Ocular Anatomy & Clinical Correlations Flashcards
cornea
- location
- components
- role
- location: ocular surface
- components: epithelium, stroma, and endothelium
- stroma = collagen: type I, IV, V
- role: 70% of light focusing power
lens
- structure
- roles
- clinical relevance
- structure: suspended by zonules to attached to ciliary body
- role:
- 30% of light focusing of the eye
- accomodation (via ciliary body attachment)
- separates anterior / posterior chambers
- clinical:
- hardening thru age = decreased accomodation (presbyopia)
- clouding thru age = reduce vision (cataract)
how does the lens evolve throughout age structurally and why is this important?
- becomes harder → presbyopia: reduced accomodation
- becomes cloudy → cataracts: reduced vision
the uvea consists of___?
iris
ciliary body
choroid
the ciliary body
- is part of what eye structure?
- interacts with what eye structures?
- has what roles?
- part of: the uvea
- interacts with: the lens via zonula fibers
- has what roles:
- holds lens in place (via zonula fibers)
- accomodation (via zonula fibers)
- produces aqeous humor that bathes the anterior chamber
the iris
- is part of what eye structure?
- has what role?
- part of: the uvea
- role: controls pupil size to augment light reaching the retina
the choroid
- is a part of what eye structure?
- has what role?
- is a part of the uvea (most posterior)
- role: highly vascular - provides majority of blood flow to retina
vitreous humor
- structure
- clinical significance
- made of:
- type II collagen
- hyaluronic acid
- water
- clinical: liquefaction throughout age → vitreous detachment → possible retinal tears → possible retinal detachment
the stroma of the cornea is made of what types of collagen?
- type I
- type IV
- type V
nasolacrimal duct obstruction in an infant
- presentation
- management
- presentation: recurring tearing & discharge
- management: warm digital massage over duct
- if not resolved in 12 months → opthalmologist can probe to open
orbital septum
- definition
- clinical significance
- definition: fibrous layer running from skull periosteum → eyelids
- clinical significance: differentiates periorbital from orbital cellulitis
- periorbital: anterior to septum
- orbital: posterior to septum
periorbital cellulitis
- definition
- incidence
- presentation
- definition: eyelid infection anterior to orbital septum
- incidence: more common than orbital cellulitis
- presentation:
- NO proptosis
- NO opthalmoplegia
- NO vision loss
- LESS pain with eye movement
- treatment: oral antibiotics
orbital cellulitis
- definition
- cause
- incidence
- presentation
- diagnosis
- treatment
- definition: inflammation of fat / ocular muscles posterior to orbital septum
- causes: infectious spread from sinuses - m/c ethmoid sinus
- incidence: less common than periorbital cellulitis
- presentation:
- opthalmoplegia
- proptosis
- more pain with eye movement > periorbital
- possible vision loss
- conjunctival chemosis*
- co-existing rhinosinusitis*
- diagnosis: CT/MRI
- management: IV antibiotics 3x / week
what are the complications of orbital cellulitis?
cavernous sinus thrombosis
meningitis
absesses
vision loss
how does the management of peri-orbital & orbital cellulitis differ?
why?
peri-orbital cellulitis: oral Abx
orbital cellulitis: dx w/ CTI/MRI → IV Abx 3x/week
- orbital celluitis is posterior to the septum, thus must be tx agressively to prevent progress to dangerous complications:
- cavernous sinus thrombosis
- meningitis
- abessess
- vision loss
orbital cellulitis often co-exists with what other presentation?
why?
rhinosinusitis
b/c the cellulitis likely arose from sinus infection - esp ethmoid sinus
what bones comprise the orbital roof?
frontal bone
lesser wing of sphenoid
which bones comprise the lateral wall of the orbit?
zygomatic bone
greater wing of sphenoid
which bones comprise the orbital floor?
maxilla
palatine
zygomatic
what bones comprise the medial wall of the orbit?
lacrimal
ethmoid
maxilla
sphenoid
“LEMS”
the sphenoid bone comprises which borders of the orbit?
- the roof - lesser wing
- the lateral wall - greater wing
- the medial wall
the zygomatic bone comprises what borders of the floor?
floor
lateral wall
the maxilla bone comprises which borders of the orbit?
floor
medial wall
which orbital wall is the thickest / strongest?
lateral wall
(zygomatic bone & greater wing of sphenoid)
which orbital wall contains the thinnest portion?
what is called?
the medial wall. in particular, the
- lamina pryracea: ethmoid bone that overlies ethmoid sinus
- posteriormedial maxillary bone
what is the lamina papyracea?
why is it clinically significant?
- the portion of the medial wall ovelying the ethmoid sinus
- is the thinnest part of the orbit, thus prone to fracture from blunt force trauma, which can lead to infections that spread thru the ethmoid sinus:
- orbital cellulitis
- proptosis
what are “trap door” fractures?
which population is susceptible?
orbital fractures to the weakest / thinnest part (lamina papyracea, postermedial maxilla) that result in incarceration & ischemia of introcular contents
younger patients with flexible bones = susceptible
what physical exam findings may be indicative of an orbital fracture?
why?
- orbital rim deformity on palpation
- impaired pupillary response - optic nerve (CN II) compression
- impaired sensation over maxillary nerve (V2) distribution - compression of infraorbital nerve in infraorbital fissure
- imapired visual acuity
what is the work-up in a suspected obital fracture?
CT with contrast of face & orbit
what neurovascuature exit the skull via the superior orbital fissure?
- CN III - VI (V = V1, opthalmic division of trigeminal nerve)
- sympathetic fibers
- opthalmic vein
which neurovasculature exits the skull via the optic canal?
- CN II
- opthalmic artery
- central retinal vein
which neurovasculature exits the skull via the inferior orbital fissure?
- CN V - V2 (maxillary division of trigeminal nerve) inferior opthalmic vein
where do the opthalmic vein & artery exit the skull?
- vein - superior orbital fissure
- artery - optic canal
list the cranial nerves that exit through the
- superior orbital fissure
- optical canal
- inferior orbital fissure
- superior orbital fissure: III-IV, V = V1 (opthalmic division of V)
- optic canal: II
- inferior orbital fissure: V2 (maxillary division of V)
how do branches of the trigeminal nerve exit the skull?
- V1 (opthalmic division) - superior orbital fissure
- V2 (maxillary divsion) - inferior orbital fissure
which parts of the ocular region do the carotids perfuse?
- internal carotid - majority of eye
- external carotid - eyelids / conjunctiva
which cranial nerves innervate the extra-ocular muscles?
III (oculomotor)
IV (trochlear)
VI (abducens)
CN III controls which extra-ocular muscles / actions?
- medial rectus → adduction
- superior rectus → elevation, adduction, inorsion
- inferior rectus → depression, adduction, extorsion
- inferior oblique → extorsion, abduction, depression
CN III innervates muscles that all share what motion?
what is the exception?
adduction
exception is the inferior oblique, which abducts
CN IV controls which extra-ocular muscles / actions?
superior oblique: intorsion, elevation, abduction
CN VI controls what extra-ocular muscles / actions?
lateral rectus - abduction
which extra-ocular muscles abduct the eye?
lateral rectus (VI)
the obliques - superior oblique (VI), inferior oblique (III)
which extra-ocular muscles elevate the eye?
- superior rectus (III)
- superior oblique (VI)
which extra-ocular muscles depress the eye?
- the inferior rectus (III)
- inferior olique (III)
which extra-ocular muscles adduct the eye?
all the rectuses execpt for the lateral rectus
which extra-ocular muscles & nerves deviate the eye to the
- temporal side
- nasal side
- temporal - lateral rectus (CN VI)
- nasal - medial rectus (CN III)
describe the presentation of an oculomotor nerve palsy that damages somatic fibers
“down and out” gaze
ptosis
describe the presentation of an oculmotor nerve palsy that damages autonomic fibers?
mydriasis / diminished pupillary reflex
loss of accomodation
in which part of the oculomotor nerve (CN III) are somatic vs autonomic fibers carried?
- somatic = central
- autnomic = peripheral.
what are the most common causes of a oculomotor (III) nerve palsy?
- microvascular disease - HTN, DM
- external compression
- PCOM or SCA aneurysm
- uncal herniation
- neoplasm
what is a “blown” pupil?
what medical management does it necessitate?
why?
a dilated pupil (mydriasis)
- requires emergent CTA / MRA
- could be indicative of a oculomotor (III) nerve palsy, and thus a PCOM aneurysm, which must be fuled out
internuclear opthalmoplegia
- definition
- cause
- presentation
- definition: conjugate horizantal gaze palsy
- cause: MLF lesion → failure of CN-III to fire → ipsilateral medial rectus paralysis → failed adduction
- presentation: nystagmus of the eye contralateral to the defect
- (still from functioning contralateral CN IV)
contrast the presentation of a CN VII LMN lesion to a CN VII UMN lesion
- LMN: paralysis of
- forehead
- ipsilateral face
- UMN: paralysis of
- contralateral lower face
which type of facial nerve palsy will spare the forehead?
why?
an upper motor neuron lesion
because UMN innervation to the forehead is bilateral, whereas LMN innervation is unilateral
facial nerve palsy
- causes
- treatment
- prognosis
- causes: idiopathic = bell’s palsy (m/c), lyme disease, HSV (ramsay hunt)
- treatment:
- systemic - corticosteroids
- eye - lubricants*
- prognosis: gradual recovery
horner syndrome
- definition
- cause
- presentation
- definition: sympathetic denervation of face
- cause: ipsilateral sympathetic trunk damage
- presenation:
- miosis*
- ptosis
- anihidrosis - absence of sweating
what is the consensual light reflex?
bilateral pupillary constriction even if light is shined only in one eye
what are argyll robertson pupils ?
what can cause them?
working accomodation but NO pupillary reaction (no constriction on light)
a/w neurosyphilis
what is marcus gun pupil?
what can cause it?
impaired consensual reflex (no bilateral constriction) when light is shown in one damaged eye
light shining in unaffected eye yields normal reflex
a/w optic neuritis (MS), acute CNS demylination
what is the ocular treatment for facial nerve palsy?
lubricating drops
