Eye, Oculomotor Nerve, Extraocular Muscle Testing Flashcards
what are the 3 layers of the eyeball?
- sclera: tough, white fibrous layer into which extraocular muscles insert + cornea (transparent anterior portion)
- uvea: choroid (vascular layer) + ciliary body + iris
- retina: contains rods and cones
in what layer of the eyeball is the vasculature contained?
choroid - part of the middle uvea layer
which smooth muscle controls accommodation of the eye lens?
ciliary muscle - contained in the middle uvea layer, controls shape of the lens
contraction —> decreases radius of ciliary body, allowing slackening of suspensory ligaments and elasticity of the lens to allow it to become thicker and more refractive - near objects/ accommodation reflex
relaxation —> increase radius of ciliary body, tightening suspensory ligaments and stretching the lens to make it thinner/ less refractive - distant objects
what secretes aqueous humor in the eyeball
ciliary process - part of the middle uvea layer, also supports suspensory ligaments
which 2 smooth muscles control size of the pupil?
- dilator papillae
- sphincter papillae
contained within the iris
what is contained in the blind spot vs fovea?
blind spot = optic disk, where all axons of retina form optic nerve, no receptor cells here
fovea contains greatest density of cones and is located in the center of the yellow spot macula lutea just lateral to the optic disk
how does the ciliary muscle of the eye respond to near vs distant objects?
near/ accommodation reflex: contraction —> decreases radius of ciliary body, allowing slackening of suspensory ligaments and elasticity of the lens to allow it to become thicker and more refractive
distant objects: relaxation —> increase radius of ciliary body, tightening suspensory ligaments and stretching the lens to make it thinner/ less refractive
why does presbyopia occur?
lens loses elasticity with aging, such that even when ciliary muscle of the eye contracts, the lens does not spring back and become thicker, which is needed to create more refraction for near objects
presbyopia = age-related compromise of near vision (why many people need reading glasses)
where is the vitreous vs aqueous humor found in the eye?
region Anterior to the lens contains Aqueous humor
region posterior to the lens contains vitreous humor
how is aqueous humor circulated through the anterior chamber and posterior chamber of the eye?
anterior chamber (between cornea and iris) and posterior chamber (between iris and lens) communicate via pupil
ciliary process secretes aqueous humor into posterior chamber —> passes through pupil —> enters venous channels (canal of Schlemm) in the anterior chamber
which cranial nerve is actually part of the CNS, and therefore affected by demyelination disease (such as multiple sclerosis)?
optic nerve (CN II) - myelinated by oligodendrocytes
also surrounded by meninges (“optic nerve sheath”)
what make up the 4 walls of the orbit bone?
roof = frontal bone
floor = maxilla
medial wall = ethmoid and sphenoid bones
lateral wall = zygoma and sphenoid bones
what are the 3 posterior openings of the orbit? what do they contain?
- optic canal: contains optic nerve (CN II) + ophthalmic artery
- superior orbital fissure: contains superior ophthalmic vein (to cavernous sinus) and CN III, CN IV, CN V1, CN VI
- inferior orbital fissure: contains inferior ophthalmic vein and CN V2 (infraorbital nerve + zygomatic nerve)
what kind of veins are the superior and inferior ophthalmic veins, and why is this clinically important?
ophthalmic veins communicate with veins of face, cavernous sinus, and pterygoid venous plexus
thus, they are emissary veins - can be important for spread of infection from face to deeper intracranial or extra-cranial regions
explain how the supraorbital artery creates an anastomosis between the internal and external carotid arteries
supraorbital artery is a branch of ophthalmic artery, which is itself a branch of the internal carotid artery
when it exits the supraorbital foramen, it anastomoses with the transverse facial artery, which is a branch of the superficial temporal artery, which itself is a branch of the external carotid artery
normally, pressure gradient causes flow from ICA to ECA, but if there is an occlusion of ICA, pressure gradient will reverse from ECA to ICA (can be detected via Doppler)
describe how lacrimal fluid circulates in the eye
- secreted by lacrimal gland in superolateral wall of orbit into conjunctival sac
- lacrimal fluid flows from lateral to medial to drain into lacrimal canaliculi, leading into nasolacrimal duct
where do the rectus vs oblique muscles of the eye insert?
rectus muscles (superior, inferior, medial, lateral) have origins at common ring tendon and insert on front of eyeball
oblique muscles (superior, inferior) have independent origins from the wall of the orbit and insert on the back of eyeball
which extraocular muscle utilizes a pulley system?
tendon of the superior oblique passes through the trochlea (fibrocartilage pulley) before turning back to insert on the back of the eyeball
(this makes sense because it also has its origin near the back of the orbit)
what 2 extraocular muscles must work together to create pure elevation vs depression?
superior rectus + inferior oblique = pure elevation
inferior rectus + superior oblique = pure depression
explain why either a CN III lesion or sympathetic lesion can result in ptosis
the levator palpebrae superioris is composed of skeletal muscle innervated by CN III + smooth muscle (aka superior tarsal muscle) innervated by sympathetic fibers
what type of autonomic innervation do the following structures in the orbit receive?
a. dilator pupillae muscle
b. constrictor pupillae muscle
c. ciliary muscle
d. levator palpebrae (smooth muscle)
e. lacrimal gland
a. dilator pupillae muscle - SNS
b. constrictor pupillae muscle - PNS
c. ciliary muscle - PNS
d. levator palpebrae (smooth muscle) - SNS
e. lacrimal gland - SNS + PNS
from where is the parasympathetic innervation for each of the following? state pre and postganglionic
a. constrictor pupillae and ciliary muscles
b. lacrimal gland
a. constrictor pupillae and ciliary muscles - CN III (preganglionic) + ciliary ganglion (postganglionic)
b. lacrimal gland - CN VII (preganglionic) + pterygopalatine ganglion (postganglionic)
which branches of the ophthalmic division of the trigeminal (V1) provide general sensation to the eyeball?
long and short ciliary nerves
[recall all sensory nerve fibers of the trigeminal have their cell bodies in the trigeminal ganglion in the middle cranial fossa]
prior to entering the orbit, CN V1 (ophthalmic) divides into… (3)
- lacrimal nerve: innervates superolateral to the orbit, note PNS fibers hitch a ride to lacrimal gland
- frontal nerve: divides into supraorbital and supratrochlear nerves
- nasociliary nerve: divides into long/short ciliary nerves + ethmoidal nerves + infratrochlear nerve
prior to entering the orbit, CN III (oculomotor) divides into… (2)
- superior division: innervates levator palpebrae and superior rectus
- inferior division: innervates inferior rectus, medial rectus, inferior oblique + PNS hitches a ride to ciliary ganglion
what is the sole blood supply to the visual receptor cells of the retina?
central artery of the retina, a branch of the ophthalmic artery (enters via optic canal with optic nerve)
esotropia vs exotropia
esotropia = medial strabismus
exotropia = lateral strabismus
what is the clinical triad of uncal herniation?
- oculomotor nerve: ipsilateral CN III signs (with “blown” pupil)
- cerebral peduncles: contralateral hemiplegia
- reticular formation: decreased consciousness or coma
the medial longitudinal fasciculus (MLF) is the ascending portion of the…
… medial vestibulospinal tract, which controls head position in response to body movement
how would a lesion to the following locations present:
a. frontal eye fields
b. superior colliculus
c. PPRF
a. FEF —> transient horizontal gaze palsy to contralateral side, gaze preference to side of lesion
b. superior colliculus —> transient deficit in accuracy, frequency, and velocity of saccades + permanent loss of reflexive saccades to visual or auditory stimuli
c. PPRF —> horizontal gaze palsy to ipsilateral side
what is the specific function of the superior colliculus?
reflexive eye movements towards visual or auditory stimuli + corrective movements (tectoreticulospinal pathway)
what would be the consequence of a lesion to the ventral vs dorsal gaze center in the rostral (upper) midbrain?
ventral gaze center is for downgaze; lesion —> upward looking eyes
dorsal gaze center is for upgaze; lesion —> downward looking eyes (“setting sun eyes”)
what ocular symptoms present with Parinaud’s Syndrome (3)?
Parinaud’s syndrome: compression of dorsal rostral (upper) midbrain caused by increased pressure —>
- “setting sun” eyes: paralysis of upward gaze (dorsal vertical gaze center)
- “blown out” large pupils: compression of Edinger-Westphal fibers
- light-near dissociation - loss of convergence
axons from the _____ half of the retina will NOT cross at the optic chiasm
axons from the TEMPORAL half of the retina will NOT cross at the optic chiasm = nasal visual hemifields
90% of optic tract axons from the retina travel to the lateral geniculate nucleus (LGN) in the thalamus; the other 10% go to which 3 destinations?
- suprachiasmatic nucleus of hypothalamus - circadian rhythm
- pretectum - pupillary light and accommodation reflexes
- superior colliculus - visual motor reflexes, orient eyes in response to new stimuli, move fovea to objects of interest
describe the organization of the LGN (lateral geniculate nucleus) of the thalamus
organized in 6 layers, each layer receiving one portion of the visual fields from each eye, each layer innervated by only one eye
- contra 2. ipsi 3. ipsi 4. contra 5. ipsi 6. contra
[See I? I see, I see! —> think about it phonetically silly]
Meyer’s loop contains fibers representing _____ retinal quadrants, while Baum’s loop contains fibers representing ______ retinal quadrants
to where does each bundle of fibers travel? what are the respective effects of a lesion?
Baum’s loop (parietal lobe) = superior retinal quadrants (INFERIOR visual fields) —> Cuneus gyrus; lesion —> “pie in the floor”
Meyer’s loop (temporal lobe) = inferior retinal quadrants (SUPERIOR visual fields) —> Lingual gyrus; lesion —> “pie in the sky”
what visual input is received by the Cuneus gyrus vs Lingual gyrus (separated by the calcarine fissure)?
Baum’s loop (parietal lobe) = superior retinal quadrants (INFERIOR visual fields) —> Cuneus gyrus
Meyer’s loop (temporal lobe) = inferior retinal quadrants (SUPERIOR visual fields) —> Lingual gyrus
where does the lesion occur if there is a normal vs abnormal pupillary reflex? explain.
abnormal pupillary reflex = optic nerve or optic tract lesion
normal pupillary reflex = optic radiation or visual cortex lesion
why? because axons reaching pretectum will leave before making synapse in the LGN (thalamus)
what type of visual field defect would occur with unilateral aneurism of internal carotid artery?
unilateral nasal hemianopia, aka loss of nasal vision in 1 eye
pressure would be on optic chiasm on laterally placed axons, which carry nasal visual hemifield input
how to differentiate optic tract lesion from primary visual cortex lesion?
optic tract lesion = contralateral homonymous hemianopia
primary visual cortex lesion = contralateral homonymous hemianopia with MACULAR SPARING due to dual blood supply to macula (PCA + MCA)
