Medical Management of Glaucoma

PGAs: Uveoscleral Outflow Champs

• Mechanism: ↑ uveoscleral outflow.
• Examples: Latanoprost, Travoprost, Bimatoprost, Tafluprost. 📌 Mnemonic: 'Lashes Grow Beautifully Tonight' (Latanoprost, Growth-eyelash, Bimatoprost, Travoprost)
• Dosing: Once daily (evening).
• IOP Reduction: ~25-35%.
• Key Side Effects:
  • Iris hyperpigmentation
  • Eyelash growth (hypertrichosis)
  • PGFE (Prostaglandin-Associated Periorbitopathy)
  • CME (Cystoid Macular Edema) - esp. in aphakic/pseudophakic eyes
  • Reactivation of herpetic keratitis

⭐ Exam Favourite: Prostaglandin analogues are typically the first-line medical therapy for open-angle glaucoma due to high efficacy and convenient once-daily dosing.

Beta-Blockers: Aqueous Production Cutters

• Mechanism: ↓ aqueous humor production by ciliary body.
• Types:
  • Non-selective: Timolol, Levobunolol, Carteolol.
  • Beta-1 selective (cardioselective): Betaxolol.
• Dosing: Usually BID (e.g., Timolol 0.5%).
• IOP Reduction: ~20-25%.
• Systemic Side Effects: Bronchoconstriction, bradycardia, hypotension, fatigue, masking hypoglycemia.
  • 📌 Mnemonic: 'BBs Can Cause Big Problems'
• Ocular Side Effects: Allergic reaction, corneal anesthesia, dry eye, punctate keratitis.
• Contraindications: Asthma, COPD, significant heart block/bradycardia, overt cardiac failure.

⭐ Exam Favourite: Betaxolol, being beta-1 selective, has a relatively safer systemic side effect profile, especially concerning respiratory issues, compared to non-selective beta-blockers like Timolol. It is preferred in patients with mild to moderate pulmonary disease where a beta-blocker is necessary for IOP control, though caution is still advised.

Alpha Agonists & CAIs: Dual-Mode IOP Droppers

• Alpha-Adrenergic Agonists:
  • Mechanism: Dual action - ↓ Aqueous humor production & ↑ Uveoscleral outflow (especially Brimonidine).
  • Examples: Apraclonidine (acute IOP spikes), Brimonidine (long-term/chronic use).
  • IOP Reduction (Brimonidine): ~15-25%.
  • Side Effects (Brimonidine): High allergy rate (follicular conjunctivitis), dry mouth, fatigue. 📌 Contraindicated in children <2 years (risk of CNS depression, apnea).
• Carbonic Anhydrase Inhibitors (CAIs):
  • Mechanism: ↓ Aqueous humor production by inhibiting carbonic anhydrase in ciliary epithelium.
  • Topical: Dorzolamide, Brinzolamide.
    • IOP Reduction: ~15-20%.
    • Side Effects: Stinging, burning, bitter taste, superficial punctate keratitis (SPK).
  • Systemic: Acetazolamide (oral/IV).
    • Side Effects: Paresthesias, metabolic acidosis, hypokalemia, renal stones, sulfa allergy, aplastic anemia (rare).

⭐ Systemic acetazolamide is crucial in managing acute angle-closure glaucoma for rapid and significant IOP reduction.

Miotics & Combos: Teamwork Tactics

• Miotics (Parasympathomimetics):
  • Mechanism: ↑ Trabecular outflow (ciliary muscle contraction).
  • Example: Pilocarpine. IOP Reduction: ~15-20%.
  • Side Effects: Miosis, brow ache, accommodative spasm, induced myopia. ⚠️ Risk of retinal detachment.
  • Use: Limited in OAG; key in pupillary block (Angle Closure Glaucoma).
• Combination Therapy:
  • Goal: Achieve target IOP with additive effects from different mechanisms.
  • Fixed Combinations (FCs): Improve adherence, ↓ preservative load. Examples: Timolol/Dorzolamide (Cosopt), Timolol/Brimonidine (Combigan), Timolol/Latanoprost (Xalacom).

⭐ Exam Favourite: Fixed-combination drops are preferred over multiple individual bottles to enhance patient compliance and reduce the 'washout' effect.

High‑Yield Points - ⚡ Biggest Takeaways

• Prostaglandin analogs (e.g., Latanoprost) are first-line; ↑ uveoscleral outflow.
• Topical beta-blockers (e.g., Timolol) ↓ aqueous humor production; caution in asthma.
• Alpha-2 agonists (e.g., Brimonidine) have dual mechanism: ↓ production, ↑ outflow.
• Carbonic anhydrase inhibitors (e.g., Dorzolamide) ↓ aqueous production; sulfa allergy risk.
• Pilocarpine (miotic) ↑ trabecular outflow; side effects: miosis, brow ache.
• Medical therapy goal: Lower IOP to prevent optic neuropathy and vision loss.
• Combination therapy is common if monotherapy fails to reach target IOP.