## Clinical Scenario: Progressive POAG Despite Monotherapy ### Assessment of Current Status **Key Point:** This patient demonstrates *progressive glaucomatous damage* despite seemingly adequate IOP control on monotherapy: - IOP 18–19 mmHg on latanoprost (within "normal" range) - BUT: New visual field defect (superior nasal step) on repeat testing - AND: Progressive optic nerve head changes on OCT (rim thinning) - This indicates the current IOP is still above the patient's "target pressure" **High-Yield:** In POAG, the absolute IOP value matters less than whether damage is progressing at that pressure. Progressive structural and functional loss despite seemingly controlled IOP indicates inadequate pressure reduction for *this individual patient*. ### Concept of Target Intraocular Pressure ```mermaid flowchart TD A["POAG on monotherapy"]:::outcome --> B{"Structural or<br/>functional<br/>progression?"}:::decision B -->|"No progression<br/>IOP stable"| C["Continue current<br/>therapy"]:::action B -->|"Yes: VF loss<br/>or rim thinning"| D{"IOP at<br/>target?"}:::decision D -->|"No: IOP still<br/>elevated"| E["Intensify therapy:<br/>add 2nd agent"]:::action D -->|"Yes: IOP at<br/>target but<br/>still progressing"| F["Consider laser or<br/>surgery"]:::action ``` **Clinical Pearl:** Target IOP is individualized based on baseline damage severity and rate of progression. In this patient with moderate-to-advanced damage (mean deviation −8 dB), an IOP of 18–19 mmHg is insufficient to halt progression. ### Why Add a Second Agent? **Key Point:** The standard approach to progressive POAG is stepwise IOP reduction: 1. Optimize monotherapy (ensure compliance, correct instillation technique) 2. Add a second agent from a different drug class 3. If still progressing, add a third agent or consider laser/surgery **Mnemonic: ABCDE of glaucoma agents** - **A** = Alpha-2 agonists (brimonidine) - **B** = Beta-blockers (timolol, betaxolol) - **C** = Carbonic anhydrase inhibitors (dorzolamide, brinzolamide) - **D** = Prostaglandin analogs (latanoprost, travoprost, bimatoprost) - **E** = Epinephrine/sympathomimetics (rarely used) ### Choice of Second Agent | Agent Class | Mechanism | IOP Reduction | Advantage | Disadvantage | |-------------|-----------|---------------|-----------|---------------| | **Beta-blocker** (timolol) | ↓ aqueous production | 20–25% | Additive with PGA; good efficacy | Systemic absorption; bradycardia, bronchospasm | | **CAI** (dorzolamide) | ↓ aqueous production | 15–20% | Additive with PGA; topical | Taste disturbance; corneal endothelial effects with long-term use | | **Alpha-2 agonist** (brimonidine) | ↓ production + ↑ outflow | 15–20% | Neuroprotective properties | Tachyphylaxis; allergic reactions | **High-Yield:** Timolol or dorzolamide are most commonly added to latanoprost because they work via different mechanisms (decreased aqueous production vs. increased uveoscleral outflow), providing additive IOP reduction of 5–8 mmHg beyond monotherapy. ### Why Not the Other Options? **Option A (Continue monotherapy):** Contraindicated. The patient has documented *progression* on current therapy. Continuing without intensification risks further irreversible vision loss. **Option C (Switch to different PGA):** Not indicated. All prostaglandin analogues have similar efficacy (25–35% IOP reduction). Switching within the same class will not provide additional benefit. The problem is insufficient total IOP reduction, not inadequate PGA choice. **Option D (Laser/surgery):** Premature. Laser trabeculoplasty or filtration surgery is reserved for patients who have failed maximum tolerated medical therapy (3–4 agents) or who are non-compliant. This patient is still on monotherapy and has not yet tried combination medical therapy. 
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