Eye (year 2) Flashcards
what do topical drugs have to cross to penetrate the eye?
cornea, conjunctiva, sclera
what are the advantages of topical administration?
specific
minimal side effects
easy
convenient
what are the advantages of systemic delivery?
better for posterior segment
easier in fractious animals
where may a drug be distributed when delivered topically to the eye?
into the eye
drain into lacrimal duct
enter systemic circulation through nasal mucosa/conjunctiva
fall off eye
why must a gap be left when administered two drops of different topical drugs to the eye?
eye can only hold half a drop so if both applied the efficacy will be reduced
what ways can topical ocular drugs be improved?
increase retention time
optimise ability to penetrate cornea
retention time of a drug depends on the formulation, name these from shortest to longest retention time
solution suspension ointment viscous gel colloidal system solid delivery sub-conjunctival injection
what does corneal penetration of the drug depend on?
solubility
what does corneal epithelium have that limits paracellular absorption?
tight junction
what route do lipid soluble drugs take through tissue?
trancellular
what route do water soluble drugs take through tissue?
paracellular
what part of the eye do water soluble agents easily cross?
stroma
what part of the eye do lipid soluble agents easily cross?
epithelium
what does a drug need to penetrate the cornea?
both hydrophilic and lipophilic characteristics
what effects the water and lipid solubility of a dug?
its ionisation
ophthalmic drugs have what type of pH?
weak acids or bases so have both ionised and unionised forms
is the ionised portion of the drugs water or lipid soluble?
water
is the unionised portion of the drugs water or lipid soluble?
lipid
describe the ionisation as ocular drugs move through the cornea?
unionised form moves through corneal epithelium with ease, it then ionises due to the abundance of unionised drug allowing it to move through the stroma, it then becomes unionised again to pass through the endothelium
what clinical factor may increase the absorption of topical ocular drugs?
corneal ulcers mean increased penetration for water soluble drugs
how can large hydrophilic molecules be absorbed into the eye?
via conjunctiva and sclera as they permit more paracellular movement
where can drugs enter from the sclera?
posterior segment
ciliary body
how is much of the topically administered drug absorbed systemically?
via the nasolacrimal duct
do topical drugs that penetrate via a non-corneal route have higher levels in anterior uvea or aqueous humour?
anterior uvea as they don’t pass through the aqueous humour to reach it but instead go through the ciliary body
what does the blood:ocular barrier consist of?
blood:aqueous and blood:retinal barriers
what is the blood:aqeuous barrier?
barrier between the blood in the vessels of iris/ciliary body and aqueous humour
what is the blood:retinal barrier?
barrier retinal pigment epithelium and the retinal capillary endothelium
why may pupil size want/need to be altered?
dilate for fundic exam
relax ciliary body to relieve spasms
constrict to open drainage angle
diagnostic tool
what is the term used for pupil dilation?
mydriasis
what is the term used for pupil constriction?
miosis
what is the term used to describe relaxation/paralysis of the ciliary body?
cycloplegia
what is a two groups of drugs that cause mydriasis?
parasympatholytics
sympathomimetics
what do parasympatholytics do to the eye?
relax the iris sphincter muscle to cause dilation
what do sympathomimetics do to the eye?
contact the dilator muscle to cause pupil dilation
name two parasympatholytics that cause mydriasis
atropine and tropicamide
name a sympathomimetic that causes mydriasis
phenylephrine
describe the pharmacokinetics of atropine?
slow onset but a very long duration of action
when is tropicamide used and why?
during pupil dilation exam due to its rapid onset and short duration of action
what are the three components of tear film?
lipid, aqueous and mucin
name two drugs that stimulate tear production
ciclosporin and pilocarpine
what is ciclosporin used for?
directly stimulate tear production and addresses underlying immune mediated cause as it is an immunosuppressant
what type of drug is pilocarpine?
parasympathomimetic
what are the categories tear substitutes fall into?
aqueous substitutes
mucin replacements
lipid replacements
give an example of a mucin replacement
carbomer gel
what type of acid is a good mucin replacer?
hyaluronic
what are lipid replacements used for?
increase tear retention time
what is glaucoma?
sustained increase in intraocular pressure
what can glaucoma cause?
pain, blindness, irreversible structure changes
what is glaucoma usually due to?
decreased aqueous humour outflow
what are the aims of glaucoma treatment?
increase aqueous humour outflow
decrease aqueous humour production
both
what drugs can be used in acute first line treatment of glaucoma?
osmotic diuretics
what do osmotic diuretics require to work?
intact blood:ocular barrier
how do osmotic diuretics work?
increase blood tonicity causing water to be drawn out of the aqueous humour
name the groups of drugs that can be used to treat glaucoma
carbonic anhydrase inhibitors
prostaglandin analogues
beta blockers
parasympathomimetics
how do carbonic anhydrase inhibitors work?
reduce the formation of bicarbonate in the ciliary body epithelium which reduces the blood drawn into the aqueous humour
how are carbonic anhydrase inhibitors administered?
topically
how do prostaglandin analogues work to treat glaucoma?
increase the outflow of aqueous humour by increasing uveoscleral outflow by altering the structure of the outflow tract
prostaglandin analogues are thought to also preserve vision in glaucoma patients, how?
increase perfusion of optic nerve head by vasodilation
what is an adverse effect of prostaglandin analogues?
can be irritants
give an example of a beta blocker used to treat glaucoma
betaxolol - topical beta1 antagonist
how do parasympatheticomimetics work to treat glaucoma patients?
contact ciliary body to constrict the pupil and open the drainage angle to increase the outflow of aqueous humour
name a parasympatheticomimetics used to treat glaucoma
pilocarpine
what do parasympatheticomimetics rely on to work in glaucoma patients?
an intact drainage angle
