Lecture 25: Brainstem 4, Pupil and Optic Nerve Flashcards
Pupillary light reflex
Parasympathetic pathway
Input: light enters one eye, stimulates the photoreceptors ganglion cells optic nerve lateral geniculate nucleus Superior Colliculus mesencephalic pretectal nucleus EDINGER-WESTPHAL nucleus
Output: edinger-westphal nucleus ciliary ganglion contraction of both eyes
Near response:
Drawing your finger near your eyes
consists of a triad
i. pupillary constriction
ii. accommodation (lens becomes spherical)
iii. convergence of the eyes
Input output is not clear but probably involves Edinger-Westphal, pretectum and mesencephalic reticular formation
Sympathetic innervation of pupil and eyelids:
First order hypothalamic neurons descend through brainstem and cervical cord synapse at C8, T1, T2 second order-fibers travel to sympathetic chain (inferior and superior cervical ganglion) to synapse there axons then travel within carotid plexus (which surrounds internal carotid artery) cavernous sinus V1 long ciliary nerve
Left afferent pupillary defect:
- the way to determine that the optic nerve is affected is to evaluate response to light
- consensual contriction = if you shine the light on normal eye, then both eyes will constrict because of this consensual shit
- if you shine the light on the abnormal eye, then both eyes will remain dilated because the affected eye will not instigate the consensual constriction
Anisocoria
a condition that is characterized by an unequal size of the pupils
Physiological anisocoria
- 20% of population is normal
- relative difference between pupil size should remain the same from dilation to constriction
Pathological anisocoria:
Could be a sympathetic or parasympathetic problem
It is sympathetic if your constricted eye fails to dilate in the dark (because sympathetics makes your shit dilate)
It is parasympathetic if eye does not constrict in light
What is Dilation lag?
Although dark exacerbates anisocoria, if you leave patient in dark long enough, pupil will slowly dilate
Ptosis
: levator dehiscence (bursting open or splitting along natural/sutured lines)
-could be NMJ, myopathic or neurogenic
Cocaine test:
cocaine blocks the reuptake of norepinephrine
- cocaine drops should give you dilation of pupil - if cocaine does not dilate the pupil, then horners syndrome is present
Ciliospinal center of budge:
area that includes C8, T1 and T2 spinal cords
-where the descending hypothalamic tract go down towards
3 types of horner’s syndrome
1st order neuron: lesion in brainstem/spine
-can’t sweat on sweat face and body; ipsilateral
Cause: lateral medullary syndrome
2nd order neuron: lesion in brachial plexus/lung apex
-cant sweat on face; ipsilateral
Cause: pancoast tumor, injury to neck (chiropractor)
3rd order neuron: carotid dissection (painful), cavernous sinus lesion
-cant sweat on V1distribution; ipsilateral
Cause: trauma to head near the eye…
What is the most important cause of Horner’s syndrome to recognize in childhood?
Neuroblastoma
What is significance of heterochromia?
Horners is congenital and not neuroblastoma
What are other potential causes of dilated pupil?
Transderm SCoP, dilating drops, torn iris muscle
Adie’s tonic Pupil
CN III palsy
Why is it important to distinguish between preganglionic and postganglionic Horner’s?
Because preganglionic Horner’s could be a sign of neoplasm
How do you differentiate second and third order Horner’s?
Use hydroxyamphetamine (Paredrine) to release norepinephrine from third order terminal
- if postganglionic neuron is injured, the pupil will stil not dilate/will poorly dilate…meaning that even hydroxyamphetamine (paredrine) cannot induce 3rd order neuron to do its thing…this means it is not a tumor
- if hydroxyamphetamine (paredrine) lets eye dilate, then it is likely to be a 2nd order horners…and you have to watch out for neoplasm
What is Adie’s tonic pupil? Significance?
Example of a pupil that is dilated but not Horner’s
No reaction to light
But the eye constricts to near response!!!!
supersensitive to dilute pilocarpine
Mechanism: ciliary ganglion injury
Why is accommodation spared and light reflex is not when ciliary ganglion is damaged?
Because there is a 30:1 ratio between accommodation response and light reflex fibers…so if there is damage, there is a much greater chance that the reflex fibers will be harmed but enough accommodation fibers will be left to be functional
How can you tell if a dilated pupil is Adie’s tonic pupil?
It restricts to near response!
- absent reflexes (absence of deep tendon reflexes)
- near response is slow!
Aside from pharmalogical, tonic and Horner’s cause of dilated pupil, what else can cause a dilated pupil?
CN III palsy
-symptoms would be ptosis, dilated eye, down and out
What are Argyll Robertson pupils?
Classical symptom for neurosyphilis
i. accommodation is intact
ii. light reflex is fucked
How do you differentiate Adie’s pupil from Argyll Robertson pupils?
Argyll-Robertson = brisk response to near target Adies = slow and tonic response to near target
What do we want to remember?
i. the afferent pupillary defect signifies optic nerve (CN II) disease
ii. carotid dissection (painful Horner’s)
iii. Posterior communicating (PComm) artery aneurysm (pupil involving 3rd in palsy)
Most important question to ask for Horner’s?
Is it painful?
If it is, then it is carotid dissection until proven otherwise
If patient says that he or she has weakness/numbness in hands and fingers with Horner’s, then this suggests what kind of Horner’s?
Second order (pancoast tumor)
What spinal cord structural malformation can lead to second order horners?
Syrinx (syringomyelia):
damage to the spinal cord due to a fluid-filled hole that forms in the cord.
