Eye Pharmacology Flashcards
What NT is utilized by the parasympathetic system? How about the sympathetic system?
On what receptors in the case of the eye?
parasympathetic = ACh on muscarinic
sympathetic = NE on alpha and beta
What is the sympathetic action on the pupil? How?
Dilates the pupil
activating alpha1 receptors to contract the pupillary dilator muscle
What is the sympathetic action on the eyelid? How?
holds it open
activates alpha1 receptor to contract the superior tarsal muscle (smooth muscle)
What is the sympathetic action on the lens? How?
It relaxes the ciliary muscle to flatten the lens for far vision
activates beta2 receptors
What is the sympathetic action on aqueous humor if activating alpha2 reeptors? beta receptors?
alpha2 = inhibits aqueous humor formatoin
beta = increases aqueous humor formation
What will the parasympathetic action be on the lens?
It contracts the ciliary muscle, thus making the lens fatter for near vision
What will the parasympathetic action be on the pupil? How?
it will constrict the pupil by activating msucarinic receptors on the pupillary sphincter muscle to contract it
What will the parasympathetic action on aqueous humor be?
enhance drainage of the humor thorugh the trabecular meshwork and canal of schlemm
Generally speaking, what are the two ways you can cause mydriasis?
mydriasis is pupil dilation!
you can either enhance sympthetics or inhibit parasympathetics
What alpha1 adrenergic stimulant is used to dilate the pupil during eye exams?
phenlephrine (mydrifin)
Besides dilating the pupil, what can phenylephrine do in theory?
reverse ptosis in Horner’s syndrome
What drug will cause mydriasis by inhibiting the parasympathetics?
atropine (a muscarinic antagonist)
What effect will epinephrine have on the aqueous humor?
It is an alpha1 stimulant, so it will increase humor outflow and inhibit formation
used as a late-line drug for glaucoma
How does cocaine cause pupil dilation?
it blocks the axoplasmic pump, increasing NE iconcentrations in the vicinity of the adrenergic receptors
How does amphetamine cause pupil dilation?
It reverses the axoplasmic pump, pumping NE out of the nerve and increasing its concentration near the adreneric receptors
If pupils are not equal in size and on is more cosntricted than it should be, how can you pharmacologically distinguish whether the damage is int he eye itself or in the sympathetics?
- give cocaine, which will dilate the eye if the sympathetics are intact
- then give amphetamine, which will dilate the eye if the postganglionic nerve is intact
so negative cocaine, positive amphetamine = Horner’s sydnrome with lesion BEFORE the postganglionic nerve
negative cocaine, negative amphetamine = Horner’s syndrome with lesion in the postganglionic
As a muscarinic receptor antagonist, atropine will cause dilation of the pupil and what effect on vision?
cycloplegia - inability to accomodate to near vision
How can you test nerve vs eye dyxfunction on the parasympathetic side of things?
see if the eye responds to a muscarinic agonist:
if eye reponds to pilocarpin with pupil constriction, then the problem is with the CN3
If the eye does NOT respond to pilocarpine, then the problem is in the eye itself
In general, how can you cause miosis?
miosis = pupil dilation
augment the parasympathetics and inhibit the sympathetics
How do pilocarpine and acetylcholine cause miosis?
they are muscarinic agonists
Besides using a muscarinic agonist, how can you make the muscarinic receptors more likely to fire, thus leading to pupil constriciton?
prevent ACh degradation with physostigmine or Ecothiophate
What drug has ocular side effects because it’s an alpha1 receptor antagonist? What effect?
Terazosin - it causes constriction
What drug has constriction as a side effect because it depletes norepinephrine?
Reserpine
If a patient is exhibiting miosis and you want to treat it pharmacologically, what is the best way to od so?
since they have excessive miosis, their parasympathetic system is overactive
thus you need to treat it with a parasympathetic antagonist like atropine
How will beta blockers help with glaucoma?
They block the Beta2 receptors, thus decreases aqueous humor production
Which beta blocker is used for glaucoma most often?
timolol
How do muscarinic receptor agonists like pilocarpine treat glaucoma?
they enhance drainage
How do anticholinesterases like physostigmine and ecothiophate treat glaucoma?
they enhance aqueous humour drainage
How do alpha2 agonists like epinephrine treat glaucoma?
increases ouflow and suppresses production
How do prostaglandin derivatives treat glaucoma? Which is the most commonly used?
it sill increase outflow
latanoprost is most common
How does acetazolamide treat glaucoma?
it blocks carbonic anhydrase, so you don’t get the swap of Cl- for bicarb and thus you have no osmotic force to drive water into the eye for the humor production
How can you treat eye probems caused by muscle spasm?
botulinum toxin (botox)
it inhibits ACh release from somatic nerves, relieving the spasms
What are the 5 potential causes of ptosis?
Horner syndrome - loss of sympathetic innervation
myasthenia gravis
botulinism
occulomotor palsy
muscular dystropy
