A 52-year-old woman with confirmed Primary Open-Angle Glaucoma has been on monotherapy with latanoprost 0.005% once daily in the evening for 3 months. Her baseline IOP was 26 mmHg in both eyes. Current IOP measurements are 22 mmHg (OD) and 23 mmHg (OS). Visual field and optic disc imaging remain stable. The target IOP for this patient (based on initial optic nerve damage severity) is 18 mmHg or lower. What is the most appropriate next step?

Explanation

## Clinical Assessment This patient has achieved a **partial but inadequate IOP reduction**: - Baseline IOP: 26 mmHg - Current IOP: 22–23 mmHg (reduction of ~3–4 mmHg) - Target IOP: ≤18 mmHg - **IOP gap: 4–5 mmHg above target** ## Why Monotherapy Is Insufficient **Key Point:** A single prostaglandin analogue typically reduces IOP by 25–35% from baseline. This patient's reduction (~13–15%) suggests either: 1. Inadequate response to latanoprost, or 2. Tachyphylaxis (loss of effect over time) Since the target IOP has not been reached and the patient requires further reduction, **escalation to combination therapy is indicated**. ## Treatment Escalation Strategy **High-Yield:** POAG therapy follows a stepwise approach: | Step | Approach | Expected IOP Reduction | |------|----------|------------------------| | 1 | Monotherapy (prostaglandin, beta-blocker, or CAI) | 25–35% | | 2 | Dual therapy (different classes) | 35–50% | | 3 | Triple therapy or adjunctive laser | 50–60%+ | | 4 | Glaucoma surgery (trabeculectomy, MIGS) | 60%+ | **Clinical Pearl:** When adding a second agent, choose a drug from a **different pharmacologic class** to maximize additive IOP-lowering effect. Combining two prostaglandins offers no additional benefit. ## Recommended Second Agent Options - **Topical beta-blocker** (timolol 0.5%, twice daily): reduces IOP by ~25%; contraindicated in asthma, COPD, bradycardia - **Topical CAI** (dorzolamide 1%, three times daily): reduces IOP by ~20%; safe in systemic disease - **Topical alpha-2 agonist** (brimonidine): reduces IOP by ~20%; risk of allergic conjunctivitis - **Rho kinase inhibitor** (netarsudil): newer agent; reduces IOP by ~20%; may cause conjunctival hyperemia **Mnemonic: PBCA** — Prostaglandins, Beta-blockers, Carbonic anhydrase inhibitors, Alpha-2 agonists (the four main topical classes). ## Algorithm for Escalation ```mermaid flowchart TD A[POAG on monotherapy]:::outcome A --> B{IOP at target?}:::decision B -->|Yes| C[Continue monotherapy, monitor]:::action B -->|No| D{How far from target?}:::decision D -->|1-2 mmHg| E[Optimize timing/compliance, reassess]:::action D -->|>2 mmHg| F[Add second agent from different class]:::action F --> G[Recheck IOP in 4-6 weeks]:::action G --> H{IOP at target?}:::decision H -->|Yes| I[Continue dual therapy, monitor]:::action H -->|No| J[Add third agent or consider laser/surgery]:::action ``` **Tip:** Always counsel the patient on compliance and correct instillation technique before escalating therapy — poor adherence is a common cause of apparent treatment failure.