Anatomy-Eye Movements Flashcards
Conjugate eye movements
Eyes move in same direction
Vergent eye movements
Eyes move in opposite direction (converge or diverge)
Saccadic eye movements
Rapid eye movements, no sensory feedback
Requirement for smooth eye movements
Sensory feedback
Intorsion
Top of eye rotates medially
Extortion
Top of eye rotates laterally
Strabismus
Misalignment of eyes
Diplopia
Double vision
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Esotropia. Bad eye pointed inwards.
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Exotropia. Bad eye pointed outwards.
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Hypertropia. Bad eye pointed upwards.
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Hypotropia. Bad eye pointed downwards.
What brainstem nuclei do the lower motor neurons that innervate the extra ocular muscles come from?
Abducens, trochlear & oculomotor nuclei. They are all in the same column as the hypoglossal nucleus.
What components are contained in the abducens nucleus shown below?
1) LMNs that form CN VI and innervate lateral rectus 2) Internuclear neurons that pass through the contralateral MLF on their way to the oculomotor nucleus, here they synapse on the neurons that innervate the medial rectus. This system makes sure that the medial & lateral rectus contract simultaneously.
What role does the abducens nucleus play in convergence?
None. Stimulation goes straight to the medial rectus muscles to cause convergence when an object is close.
List 4 ways you could damage the abducens nerve.
ICA aneurism, increase ICP that compresses it on the petrous temporal bone, AICA aneurism or a stroke of the ventral pons.
A patient presents to the ED after a car accident. He has increased intracranial pressure and is complaining of horizontal diplopia. Physical exam reveals an adducted right eye on attempted forward gaze. What other physical exam tests will you do?
This patient likely has a right CN VI injury. You would have the patient attempt to gaze right. The right eye would remain forward and the left eye would go right. On attempted left gaze and convergence everything should be normal because you do not need the lateral rectus to do these things.
A patient presents to the ED after a car accident. He has increased intracranial pressure. Physical exam reveals that both eyes deviate left on attempted forward gaze. What other physical exam tests will you do?
This patient has a lesion in the right abducens nucleus. This causes unopposed action of the right medial rectus and left lateral rectus and patients can’t look towards the side of the lesion. When asked to look right, the patient will only be able to look forward. Looking left & convergence will be normal.
A patient with MS presents with a left eye that is slightly turned outward. On physical exam, the patient cannot move the left eye past the midline when asked to look right. He also has monocular nystagmus in the right eye. What is your diagnosis?
He has a right MLF lesion affecting the medial rectus movements. Left gaze & convergence will be normal.
Where do the structures indicated below course as they exit the brainstem?
These are trochlear nerves. they cross and go around the brainstem to innervate the contralateral superior rectus muscle.
Main actions of the superior oblique muscle when looking forward. What happens when CN IV is lesioned?
Intortion and depression. When lesioned the eye will extort and elevate.
Main actions of the superior oblique when the eye is adducted. What happens when CN IV is lesioned?
Depress. When lesioned it will present as elevated when adducted.
How do children compensate for superior oblique weakness?
When the superior oblique, the eye is extorted and elevated. They will compensate by tilting their head to line up the bad eye’s visual axis and a vestibulocular reflex causes the good eye to intort and match it.
A patient presents with complete right-sided ptosis. You lift up the eyelid and the eye is abducted and depressed. The pupil is blown. Physical exam reveals no pupillary light reflex in the right eye and inability to accommodate as you move your finger toward his nose. What is causing these symptoms?
CN III lesion. This causes all muscles except the lateral rectus (abduction) and superior oblique (abduct & depress) to be paralyzed, pushing the eye down and out. It also gets the LPS muscle, causing complete ptosis. Destruction of preganglionic sympathetic fibers causes absence of pupillary light reflex in the affected eye.
What is the pathway to produce conjugate saccade to the lateral side?
The cortex sends a signal to the horizontal gaze center (near the reticular formation in the pons). The horizontal gaze center sends an excitatory signal to the abducens nucleus. This causes direct firing of the lateral rectus and stimulation of CN III nucleus to fire the contralateral medial rectus.
What is the pathway to produce conjugate vertical saccade?
The cortex sends a signal to the vertical gaze center (near the reticular formation in the midbrain). The vertical gaze center sends an excitatory signal to the ipsilateral CN III & IV nuclei and contralateral vertical gaze center via the posterior white commissure.
How does movement of your head to the right initiate movement of your eyes to the left?
Firing of the RT vestibular nerve -> RT vestibular nucleus -> Left CN VI nucleus -> left CN VI goes to lateral rectus -> right CN III nucleus -> right CN III goes to right medial rectus
What if your are turning your head to the right, but you don’t want the vestibulocular reflex to push the eyes to the left?
The cerebellum sends an inhibitory signal to the right vestibular nucleus -> Inhibits stimulation of the left CN VI nucleus
What region of the brain is involved in reflex saccades in response to stimuli?
Superior colliculus. It has projections that go to the contralateral horizontal & vertical gaze centers.
What cortical region produces contralateral horizontal gaze movements?
The frontal eye field sends projections to the contralateral gaze centers to produce vertical or horizontal voluntary saccades.
What cortical region produces saccades in response to trying to focus on a visual target.
Posterior parietal area. It connect to the frontal eye field and gaze centers to produce visually guided saccades.
A patient presents to the clinic with an inability to look to his left and a preference to gaze towards his right. What other assessments might you do to determine where his possible lesion is?
The frontal eye field and CN VI both produce lateral gaze movements. A FEF lesion would also come with motor symptoms because it is near the motor cortex. If this patient had a FEF lesion it would be on the right because the fibers cross the the horizontal gaze centers and the patient would not be able to look left.
What cortical region conveys information about a visual target to the cerebellum?
V5.
