A 52-year-old woman from Mumbai with primary open-angle glaucoma has been on topical latanoprost monotherapy for 8 weeks. Her baseline IOP was 26 mmHg (both eyes). Current IOP is 24 mmHg OD and 23 mmHg OS. She has no ocular or systemic contraindications to further therapy. Visual fields show early glaucomatous changes. What is the most appropriate next step?

Explanation

## Clinical Context This patient has POAG on monotherapy with suboptimal IOP control. Despite 8 weeks of latanoprost, the IOP reduction is only ~8% (from 26 to 24 mmHg OD), which is insufficient given the presence of glaucomatous visual field changes. The target IOP should be lower to halt disease progression. ## Assessment of Therapeutic Response **Key Point:** A prostaglandin analogue typically achieves 25–35% IOP reduction. This patient's 8% reduction suggests inadequate response and need for escalation. **High-Yield:** When monotherapy fails to achieve target IOP after 4–8 weeks, the next step is to add a complementary second agent rather than switch monotherapy. ## Rationale for Adding Beta-Blocker ```mermaid flowchart TD A[POAG on monotherapy<br/>IOP still elevated]:::outcome --> B{Adequate IOP reduction?}:::decision B -->|No| C[Add second agent]:::action C --> D{Choose agent based on<br/>contraindications & comorbidities}:::decision D -->|No systemic CI| E[Beta-blocker or CAI]:::action D -->|Asthma/COPD| F[CAI or alpha-2 agonist]:::action D -->|Renal disease| G[Avoid CAI; use alpha-2 agonist]:::action E --> H[Recheck IOP in 4 weeks]:::action F --> H G --> H ``` ## Why Add Rather Than Switch? | Strategy | Rationale | |----------|----------| | **Add second agent** | Synergistic IOP reduction; different mechanism of action (prostaglandin + beta-blocker = ~40–50% total reduction). Proven approach. | | **Switch monotherapy** | Wastes time; no evidence that a different prostaglandin will work better if latanoprost has failed. | **Clinical Pearl:** Beta-blockers (timolol 0.5% BID) are excellent second agents because they: - Reduce aqueous humor production - Are well-tolerated topically - Have no systemic contraindications in this patient - Provide additive IOP reduction with prostaglandins **Tip:** Always check for contraindications (asthma, COPD, heart block, bradycardia) before prescribing beta-blockers. If present, use a carbonic anhydrase inhibitor (dorzolamide/brinzolamide) or alpha-2 agonist instead. ## Why Not the Other Options? | Option | Reason | |--------|--------| | Continue monotherapy | IOP reduction is inadequate (only 8%). Continuing without escalation risks progressive optic nerve damage. | | Switch to different prostaglandin | No evidence that switching prostaglandins improves response if one has already failed. Delays necessary escalation. | | Laser trabeculoplasty | Premature. Medical therapy escalation (adding a second agent) should be attempted first. Laser is indicated after failure of maximum medical therapy. |