Ophtho3- Neuro-Ophtho

• II
• III
• IV
• V
• VI
• VII
• VIII
• X

• the more laterally placed the globes (prey species), the less binocular overlap (eyes are not seeing the same thing), the more decussation is needed to process what the eyes are seeing (because there is less overlap)
• this is vice versa for more medially placed eyes in predator species

• axons enter the eye at the optic disc to form optic nerve
• optic nerves decuss (cross) at the chiasm and travel at the optic tract to brain nuceli

• visual fibers
• pupillary motor fibers

blindness, dilated pupil, absent PLR

• [oculomotor nerve]
• parasympathetic motor fibers to pupil (pupil constriction)
• motor innervation to all extraocular muscles (EXCEPT lateral rectus, retractor bulbi, dorsal oblique)

• dilated pupil
• ventro-lateral strabismus
• ophthomoplegia
• ptosis

• [trochlear n]
• motor innervation to superior oblique extraocular muscle

• [rare to have CN IV lesion alone but...]
• extorsion (dorsal globe rotated laterally- since it normally rotates the dorsal globe medially)

• Ophthalmic branch: sensory fibers from cornea, conj, and upper eyelid; afferent branch of the oculomotor reflex
• Maxillary branch: sensory to skin of lower eyelid
• Mandibular branch: motor to muscles of mastication

• loss of sensation
• decreased reflex tear production

loss of sensation to the lower eyelid

masticatory muscle atrophy (enophthalmia)

motor to lateral rectus extraocular muscle and retractor bulbi muscle

• [CN VI]
• [isolated lesion of CN VI is very rare but...]
• medial globe deviation (LR muscle), inability to retract globe (absent corneal reflex d/t damage to retractor bulbi)

• [facial nerve]motor to muscle of facial expression (closure of eyelids, ear position, lip movement nares movement)
• parasympathetic fibers to lacrimal gland (efferent arm of lacrimation)

• drooping upper eyelid (ptosis)
• incomplete blink reflex (lagophthalmos)
• decreased lacrimation (low STT)
• abnormalities of ear/ lip/ nare position and movement

otitis, hypothyroidism, trauma, temporohyoid osteoarthropathy, etc

• afferent component of ocular position
• controls EOM position so that the eyes can remain fixed while the head turns (vestibular)

• [CN VIII]
• nystagmus
• eye drop

efferent arm of the oculocardiac reflex (intraoperative handling of the eye results in bradycardia)

• stop handling the eye
• retrobulbar nerve block
• administer parasympatholytic agent (atropine)
• keep animal under deep anesthesia and well oxygenated

• first neuron: midbrain to T1-T3
• second neuron: thorax/ neck
• third neuron: cranial cervical ganglion to eye

• dilator muscle of the pupil--> mydriasis
• Muller's muscle--> elevation of superior eyelid
• smooth muscle of the periorbital fascia--> globe positioned forward
• smooth muscle of blood vessels of conj and skin--> vasoconstriction

• ptosis
• enophthalmos
• protrusion of NM
• miosis
• vasodilation of affect side of face and eye
• [horses] unilateral sweating

ocular pain

• first order: CNS disease
• second order: cervical or thoracic disease
• third order: middle/ inner ear disease, endocrinopathies

• utilizes principals of denervation hypersensitvity to first confirm or rule out 3rd order lesion[increased number and sensitivity of receptors to applied neurotransmitter due to decrease or absence of endogenous neurotransmitter, NE]
• put phenylephrine in eye b/c it mimics NE--> positive and timely resolution of clinical signs--> confirms third order lesion [lack of response--> second or first order lesion--> rule out or confirm 2nd order lesion by screening for cervical or thoracic trauma or mass]
• keep in mind- very early or very chronic third order lesions may not respond; also, first order lesions are very rare and would be accompanied by many CNS signs

• result in pupil constriction/ miosis (pupillary fibers originate in nucleus of CN III)
• lacrimal gland fibers (travel with CN VII)
• innervate lateral nasal gland

• mydriasis
• internal ophthalmoplegia
• decreased STT/ KCS
• dry nose

• afferent fibers of CN V (ophthalmic and maxillary sensory branches to eyelids)
• efferent branches of CN VII (motor to eyelids)

• afferent fibers of CN V (sensory to cornea)
• efferent fibers of CN VI and VII (motor to retractor bulbi and eyelids)

• afferent fibers of retina and optic nerve (can it see the light)
• efferent parasympathetic fibers with CN III (can the pupil constrict)

• direct: stimulated pupil constricts
• consensual: contralateral pupil constricts because of the decussation of the optic nerve, both eyes see the light

retina and optic nerve--> optic chiasm--> optic tracts to pretectal nucleus and central decussation

parasympathetic nucleus of CN III (EWN)--> ciliary ganglion--> short ciliary nerves--> iris sphincter muscle

pupil was consensually constricted, but dilates in the face of direct light--> indicates afferent lesion (retina or optic nerve to that eye)

• subcortical reflex (does not involve the visual cortex- positive dazzle does not indicate vision but it does indicate light perception)
• normal response to very bright light is squinting and/ or globe retraction
• less than 5% of retinal function required for this reflex

• menace reflex
• tracing a cotton ball
• maze test
• visual placing

lateral retina and optic nerve (binocular vision); medial retina and optic nerve (peripheral vision/ monocular vision)

• afferent fibers of the retina and optic nerve (can it see the stimulus)
• efferent fibers of CN VII (can it blink in response tot he stimulus)
• cerebellum

• just before the lateral geniculate nucleus, where the afferent PLR pathway splits off to synapse on the pretectal nucleus
• the efferent PLR pathway is completely independent of the vision pathway

retina/ optic nerve--> chiasm--> optic tracts to lateral geniculate nucleus--> optic radiations--> visual cortex of the brain

absent PLR AND blindness

blindness with NORMAL PLR

absent PLR but NORMAL vision

quality and quantity of light (cataracts cause blindness)

quantity of light (ie. PLR is normal through a cataract)

• when light is shown in affected eye, no direct PLR, no consensual PLR
• when light is shown in the unaffected eye, both pupils constrict normally
• lesion of retina or optic pathway up to the optic chiasm

• when light is shown in affected eye, no direct PLR, normal consensual PLR
• when light is shown in unaffected eye, normal direct PLR, no consensual PLR
• lesion of EWN, CN III, or iris sphincter

• afferent PLR deficit
• absent dazzle reflex

• afferent PLR deficit
• absent dazzle reflex

• normal PLR
• blindness

• afferent PLR deficit
• absent dazzle reflex

• dilated pupil due to a lesion of the parasympathetic innervation to the pupil
• dogs- round, fully-dilated pupil
• cats- may be fully dilated; may have only nasal or temporal nerve affected and have a D-shaped pupil

retinal detachment, optic nerve atrophy, chronic glaucoma

• CN3/ PSN denervation
• posterior synechia (iris is mechanically fixed and physically cannot constrict)
• atropine/ tropicamide (parasympatholytic drogs)
• iris atrophy (age-related, inflammation-related)