Neuro-ophtho Flashcards
CN II
Optic nerve
Exits at optic foramen
Axons of retinal ganglion cell
Function - carry electrical signal from retina to brain
CN III, IV, VI
All exit at orbital fissure
Function - Innervation of Extraocular muscles
III - Oculomotor
IV - trochlear
VI - abducens
CN III
Innervates the DR, MR, VR, VO and levator palpebral superioris
– Helps you look up, toward the nose, down & centralize pupil by counteracting the dorsal oblique
- lifts upper lid
PSN Innervation to Iris sphincter muscle and ciliary body (miosis)
Lesion to III causes what strabismus s
Down and out strabismus
CN IV
Innervates dorsal oblique muscle - helps centralize pupil in counteracting the ventral oblique muscle
Trochlear nerve lesion causes what kind of strabismus
Inward/cross eyed strabismus
CN VI
Innervates lateral rectus and retractor bulbi
Moves laterally, sucks eye inward = moving 3rd eye lid
Abducens nerve lesion leads to what kind of strabismus
Unilateral medial strabismus
Remember 3
DO4LRRB6Rest3
Dorsal oblique - CN 4
Lateral recuts & retractor bulbi - CN 6
Rest of the muscles - CN 3
CN V
Ophthalmic branch exits orbital fissure
Maxillary branch exits round foramen via rostral alar canal
Mandibular branch exits oval foramen
CN V innervation
Ophthalmic brachial provides sensory to the orbit, medial canthus, conjunctiva and cornea
Maxillary branch provides sensory to lateral canthus
Mandibular provides to muscles of mastication
CN VII
Exits stylomastoid foramen
Function - innervation to orbicularis oculi = blinking
PNS Innervation to lacrimal gland & 3rd eyelid gland
VIII
Exits internal acoustic meatus
Functions to coordinate eye movement with head movement so vision isn’t blurry
Works with the medial longitudinal Faciculus
CN X
PSN tone in decreasing heart rate - pressing on eyelids*
Beneficial for vagal maneuvers
Can be detrimental - oculocardiac reflex
Parasympathetic input on CN III
Parasympathetic nucleus of CN III, aka Edinger-Westphal nucleus
• Innervation to iris sphincter muscle and ciliary muscles
• Functions: miosis and accommodation
Parasympathetic input for CN VII
Parasympathetic nucleus of CN VII
Innervation to lacrimal /3rd eyelid glands
Functions: lacrimation & nasal wetting
neurogenic KCS: dry eye
Stimulation a Parasympathomimetics - pilocarpine
Inhibition w parasymatholytics/anticholinergic - atropine, glycopyrrolate
Xeromycteria
Commonly occurs with neurogenic KCS
Dry eyes and dry nose
Testing vision
Menace response
Cotton ball test
Menace response
Afferent info - CN II
Efferent info - CN VII = blinking & CN VI = globe retraction
Not a reflex, its a learned response. Will be absent in young puppies/animals (<12 wks)
cotton ball test
Evaluates CN II (afferent)
Tracking moving object w eyes
Inconsistencies in results
Age - learned response vs reflex
Stoic animals
Pain (ocular or systemic)
Cats - wont menace
Exotics - birds/reptiles
Testing sensation
Palpebral reflex - blinking in response to touch,
A info - CN V opthalmic branch/max branch
E info - CN VII
Corneal reflex - blinking in response to touch on cornea
A info - CN V ophthalmic branch
E info - CN VII (blink) and CN VI (globe retraction)
Testing movement
Oculocephlic reflex - dolls eye reflex, moving head to Track movement
Afferent info - CN VII
Efferent info - CN III, IV, VI
Dazzle reflex
Stimulated with bright light = blink and globe retraction
Afferent - CN II
Efferent - CN VII and CN VI
It’s a pain reflex due to bright light, its pre-cortical and does not signify vision
Visual pathway
Nasal and lateral hemiretinas - optic nerve - cross over at optic chiasm - optic tract = Lateral geniculate nucleus = visual cortex
PLR
Afferent - CN II
Nasal & lateral hemiretinas - optic nerve - optic chiasm X - optic tract - retractable nucleus —> 2nd cross over
50% of fibers cross to ipsilateral side
PLR efferent
efferent CN III
Parasympathetic nucleus of CN III (edinger-Westphal nucleus) —> CN III efferent tract —> ciliary ganglion —> Irish sphincter muscle
Vision vs PLR
Vision
Requires function of millions of photoreceptors
Cortical input and process aka higher centers in brain
Vision vs PLR*
Doesn’t requires many functional receptors
PLR
Parasympathetic tone
Pretectal nucleus
Precortical response
Reflexes dont see the higher centers of the brain aka reflexes don’t signify vision
However this tract has a double cross over at axons and its not 50:50 in domestic species
Direct response
Direct is an ipsilateral response which has a greater magnitude than consensual or indirect response
100% cross over
Occurs in birds - 100% cross over means there will be no consensual PLR
50% cross over
Species with 50% cross over, a direct and consensual response results in equal PLRs
Abnormal PLRs
Afferent lesions
Retina - retinal detachment/degeneration
Optic nerve - neuritis, avulsion, entrapment
Chiasmal lesion - tumor, traction
Optic tract - prior to split to visual and PLR pathways
Abnormal PLRs
Efferent lesions
Common in CN III
High intracranial pressure, midbrain lesions, orbital fissure syndrome, retrobulbar disease
End organ lesions - abnormal PLRS
Junctionopathies
High IOP
Synechiae
Lens lux/sublux
Iris atrophy
Pharmacological mydriasis (atropine, Tropicamide)
Cataracts, SARDS, central blindness
Severe cataracts can be blinding
Sudden acquired retinal degeneration syndrome is acutely blinding disorder
Central or Cortical vision loss does not necessarily involve the PLR pathways
Blindness diseases PLR should be present
PLRs abnormal - suspect concurrent problems
Cataracts is a common result from retinal detachment and retinal degeneration
SARDs is the most commonly caused by glaucoma/optic neuritis
Central blindness common cause is multi focal disease
Swinging flashlight test
Detecting difference between two eye in how they respond to light being shone in one eye at a time
Marcus Gunn pupil
Use of swinging flashlight test
Detecting unilateral or asymmetrical disease of the retina or pre chiasm optic nerve
- unilateral retinal detachment
- unilateral optic neuritis
Horners syndrome
Sympathetic denervation
Classical signs - enophthalmos, ptosis, miosis, protrusion of 3rd eye lid
Other signs: conjunctival hyperemia, equine sweating, bovine nasal plenum anhydrosis
Pathway for Horner’s syndrome
Hypothalamic neurons (1st order) - synapse on sympathetic pre gang neurons (2nd order) - synapse at cranial cervical ganglion on sympathetic post ganglion neurons (3rd order) - enter cranial vault = end at orbital fissure
testing for Horner’s syndrome
1 drop of 10% phenylephrine
Signs should resolve partially to complete
Faster response suggests 3rd order lesion
Mydriasis: normal eye & 1st order - 60-90 minutes
2nd order Horners - 20-60 minutes
3rd order - <20 minutes
Honers syndrome DDX - pregang disease
Brainstem - neoplasia, inflammatory, vascular trauma
Cervical SC - Neoplasia, trauma, FCS, IVDD, luxation
T1-3 SC - neoplasia, trauma, FCE, IVDD, luxation
Brachial plexus: trauma, avulsion, neoplasia
Mediastinal mass, trauma, carotid ligation
Neck: aggressive jug stick, accidental carotid stick, bite
Horners syndrome DDX - post gang disease
Middle ear - otitis media/intera, polyp, guttural pouch disease, trauma, neoplasia
Cavernous sinus - neoplasia, inflammatory disease, vascular disease/aneurysm
Retrobulbar - neoplasia, abscess, trauma
