ocular pharmacology

pupillary constriction

• acetylcholine via muscarinic receptors

• parasympathetic stimulation of circular muscle

• parasympathetic stimulation causes constriction of the pupil (miosis)

pupillary dilation

• noradrenaline via alpha1-adrenergic receptors

• sympathetic stimulation of radial muscle

• sympathetic stimulation causes dilation of the pupil (mydriasis)

ciliary smooth muscle

• circular muscle surrounding the lens

• usually the lens is held taut by the intraocular pressure

what does a thin lens mean in the ciliary muscle

• lens allows focussing on distant points

• lens more flat to see things further away

what does a fat lens mean in the ciliary muscle

• lens allows focusing on near points

• contraction of the smooth muscle causes the lens to relax (high curvature)

what is the ciliary muscle innervated by

parasympathetic innervation

what should you remember about the iris and ciliary body

they are separate systems!!!!!!

what is the smooth muscle of the iris important for

important in controlling the amount of light entering the eye

what is the smooth muscle if the ciliary body important for

important in accommodation

what will drugs that mimic stimulation of the sympathetic nervous system do to the pupil

• cause dilation of the pupil

• with no effect on accommodation

examples of drugs which mimic stimulation of the sympathetic nervous system

• alpha 1-adrenergic receptor agonist- phenylephrine

• indirectly acting sympathomimetics- ephedrine and amphetamine

• reuptake inhibitors- cocaine

what will drugs which mimic stimulation of the parasympathetic nervous system do to the pupil

• constriction of the pupil

• constriction (paralysis) of the ciliary muscle

examples of drugs that mimic the stimulation of the parasympathetic nervous system

• muscarinic agonists- pilocarpine and carbachol

• acetylcholinesterase inhibitors- physostigmine and ecothiapate

what do drugs which inhibit stimulation of the parasympathetic nervous system do to the pupil

• causes dilation of the pupil

• relaxation (paralysis) of the ciliary muscle

examples of drugs which inhibit stimulation of the parasympathetic nervous system

• muscarinic antagonists- atropine

• botulinum toxin

what are mydriatics

causes the pupil to dilate

what are cycloplegics

cause paralysis of the ciliary smooth muscle and hence inhibit accommodation

examples of antimuscarinics

• atropine

• homatropine

• cyclopentolate

• tropicamide

uses of antimuscarinics

• examination of retina

• cataract surgery

• tropicamide- shorter acting

what way are antimuscarinics given

• given topically (eye drops)

• limits systemic side effects

• patients shouldn’t curve for 1-2 hrs after mydriasis

what can mydriasis and cycloplegics cause

• increase in intraocular pressure

• rarely can precipitate acute angle-closure glaucoma

what is POAG

• primary open angle glaucoma

• optic neuropathy degeneration of the retinal ganglion cells accompanied by visual field loss and eventual blindness

what is the major risk factor for POAG

raised intraocular pressure

what is the aim of therapy of POAG

to lower IOP to prevent further visual field defects

what does the aqueous humour do

supplies nutrients to and removes waste products from the vascular organs of the anterior (lens and cornea)

what is the rate of aqueous humour being produced

2-4 ul/min

how much of the aqueous humour leaves via the outflow pathway

70-90%

how much of the aqueous humour leaves via the u8ncovential pathway (uveoscleral)

10-30%

what is the normal eye rate of production and rate of outflow

• balanced IOP of 10-20mmHg

in POAG what happens to outflow and IOP

• decreased outflow

• increased IOP

what are the types of ways drugs are used to lower IOP

• decrease production or

• increase outflow

what is the aqueous humour secreted by

• ciliary epithelium

• at the surface of the ciliary body

what type of control is the aqueous humour under

• autonomic (sympathetic) control

• stimulation of the sympathetic devours system causes a increase production of AH

what does stimulation of the beta 2 receptor cause

increase in AH production

what does stimulation of alpha 2 receptors cause

decrease in AH production

what are the types of drugs used in treatment of glaucoma which reduce AH secretion

• beta blockers- antagonists at beta adrenal receptors

• alpha 2 agonists- stimulate alpha 2 adrenoreceptors

beta blockers that treat glaucoma

• timolol

• carteolol

• betaxolol

• produce a 15-50% inhibition of AH production

what are the side effects of beta blockers when treating glaucoma

• administered topically but can cause systemic side effects

• bradycardia, hypotension, bronchospasm

• should not be used in patients with asthma unless no other alternative

examples of alpha 2 agonists

• brimonidine

• not extensively used

aqueous outflow via the trabecular meshwork is

• facilitated by construction of the pupil

• inhibited by dilation of the pupil

• facilitated by contraction of the ciliary muscle

what do miotics do

• cause the constriction of the pupil and ciliary muscle

• therefore increase aqueous outflow

example of msucarinic agonists

pilocarpine

examples of anti cholinesterase inhibitors

ecothiapate

what are some disadvantages of drugs used to treat glaucoma

blurred vision

what are the most used therapy currently to treat glaucoma

• prostaglandin analogues

• e.g. latanoprost (mechanism of action doesn’t involve the autonoc=mic nervous system)