Ocular Pharmacology

Question 1

sub-tenon adminstration

Answer 1

retro-orbital space

Question 2

intra vitreal injection

Answer 2

delivers concentration at target site instantly

however, many drugs are toxic to the retina

Question 3

when are intra vitreal injections used

Answer 3

to deliver ABx in endophthalmitis

intra-ocular steroids

anti-VEGF

Question 4

intra cameral administration

Answer 4

Question 5

what must drugs be to penetrate the epithelium

Answer 5

lipophilic or hydrophobic

Question 6

what must drugs be to penetrate the stroma

Answer 6

hydrophilic or lipophobic

Question 7

what must drugs be to penetrate the cornea, and give an axample

Answer 7

lipophilic and hydrophilic properties eg chloramphenicol

Question 8

what can ocular surface inflammation do to the properties of the endothelium

Answer 8

make it less hydrophobic

Question 9

what is also on the surface of the cornea and may impede drug penetration

Answer 9

lipid layer of tear film

Question 10

what makes steroids more hydrophobic

Answer 10

alcohol and acetate

Question 11

what makes steroids more hydrophilic

Answer 11

phosphate

Question 12

when would Prednisolone acetate be used

Answer 12

it is hydrophobic so has good penetration in the uninflamed cornea

often used post-op

Question 13

when would Prednisolone phosphate be used

Answer 13

it is hydrophilic so will have better penetration in the inflamed cornea

can also be used in the uninflamed cornea for lower dosage

Question 14

what can be used to enhance corneal penetration

Answer 14

Benzalkonium - preservative that also disrupts the lipid layer of the tear film on the cornea

Question 15

how can systemic absorption of topical drugs be limited

Answer 15

tears are rapidly pumped out of lacrimal sac into nasolacrimal duct where there is systemic absorption at the nasopharynx

can be limited by punctal occlusion (for 5 minutes)

Question 16

what local anaesthetic is used

• mechanism
• use

Answer 16

tetracaine 1%

blocks Sodium channels and impedes nerve conduction

used for FB removal, tonometry (IOP measurement),corneal scraping, comfort, opening of eye

Question 17

what can fluoroscein be use din the diagnosis of (lacrimal ducts)

Answer 17

lacrimal duct obstruction - retained dye in a thickened tear strip is diagnostic

Question 18

mydriatics

Answer 18

eg tropicamide, cyclopentolate

cause pupillary dilation by blocking the parasympathetic supply to the iris

also cause cycloplegia (stop the lens from focusing)

however, this effect is only noticed in younger people, as in older people the lens is stiffer and not so good at focusing anyway

Question 19

side effects of mydriatics

Answer 19

cycloplegia (blurring)

very rarely AACG

Question 20

how do mydriatics (rarely) cause AACG

Answer 20

dilated pupil lessens the corneoscleral angle

• this is why closed angle glaucoma is worse at night, becuase the pupil dilates
• and why pilocarpine is part of the treatment

Question 21

Sympathomimetics

Answer 21

act on the sympathetic system causing the pupil to dilate

do not affect the ciliary muscle

eg phenylephrine and atropine

Question 22

what diagnostic tool is phenylephrine used for

Answer 22

differentiate between episcleritis and scleritis

Question 23

what can ethambutol (TB) cause

Answer 23

optic neuropathy and colour blindness

Question 24

what can chloroquine (anti-malarial) cause

Answer 24

maculopathy