Pharmacology for the eye

Question 1

What are the 7 things a vet should know about drugs for the eyes?

Answer 1

1. How to control pain to examine cornea
2. Routes for medications to infiltrate ocular
   structures
3. Selection of topical ocular and systemic anti‐
   infectives
4. Topical antivirals for active herpes
5. Selection of topical anti‐inflammatories &
   immunosuppressive drugs
6. Medication to change pupil diameter
7. Medication to reduce pressure in anterior
   chamber

Question 2

What topical drug can be used to control pain to examine the cornea?

Answer 2

• Local anaesthetic drops = lignocaine opthalmic drops. Rapid onset and duration of around 30-120 mins.
• This may be insufficient due to the severity of pain. Sedation or general anaesthesia may be required

Question 3

What barriers are there in the eye?

Answer 3

• Blood-ocular barriers -> the blood-aquesous barrier and the blood-retinal barrier

Question 4

What is an amphipathic drug?

Answer 4

Able to cross lipid and water

Question 5

What are the three routes of topical ocular and systemic administration?

Answer 5

1. Across the cornea
2. Absorption by conjuntival blood vessels that flow into the ciliary body
3. Drug exit via nasolacrimal duct

Question 5

What are the three routes of topical ocular and systemic administration?

Answer 5

1. Across the cornea
2. Absorption by conjuntival blood vessels that flow into the ciliary body
3. Drug exit via nasolacrimal duct

Question 6

For topical formulations, how much drug is required to be effective?

Answer 6

• Only 10 – 25 uL are retained in conjunctival fornix & tear film after immediate overflow
• Commercial droppers deliver 25 – 50 µL of drug formulation / drop -> thus 1 drop is sufficient
• Best to use less more frequently
• After 5 minutes only 20% of drug remains on the ocular surface (as some drug may go through cornea, absorbed by blood vessels or goes out nasolacrimal drainage into the mouth).

Question 7

How would you treat a sterile corneal ulcer?

Answer 7

Using proteinase inhibitors such as tetracycline or acetylcysteine drops to inhibit corneal proteolytic activity

Question 8

How would you treat a traumatic or infected corneal ulcer in a dog?

Answer 8

Use an ointment that covers gram positives and gram negatives (something like tricin).
- Gram positives = bacitracin
- Gram negatives = polymixin or aminoglycosides

Question 8

How would you treat a traumatic or infected corneal ulcer in a dog?

Answer 8

Use an ointment that covers gram positives and gram negatives (something like tricin).
- Gram positives = bacitracin
- Gram negatives = polymixin or aminoglycosides

Question 9

What is the issue with using topical tetracycline eye ointment?

Answer 9

• Topical tetracyclines can irritate the cornea
• Currently only available through compounding pharmacies

Question 10

How would you treat ocular signs associated with mycoplasma felis?

Answer 10

• Tetracycline ointment OR systemic therapy such as orla doxy or fluoroquinolones

Question 11

How would you treat ocular chlamydiosis?

Answer 11

• Treated as for Mycoplasma spp.
• Tetracycline ointment OR systemic therapy such as orla doxy or fluoroquinolones
• NOTE: Doxycycline can be administered to kittens and pups > 4 weeks old without enamel discolouration

Question 12

What are the topical anti-viral eye formulations that are available?

Answer 12

• Trifluridine - irritates cornea
• idoxuridine - drops do not penetrate the conjunctiva and cornea well except where there is ulceration
• cidofovir - BID drops. Carcinogenic.

Question 13

Can antivirals eradicate latent infections?

Answer 13

• They are virostatic ‐ this means they are only effective in treating actively replicating virus and cannot eradicate latent infections

Question 14

In what circumstance would you use a glucocorticosteroid?

Answer 14

• to delay healing such as reducing corneal scar tissue and optimise corneal opacity ‐ used only after the infection is eradicated.
• Would be used alongside an antibiotic (joint formulations (chloropstsone) are available

Question 15

What is the difference between chloroptsone and chloropt?

Answer 15

Chloroptsone = chloramphenicol with GCS
Choropt = chlorampenicol ONLY

Question 16

What is an example of an immune mediated ocular disease and how might it be treated?

Answer 16

• Pannus (chronic superficial keratitis)
• Treatment: topical GCS but requires continual therapy

Question 17

How would you treat ‘dry eye’ or keratoconjunctivitis sicca?

Answer 17

• Use an immunosuppresive drug
• +/- antibacterial
• artificial tears

Question 18

What do GCS such as prednisolone and dexamethasone do in the eye?

Answer 18

Immunosuppressive - inhibits T lymphocyte and macrophage action

Question 19

What is the mechanism of action of steroid sparing drugs such as cyclosporine and tacrolimus?

Answer 19

Inhibit T lymphocyte action

Question 20

What is mydriasis?

Answer 20

To dilate pupil

Question 21

What is myosis?

Answer 21

To constrict pupil

Question 22

What are some drugs that dilate the pupil (mydriatic) and what might it be used to examine?

Answer 22

• Muscarinic receptor antagonist such as atropine
• Used to examine the retina and fundus

Question 23

What are some drugs that constrict the pupil?

Answer 23

• muscarinic receptor agonist such as pilocarpine

Question 24

What are some drugs that reduce pressure in the anterior chamber?

Answer 24

• Carbonic anhydrase inhibitors such as dorzolamide or acetazolamide.
• Topical beta blockers (on ciliary epithelium) = timolol maleate