its muscles, nerves, vessels and most of lacrimal apparatus
what forms the fascial sheath of the eyeball?
periosteum (periorbita) lining bones of orbit
where is the periorbita continuous with the periosteal layer of dura mater?
at optic canal and supraorbital fissure
what are the eyelids lined by in the inner surface?
conjunctiva
how are the eyelids strengthened?
tarsal plates- dense bands of CT
how are the eyelids prevented from sticking together when they close?
secretion from tarsal glands contained in tarsal plates, which lubricates edges of eyelids
what does the lacrimal apparatus consist of?
lacrimal glands, lacrimal ducts, lacrimal canaliculi
what is a blowout fracture?
indirect trauma or injury that displaces orbital contents
when does a stye form in the eyelid?
when ducts of ciliary glands become obstructed
facial nerve is damaged, how does this affect eye protection?
protection lost as loss of orbicularis oculi function which allows eyelids to close, so loss of protective blinking
so cornea becomes dry and is left unprotected from dust and other particulate mateial
eyeball irritation causes excessive tear formation
how is attachment of extraocular muscles provided?
by outer protective layer of eyeball, comprising sclera and cornea, which is fibrous
what does middle coat of eyeball comprise?
iris, choroid and ciliary body
what is the inner layer of the eyeball?
retina, consisting of optic and non-visual parts
what does the choroid lie between?
the sclera and the retina
what does the choroid terminate as anteriorly?
ciliary body
what does ciliary body connect?
the choroids with the iris
where is the aq humour that fills the chambers of the eye secreted from?
the ciliary body
where is the anterior chamber of the eyeball located?
between cornea and iris
where is posterior chamber of eyeball located?
between iris and ciliary body and lens
what name is given to the central aperture of the iris?
pupil
how is the lens attached to the ciliary body?
by suspensory ligaments
what does the cavity behind the lens contain?
vitreous humor- supports lens and holds retina in place
what is the area of most acute vision?
the fovea centralis
arterial supply of retina?
central artery of the retina
how would damage to opthalmic division of trigeminal nerve affect the eye?
cornea would be rendered vulnerable to foreign objects
what is opacity of lens known as?
cataracts
2 layers of optic retina?
neural layer- light-receptive
pigmented layer
where does optic nerve enter eyeball?
at optic disc
what is a detached retina?
separated neural and pigmented layers of retina, may occur with blow to the eye
what are the muscles of the orbit?
levator palpebrae superioris
superior, inferior, medial and lateral recti
superior and inferior oblique
all supplied by oculomotor except superior oblique- trochlear, and lateral rectus- abducent
where do recti muscle arise from?
common tendinous ring- fibrous cuff
where do opthalmic veins drain?
into cavernous sinus
result of blockage of central retinal veins?
gradual loss of vision
what may cause sudden painless loss of vision?
retinal vascular occlusion
retinal detachment
when is gradual painless loss of vision commonly seen?
in chronic simple glaucoma
when is pain in the eye seen with blinking?
corneal abrasions with presence of FBs in eye
why are diseases of cornea associated with significant pain?
rich nerve supply of cornea
when is pain on motion of eye seen?
optic neuritis
how may severe coughing spells and recurrent vomiting damage the eye?
can cause a conjunctival haemorrhage
how might a patient try and relieve diplopia?
by closing 1 eye or compensatory head posture
which bones form the roof of the orbit?
frontal and sphenoid
which bones form floor of orbit?
maxilla, zygomatic (and palatine)
which bones form medial wall of orbit?
ethmoid, maxilla and lacrimal bones
which bones form lateral wall of orbit?
zygomatic and sphenoid
within which bone is the optic canal?
sphenoid
which structures pass through superior orbital fissure?
lacrimal nerve frontal nerve trochlear nerve superior branch of oculomotor nerve nasociliary nerve inferior branch of oculomotor nerve abducent nerve opthalmic veins sympathetic nerves
why does a blockage of the central artery of the retina cause instant and total blindness?
terminal branches of artery are end arteries, so provide only source of blood to internal aspect of retina
what is inside each cavernous sinus?
internal carotid artery with its small branches, surrounded by carotid plexus of sympathetic nerves, and abduncent nerve. Oculomotor and trochlear nerves, plus 2 of the 3 divisions of trigeminal, embedded in lateral wall.
heat exchange occurs to conserve energy or cool arterial blood *similar to pampiniform venous plexus in spermatic cord
what is the 1st sign of compression of oculomotor nerve?
ipsilateral slowness of pupillary response to light- pupils slow to constrict
where does CNI leave skull base?
cribiform plate of ethmoid bone
where does CNII leave skull base?
optic canal
where does CNsIII, IV, Vi and VI leave skull base?
superior orbital fissure
where does CNVii leave skull base?
foramen rotundum
where does CNViii leave skull base?
foramen ovale
where do CNsIX, X and XI leave skull base?
jugular foramen
where does CNXII leave skull base?
hypoglossal canal
name of disease in which lacrimal fluid not produced, in association with xerostomia?
sjrogens syndrome
which sinuses may be involved in medial wall of orbit fracture?
ethmoidal and sphenoidal
which sinuses may be involved in inferior wall of orbit fracture?
maxillary
how can the superior wall of the orbit be penetrated?
sharp object may pass through it and enter frontal lobe of brain
which muscle lies on top of the superior rectus muscle?
levator palpebrae superioris
how is the superior oblique muscle tested for?
ask patient to look inwards and dwards e.g. reading a book
3 actions of superior oblique?
medial rotation
depression
abduction
arteries of orbit?
opthalmic- branch of internal carotid, via optic canal, gives rise to central artery of retina
infraorbital- branch of external carotid
veins of orbit?
S and I opthalmic, exit via superior orbital fissure to cavernous sinus
central vein of retina, either directly to cavernous sinus or joins opthalmic veins
INFECTION can spread to brain via veins
name given to opening created by retraction of upper and lower eyelids?
palpebral fissure
in what 4 ways is the blinking reflex triggered?
drying of cornea: blinking moistens cornea, lacrimal fluid
irritation of cornea: blinking to shut eye and prevent entry of irritants
touching of cornea: perceived as pain, triggering eye closure
sight of on-coming irritant to eye: in anticipation of painful stimuli irritating sensory apparatus
origin of central artery of retina?
opthalmic artery- branch of ICA
composition of lacrimal fluid?
water- from lacrimal glands
mucins- from conjuctival goblet cells
oil- from mebomian glands which forms a barrier against vapourisation of lacrimal fluid, so blink less
bactericidal enzymes + antibodies- from lacrimal gland
fluid swept across surface of eye on blinking, and keeps cornea moist and healthy
infermomedial drainage
provides some nutrients and dissolved O2 to cornea
where does the lacrimal gland lie?
in a fossa on superolateral part of orbit
what happens to lacrimal fluid formation if eyelids prevented from closing properly?
protective blinking lost so cornea becomes dry and left unprotected from dust and particulate material, so irritation of eyeball causes excessive tear formation
what happens to the eye if orbicularis oculi is paralysed?
failure to close also paralysis of LPS as inserts into OO failure to blink failure to spread lacrimal fluid likelihood of eye infection, can lead to blindness can use eyedrops
what is harlequin syndrome?*
presentation of hemifacial sweating and flushin on unaffected side due to sympathectomy
how does aq humor drain?
via trabecular meshwork into scleral venous sinus
ciliary muscle function in near vision?
contracts in accomodation- lens made more convex under PSNS activity via CN III
what is mydriasis?
dilation of pupil, result of reduced PNS activity to sphincter pupillae, or increases SNS to dilator, may be due to raised IC pressure
what might a patient with a detached retina complain of?
flashes of light or specks floating in front of the eye
what is a coloboma?
an absence of a section of the iris
what is a hyphema?
Haemorrhage within the anterior chamber of the eyeball usually results from blunt force trauma to the eyeball.
what may cause unilateral exophthalmos?
aneurysm
haematoma
why can an increase in CSF pressure cause blindness?
may compress optic nerve as nerve surrounded by meninges with CSF in subarachnoid space, and this can then compress blood vessels supplying retina as run within optic nerve
