PT9: Ocular Pharmacology Flashcards
what are the features of the iris smooth muscle
radial (dilator), sphincteric (constrictor)
regulate pupil size and the amount of light reaching retina
what is the function of the ciliary muscle in the eye
changes refractive index of lens, accommodation
what parts of the eye are smooth muscle
iris, ciliary
what do cranial parasympathetic axons in the iris do
innervate the ciliary ganglion (back of the eye)
what do postganglionic fibers do in the iris
innervate the sphincteric constrictor smooth muscle
what does high basal tone mean
small pupils at rest
what causes pupil constriction
contraction of sphincteric constrictor smooth muscle
what causes pupil dilation
contraction of radial dilator smooth muscle
what is the smooth muscle response to bright light
miosis
what is the smooth muscle response to low light
mydriasis
what is consensual pupil response
response in one eye will stimulate same response in the other
what is the parasympathetic tone
increase in miosis, ACh acts on M3 muscarinic receptors
what is the sympathetic tone
mydriasis, NA acts on alpha1 adrenoceptors
what do alpha 1 adrenoreceptors agonists cause
mydriasis
what do alpha 1 adrenoreceptor antagonists cause
miosis
what is the autonomic action of the eye
calcium/calmodulin binds to myosin light chain kenase (MLCK) which uses ATP to phosphorykate myosin cross bridges; phosphorylated cross bridges bind to actin which produces tension
what are two examples of muscarinic antagonists in the eye
mydriatics and cycloplegics
what do mydriatics do
block constrictor muscle which causes pupillary dilation
what do cycloplegics do
paralyse ciliary muscle which blocks accommodation
what are the uses of muscarinic antagonists
anterior uveitis (inflammation), ocular examination, amblyopia (lazy eye)
what causes glaucoma
damaged optic nerve, usually a consequence of raised intra-ocular pressure
what determines intraocular pressure
determined by rate of formation and rate of drainage of aqueous humour
AH produced by ciliary body epithelium
what is the purpose of aqueous humour
maintains intraocular pressure, provides nutrients to the cornea, lens etc, released into posterior chamber
how does drainage occur in the eye
through trabecular meshwork and canal of Schlemm
what is aqueous humour formation stimulated by
beta agonists
what is aqueous humour formulation inhibited by
alpha agonists
what are the three inhibitors of aqueous humour formation
alpha1 agonists
alpha2 agonists
beta adrenoreceptor antagonists
what do alpha 1 agonists do
vasoconstrictors that reduce blood supply to ciliary body
what do alpha 2 agonists do
reduce cAMP
directly inhibits aqueous humour formation and reduce NA release from sympathetic fibres
what do adrenoreceptor agonists do
reduce aqueous humour production
what does aqueous humour formation require
active transport of HCO3- out of the ciliary body
carbonic anhydrase catalyses which then dissociates to HCO3-
what do carbonic anhydrase inhibitors do
decrease intracellular bicarbonate; decrease carbonic anhydrase which impairs aqueous humour secretion
what are the steps of circulation of aqueous humour
AH produced by ciliary body, AH flows from the posterior chamber through the iris into the anterior chamber, trabecular meshwork (canal of Schlemm and into vein), uveoscleral outflow
what does drug therapy do in glaucoma
improves drainage of aqueous humour through trabecular network, useful in raised and normal pressure glaucoma (miotics make pupil smaller, muscarinic agonists (carbachol, pilocarpine, ACh)
improved drainage through uveoscleral outflow, prostaglandin analogues, latanoprost PGF2alpha analogue
what is closed-angle glaucoma
angle between iris and cornea is narrowed, blocks flow of aqueous humour from posterior to anterior chamber, onset can be sudden and result in rapid irreversible damage
what is the emergency treatment for closed-angle glaucoma
relieves intra-ocular pressure
increase blood osmolarity; water out of vitreous humour to decrease volume of VH and intra-ocular pressure
what are three treatment for glaucoms
laser trabeculoplasty, surgical scleral flap, laser iridectomy
what is age-related macular degeneration
‘dry’ AMD is geographic atrophy with no successful treatments
‘wet’ AMD is neovascular and has a rapid onset
