Brainstem 4: The Pupil Flashcards
What’s the near reflex (aka acomodation)? Cranial nerves and nuclei involved?
Pupil constricts when eyes are fixating on near object. CN II, CN III (the Edinger Westphal Nucleus). Determination that an object is near uses the cerebral cortex.
How do you test the near response?
Have the patient look at their own finger, not your finger. (probably not on the test, but good to know)
If when you shine a light in a patient’s right eye, neither eye contracts, would you expect acuity problems in the right eye?
Yes. CN I is affected.
Why might the eye on the side of a CN I deficit dilate when you shine light on it?
It’s getting less light than the other eye…
What’s anisocoria? 3 reasons for it (broadly)?
Pupils aren’t the same size.
“Physiological” - it’s normal for the patient (look at old photos)
Small pupil can’t dilate due to Horner’s.
Large pupil can’t contract due to CN III lesion.
What’s the rough difference threshold for physiologic (i.e. non-pathological) anisocoria? How can you assure yourself it’s physiological?
Difference of 0.4mm or less is normal. Difference stays constant during light/dark reflexes and near response. (looking at old photos helps too).
What do Horner’s syndrome pupils do when you turn the lights in the room off?
Dilate much more slowly, but they do usually dilate. “dilation lag”
How do you test definitively that miosis in a patient is due to Horner’s syndrome? How/why does that test work?
Cocaine test - drip it in the eye. Norepinephrine (NE) in synapse causes pupil dilation. Cocaine blocks the reuptake of NE in the synapse. Pupils won’t dilate in Horner’s in response to cocaine, because there’s no NE to block the reuptake of.
What are the 3 “orders” of Horner’s syndrome?
1st order: brainstem/spine (running with the spinothalamic tract)
2nd order: near the lung apex/brachial plexus (often will see distal upper limb weakness)
3rd order: in the carotid plexus (carotid dissection)
Where does one lose sweating in 1st, 2nd, and 3rd degree Horner’s?
1st: Whole side of body.
2nd: Half of face.
3rd: Half of upper face. (V1 region)
Painful Horner’s is what until proven otherwise?
Carotid dissection.
Whose pupil will dilate in response to apraclonidine: Horner’s or non-Horner’s patient?
Horner’s patient - the pupil for some reason becomes hypersensitive to apraclonidine.
What’s one way that trauma can cause a dilated pupil?
Iris disinsertion.
If a pupil doesn’t constrict in response to constriction-inducing eyedrops… what might be the cause?
Someone had put dilating drops in. (Dr. Banwell requests you to please put up signs saying you’ve dilated a patient’s pupil when you’ve done so)
What’s a drug that constricts the pupil (but usually won’t dilate a pharmacologically dilated pupil)?
Pilocarpine
