8.1 Cranial Nerve Examination

What tests are used for vision and light reflex?

Tracking object - assessing that the animal can see

Menace response - for vision assessment but the pathway involves other areas of brain and facial nerve

Pupillary light reflex (PLR) - reflex to bright light. useful for localising blindness

What is the nervous pathway for the menace response?

Optic nerve

Optic chiasm

Relays through thalamus and then up to visual cortex

Motor cortex

Pons

Cerebellum

Facial nerve - eye closes

Learned response - animal needs to be mature enough to close eye in response to object

What is the nervous pathway for the pupillary light reflex (PLR)?

Response to light

Light goes through optic nerve to optic chiasm

Relays through rostral colliculus

PS CNIII

Oculomotor nerve

How will PLR be different in an animal if they have an optic nerve lesion?

Pupil won’t constrict when light shines

Reflex to light unable to pass

How can we use PLR to determine a central lesion?

No menace response - assume eye, optic nerve and optic chiasm are functioning normally

Eyes remain dilated - pupil unable to respond to light

What are symptoms cerebellar disease?

Animal gait

Bobbing of head - common tremor in cerebellar disease

What is Horner syndrome? What can cause it?

Collection of signs:

Miosis (constricted pupil)

3rd eyelid protrusion

Sunken globe

Narrowed palpebral aperture

Due to damage to sympathetic supply to eye

Lesion in PLR pathway

What is the phenylepinephrine test?

Used for Horner syndrome

Lack of sympathetic supply to eye

Add epinephrine can reverse Horner syndrome

Result - dilation of eye. other eye not affected

Closer to the eye the lesion is, the more quickly the eye will respond to epinephrine

What is nystagmus?

Rhythmical, repetitive movement of the eye

Eyes should be able to retain position centrally in head

Physiological, spontaneous, positional

Can indicate vestibular syndrome if not physiological- keep eyes central in body

What is strabismus?

Both eyes dont line up in the same direction

Combatant, vestibular

What is hydrocephalous?

Skull failed to fuse as brain has been expanding

What is lateral strabismus?

Occular motor nerve innervates: medial, dorsal, rectal and ventral oblique muscles

Lateral - ends up dominant as not controlled by occular motor neuron

Deviation of eye laterally as muscle pulling eye laterally

What is trochlear nerve palsy?

Trochlear nerve - twists the eye ball

Noticeable in animals that dont have round pupil e.g horse, ruminants, cats

Deviation of eyeball

May have compensatory head tilt to opposite side

What is medial strabismus?

Due to problem with cranial nerve VI

CN VI innervates lateral rectus

Eyeball pulled medially

What is vestibular strabismus?

Lift head up and pupil deviates downwards

What is extraocular muscle weakness?

Autoimmune disease of extraocular muscle

Eyes disappear into head

Severe weakness and eyes deviated down

Responds to steroids

How can we assess facial sensation?

Trigeminal nerve

Palpebral reflex

Corneal reflex

Sensation head (ear, lip, nose)

Assessing cranial nerve V-VII

Facial sensation - trigeminal nerve

Facial movement - facial nerve

What muscles are in the head?

Masticatory muscles:

Temporal muscle mass

Jaw tone - opening mouth

Innervated by trigeminal nerve

What is bilateral trigeminal palsy?

Difficulty closing jaw - trigeminal nerve

Dysphagia - swelling problems as unable to close jaw

How can we assess facial muscles?

Innervated by facial nerve

Palpebral reflex

Corneal reflex

Menace response

Facial symmetry

What nerve control facial functions?

Swallowing/gag reflex - CNIX and X

Oesophageal function/regurgitation - CNX

Vocalisation - CNX

Tongue movement - CNXII

What can an inability to swallow indicate?

Glossopharyngeal or vagus nerve

CN nuclei in medulla

Neuromuscular diseases:

Polymyositis, myasthenia gravis, hereditary myopathies