Ocular pharmacology

Question 1

How do the eyes constrict?

Answer 1

Parasympathetic nerves innervate the sphinteric muscle

Pupils are generally rather small hence there is a high basal level of activity

Muscarinic agonists will therefore constrict the eye (miosis) and antagonists will dilate the eye

Question 2

How might the eyes dilate?

Answer 2

Radial muscles in the iris are innervated by sympathetic nerves

Their contraction will dilate the eyes (mydriasis)

Agonists will dilate and antagonists will constrict the eyes

Question 3

What do the ciliary muscles do and how do they work?

Answer 3

They have parasympathetic innervation

When they contract, the ligaments attached to the lens go slack and allows for focus on near objects

When they are relaxed, the ligaments go taut and stretch the lens out allowing for focus on far objects

Very little adrenergic innervation

Question 4

What does the ciliary body epithelium do?

Answer 4

Produces aqueous humour which:
Maintains intraocular pressure
Provides nutrient to eye
Released into posterior chamber

Question 5

How can we control the formation of aqueous humour?

Answer 5

alpha1 agonists: constrict blood flow thereby by reducing blood supply and pressure to ciliary body

alpha2 agonists: reduces cAMP which reduces the vol of AH produced

beta1 agonists: increases the amount of AH produced

Hence to limit the amount of AH produced we use alpha agonists (clonidine) or beta blockers (timolol)

Question 6

Dipiveferin

Answer 6

Pro-drug of adrenaline

Consists of adrenaline ester bonded to lipd molecule

Esterase breaks the ester bond allowing adrenaline to interact with receptors

Not very selective hence not licensed in UK

Question 7

Acetazolamide- How does it work?

Answer 7

Production of AH is dependent on the active transport of HCO3- hence if you can inhibit the production of HCO3- you can reduce production of AH

Acetazolamide inhibits carbonic anhydrase reducing production of HCO3-

Brinzolamide is same mechanism but has long half life

Question 8

How can we improve the drainage of AH?

Answer 8

Muscarinic agonists constrict the ciliary muscle as when it is relaxed the extra bulk can block the drainage

Uveosclereal flow can be improved via use of prostoglandin analogues (Latanoprost)

Question 9

What abnormality causes closed angle glaucoma?

Answer 9

The iris deforms and blocks the trabecular network and uveosclereal canal

While open angle glaucoma is slow onset and progressive, closed angle is rapid onset and can cause irreversible damage

More common amoungst asians and inuits

Question 10

Treatment for closed angle glaucoma

Answer 10

Osmotic drugs to remove water from aqueous humour reducing its vol. thereby reducing intraocular pressure however it is only a temporary fix

The only permanent treatment is surgery

Question 11

The 2 types of age related macular degeneration (AMD)

Answer 11

Macula necessary for sharp vision

Dry AMD- slow onset, caused by degeneration of one area, no treatment

Wet AMD- rapid onset, can be treated by reducing leakage of local vasculature

Question 12

Wet AMD

Answer 12

Caused by growth of leaky blood vessels under retina

Treatment with photodynamic therapy
-verteporforin photoactivated by red low energy laser
Causes occlusion of vasculature meaning that they don’t leak anymore

Vascular endothelial growth factor (VEGF) causes such leakge so can be used as a target for inhibition (anti-VEGF)

Question 13

Screening for glaucoma

Answer 13

If 35-50yrs then eye check every 4 yrs
If>50yrs the eye check every 2yrs
Also consider at risk groups:
afro/carribean
family history
short sightedness
diabetes

Question 14

First line treatment for chronic open angle glaucoma (COAP)

Answer 14

Generic PGA (eg. Latanoprost) if there is risk of COAP in their lifetime 
Offer additional topical treatment if not sufficiently controlled with monotherapy 
If not controlled with double therapy then refer to specialist 
Do not offer treatment to those with intraoculaar pressure less than 24mmHg

Question 15

Pharmacological augmentation in surgery

Answer 15

Mitomycin C to prevent scar tissue from blocking drainage tubes

Question 16

Common side effect of PGA eye drops

Answer 16

Conjunctival hyperaemia- eye becomes pink/red

This is due to more blood in the conjunctiva as a result of the dilation of the supplying arteries

Question 17

Can patients apply two eye drops at once?

Answer 17

Not recommended as it would cause overflow hence most of the drug would be lost

leave at least 5 mins between the application of each

Always check patients eye drop technique as they could be rubbish at it so their condition doesn’t improve

Question 18

How can patients absorb systemic absorption of their drugs?

Answer 18

Keep eyes closed for 2 mins after administration

Keep pressure on lacrimal punctum (press on the tiny knobbly bit of the eyelid)

Question 19

Can the patient use contact lenses with eye drops?

Answer 19

Unless medically indicated remove contacts before application

Contra indicated for ointments/oily formulations

For long term therapy unpreserved drops can be used

Question 20

Cautions for PGA’s (Latanoprost)

Answer 20

Care need in patients with COPD, asthma or compromised respiratory function

Question 21

Cations for beta blockers (Timolol)

Answer 21

Contraindicated in patients with bradycardia, heart block or heart failure
Do not use in patients with respiratory conditions

Question 22

Cautions for carbonic anhydrase inhibitors (Dorzolamide, brinzolamide)

Answer 22

Stop if sulfonimide like reaction occurs

Can enhance effect of ACE inhibitors and other anti hypertensives

Question 23

Cautions of alpha2 agonists (clonidine, brimonidine)

Answer 23

Cautioned against use where there is CVD cerebral deficiency, raynauds syndrome, hypotension, depression