5-autonomic-eyeball! Flashcards
what does morphine do to pupil
miosis
what does organophostate poisoning do to pupil
miosis
what does cocaine do to pupil
mydriasis
what does amphetamine do to pupil
mydriases
what is mydriasis
dilation of pupil
what is the role of the pupillary dilator muscle
cause mydriasis with alpha adrenoceptor stimulation. when contracted, it results in pupil dilation
what is the role of the iris spincter
site of action of the PSNS (where M3 receptors are found), when constricting, causes miosis (pinpoint pupils)
what kind of receptor stimulation happens with the iris sphincter
muscarinic M3 (Gq GPCR)
what kind of receptor stimulation happens with the circular pupillary dilator muscle
alpha
what kind of activation do ciliary muscles require
muscarinic
what does muscarinic activation do to ciliary muscles
contraction, more round lens, increased focusing power, accomodates for near vision (myopia)
what does the trabecular meshwork do
moves do that fluid can leave through the canal of schlemm
what does the canal of schlemm do
let fluid leave the eye
what causes the trabecular meshwork to move
ciliary muscle activation
how do ciliary muscles help with removing aqueous humor
puts tension on trabecular meshwork which opens pores to let outflow of aqueous humor in canal of schlemm
what does the ciliary epithelium do
produces the aqueous humor
what kind of receptors stimulate the ciliary epithelium? what happens?
beta, resulting in increased secretion of aqueous humor
how do beta blockers reduce IOP
reduces aqueous humor release from the ciliary epithelium (ciliary epithelium has beta adrenergic receptors)
how do muscarinic agonists reduce IOP
because it contracts ciliary muscles which puts tensions on the trabecular meshwork to open pores and let aqueous humor out into the canal of schlemm
what is glaucoma and what can it cause
elevated IOP and it can cause optic nerve damage and blindness
what are the two types of glaucoma
open angle and angle closure glaucoma
what is open angle glaucoma
high pressure between cornea and iris, common and easily treated
what is angle closure glaucoma
high pressure between ciliary body and iris
what is the course of treatment for open angle glaucoma (4)
- topical beta blocker (stop ciliary body secretion)
- cholinergic agonist/cholinesterase inhibitor (trigger M3 on ciliary muscle)
- add adrenaline or apraclonidine (reduces blood flow to ciliary body)
- carbonic anhydrase inhibitor (affects ciliary body secretion)
why is it safe to take glaucoma meds if you have systemic circulation issues
the eye drops have very poor access to systemic circulation
what is Timolol (drug class)
beta blocker
describe the effectsof timolol
beta blocker with no local anesthetic effects like propanolol
reduces secretion of aqueous humor from ciliary body and lower IOP
what is pilocarpine (drug class)
muscarinic agonist
what does pilocarpine do
cause ciliary muscle contraction
increase outflow of aqueous humor into circulation, reduce IOP
what are the untoward effects of pilocarpine
since pilocarpine is a muscarinic agonist (PSNS), it causes miosis (by iris sphincter)
myopia (by ciliary muscle)
what is physostigmine
anticholinesterase
what does physostigmine do to eye
since it’s an anticholinesterase, ciliary muscle contraction via M3 receptors, increase outflow of aqueous humor, reduce IOP
what does apraclonidine do
vasoconstrict via alpha 1, reduce blood flow to ciliary body, less aqueous humor secreted, IOP decreased
what do cannabinoids do to eye
lower IOP likely by relaxing the trabecular network
what is anandamide? describe the mechanism of action
endogenous ligand of the CB1 and CB2 receptors, activates Gi signalling pathway resulting in decreased NT release
what signalling pathway do CB1 receptors use?
Gi which reduces NT release by activating Ca2+ and GIRK channels
what direction does GIRK channels go
releases K+ from nerve terminal!
what does atropine do to the eye
muscarinic antagonist, so dilate pupil for ocular examination
what kind of drug is atropine
muscarinic antagonist
what causes Horner’s syndrome
head trauma or stroke in brainstem
even if the damage is unilateral
can damage to parasympathetic nerves cause horners syndrome
no
what characterizes horners syndrome
interruption of oculosympathetic pathway resulting in ocular sympathetic dennervation somewhere between hypothalamus and eye
what are the 3 neurons that could be damaged to cause horners syndrome
1-hypothalamus to spinal cord
2-sympathetic preganglionic neuron
3-sympathetic ganglion neuron
what would you expect cocaine to do to the pupil
cause dilation (indirect sympathomimetic)
if cocaine doesn’t cause pupil dilation, where would the lesion be
neurons 1 2 or 3
how can you use amphetamines to test for horners syndrome
test neuron 3
-if it is intact, the pupil will dilate (it releases NA REGARDLESS of the condition of neuron 1 and 2 or sympathetic outflow to neuron 3)
in summary, what do alpha adreoceptor agonists do to eye
lowers IOP (decrease flow to ciliary body) by causing smooth muscle contraction via alpha 1 receptors
mydriases (increase pupil size from pupillary dilator/iris radial muscle)
in summary, what do muscarinic agonists do to eye
miosis (pupillary constrictor/iris sphincter)
myopia (ciliary muscle contraction, accomodation for near vision)
lower IOP (activate M3 receptors -contract ciliary muscle - tension on trabecular meshwork - aqueous humor squeezed out into circulation)
in summary, what do beta adreoceptor antagonists do to eye
decrease activation of beta receptors on ciliary epithelium, decrease Gs response, lower IOP (blocks humor production by ciliary body)
why can atropine be bad for glaucoma
since atropine is a muscarinic antagonist, it will block PSNS (sympathomimetic effects), beta receptors on ciliary epithelium are activated
it can relax the ciliary muscle
