B7.040 Eye, Orbit, and Cranial Fossa Flashcards
sclera
dense connective tissue continuous with dura mater of optic nerve and brain
white of eye
iris
pigmented diaphragm which surround the pupil
cornea
clear extension of the sclera which covers both the iris and pupil
provides 2/3 of focusing power of the eye
bulbar conjunctiva
thin, moist mucous membrane covering sclera
papebral conjunctiva
mucous membrane on inner surface of eyelids
lacrimal apparatus
lacrimal gland keeps mucous membranes of the eye moist
lacrimal caruncle in medial angle accumulates tears
superior lacrimal punctum is just lateral to the caruncle and is the beginning of the lacrimal canaliculus where tears are carried to the lacrimal sac
tears end up in nasolacrimal duct and drain into nasal cavity
pathway of tears
lacrimal gland caruncle punctum canaliculus sac nasolacrimal duct
why do you sniffle when you cry
tears usually dry up before entering the nasal cavity, but with excessive tears they do not and they cause sniffles
lacrimal gland
almond sized
in anterior/superior portion of orbit
produces 1 ml of tears each day
controlled by parasympathetic nerves from CN VII
eyelids
protect eye from drying and light
lined by thin skin on external surface and highly vascular palpebral conjunctiva on inner surface
tarsal plate
dense connective tissue plate that gives form to each eyelid
Meibomian glands
glands within the tarsal plates which secrete fatty lubricants which prevent the lids from sticking
orbital septum
normally keeps orbital fat within orbit
prevents herniation
what is a sty
acute purulent inflammation of the eyelid, generally caused by staph aureus
treatment of sty
resolves in days to weeks
warm washcloth helps melt lipids that cause blockage of sebaceous glands
internal sty
inflammation of a Meibomian gland just under conjunctival side of eyelid
external sty
arises from an eyelash follicle or lid-margin gland (sebaceous or apocrine)
chalazion
Meibomian gland lipogranuloma
lump on eyelid as a result of chronic blockage of a tarsal gland
same treatment as sty, may require lancing if warm compresses doesn’t work
usually not infected and not painful
conjunctivitis
can be called pinkeye
commonly caused by allergic reaction (non infectious) or infections which are usually viral, but sometimes bacterial
allergic conjunctivitis
typically itchy
viral conjunctivitis
associated with a cold
watery discharge, variable itch
bacterial conjunctivitis
marked grittiness/irritation and a stringy, opaque, grey or yellowing mucopurulent discharge that may cause the lids to stick together
conjunctivitis prophylaxis
newborns delivered vaginally get antibacterial agents to protect against venereal diseases
2 muscles which raise the upper eyelid
levator palpebrae superioris superior tarsal (Muller)
levator palpebrae superioris
skeletal muscle under voluntary control innervated by CN III
main elevator
superior tarsal
smooth muscle innervated by sympathetic fibers
if innervation is lost, can cause 2 mm droop (ptosis)
horner’s
- ptosis (loss of superior tarsal innervation)
- miosis (loss of dilator muscle in pupil)
- anhidrosis (loss of sym input to sweat gland)
muscle that closes the eyelid
orbicularis oculi
innervated by CN VII
what is an orbital blow out fracture
breakage of maxillary bone (inferior wall of orbit) with subsequent protrusion of orbital contents into maxillary sinus
clinical features of orbital blow out
inability to look up due to trapping of inferior rectus in the maxillary bone fracture
lowered globe level cause by prolapse of soft tissue
superior orbital fissure
located at apex of orbit
between lesser and greater wings of sphenoid bone
transmits CN III, CN IV, ophthalmic CN V1, CN VI, and superior ophthalmic vein into orbit
optic canal
transmits optic CN II and ophthalmic artery
rectus muscles
move orbit and pull eye deeper into socket
oblique muscles
cause torsion of the orbit and protrusion of the eye forward within the orbit
graves disease eye findings
hyperthyroidism
eyes protrude slightly (proptosis)
exophthalmos - may be due to increased size of EOMs and edema within the orbit due to autoimmune reaction to thyrotropin (TSH) receptor antigen which is expressed in retroorbital tissues
annual ring of Zinn
common tendinous ring which surrounds the optic canal and superior orbital fissure
4 rectus muscles arise from here
origin of superior oblique
runs through a pulley, the trochlea, which is attached to the superior/medial margin of the frontal bone
origin of inferior oblique
arises from the maxillary bone margin just lateral to the nasolacrimal duct
insertion of superior oblique
sclera of eye in the superior, posterior, and lateral portion
insertion of inferior oblique
sclera of the eye in the inferior surface in the posterior, lateral quadrant
strabismus
pathological misalignment of the visual axes that cause a loss of depth perception and binocular vision
incidence of strabismus
2-3% of general population 3 mil in US annually more prevalent in Caucasian females multifactorial inheritance onset before age of 5
cause of strabismus
variation in the insertions of EOMs into orbit
esotropia
one or both eyes turn inward
“cross eyed”
exotropia
one eye deviates outward
less common
eye adductors
MR
SR
IR
eye abductors
IO
SO
LR
eye elevators
IO
SR
eye depressors
SO
IR
medial rotators (intorsion)
SR
SO
lateral rotators (extorsion)
IR
IO
H test important
when lateral: SR and IR do vertical movements
when medial: IO and SO do vertical movements
oculomotor nerve lesion
- lateral strabismus (down and out due to unopposed LR and SO)
- ptosis (paralysis of levator palpebrae)
- dilation of pupil
- loss of lens accommodation
causes of sudden CN III palsy
aneurysm within posterior communicating
cavernous sinus thrombosis
subarachnoid hemorrhage
contraction of SO muscle
eye rotates outward, downward, and with intorsion
lesion of CN IV
patient tilts head toward unaffected side bc side with lesion is extorted
CN VI palsy
weakness or paralysis of LR
eye on affected side rotates inward, medially due to unopposed MR action
causes diplopia
cause of CN VI palsy
conditions which increase ICP stretch the abducens nerve as brainstem is pushed into foramen magnum
most common CN palsy, found in diabetics
anterior chamber
anterior to iris and pupil
filled with aqueous humor
drains in canal of Schlemm at junction of the iris which the cornea and sclera (anterior chamber angle) into the venous blood
posterior chamber
posterior to iris and pupil, but in front of lens and ciliary process
contains ciliary body which produces aqueous humor which flows out of pupil into anterior chamber
glaucoma
excessive pressure within the eye
second leading cause of blindness in the world (leading in AAs)
closed angle glaucoma
10%
blockage of fluid drainage at the canal of schlemm
glaucoma exam
blowing a jet of air into the cornea and measuring the deformity
open angle glaucoma
90%
overproduction of aqueous humor
muscles in the iris
- radial, dilator muscle
2. circular, sphincter muscle
pupil dilator muscle
myoepithelial cells innervated by ganglionic sympathetics from superior cervical ganglia
a1 receptors
respond to NE
cocaine
inhibits reuptake of NE, dilating eye
pupil sphincter muscle
smooth muscle innervated by postganglionic parasympathetic fibers from ciliary ganglia via short ciliary nerves
muscarinic ACh receptors
anticholinergics
atropine and tropicamide
cause pupil dilation as dilator muscle is unopposed
accommodation
lens changes shape to focus on near objects
distance vision
ciliary muscle is relaxes, ligaments pull on and flatten the lens
near vision
ciliary muscle contracts, releases tension on the ligaments and the lens becomes more rounded
presbyopia
lens elasticity lost with age
common
many older individuals have difficult reading without the aid of reading glasses (far sighted)
lens does not round up as much as it used to
cataract
clouding of the lens
common (half of people in US have them by 80)
develop slowly and can affect one or both eyes, typically in those over 50
risk factors for cataracts
diabetes, smoking, prolonged sun exposure, alcohol, genetics
exposure of central vein and artery to CSF pressure
course inside the optic nerve
CSF pressure is transmitted into the orbit
papilledema
excessive CSF pressure as determined via exam of fundus
causes optic disc to swell and blood, especially venous blood to pool in the veins on the surface of the retina
fundus during hypertension
arteries become swollen and tend to restrict venous return
venous nicking
cavernous sinuses
dural sinuses 2 cm long and 1 cm wide located on each side of the sella turcica and body of sphenoid bone
connected by intercavernous sinuses and receive blood from superior and inferior ophthalmic veins, superficial middle cerebral, and sphenoparietal sinus
rained by superior and inferior petrosal sinuses
carotid-cavernous sinus fistula
rare
if an aneurysm in the internal carotid artery ruptures into the cavernous sinus, then the affected eye/orbit may fill with blood and pulsate
blood suddenly appears in sclera and orbital tissue as superior and inferior ophthalmic veins become pressurized close to arterial pressures
AVMs
arterial venous malformations
cerebral arteries and veins form abnormal tangles or webs
can be clinically silent or bleed and cause infarction in nearby parts of the brain
symptoms of carotid-cavernous sinus fistula
pulsating exophthalmos (forward protrusion of the eye) extraocular palsies (CN III, IV, and VI run through cavernous sinus)
treatment of carotid-cavernous sinus fistula
insertion of a balloon or coil into shunt via a catheter or surgery
corneal reflex
mediated by sensory fibers of CN V1 and motor fibers of CN VII
bilateral blink response when edge of cornea is touched
example of cause of dysfunction of corneal reflex
VIII tumors (acoustic neuromas) can compress CN VII in acoustic meatus
contents of anterior cranial fossa
frontal lobes of the cerebral hemispheres
orbital plates of frontal bones
crista galli and cribriform
plate of the ethmoid bone; the falx cerebri
sphenoid ridge
clinoid processes
falx cerebri
attaches to frontal crest and crista galli
sphenoid ridge
formed by lesser wing of the sphenoid
clinoid processes
site of attachment for tentorium cerebelli
contents of middle cranial fossa
temporal lobes dorsum sellae posterior clinoid processes petrous squamous
dorsum sellae
behind sella turcica of sphenoid bone
posterior clinoid processes
of sphenoid bone
petrous
portion of temporal bones
squamous
portion of temporal bones
posterior cranial fossa
occipital lobes lying on tentorium cerebelli, cerebellum, pons, and medulla
occipital bone
tentorium cerebelli
