Flashcards in Neuro-Ophthalmology Deck (51):
90% of retinal axons terminate where?
the lateral geniculate nucleus, which is the principal sucbcortical structure that carries visual info to the cerebral cortex through the optic radiations
Where is the primary visual cortex?
Brodmann's area 17, or striate cortex
Where does the visual information go after the striate cortex, or V1?
the associative visual cortex, areas 18 and 19
If visual acuity is decreased, where is the issue typically localized?
either to the eye's inherent refractive mechanism (and will improve if you test the VA through a pinhole) or to the optic nerve (and will NOT improve through a pinhole)
Early optic nerve problems can present with difficulty perceiving which color?
red (a particularly common presentation for MS optic neuritis)
How do you test for an afferent pupillary defect (marcus gunn pupil)?
Flash a bright light alternately for 2-3 sec in each eye
if the ipsilateral pupil appears to dilate when the light is directed toward that eye, an afferent pupillary defect is present
What visual defect will occur with right optic nerve damage?
right eye blindness
What visual defect will occur with chiasm pathology?
What visual defect will occur with damage to the right optic tract?
left homonymous hemianopsia
What visual defect will occur with damage to the right parietal optic radiation?
left inferior homonymous quandrantonopia
What visual defect will occur with damage to the right temporal optic radiation?
left superior homonymous quadrantonopia
What visual defect will occur with both optic radiations are damaged?
left homonymous hemianopia (just like with the right optic tract)
What visual defect will occur with damage to the right visual cortex?
left homonymous hemianopia with macular sparing
What is the technical term for unequal pupil size? In what percentage of people can this be normal?
normal in 25%
For the pupillary light reflex, the afferent signal follows the initial visual pathway: retina to optic nerve, chiasm, optic track and then synapses where?
the edinger-westphal nucleus in the rostral aspect of the third nerve nucleus
Efferent fibers from the Edinger-Westphal Nucleus then travel with the third cranial nerve. Are these fibers sympathetics or parasympathetics?
These parasympathetic fibers ultimately synapse in what ganglion prior to reaching the pupilloconstrictor?
ciliary ganglion (located in the posterior orbit)
The pupillodilator is innervated by sympathetics. Where do these sympathetic fibers start?
in the ipsilateral posterolateral hypothalamus
Where do these sympathetic fibers project to?
they descend down the brainstem to the interomediolateral cell column at the C8-T1 spinal level
The second order neurons go from C8-T1 to synapse in what ganglion?
superior cervical ganglion
The third order sympathetics travel from the superior cervical ganglion to the eye along what structure?
the internal carotid artery into the cavernous sinus
What characterizes Horner's Syndrome?
ipsilateral miosis (small pupil)
ptosis (drooping of upper lid)
inverted ptosis (elevation of the lower lid)
and depending on the level of the lesion...
impaired ipsilateral facial flushing and sweating
What effect will cocaine have on the pupil in horner's syndrome?
cocaine drops will fail to dilate the abnormal pupil (because cocaine inhibits the reuptake of NE from the synaptic cleft, but if the sympathetics aren't working, this won't do anything)
Cocaine will fail to dilate the pupil, but what will succeed?
apraclonidine (a weak direct-acting alpha1 and alpha2 agonist that dilates the affected eye due to denervation supersensitivity of the iris dilator muscle)
What drug will help differentiate between a preganglionic horner syndrome and a postganglionic horner syndrome?
hydroxyamphetamine - the eye will dilate if the damage is in the preganglionic, but won't with the postganglionic
What are the characteristics of a CN III palsy?
(down and out)
What will you lose first with optic nerve compression - pupil dilation or eye movement?
you'll have a dilated pupil, but eye movements will be preserved because the parasympathetics run on the outer edge of the nerve
What will you lose first with optic nerve ischemia - pupil dilation or eye movement?
you'll lose eye movements, but pupil response will be intact because the parasympathetics on the outside have additional blood supply from elsewhere
What causes a tonic (Adie's) pupil?
interruption of the parasympathetic supply from the ciliary ganglion
What are the symptoms of a tonic pupil?
blurred near vision (bc of some accommodation paresis)
poor light reaction (with the typical segmental contraction
Describe an Argyll Robertson pupil
impaired light reaction, but intact light-near dissociation (accommodates, but doesn't react)
typically associated with syphilis
What's the most common symptom of optic disc swelling?
dimming or blacking out of vision usually lasting a few seconds
usually precipitated by changes in posture or valsalva
What are the three most common causes of unilateral optic disc swelling?
acute ischemic optic neuropathy (AION)
orbital compressive lesions
Ipsilateral optic disc atrophy due to compression of the optic nerve by a space-occupying lesion in the frontal lobe with papilledema in the contralateral optic disc due to increased ICP is known as what syndrome?
Foster Kennedy Syndrome
What is the difference between comitant strabismus and incomitant strabismus and where is the issue in each?
comitant strabismus occurs when the misalignment is constant in all directions of gaze and each eye has full range of motion (usually an ophthalmologic problem)
incomitant strabismus is when the degree of misalignment varies with the direction of gaze (usually a neurological problem)
What is the term for misalignment of the eyes when binocular vision is absent (cover-uncover test)?
phoria (esophoria or exophoria depending on the direction the eye goes)
What is the term for misalignment of the eyes when both eyes are opened and binocular vision is possible/
tropia (esotropia or exotropia)
What extraoccular muscles are innervated by CN III?
inferior oblique muscles
(all but the lateral rectus and superior oblique)
What nerve innervates the superior oblique muscle?
CN IV (which intorts and depresses the adducted eye)
A IV nerve palsy will cause what?
oblique diplopia that is worse on down-gaze when the affected eye is adducted (so they usually complain of diplopia when they're reading or going down stairs)
they will compensate with a lateral head tilt (away from the side of the lesion)
(on exam they'll have a slightly raised eye when adducted)
What does a CN VI nerve palsy cause?
esotropia, especially with ipsilateral gaze (because they can't abduct)
What structures are connected by the MLF?
the contralateral abducens nucleus and paramedian pontine reticular formation with the ipsilateral IIIrd nerve nucleus
so a lesion will cause intranuclear opthalmoplegia (inability to adduct the ipsilateral eye in contralateral gaze, plus nystagmus of the abducting eye)
True or false: convergence is preserved in intranuclear opthalmoplegia.
true; convergence does not depend on the MLF
What is the differential diagnosis for bilateral intranuclear opthalmoplegias?
Describe "one and a half syndrome"
it occurs as a consequence of a lesion involving the Paramedian pontine reticular formation or the VIth nerve nucleus and the adjacent ipsilateral MLF
you get an ipsilateral gaze palsy and INO on the opposite side (so one and a half) - the only eye movement you get in the lateral plane is abduction of the contralateral eye
What region controls vertical eye movements?
the rostral interstitial nucleus of the MLF (riMLF)
Where is the rostral interstitial nucleus of the MLF?
in the pretectal midbrain area, near the CN III nucleus
Do the fibers controlling upward gaze from the riMLF go to the ipsilateral or contralateral inferior oblique and superior rectus subnuclei?
What syndrome is characterized by upgaze disturbance, convergence-retraction nystagmus on attempted up-gaze and light-near dissociation?
What is the typical cause of parinaud's syndrome?
a pineal tumor compressing the dorsal midbrain