Week 6 - Optho Flashcards
What are the afferent and efferent parts of the PLR?
A: CNII
E: CNIII
What are the afferent and efferent parts of the menace response?
-remember - NOT a reflex
-A: CNII
-E: CNVII and obicularis oculi
What are the afferent and efferent parts of the Palpebral reflex?
A: CNV
E: CNVII and obicularis oculi
What is the Pupillary Light Reflex?
A reflex to a bright light stimulus
- Direct PLR – stimulated eye constricts
- Consensual PLR – non-stimulated eye constricts
–Less strong than the direct PLR
–Domestic animals only (absent in birds)
What are the tips for PLR?
-perform under bring and dim conditions
-false negatives
–high sympathetic tone - STRESS
–iris atrophy - difficult for sphincter to constrict
–posterior synechiae (wont see PLR bc of mechanical reasons)
-will be present at birth
-intact WITH BLINDNESS
-consensual PLR - useful for opaque ocular media
What is the Menace Response?
- A learned response to a threatening gesture - absent at birth
–Absent in young animals (<3 months in cats & dogs)
–learned around 3-4 months - CNs II, VII, cortex & cerebellum
-CRUDE test of vision
-could better test vision with maze tests, cones, anything on a string for a cat
What are tips for a menace response?
-check each eye separately
-cover opposite eye while testing
-avoid touching vibrissae or creating air currents
-perform PALPEBRAL reflex immediately prior - increases patient’s awareness
-inconsistent or absent in patients that are:
–stoic
–depressed
–stressed
Palpebral & Corneal Reflexes are reflexes following touch of:
- Periocular skin (palpebral)
–Stimulate both medial & lateral canthi
–Perform prior to the menace response - Cornea (corneal)b- if you suspect trigeminal nerve paralysis
- CNs V & VII
Neuro-opthalmic functions are (3)
- Eyelid closure
*Orbicularis oculi muscle
* CN VII - Eyelid opening
* Levator palpebrae superioris
* CN III - Sensory innervation to cornea & eyelids
* CN V
- PLR regulates light entry
- Eyelid opening and closure
- Eye motility
- Protection of the globe
- Sympathetic innervation:
–Regulates amount light entering eye
–Position of the globe
–Position upper eyelid (Müller’s muscle)
General signs of neuro-opthalmic dz
- Abnormal pupil size or reactivity
- Abnormal globe position
- Abnormal eyelid position (ex. ptosis - eyelid drooping)
*Inability to close eyelids → Corneal disease - Third eyelid protrusion
What is Horner’s Syndrome?
- Compromise of sympathetic innervation to the eye and its related structures
-route involves 3 neurons
1st neuron - starts in midbrain, goes to spinal cord T1-T3
SYNAPSE
2nd neuron - goes back thru mediastinum/chest to tympanic bullae
SYNAPSE in cranial cervical ganglia with trigeminal nerve
3rd neuron - goes to eye
With Horner’s Syndrome, what anatomical structures does it innervate? (what are the Postganglionic sympathetics?)
What are the normal results/sympathetic function of the anatomical structures, in reference to Horner’s syndrome?
- Smooth muscle periorbita
- Müller’s muscles of eyelids
- Iris dilator - stimulates
- Iris sphincter - inhibits
- Slight protrusion of globe
- Retraction of third eyelid
- Opening palpebral fissure
- Pupil dilation
CS of Horner’s Syndrome
- Miosis
- Ptosis
- Enophthalmos
- Protruded third eyelid (result of enopthalmos)
not painful, but could be suspected by owners
What CAUSES Horner’s Syndrome?
- Idiopathic- the #1 “cause”
- Head, neck, or chest trauma
- Head, neck or chest neoplasia
- Chronic otitis media
- Ear cleaning
- Retrobulbar disease
- Metabolic disease
–Diabetes mellitus
–Hypothyroidism
How do you DIAGNOSE Horner’s Syndrome?
- Clinical signs
- Complete physical exam
–Otic exam - Pharmacologic testing
–Allows localization pre- or post-ganglionic lesion
–Direct sympathomimetic (1% phenylephrine) - Radiography
- Advanced imaging
- Blood work
What is the idea of denervation hypersensitivity in terms of pharmacological testing for Horner’s Syndome?
s-after denervation, there is increased sensitivity of muscle to neurotransmitters – so more receptors are made!
Pharmacologic testing:
* Direct-acting sympathomimetic
–1% Phenylephrine (acts like eps)
- Post-ganglionic lesion
–Dilate pupil w/in 20 min
–dilates quickly bc hypersensitive to the syndrome - Pre-ganglionic lesion
–Dilation takes significantly longer
How do you TREAT Horner’s Syndrome?
-address underlying cause if present
-topical phenyl epinephrine can relieve signs but is short acting
What is the PROGNOSIS Horner’s Syndrome?
-depends on underlying cause
-most postganglionic cases resolve in <6 months
What is Facial Nerve Paralysis?
- Orbicularis oculi innervated by CN VII
- Loss of function results in the inability to close the eyelids (obicularis oculi CLOSES the eyelid)
- Lacrimal nerve runs with CN VII – concurrent decrease in tear production
CS of Facial Nerve Paralysis
- Widened palpebral fissure due to drooping lower lid
- Increase visible sclera, especially ventrolaterally
- Drooping of ear and lip
- Nose “pulled” toward normal side
- Loss of palpebral and corneal reflexes
- Inability to blink results in secondary exposure keratitis
- Ulceration and infection are common
What CAUSES Facial Nerve Paralysis?
- Idiopathic (Cockers, Boxers)
- Iatrogenic (surgery to head or neck)
- Otitis media/interna
- Neuromuscular disease
- Intracranial disease (neoplasia)
- Hypothyroidism
- Trauma to head or neck (HBC, etc.)
How do you DIAGNOSE Facial Nerve Paralysis?
- Clinical signs
- Complete physical exam
- Otic exam
- Neurologic exam
- Radiography
- Advanced imaging
- Bloodwork
