Test 2: lecture 23: neuro-ophth Flashcards
relays visual signal from retina to CNS
Optic : CN II
innervates four extraocular mm (dorsal, medial, ventral
recti and ventral oblique) and levator palpebrae muscle (elevating upper
eyelid); also provides parasympathetic innervation to iris sphincter
Oculomotor : CN III
innervates dorsal oblique
Trochlear: CN IV
ophthalmic and maxillary branches provide sensory innervation to eye and accessory organs, including cornea, conjunctiva, lacrimal gland, and periocular skin
Trigeminal : CN V
—innervates lateral rectus and retractor bulbi muscles
Abducens: CN VI
innervates various mm controlling blink response
Facial: CN VII
if eye stuck like this what nerve has damage
medial rectus muscle not working ( oculomotor CN3)
eye also dilated- PARA to eye to keep it constricted is by CN3
what is not working
lateral rectus
abducent CN 6
what muscle not working?
superior dorsal oblique
trochlear (CN4)
what are the two functions of CN2
optic nerve
vision: relays visual signal from retina to CNS
pupillary light reflex: Some CN II fibers leave optic tract before synapsing in LGN to synapse in pretectal nucleus, providing afferent input to PLR
what does CN3 do
oculomotor nerve
Extraocular muscles
* Dorsal, ventral, medial rectus muscles
* Inferior oblique muscle
Eyelid muscle
* Levator palpebrae muscle
PARA
* iris sphincter muscle (PLR)
* ciliary muscle (accommodation)
CN 4
trochlear nerve
Dorsal oblique muscle
CN 5
trigeminal nerve
Ophthalmic branch of trigeminal nerve
Sensory fibers
* Pain and pressure from the cornea and eyelids
what provides sensory to eyelids
CN 6
abducens
Motor fibers
* Extraocular muscle:
* Lateral rectus muscle
* RETRACTOR BULBI MUSCLE
Sympathetic fibers
* Sympathetic innervation of cat’s
third eyelid
CN7
facial
Motor fibers
Eyelid muscles (closure)
* Orbicularis oculi muscle
Parasympathetic fibers
* Lacrimal glands
what nerves for palpebral reflex
blink response
CN V trigeminal: sensory to eyelid and cornea)
* Reflex closure of lid in response to touching face
CN VII facial close eyelid
* Orbicularis oculi muscle
corneal reflex is controlled by
CN V and CN VII & CN VI
* Similar to palpebral reflex
* Reflex closure of lid & globe retraction in response to touching cornea
CN 5: tigeminal: pain and pressure from eyelid and cornea
CN6: abducens: motor to retractor bulbi and lateral rectus, SYM to cat’s 3rd eyelid
CN7: facial : close eyelid, PARA to lacrimal glands
dazzle reflex
shine light in eye and blink
CN II and CN VII
* Involuntary avoidance reflex to bright light shined in eye (“squinting”)
* Neuroanatomical pathway not completely understood
* Does not test vision, but positive suggests normal retinal, optic nerve function in opaque eyes, when PLR, menace response cannot be evaluated
CN7: facial : close eyelid, PARA to lacrimal glands
CN2: optic nerve: sight and PLR
menace response is what nerves
Learned response, NOT a reflex!
CN II and CN VII
- Reflex closure of palpebral fissure, turning head away
- Tests vision! Requires intact visual cortex
- Ability to blink
- Present at 10-12 weeks in puppies, kittens; 5-7 days in foals, calves
CN7: facial : close eyelid, PARA to lacrimal glands
CN2: optic nerve: sight and PLR
how to test vision
- Tracking moving objects (cotton ball for dogs, laser pointer for cats)
- Maze test
- Visual placing response
- Menace response
PLR, dazzle reflex do not assess vision, but help to evaluate integrity of neuroanatomical pathways
how does swinging flashlight test work
can tell if direct and indirect PRL is working
if you shine light in one eye the other eye should constrict at same time
positive= no direct, swing and then contricts (tells you first retina isn’t working)
marcus gunn sign
what part of the nerve is damaged with vision loss and direct PRL/dazzle deficit and no indirect PRL to other eye
afferent arm
which part of the nerve for no vision loss, one eye always responds (PRL and dazzle) the other eye does not
efferent arm
what part of the pathway damaged with vision loss, PRL and dazzle are normal
cortical
afferent arm defect
vision loss
no PLR/dazzle
no indirect PLR to other eye
efferent arm defect
No vision loss
one eye always responds (PLR & dazzle)
other eye does not
cortical defect
vision loss
PLRs & dazzle are NORMAL
where are lesions with blind patient with normal PLR
lesion after afferent fibers of PLR have diverged to midbrain – lesion in LGN, optic radiation, cerebral cortex
* Cerebral edema (trauma, seizure), inflammatory (GME), metabolic (hypoglycemia, hepatic encephalopathy), toxic
blind patient with abnormal PLRs will have lesion
in pathway common to vision and PLR – retina, optic nerve, optic chiasm
* Unilateral: retinal detachment, glaucoma, retrobulbar abscess/neoplasia
* Bilateral: same as unilateral, plus SARD, pituitary tumor, intracranial neoplasia
visual patient with abnormal PLR will have lesion —
lesion localized to oculomotor n. after exited forebrain; will have three
signs:
* Internal ophthalmoplegia: fixed, dilated pupil caused by loss of parasympathetic innervation to iris sphincter
* External ophthalmoplegia: Ventrolateral strabismus caused by loss of innervation to dorsal, medial, and ventral recti and ventral oblique muscles
* Ptosis of upper eyelid caused by loss of innervation to levator palpebrae muscle
what are some non neurologic diseases that can cause abnormal PLR
- Iris atrophy, hypoplasia
- Glaucoma
- Anterior uveitis
- Ocular pain
- FeLV
- Prior treatment with parasympatholytic agents
Unequal pupil size
anisocoria
what can cause mydriasis
‣ Drugs (atropine)
‣ Iris atrophy
‣ Fear (esp. cats)
‣ Complete retinal atrophy
‣ Optic neuritis
‣ Optic nerve hypoplasia
‣ Glaucoma
‣ Third nerve palsy
what are some things that can cause miosis
‣ Uveitis
‣ Drugs (pilocarpine)
‣ Horner’s syndrome
‣ Organophosphate toxicity
horner’s syndrome
Loss of sympathetic innervation to eye and adnexa
clinical signs of horner’s syndrome
Miosis
Enophthalmos: shrunken eye
Ptosis (loss of innervation to Muller’s muscle in upper eyelid)
Protrusion of the third eyelid (passive in dogs, due to loss of sympathetically mediated smooth-muscle tone in cats
loss of sympathetic innervation to eye and adnexa
clinical signs of horner’s syndrome
Miosis
Enophthalmos: shrunken eye
Ptosis (loss of innervation to Muller’s muscle in upper eyelid)
Protrusion of the third eyelid (passive in dogs, due to loss of sympathetically mediated smooth-muscle tone in cats
loss of sympathetic innervation to eye and adnexa
1st order neuron for sympathetic innervation of eye is by —
central
begins in hypothalamus, moves through brain stream to throacic spinal tracts
D evelopment of — lesion unlikely in absence of thalamic, brainstem, myelopathic deficits
1st order (central)
2nd order neuron in sympathetic innervation
starts in gray matter of first 3 throacic spinal cord segments, continues through ramus communicans, travels through thorax with sympathetic trunk, passes through but does not synapse with cervicothoracic and middle cervical ganglia
2nd order sympathtic innveration to the eye is close to —
brachial plexus and carotid artery
3rd order sympathetic innervation to the eye
path of 3rd order neuron not well defined
axons exit cranial cervical ganglion, form plexus around carotid and become nasociliary nerve, long ciliary NERVE (which supplies iris dilator and blood vessels of uveal tract, smooth muscle of periorbita)
3rd order sympathetic nerves to the eye are close to
Middle ear, guttural pouch – but path of 3rd order neuron not well defined
which neurotransmitter is released by sympathetic innervation to the eye
norepinephrine
binding to α-adrenergic receptors
what happens when you give phenylephrine to horner’s syndrome
eye with horner’s syndrome will have denervation hypersensitivity
normal eye takes 20 mins for dilation
nerve does not release NE on its own, cells try to find NE by increasing receptors on its membrane, when you give a little NE they have very big reaction
how to test for horner’s syndrome
Phenylephrine 1% ophthalmic solution: direct sympathomimetic
Quicker than normal mydriasis if lesion in post- ganglionic neuron because of denervation hypersensitivity (increased number of receptors or lack of degradation of neurotransmitter in face of insufficient neurotransmitter)
most common cause of horner’s in dogs
idiopathic
head trauma
most frequent cause of horner’s in cats
trauma
then ear issues or idiopathic
