Test 2: lecture 23: neuro-ophth Flashcards by jillian Bastidas

relays visual signal from retina to CNS

Optic : CN II

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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

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innervates dorsal oblique

Trochlear: CN IV

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ophthalmic and maxillary branches provide sensory innervation to eye and accessory organs, including cornea, conjunctiva, lacrimal gland, and periocular skin

Trigeminal : CN V

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—innervates lateral rectus and retractor bulbi muscles

Abducens: CN VI

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innervates various mm controlling blink response

Facial: CN VII

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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

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what is not working

lateral rectus

abducent CN 6

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what muscle not working?

superior dorsal oblique

trochlear (CN4)

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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

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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)

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CN 4

trochlear nerve
Dorsal oblique muscle

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CN 5

trigeminal nerve

Ophthalmic branch of trigeminal nerve

Sensory fibers
* Pain and pressure from the cornea and eyelids

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what provides sensory to eyelids

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CN 6

abducens

Motor fibers
* Extraocular muscle:
* Lateral rectus muscle
* RETRACTOR BULBI MUSCLE

Sympathetic fibers
* Sympathetic innervation of cat’s
third eyelid

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CN7

facial

Motor fibers
Eyelid muscles (closure)
* Orbicularis oculi muscle

Parasympathetic fibers
* Lacrimal glands

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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

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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

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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

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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 ## Footnote loss of sympathetic innervation to eye and adnexa

clinical signs of horner's syndrome

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