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Mind, Brain, and Behavior > Eye Movements and Pupillary Reactions > Flashcards

Eye Movements and Pupillary Reactions Flashcards

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1
Q

Six muscles that control eye movement

A
  • Four rectus muscles
    • Superior
    • Inferior
    • Medial
    • Lateral ( CN 6 )
  • Two oblique
    • Superior ( CN 4 )
    • Inferior
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2
Q

CN 4 controls the __ muscle.

CN 6 controls the __ muscle.

CN 3 controls __.

A

CN 4 controls the superior oblique muscle.

CN 6 controls the lateral rectus muscle.

CN 3 controls everything else

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3
Q

Four principal eye movements

A
  • Lateral eye abduction - lateral rectus, supplied by CN 6 (hence abducens)
  • Medial eye adduction - medial rectus, supplied by CN 3
  • Eye elevation - superior rectus, supplied by CN 3
  • Eye depression - inferior rectus, supplied by CN 3
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4
Q

Eye movement diagram

A
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5
Q

Intorsion

A

Rotation of the eye toward the nose/midline

Supplied by the superior oblique muscle

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6
Q

Extorsion

A

Rotation of the eye toward the ear

Supplied by the inferior oblique muscle

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7
Q

As the head is tilted to the right, the right eye ___ and the left eye ___

A

As the head is tilted to the right, the right eye intorts and the left eye extorts

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8
Q

The trochlea

A

Bony part of the pully system that the superior oblique muscle utilizes.

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9
Q

In addition to moving the eye upwards and downwards, the superior and inferior rectus muscles also . . .

A

. . . aid in eye rotation.

The superior rectus works with the superior oblique to perform intorsion,

while the inferior rectus works with the inferior oblique to perform extorsion

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10
Q

mnemonic to recall that inferior muscles extort and superior muscles intort

A

InfEXions will leave you SupINe

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11
Q

From the midbrain and pons, how do CN 3, 4, and 6 reach the orbit?

A

They travel through the subarachnoid space, through the cavernous sinus, then out into the orbit

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12
Q

Fascicle

A

Portion of a cranial nerve that is still in the brainstem

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13
Q

Four locations that may be sites of CN 3, 4, or 6 lesions

A
  • The brainstem (medulla or pons)
  • The CN in the subarachnoid space
  • The cavernous sinus
  • The orbit
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14
Q

Symptoms of complete CN 3 palsy

A
  • Weakness of the four supplied muscles, leaving the eye down and out: down due to the unopposed action of the superior oblique (CN 4) and out due to the unopposed action of the lateral rectus (CN 6)
  • Weakness of the levator palpebrae, causing ptosis
  • Decreased parasympathetic input to the pupil, leading to pupillary dilation (mydriasis)
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15
Q

Due to the way the different fibers run in the third nerve, partial lesions of the third nerve can affect . . .

A

Due to the way the different fibers run in the third nerve, partial lesions of the third nerve can affect the pupillary fibers in isolation or the ocular motor fibers in isolation.

The pupillary fibers run on the medial exterior part of the nerve, whereas the oculomotor fibers run on the inside of the nerve. As such, compression causes pupillary problems, while ischemia causes occulomotor problems

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16
Q

Pupil-sparing third nerve palsy is most commonly due to . . .

A

. . . nerve infarct caused by diabetes, which usually resolves over months.

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17
Q

Pupil-involving third nerve palsy requires . . .

A

Pupil-involving third nerve palsy requires urgent neuroimaging to evaluate for aneurysm or other intracranial mass lesion.

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18
Q

Lesions of the third nerve nucleus cause ___

A

Lesions of the third nerve nucleus cause bilateral superior rectus weakness or and/or bilateral ptosis because the affected superior rectus subnucleus projects contralaterally

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19
Q

Unilateral ptosis with contralateral weakness and upper motor neuron signs likey results from a lesion that localizes to . . .

A

. . . the ipsilateral fasciculus of CN 3 in the midbrain, but not the nucleus itself.

It may also involve the red nucleus, causing contralateral ataxia as well, or the substantia nigra, causing contralateral movement disorder.

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20
Q

When the head is tilted to one side, the eye that intorts is the one . . .

A

When the head is tilted to one side, the eye that intorts is the one on the side of the head to which the patient is tilting the head

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21
Q

When intorsion is impaired due to a CN 4 palsy, double vision (diplopia) occurs when . . .

A

When intorsion is impaired due to a CN 4 palsy, double vision (diplopia) occurs when the head is tilted toward the affected side since that eye cannot intort to maintain fixation.

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22
Q

Cranial nerve 4 palsy diagram

A

Palsy is in the right eye

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23
Q

A patient with a CN 4 palsy will often prefer to . . .

A

. . . tilt the head slightly away from the affected side

This is becaue they do not experience double vision when they do so.

24
Q

An abducens palsy leads to failure to . . .

A

An abducens palsy leads to failure to laterally abduct the affected eye

25
Q

Cranial nerve 6 palsy image

A

Palsy is on the right side

26
Q

“False” localizing sign of 6th nerve palsy

A

The 6th cranial nerve has a particularly long and turtuous path as it transits from the pons to the cavernous sinus, and tends to be affected whenever there is greatly increased intracranial pressure.

So, while lesions to the abducens nucleus can and do occur, it is also commonly the nerve that is involved, and in the absence of other signs does not necessarily indicate brainstem pathology.

27
Q

If CN 6 is affected with CN 3 and/or CN 4 without involvement of CN 2, localization of the lesion in ____ should be considered.

A

f CN 6 is affected with CN 3 and/or CN 4 without involvement of CN 2, localization of the lesion in the cavernous sinus should be considered.

28
Q

If CN 6 and CN 7 are affected on the same side, this suggests . . .

A

If CN 6 and CN 7 are affected on the same side, this suggests pontine localization since the CN 6 and CN 7 nuclei are adjacent in the pons.

29
Q

Quick tests for which cranial nerve is affected in neural diplopia

A
  • If the patient can’t move their eye to the midline, it’s CN 3 (also w/ ptosis and pupillary reflex loss)
  • If the patient can’t rotate their eye when they tilt their head towards the affected side, it’s CN 4
  • If the patient can’t move their eye laterally, it’s CN 6
30
Q

In the cortex, the ___ initiate intentional saccades, and the ___ are involved in reflex saccades and smooth pursuit.

A

In the cortex, the frontal eye fields initiate intentional saccades, and the parietal eye fields are involved in reflex saccades and smooth pursuit.

31
Q

Medial longitudinal fasciculus

A

A tract that connects each CN 6 nucleus with the contralateral CN 3 nucleus in order to facilitate conjugate horizontal eye movements.

This tract crosses from the CN 6 nucleus en route to the contralateral CN 3 nucleus almost immediately, spending most of its course contralateral to its point of origin. They are named for their side of destination (which CN 6 nucleus they synapse upon)

32
Q

Paramedian pontine reticular formation

A
  • The voluntary horizontal gaze center
  • Cortex sends signals here, then from here signals are sent to occulomotor nerves, which then communicate with each other and execute movements
  • There is a left PPRF in the left pons for leftward gaze and a right PPRF in the right pons for rightward gaze
33
Q

The flow of information for horizontal gaze

A

frontal eye fields→contralateral PPRF→CN 6 nucleus→contralateral MLF→contralateral CN 3 nucleus

34
Q

A lesion of the right frontal eye field, the left PPRF, or the left CN 6 nucleus all lead to . . .

A

A lesion of the right frontal eye field, the left PPRF, or the left CN 6 nucleus all lead to impaired voluntary left gaze in both eyes

35
Q

A patient with a large middle cerebral artery (MCA) stroke that affects the frontal eye field will have gaze deviation . . .

A

toward the hemisphere of the stroke, which is away from the side of the hemiparesis

For example, a large right MCA stroke can cause left hemiparesis and right gaze deviation with inability to look to the left

36
Q

Patients with unilateral pontine stroke affecting the not-yet-crossed corticospinal tract and the lateral gaze center on one side will be unable to . . .

A

. . . look toward the side of the lesion, which can produce gaze deviation toward the side of the hemiparesis, which is away from the side of the lesion

For example, a right pontine stroke can cause left hemiparesis with gaze deviation to the left and inability to look right

37
Q

Gaze deviation in stroke and seizure

A

A: Gaze deviation in right MCA stroke. The patient has right gaze deviation and a left hemiparesis. B: Gaze deviation in right pontine stroke: the patient has left gaze deviation and a left hemiparesis. C: Gaze deviation in focal seizure originating in the right hemisphere: the patient has left gaze deviation and left-sided tonic-clonic movements.

38
Q

If seizure activity reaches a frontal eye field and activates it, this will cause the eyes to look ___

A

If seizure activity reaches a frontal eye field and activates it, this will cause the eyes to look contralaterally (i.e., deviate away from the seizure focus and toward the shaking limb if the seizure is focal)

When the seizure is over and the seizure focus is in a refractory state, the eyes may deviate toward the focus in the postictal period (which would be away from the side of a Todd’s paralysis, if present).

39
Q

Internuclear ophthalmoplegia

A

Condition caused by lesion to the MLF, which links the abducens nucleus to the contralateral occulomotor nucleus. This leads to inability to adduct the eye on the side of the MLF lesion with gaze in the opposite direction.

In INO, there is often nystagmus in the abducting eye, appearing as though it is “trying to tell the other (non-adducting) eye to come along.”

40
Q

If the right eye can abduct, but the left eye experiences symptoms of INO, what side is the lesion on?

A

The left LMF.

This gets at the naming of the LMF. It is named for the CN 3 nucleus it synapses upon, which is contralateral to the CN 6 nucleus that is controlling the abduction of the leading eye.

41
Q

Internuclear ophthalmoplegia is commonly seen in ___.

A

Internuclear ophthalmoplegia is commonly seen in multiple sclerosis.

The MLF is a highly myelinated tract, and so is a common target.

42
Q

How can INO be distinguished from simply failure of adduction due to a partial CN 3 palsy or medial rectus problem?

A

In INO, the CN 3 nucleus and nerve are functioning, but they are cut off from their communication with the contralateral CN 6 nucleus. Therefore, if the medial rectus is activated via a different pathway, it will function.

This can be demonstrated if convergence (bilateral adduction) is found to be preserved since this activates the third nerve (and nucleus) through an alternative pathway.

43
Q

Pupillary constriction is a ___ function and pupillary dilation is a ___ function

A

Pupillary constriction is a parasympathetic function and pupillary dilation is a sympathetic function

44
Q

Anisocoria

A

Pupillary asymmetry

can be caused by a variety of neurologic and ophthalmologic conditions

45
Q

___ refers to an abnormally constricted pupil, and ___ refers to an abnormally dilated pupil

A

Miosis refers to an abnormally constricted pupil, and mydriasis refers to an abnormally dilated pupil

46
Q

Pathway of visual information involved in light reflexes

A
47
Q

Relative afferent pupillary defect

A
  • When light is shined in one eye, both pupils constrict (normal). But, when light is shined in the other eye, neither does.
  • Most commonly caused by lesions in CN 2
    • but can also occur with severe unilateral or asymmetric retinal disease, or rarely with lesions in the optic chiasm, optic tract, or dorsal midbrain.
48
Q

Efferent pupillary defect

A
  • Caused by unilateral lesion in CN 3
  • Light shined in either eye will cause constriction in the pupil on the side with a functioning CN 3, but the affected side will not constrict in response to light from either pathway.
  • Since CN 3 also controls many motor features, a complete CN 3 palsy will cause multiple eye movement abnormalities in addition to pupillary dilation/lack of response to light.
    • However, since the pupillary constrictor fibers run on the medial exterior of the nerve, they can be compressed in isolation without causing eye muscle weakness
49
Q

Sympathetic pathway for pupillary dilation (diagram)

A
  1. First-order neurons travel from the hypothalamus through the brainstem to the intermediolateral column (ciliospinal center of Budge).
  2. Second-order (preganglionic) neurons travel from the spinal cord over the lung apex to the superior cervical ganglion.
  3. Third-order (postganglionic) neurons travel from the superior cervical ganglion to the eye, traveling alongside the internal carotid artery in the neck and cavernous sinus.
50
Q

Horner’s syndrome

A
  • Syndrome of lost sympathetic innervation of the eye and face
    • Miosis (from loss of sympathetic dilation)
    • Ptosis (from loss of sympathetic eyelid muscle innervation)
    • Anhidrosis (on ipsilateral side, from loss of sweat gland innervation)
      • Note that anhydrosis is present for first- and second-order neuron breaks, but not third-order neuron breaks
51
Q

The fibers for facial sweating travel with ___, whereas the fibers to the pupil and eyelid muscles travel with ___

A

The fibers for facial sweating travel with the external carotid, whereas the fibers to the pupil and eyelid muscles travel with the internal carotid

Therefore, if Horner’s syndrome is due to third-order neuron pathology (i.e., along the internal carotid artery or in the cavernous sinus), ptosis and miosis will be present, but facial sweating will not be affected

52
Q

Workup of Horner’s syndrome

A

Depending on the symptoms and signs associated with Horner’s syndrome, radiologic tests are ordered to assess the brain, brainstem, spinal cord, lung apex, and/or neck (including vascular imaging to evaluate the internal carotid artery on the affected side). If the etiology remains unclear, a series of pharmacologic maneuvers with eye drops can aid in localization.

53
Q

An 85-year-old patient presents with sudden onset left-sided weakness, thought to be due to a stroke. His eyes are deviated conjugately toward the left and cannot look right. Which area is likely affected?

A

Right pons (affecting R PPRF)

54
Q

For a MCA stroke, gaze deviates ____ the lesion.

For a seizure, gaze deviates ____ the lesion.

For a pontine stroke, gaze deviates ____ the lesion.

A

For a MCA stroke, gaze deviates towards the lesion.

For a seizure, gaze deviates away from the lesion.

For a pontine stroke, gaze deviates away from the lesion.

55
Q

Differentiating INO from CN 3 palsy

A

Test for convergence

56
Q

Frontal eye fields connect to ___ PPRFs

A

Frontal eye fields connect to contralateral PPRFs

57
Q

Eye field and contralateral PPRF lesions can be distinguished on exam by. . .

A

. . . testing for the presence of the vestibular occular reflex by having the patient rotate their head quickly and fix on a certain point.

If they are unable to do so, the lesion is in the PPRF.

If they are, the PPRF has been spared, so the lesion must be in the FEF.

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