Eye Movements and Pupillary Control Flashcards
What is the primary action of lateral rectus?
Abduction
What is the primary action of medial recuts?
Adduction
What is the:
- primary action?
- action on eye in abducted position?
- action of eye in adducted position?
superior rectus?
- Primary: Elevation and intorsion
- Abducted position: Elevation
- Adducted Position: Intorsion
What is the
- primary action
- action on eye in abducted position
- action of eye in adducted position
of inferior rectus?
- Primary: Depression and Extorsion
- Abducted Position: Depression
- Adducted Position: Extorsion
What is the
- primary action?
- action on eye in abducted position?
- action of eye in adducted position?
superior oblique?
- Primary: Intorsion and Depression
- Abducted position: Intorsion
- Adducted Position: Depression
What is the
- primary action
- action on eye in abducted position
- action of eye in adducted position
inferior oblique?
- Primary: Extorsion and Elevation
- Abducted Position: Extorsion
- Adducted Position: Elevation
What movements of the eye occur around the A-P axis?
Intorsion & Extorsion
What movements of the eye occur around the horizontal axis?
Elevation & Depression
What movements of the eye occur around the vertical axis?
Abduction & Adduction
What muscles are innervated by CN III (Oculomotor Nerve)?
- Medial rectus, inferior rectus, superior rectus & inferior oblique
- Levator palebrae superioris
- Parasympathetic input to pupil contractor and ciliary muscle
What muscles are innervated by CN IV (Trochlear Nerve)?
Superior oblique muscles
What muscles are innervated by CN VI (Abducens Nerve)?
Lateral rectus muscle
What constitutes the somatic motor column?
- CN Nuclei (oculomotor, trochlear & abducens)
- Hypoglossal nucleus
Where does the oculomotor nerve (CN III) arise from?
- Oculomotor nuclei
- Edinger- Westphal nuclei
What two places does the Oculomotor Nerve exit?
- Upper midbrain at the level of superior colliculi and red nucleus
- Intrapeduncular fossa
Where does the oculomotor nerve travel?
- B/w posterior cerebral and superior cerebellar arteries
- In subarachnoid space near the posterior communicating artery
What is the oculomotor nerve susceptible to?
Compression from aneurysms
Damage to the oculomotor nerve causes paralysis to what?
- All ipsilateral extra ocular muscles (exceptions)
- Ipsilateral levator palpeerde superior muscle
Damage to the oculomotor nerve causes paralysis to all ipisilateral extra ocular muscles except what?
- Superior oblique
- Lateral rectus
- So eye rests in down & out position
- Causes diplopia that worsens when looking up and medially
What is ptosis?
Eye closed unless upper lid is raised with finger (complete lesion) or drooping (partial lesion)
Oculomotor nerve palsy causes a loss of ipsilateral parasympathetic input which presents as what?
Pupil dilated and unresponsive to light
What are the subnuclei of the Oculomotor Nucleus? What muscles to the innervate and what side is innervated?
Focus on Edinger-Westphal & Central Caudal
- Edinger-Westphal (parasympathetic) (Bilateral pupillary constrictors & ciliary muscle of lens)
- Central caudal (Bilateral levator palpebrae superior)
- Dorsal (ipsilateral inferior rectus)
- Intermediate (Ipsilateral Inferior oblique)
- Ventral (Ipsilateral medial rectus)
- Medial (contralateral superior rectus)
A unilateral oculomotor nucleus lesion will not cause what?
- Unilateral ptosis
- Unilateral dilated unresponsive pupil
- Unilateral superior rectus palsy
Why will a unilateral oculomotor nucleus lesion not cause unilateral ptosis, dilated unresponsive pupil, superior rectus palsy?
- Bilateral levator palpebrae superior and the pupillary constrictor muscles are innervated by a shared, central nucleus
- Unilateral lesion of the oculomotor nucleus affect both the contralateral superior rectus (contralateral innervation) and the ipsilateral superior rectus (fibers cross before exiting the nucleus)
Where doe the trochlear nerve (CN IV) arise from?
Trochlear nuclei in the lower midbrain at the level of the inferior colliculi
Which CN is the only CN to exit the brain dorsally?
CN IV Trochlear Nerve
What is the only CN to exit the brainstem and then cross to the opposite side?
Trochlear Nerve (CN IV)
The Trochlear (CN IV) is susceptible to what?
Compression from cerebellar tumors
Trochlear nerve (CN IV) is easily damaged by what?
Thin and easily damaged by shear (head trauma)
What does damage to the Trochlear Nerve (IV) cause?
- Paralysis of superior oblique muscle
- Eye Position: Hypertropia & Extorsion
- Vertical diplopia
In Trochlear Nerve Palsy how is vertical diplopia improved and how is it worsened?
- Improved: With chin tuck and head tilt away from the affected eye
- Worsens looking down & toward nose
Where does the Abducens nerve arise from and exit?
- Arise from: Abducens nuclei on the floor of 4th ventricle under the facial colliculi in the mid to lower pons
- Exits ventrally at the pontomedullary junction
What course does the abducens nerve take to reach the lateral rectus?
Long vertical course
What is the Abducens Nerve susceptible to?
Downward traction injury produced by elevated ICP
Damage to the abducens nerve causes what?
- Paralysis of lateral rectus muscle
- Horizontal diplopia
What is the eye position of abducens nerve palsy (CN VI)?
- Affected eye does not abduct normally
- Possible estropia (eye turns in)
How does horizontal diplopia from abducens nerve palsy worsen and improve?
- Worse: gaze towards impaired side & far vision
- Improve: near vision & when head turn towards affected eye
What do brainstem circuits control?
- Horizontal eye movements
- Vertical eye movements
- Vergence eye movement
What is the purpose on brainstem circuits controlling eye movements?
- Eye movement of the left & right are yoked together for conjugate gaze in all directions
- Eyes can maintain fused fixation as target move towards or away from viewer
What are the brainstem circuits for horizontal eye movements?
- Oculomotor Nucleus
- Abducen Nucleus
- Medial Longitudinal Fasciculus (MLF)
- Paramedian Pontine Reticular Formation (PPRF)
What does the oculomotor nucleus control?
Ipsilateral medial rectus muscle
What does the abducens nucleus control and function as?
- Controls: Ipsilateral rectus muscle
- Functions: As horizontal gaze center (controls horizontal eye movements for both eyes directed towards the ipsilateral side)
What is the medial longitudinal fasciculus (MLF)?
Pathway connecting oculomotor, trochlear, abducens & vestibular nucleiW
The Paramedian Pontine Reticular Formation (PPRF) provides input from where?
- Cortex
- Other pathways to the abducens nucleus
Describe the pathway for brainstem circuits for horizontal eye movement
- Cortex and other brain regions
- Right PPRF
- Right abducens nucleus (to right lateral rectus and to left oculomotor nucleus (via left MLF))
- to left medial rectus
What is the result of the brainstem circuit for horizontal eye movements?
Right eye abducts & left eye adducts to gaze to the right
What is ipsilateral lateral gaze palsy and what causes it?
- Unable to look with either eye towards the side of the lesion
- Caused: By lesion to either the abducens nucleus or PPRF
What is internucleus ophthalmoplegia and what causes it?
- Ipsilateral eye does not adduct fully on attempted horizontal gaze to the side opposite the lesion
- Spared function with convergence
- Triggers nystagmus in the opposite eye
- Caused by: lesion to MLF
What is one-and a half syndrome and what is caused by it?
- Ipsilateral eye no horizontal movement with gaze to either eye
- Contralateral eye has preserved abduction, but with nystagmus
- Caused by: lesion involving MLF & abdomen nucleus (or PPRF) on the same side
Where are structures controlling vertical eye movements located?
- Midbrain
- Rostral midbrain reticular formation
- Pretectal area
What are vertical eye movements closely coordinated with?
Movement of the upper eyelids in the same direction
What does the ventral and dorsal portion go the midbrain control?
- Ventral portion: mediates downgaze
- Dorsal portion: mediated upgaze
What does ventral and dorsal lesions cause?
- Ventral lesions: impair downgaze
- Dorsal lesions: impair upgaze
What is progressive supranuclear palsy and what does it cause?
- Midbrain atrophy
- Causes impaired vertical eye movement
What may lesions to the pons cause?
- May impair horizontal gaze (abducens) but spare vertical eye movements
- Locked in syndrome (preserved vertical eye movement used for communication)
What muscles do convergence of the eyes?
Bilateral medial recti
What muscles do divergence of the eyes?
Bilateral lateral recti
Both brainstem circuits are mediated by what?
- Mediated by separate neuron pools in the midbrain reticular formation
- Influenced by descending inputs
What does the frontal eye fields generate?
Saccades in the contralateral direction via connection to contralateral PPRF
What does Parieto-occipital- temporal cortex control?
Smooth pursuit movements in the ipsilateral direction via connection to vestibular nuclei, cerebellum & PPRF
What is cortical control of eye movement influenced by?
- Primary visual cortex & visual association cortex
- Basal Ganglia (modulated eye movements)
What are right way eyes?
- Eyes look away from side of weakness
- Impaired eye movement in contralateral direction
Lesion to what causes right way eyes?
Cerebral hemisphere
What is wrong way eyes?
Eyes look toward the side of weakness
How does wrong way eyes occur?
- Seizures (frontal eye fields & motor association cortex)
- Thalamic hemorrhage
- Lesions to pons (corticospinal + PPRF or abducens nucleus)
Describe the parasympathetic pathway for pupillary constriction
- Light enter one eye
- Projects to both optic tracts (some fibers cross at optic chiasm)
- Synapse in pretectal area (axons both cross & remain ipsilateral)
- Synapse on pregagnlionic parasympathetic fibers in bilateral Edinger-Westphal nuclei (axons both cross and remain ipsilateral to travel bilaterally in oculomotor nerve
- Synapse on post ganglionic parasympathetic in the ciliary ganglia
- Pupillary constrictor muscles
When light shone into R eye cause:
- Direct response?
- Consensual response?
- Direct response: Pupil constriction of R eye
- Consensual response: Pupil constriction of L eye
What is the pupillary light response in someone with an oculomotor nerve lesion?
- Ipsilateral pupil may appear dilated relative to opposite eye (more obvious in light room vs dark)
- Ipsilateral pupil shows a decreased or absent repose to light shone in either eye
What is the pupillary light response when there is damage to afferent pathway?
- Damage before optic chiasm
- Neither eye response to light shone in ipsilateral eye
- Both respond to light shone in contralateral eye
When a visual object moves from far to near, input from visual cortex to the parasympathetic pathways in the midbrain result in what?
- Pupillary constriction
- Accommodation of the lens (ciliary muscle)
- Convergence of the eyes
Describe the sympathetic pathway for pupillary dilation
- Descending sympathetic pathway for pupil dilation travels down from hypothalamic nuclei to T1-T2
- Synapse on preganglionic sympathetic neurons in intermediolateral cell column of upper thoracic spine
- Exit T1 & T2 nerve roots and travel around the apex of the lung to ascend in paravertebral sympathetic chain
- Synapse on postganglion sympathetic neurons in superior cervical ganglion
- Ascen through carotid plexus along with internal carotid artery
- Activates pupillary dilator muscle, superior tarsal muscle (assist with upper lid elevation) & cutaneous arteries & sweat glands
What is Horner’s Syndrome and what are the symptoms?
- Caused by disruption of sympathetic pathways to eye & face
Symptoms:
- Ptosis (upper eyelid droops)
- Miosis (decreased pupil size & impaired dilation)
- Anhidrosis (decrease sweating ipsilateral face & neck)
What are lesion locations that cause Horner’s Syndrome?
- Lateral hypothalamus
- Brainstem lesion
- Spinal cord trauma
- Damage to T1/T2 nerve roots (disc herniation, apical lung tumor)
- Cavernous sinus (thrombosis, aneurysm)
- Orbit
