A 62-year-old woman from Mumbai with a 5-year history of primary open-angle glaucoma presents for follow-up. She has been on latanoprost monotherapy for 3 years with good adherence. Current IOP is 18 mmHg in both eyes on applanation tonometry. However, automated perimetry performed 6 months ago showed a new superior arcuate defect in the left eye, and repeat testing today confirms progression of the defect with a mean deviation (MD) decline of 2.5 dB. Optic disc photography shows progressive inferotemporal notching in the left eye. The patient reports no adverse effects from latanoprost. What is the most appropriate next step?

Explanation

## Progressive Glaucomatous Damage Despite Adequate IOP Control ### Clinical Scenario Analysis **High-Yield:** This case illustrates a critical concept in POAG management: **target IOP is individualized**. Although the current IOP of 18 mmHg appears "normal," the patient is experiencing progressive optic nerve damage and VF loss, indicating that the target IOP for this patient must be lower. **Key Point:** Progressive VF loss (MD decline of 2.5 dB on repeat testing) and structural optic disc changes despite IOP control at 18 mmHg define **inadequate IOP reduction**. The target IOP must be lowered further to halt progression. ### Target IOP Determination in POAG | Clinical Factor | Target IOP Adjustment | |---|---| | Newly diagnosed POAG | 20–21 mmHg (25% reduction from baseline) | | Advanced glaucoma or young age at diagnosis | 12–14 mmHg (30–40% reduction) | | Progressive VF loss despite current IOP | Lower target by 20–30% from current level | | Baseline IOP very high (>30 mmHg) | Aggressive initial reduction (30–50%) | **Clinical Pearl:** The concept of "target IOP" is not fixed; it is dynamic and adjusted based on evidence of progression. A patient with progressive damage at 18 mmHg requires a new target of approximately 12–14 mmHg (20–30% further reduction). ### Why Add a Second Agent? Monotherapy with a prostaglandin analogue achieves approximately 25–35% IOP reduction. To achieve an additional 20–30% reduction from the current level (18 mmHg → 12–14 mmHg), a second agent with a different mechanism is required: ```mermaid flowchart TD A[POAG with progressive VF loss]:::outcome --> B{Current IOP adequate?}:::decision B -->|No - Progressive damage| C[Lower target IOP by 20-30%]:::action B -->|Yes - Stable| D[Continue current therapy]:::action C --> E{On monotherapy?}:::decision E -->|Yes| F[Add second agent]:::action E -->|No| G[Intensify regimen or consider surgery]:::action F --> H[Prostaglandin + Beta-blocker/CAI]:::outcome H --> I[Reassess IOP and VF in 3 months]:::action ``` ### Choice of Second Agent **Preferred combinations with prostaglandin analogues:** | Second Agent | Mechanism | Additive IOP Reduction | Advantage | |---|---|---|---| | Beta-blocker (timolol) | ↓ aqueous production | 15–25% | Well-established, cost-effective | | Carbonic anhydrase inhibitor (dorzolamide) | ↓ aqueous production | 15–20% | Topical; avoids systemic effects | | Alpha-2 agonist (brimonidine) | ↓ production + ↑ outflow | 15–20% | Neuroprotection postulated | **Mnemonic: POAG Escalation = Mono → Dual → Triple → Surgery** — each step aims to achieve a lower target IOP. ### Why Not Switch Prostaglandin? All prostaglandin analogues (latanoprost, travoprost, bimatoprost) have similar efficacy (25–35% IOP reduction). Switching agents without adding a second mechanism will not achieve the required additional IOP lowering. ### Why Not Laser Trabeculoplasty? Laser trabeculoplasty is considered after maximal medical therapy has been optimized. The patient is still on monotherapy; medical escalation should be attempted first. [cite:Khurana 6e Ch 10; Garg 3e Ch 7]