Eye, Oculomotor Nerve, Extraocular Muscle Testing

Question 1

what are the 3 layers of the eyeball?

Answer 1

1. sclera: tough, white fibrous layer into which extraocular muscles insert + cornea (transparent anterior portion)
2. uvea: choroid (vascular layer) + ciliary body + iris
3. retina: contains rods and cones

Question 2

in what layer of the eyeball is the vasculature contained?

Answer 2

choroid - part of the middle uvea layer

Question 3

which smooth muscle controls accommodation of the eye lens?

Answer 3

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

Question 4

what secretes aqueous humor in the eyeball

Answer 4

ciliary process - part of the middle uvea layer, also supports suspensory ligaments

Question 5

which 2 smooth muscles control size of the pupil?

Answer 5

1. dilator papillae
2. sphincter papillae

contained within the iris

Question 6

what is contained in the blind spot vs fovea?

Answer 6

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

Question 7

how does the ciliary muscle of the eye respond to near vs distant objects?

Answer 7

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

Question 8

why does presbyopia occur?

Answer 8

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)

Question 9

where is the vitreous vs aqueous humor found in the eye?

Answer 9

region Anterior to the lens contains Aqueous humor

region posterior to the lens contains vitreous humor

Question 10

how is aqueous humor circulated through the anterior chamber and posterior chamber of the eye?

Answer 10

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

Question 11

which cranial nerve is actually part of the CNS, and therefore affected by demyelination disease (such as multiple sclerosis)?

Answer 11

optic nerve (CN II) - myelinated by oligodendrocytes

also surrounded by meninges (“optic nerve sheath”)

Question 12

what make up the 4 walls of the orbit bone?

Answer 12

roof = frontal bone
floor = maxilla
medial wall = ethmoid and sphenoid bones
lateral wall = zygoma and sphenoid bones

Question 13

what are the 3 posterior openings of the orbit? what do they contain?

Answer 13

1. optic canal: contains optic nerve (CN II) + ophthalmic artery
2. superior orbital fissure: contains superior ophthalmic vein (to cavernous sinus) and CN III, CN IV, CN V1, CN VI
3. inferior orbital fissure: contains inferior ophthalmic vein and CN V2 (infraorbital nerve + zygomatic nerve)

Question 14

what kind of veins are the superior and inferior ophthalmic veins, and why is this clinically important?

Answer 14

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

Question 15

explain how the supraorbital artery creates an anastomosis between the internal and external carotid arteries

Answer 15

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)

Question 16

describe how lacrimal fluid circulates in the eye

Answer 16

1. secreted by lacrimal gland in superolateral wall of orbit into conjunctival sac
2. lacrimal fluid flows from lateral to medial to drain into lacrimal canaliculi, leading into nasolacrimal duct

Question 17

where do the rectus vs oblique muscles of the eye insert?

Answer 17

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

Question 18

which extraocular muscle utilizes a pulley system?

Answer 18

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)

Question 19

what 2 extraocular muscles must work together to create pure elevation vs depression?

Answer 19

superior rectus + inferior oblique = pure elevation

inferior rectus + superior oblique = pure depression

Question 20

explain why either a CN III lesion or sympathetic lesion can result in ptosis

Answer 20

the levator palpebrae superioris is composed of skeletal muscle innervated by CN III + smooth muscle (aka superior tarsal muscle) innervated by sympathetic fibers

Question 21

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

Answer 21

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

Question 22

from where is the parasympathetic innervation for each of the following? state pre and postganglionic
a. constrictor pupillae and ciliary muscles
b. lacrimal gland

Answer 22

a. constrictor pupillae and ciliary muscles - CN III (preganglionic) + ciliary ganglion (postganglionic)

b. lacrimal gland - CN VII (preganglionic) + pterygopalatine ganglion (postganglionic)

Question 23

which branches of the ophthalmic division of the trigeminal (V1) provide general sensation to the eyeball?

Answer 23

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]

Question 24

prior to entering the orbit, CN V1 (ophthalmic) divides into… (3)

Answer 24

1. lacrimal nerve: innervates superolateral to the orbit, note PNS fibers hitch a ride to lacrimal gland
2. frontal nerve: divides into supraorbital and supratrochlear nerves
3. nasociliary nerve: divides into long/short ciliary nerves + ethmoidal nerves + infratrochlear nerve

Question 25

prior to entering the orbit, CN III (oculomotor) divides into… (2)

Answer 25

1. superior division: innervates levator palpebrae and superior rectus
2. inferior division: innervates inferior rectus, medial rectus, inferior oblique + PNS hitches a ride to ciliary ganglion

Question 26

what is the sole blood supply to the visual receptor cells of the retina?

Answer 26

central artery of the retina, a branch of the ophthalmic artery (enters via optic canal with optic nerve)

Question 27

esotropia vs exotropia

Answer 27

esotropia = medial strabismus

exotropia = lateral strabismus

Question 28

what is the clinical triad of uncal herniation?

Answer 28

1. oculomotor nerve: ipsilateral CN III signs (with “blown” pupil)
2. cerebral peduncles: contralateral hemiplegia
3. reticular formation: decreased consciousness or coma

Question 29

the medial longitudinal fasciculus (MLF) is the ascending portion of the…

Answer 29

… medial vestibulospinal tract, which controls head position in response to body movement

Question 30

how would a lesion to the following locations present:
a. frontal eye fields
b. superior colliculus
c. PPRF

Answer 30

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

Question 31

what is the specific function of the superior colliculus?

Answer 31

reflexive eye movements towards visual or auditory stimuli + corrective movements (tectoreticulospinal pathway)

Question 32

what would be the consequence of a lesion to the ventral vs dorsal gaze center in the rostral (upper) midbrain?

Answer 32

ventral gaze center is for downgaze; lesion —> upward looking eyes

dorsal gaze center is for upgaze; lesion —> downward looking eyes (“setting sun eyes”)

Question 33

what ocular symptoms present with Parinaud’s Syndrome (3)?

Answer 33

Parinaud’s syndrome: compression of dorsal rostral (upper) midbrain caused by increased pressure —>

1. “setting sun” eyes: paralysis of upward gaze (dorsal vertical gaze center)
2. “blown out” large pupils: compression of Edinger-Westphal fibers
3. light-near dissociation - loss of convergence

Question 34

axons from the _____ half of the retina will NOT cross at the optic chiasm

Answer 34

axons from the TEMPORAL half of the retina will NOT cross at the optic chiasm = nasal visual hemifields

Question 35

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?

Answer 35

1. suprachiasmatic nucleus of hypothalamus - circadian rhythm
2. pretectum - pupillary light and accommodation reflexes
3. superior colliculus - visual motor reflexes, orient eyes in response to new stimuli, move fovea to objects of interest

Question 36

describe the organization of the LGN (lateral geniculate nucleus) of the thalamus

Answer 36

organized in 6 layers, each layer receiving one portion of the visual fields from each eye, each layer innervated by only one eye

1. contra 2. ipsi 3. ipsi 4. contra 5. ipsi 6. contra
   [See I? I see, I see! —> think about it phonetically silly]

Question 37

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?

Answer 37

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”

Question 38

what visual input is received by the Cuneus gyrus vs Lingual gyrus (separated by the calcarine fissure)?

Answer 38

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

Question 39

where does the lesion occur if there is a normal vs abnormal pupillary reflex? explain.

Answer 39

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)

Question 40

what type of visual field defect would occur with unilateral aneurism of internal carotid artery?

Answer 40

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

Question 41

how to differentiate optic tract lesion from primary visual cortex lesion?

Answer 41

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)