drugs on the eye Flashcards
(35 cards)
what is Phenylepherine ?
alpha1-adrenoreceptor agonist
what is tropicamide ?
non-selective muscarinic receptor antagonist
what is pilocarpine ?
M3 receptor agonist
what is Tetracaine ?
local anaesthetic
what is accommodation ?
the ability of the eye to focus
what is mydriasis ?
pupil dilates- gets wider
what is miosis ?
the pupil constricts
which drugs target the sympathetic nervous system ?
phenylepherine and tropicamide
What are muscarinic receptors?
GPCRs
Metabotropic
How does tropicamide work ?
It works by binding to muscarinic receptors in the eye, which prevents Acetylcholine trom binding an activating them. This prevents circular muscle contraction, as it has blocked the action ot the parasympathetic nervous system. Active opposing action of the sympathetic nervous system then causes the radial muscie to contract. This causer mydrasi which is when the pupil dilates.
The cilary muscle is controlled by the parasympathetic nervous system.
As Tropicamide blocks this, the cilary muscle cannot contract, which causes cycopiegia.
What is cycoplegia ?
Paralysis of accommodation
What is tropicamide used for ?
Eye examinations to allow ophthalmologists to examine the retina, optic nerve and internal structures of the eye more easily
Allows better exposure to the cataract during surgery
What is the onset of action of tropicamide ?
Within 15-30 minutes
How long do the effects of tropicamide last ?
Mydriasis effect lasts 4-6 hours
Cycloplegia effect can last upto 24 hours
What are the side effects of tropicamide ?
- Photophobia (extreme sensitivity to light)
- Blurred vision
- Rarely anticholinergic effects such as a dry mouth
What are the contraindications of tropicamide ?
People with closed angle glaucoma as it causes a raise in intraocular pressure which can make the condition worse
What are the circular muscles ?
They contract to make the pupil smaller- in response to bright light or when an object is close
Controlled by the parasympathetic nervous system
What are radial muscles ?
They pull the pupil open to make it bigger- in response to dim light or when you’re stressed or excited
Controlled by the sympathetic nervous system
What are the ciliary muscles controlled by ?
The parasympathetic nervous system
How does pilocarpine work ?
Pilocarpine worts by binding to the receptor, which causes activation of the Gq protein coupled pathway. This causes activation of PLC, which splits PIP2 into IP3 and DAG. IP3 stimulates the release of calcium ions, which causes the circular muscle to contract. This causes miosis, which is when the pupil constricts. This is caused by stimulation of the parasympathetic nervous system.
Pilocarpine also stimulates M3 receptors on the cilary muscle, causing it to contract. This serves two purposes:
1. thickens the lens to allow accomodation
2. It opens the canal of schlemm, which allows improved drainage of aqueous homour, causing a decrease in intraocular pressure
What is pilocarpine used for ?
Treating closed-angle gluacoma as it lowers the intraocular pressure
What are the side effects of pilocarpine ?
- Headaches
- Blurred vision
- Salivation
What are the contraindications of pilocarpine ?
Iritis and Uveitis which are inflammation in the eye, which can be made worse by the drug
How does tetracaine work ?
By binding to and blocking voltage-gated sodium channels. This prevents the influx of sodium ions, which inhibits depolarisation. This prevents an action potential, so causes a loss of sensation.
