Eye Movements Flashcards
Where is vision optimized?
Fovea
What nervous system (symp or parasymp) is working with high light?
High light, pupil constricts –> pupillary sphincter muscle –> contraction
parasympathetic
What nervous system (symp or parasymp) is working with dim light?
Pupillary dilator muscle –> contrction
(sympathetic)
What does cilliary muscle have intrinsic muscle control over?
controls lens shape (enables the lens to focus when objects are closer to the eye)
Cilliary muscles Contract to allow release of the lens –> accomodation
Extraocular muscles and actions
Define:
esotropia
eye in (medial gaze)
Define:
exotropia
Bonus: What lesion would produce exotropia?
eye out (lateral gaze of eye)
Caused by lesion affecting medial rectus
Define:
Hypertropia and hypotropia
eye up and eye down respectively
What muscles move the eye vertically when the eye is ADDucted?
oblique muscles
What muscles move the eye vertically when the eye is ABducted?
Superior and inferior rectus muscles
What is the general location of motor nuclei of eye in midbrain and pons?
dorsal medial
What are the GSE of eye movements?
(Bonus: where are the nuclei located?)
General Somatic Efferents: lower motor neurons to 4 extra ocular muscles and levator palpebrae superioris
- Oculomotor nucleus (midbrain)
- Trochlean nucleus (midbrain)
- Abducens nucleus (pons)
What is the GVE of eye movements?
Edinger-Westphal nucleus (general visceral efferent)
- Preganglionic parasympathetic to pupillary constrictor and ciliary muscle of lens
What does CN III Innervate?
4 extraocular muscles and 1 eyelid muscle (GSE)
- That is the medial rectus, inferior rectus m. superior rectus m., inferior oblique, and superior levator m.
- All except lateral rectus and superior oblique
- See red paths (only) in image
What are the extraocular actions of CN III?
- move eye up and down
- Move eye towards the nose
- Rotate it externally (with upward component)
What lesion/syndrome would you suspect with ptosis?
- CN III lesion or
- Horners syndrome
- Myasthenia gravis
What causes a blown pupil?
Bonus: what’s the medical term for it?
GVE (Edinger-Westphal nucleus) lesion –> mydriaosis
- E-W (Parasymp) innervates ciliar and constrictor muscles.
- Lesions cause mydriaosis (dialated pupil) and loss of accomodation
What is miosis and what causes it?
Miosis = constricted pupil (with Horner’s syndrome), cuased by lesion in sympathetic innervation to dilator muscle.
What is the path of light reflex (considering constriction response)?
Light to eye –> Afferent limb: CN2 –> some info crosses, some doesn’t –> Wrap around midbrain –> enter pretectal nucleus (synapse)–> send info bilaterally to E-W nucleus –> sends info bilatterally to pupillary constrictor muscles of eyes (Efferent limb: CN3)
Signs/sx of left optic nerve lesion = afferent pupillary defect
(Swinging flashlight test)
Pupil constricts to light in normal eye, but when light is moved quickly to the defective eye, it will seem to dilate in respose (bc the input is “less”)
Signs/sx of lesion of CN III
- No direct response but yes to indirect/consensual response to light
- Pure: ptosis (eye down and out); pupil blown
- Partial: (no direct or consensual response in affected, both direct and consensual response in unaffected)
- Shine light in affected eye:
- no response to light in the affected eye
- do get constriction in consensual eye
- Shine light in unaffected eye:
- direct response in affected eye
- no consensual response in unaffected
- Shine light in affected eye:
How to distinguish betwn horners and E-W or CN III lesion in a pt with ptosis?
Look to the pupils
What damage is suspected with the following sx?
- Mydriasis - on left eye
- Loss of pupillary constriction -right eye
- Loss of accomodation -right lens will not change curve to adjust to view near objects
CN III damage E-W on “right”:
- Mydriasis - pupil on affected side dilated (“blown” pupil)
- Loss of pupillary constriction - ipsilateral eye
- Loss of accomodation - ipsilateral lens will not change curve to adjust to view near objects
What do you suspect is affected?
- Mydriasis - pupil on affected side dilated (“blown” pupil)
- Loss of pupillary constriction - ipsilateral eye
- Loss of accomodation - ipsilateral lens will not change curve to adjust to view near objects
plus
- Exotropia - ispilateral eye “down and out” when pt looks straight ahead
- Inability to move the ipsilateral eye vertically or medially
- Diplopia
- Ptosis - ipsilateral eyelid droops
CN III damage to E-W with GSE components to extra-ocular muscles and eyelids
What do you suspect?
clinical triad of “blown” pupil, hemiplegia, and coma
Uncal herniation: transtentorial herniation
- Oculomotor nerve: ipsilateral (usually) CN III signs
- Cerebral peduncles: hemiplegia (contralateral)
- Reticular formation: decreased consciousness or coma
What is the innervation/action of the trochlear nerve (CN IV)?
GSE to Superior Oblique Muscle
- Primary Action: intorsion
- Also depresses (in adducted positon) and abducts
What is the clinical presentation of lesion of a right trochlear nerve?
CN IV palsy: extorsion with hypertropia (often seen with head tilt to prevent double vision)
NB: could also be a left trochlear nucleus lesion, though rare
What lesion would be responsible for paralysis of the lateral rectus, seen with esotropia?
What could be some causes?
Pathway: abducent nucleus in caudal pons to CN VI - GSE to the lateral rectus muscle
Causes: increased intracranial pressure bc the brainstem is pushed downwards and CN VI is stretched
