Ocular Pharmacology and Therapeutics
Core concepts
Separate drug classes by mechanism: beta-blockers (timolol) reduce aqueous production; alpha-2 agonists (brimonidine) reduce production and increase uveoscleral outflow; carbonic anhydrase inhibitors reduce production; prostaglandin analogues (latanoprost) increase uveoscleral outflow; pilocarpine increases trabecular outflow. Know systemic side effects: beta-blockers cause bronchospasm and bradycardia; CAIs cause paraesthesia and metabolic acidosis; alpha-agonists cause fatigue and dry mouth.
Understand pharmacokinetics: topical drops have poor bioavailability; punctal occlusion improves it. Know dilating agents: tropicamide (short), cyclopentolate (medium), atropine (long); phenylephrine is alpha-1 and does not cycloplege. Anticholinergics are contraindicated in angle-closure risk.
Traps
- Assuming all mydriatics are cycloplegic (phenylephrine is not).
- Forgetting that prostaglandins can cause iris darkening and periorbital fat atrophy.
- Mixing up which drugs are safe in pregnancy or asthma.
- Confusing steroid response (raised IOP) with steroid-induced cataract.
Rule of thumb
Match the drug to the outflow pathway: if you want to increase outflow, choose prostaglandin or pilocarpine; if you want to decrease inflow, choose beta-blocker, CAI, or alpha-agonist.
Worked example
A patient with asthma needs IOP lowering. Avoid timolol; choose latanoprost or brimonidine, and monitor for systemic effects.