Ocular pharmacology

Question 1

How can drugs be administered for ocular purposes

Answer 1

Topical

Systemic

Question 2

What are the advantages of topical administration?

Answer 2

Convenient
Sometimes easy?
Minimal systemic side effects

Question 3

Topical drugs are distributed in the eye in 3 ways. What are these?

Answer 3

Drainage by lacrimal drainage system
Penetration of eye via cornea/sclera
Through conjunction and nasal mucosal vessels

Question 4

When topical drugs are distributed via nasal/conjunctival mucosa, were do they go? What is the efficacy of this?

Answer 4

Systemic circulation

Like slow IV

Question 5

What are the disadvantanges of topical administration?

Answer 5

Drops are bigger volume than palpebral fissure can hold - excess spills out
15% tear film turned over/min - rapidly removed from surface
Poor bioavailability - only fraction of drug reaches anterior chamber

Question 6

How can the bioavailability of topical drugs be improved in the eye?

Answer 6

Increase drug retention on palpebral fissure

Increase ability to penetrate cornea

Question 7

What type of topical treatments can be applied to the eye?

Answer 7

Solution
Suspension 
Ointment
Viscous fluid/gel
Colloidal system 
Subconjunctival injection

Question 8

What is it called when drugs bind to tear film? What conditions is this suitable for?

Answer 8

Bioadhesion 
Dry eye (keratoconjunctivitis sicca)

Question 9

Why is corneal penetration and absorption of ocular drugs limited?

Answer 9

Tight junctions in corneal epithelium - limit paracellular absorption

Question 10

Topical corneal drugs can be lipid soluble or water soluble (should be both!). What parts of the cornea do they cross?

Answer 10

Lipid soluble -cross epithelium

Water soluble - cross stroma

Question 11

When drugs penetrate the cornea, what structures of the eye do they go to? Which structures receive low levels of corneally absorbed drugs?

Answer 11

Aqueous humor, iris, ciliary body

Lens, vitreous humor and posterior segment receive little of drug

Question 12

Non-corneal penetrative drugs enter the eyeball via the conjunctiva and sclera.. Are theses drugs hydrophilic or lipophilic?

Answer 12

Hydrophilic

Conjunctiva epithelum and sclera more permeable corneal epithelium

Question 13

When drugs enter the eye via the sclera, where do they go?

Answer 13

Posterior segment or scleral vessels and ciliary body

Drug level higher in anterior uvea than aqueous

Question 14

Where are topical ocular drugs metabolised?

Answer 14

In corneal epithelium

Or target tissue

Question 15

Systemic ocular drugs are better for when trying to target what segment of the eye? What are the other advantages?

Answer 15

Posterior

Easier administration?

Question 16

What is the blood ocular barrier (BOB)? What does it consist of?

Answer 16

Barrier between eye and blood stream
BAB - blood:aqueous barrier
BRB - blood:retinal barrier

Question 17

The BOB affects the ability of many drugs to penetrate the eye. Which section of the BOB (BRB or BAB) sis leakier?

Answer 17

Blood:aqueous barrier leakier - allows agents to easily cross into anterior segment

Question 18

Do lipophilic or hydrophilic drugs penetrate the BOB easier?

Answer 18

Lipophilic

Question 19

What is the word for pupil dilation? What about constriction?

Answer 19

Mydriasis - relaxation

Miosis - constrinction

Question 20

What type of drugs cause pupil dilation? (mydriasis)

Answer 20

Parasympatholytics - release iris sphincter

Sympathomimetics - contract the dilator muscle

Question 21

Why may you want to cause pupil dilation? (mydriasis)

Answer 21

Eye exam

Contract ciliary body muscles to relieve painful spasms

Question 22

What is the word for relaxation/paralysis of the ciliary muscle?

Answer 22

Cycloplegia

Question 23

What innervates the pupil dilator muscle?

Answer 23

Sympathetic innervation

Nasociliary nerve

Question 24

What innervates the pupil constrictor muscle?

Answer 24

Parasympathetic innervation

Occulomotor nerve

Question 25

What drugs can be used for pupil dilation?

Answer 25

Atropine Tropicamide Phenylnephrine

Question 26

What are the disadvantages/advantages of atropine?

Answer 26

Slow onset Long duration Causes systemic antimuscarinic effects - problem in horse (Colic)

Question 27

Atropine causes mydriasis. Is it a sympathomimetic or parasympatholytic?

Answer 27

Parasympatholytic

Question 28

Tear film maintains the health and clarity of the cornea. What do conditions like dry eye require as part of their treatment? Give an example

Answer 28

Tear substitutes | Pilocarpine

Question 29

How does pilocarpine work? When might it be given?

Answer 29

Actively increases tear production, parasympathomimetic | Dry eye, during GA to prevent eyes drying out

Question 30

What are the 3 categories of tear substitutes?

Answer 30

Aqueous substitutes Mucin layer mimics Drugs that replace the lipid portion of the tear film

Question 31

Why are aqueous substitutes of tear films limited?

Answer 31

Lost quickly from ocular surface | Need frequent application

Question 32

What is glaucoma? What does it cause?

Answer 32

Oedema of eye | Intraocular pressure damages optic nerve - pain blindness, irreversible structural changes

Question 33

What can cause an increased intraocular pressure (leading to glaucoma)?

Answer 33

Decreased aqueous outflow

Question 34

Glaucoma drugs include emergency treatment and drugs for management. What is the first line of Tx for emergency intervention? Give an example

Answer 34

Osmotic diuretics | Mannitol

Question 35

How do osmotic diuretics work to treat glaucoma? What do they rely on being intact? Why are they for short term, emergency use only?

Answer 35

Increase in blood tonicity causes water to be drawn out of aqueous and vitreous humor Intact BOB Cannot be long term --> hypovolaemia

Question 36

What drugs can be used to maintain glaucoma treatment?

Answer 36

Carbonic anhydrase inhibitors Prostaglandin analogues Beta blockers Parasympathomimetic drugs

Question 37

How do carbonic anhydrase inhibitors work to treat glaucoma? Give an example

Answer 37

Carbonic anhydrase ataylses hydration of CO2 to HCO3 and H+. HCO3 draws water into aqueous Inhibition of this - stops water being drawn into aqueous Brinzolamide

Question 38

How do prostaglandin analogues work to treat glaucoma? Give an example

Answer 38

Increase uveoscleral outflow of aqueous | Latanoprost

Question 39

How do beta blockers work? Give an example of a topical agent used

Answer 39

Reduce aqueous formation | Betaxolol

Question 40

How do parasympathomimetic drugs work to treat glaucoma? Give an example

Answer 40

Contract ciliary body and constrict pupil Widens drainage angle - increases aqueous outflow Pilocarpine