A 68-year-old man presents with progressive blurring of vision over 2 years. Slit-lamp examination reveals a nuclear sclerotic cataract with a brown nucleus. He is keen for early surgical intervention due to occupational demands. Which medication should be prescribed preoperatively to facilitate intraoperative mydriasis and prevent posterior synechiae formation?

## Preoperative Mydriasis in Cataract Surgery **Key Point:** Mydriatic agents are essential in cataract surgery to maximize pupillary dilation, improve visualization of the lens, and reduce intraoperative complications. ### Mechanism of Tropicamide + Phenylephrine Tropicamide (anticholinergic) causes cycloplegia and mydriasis by blocking muscarinic receptors, while phenylephrine (α-adrenergic agonist) provides additional mydriatic effect via sympathomimetic action. This combination achieves maximum pupillary dilation (8–9 mm) within 30–40 minutes. ### Preoperative Mydriatic Regimen | Agent | Mechanism | Onset | Duration | Use in Cataract Surgery | |-------|-----------|-------|----------|------------------------| | Tropicamide 1% | Anticholinergic | 20–40 min | 4–6 hrs | Yes — cycloplegia + mydriasis | | Phenylephrine 10% | α-adrenergic | 30–50 min | 3–5 hrs | Yes — synergistic mydriasis | | Pilocarpine 2% | Cholinergic (miotic) | 10–30 min | 4–8 hrs | No — causes miosis (contraindicated) | | Timolol 0.5% | β-blocker | Variable | 12–24 hrs | No — no mydriatic effect | | Dorzolamide 2% | Carbonic anhydrase inhibitor | 30 min | 8–12 hrs | No — used for glaucoma, not mydriasis | **High-Yield:** The standard preoperative mydriatic regimen in India is tropicamide 1% + phenylephrine 10%, instilled 3–4 times at 5-minute intervals starting 30 minutes before surgery. **Clinical Pearl:** Phenylephrine 10% should be used cautiously in patients with systemic hypertension or cardiovascular disease due to risk of hypertensive crisis; a weaker formulation (2.5%) may be safer in such cases. **Warning:** Pilocarpine causes miosis (pupil constriction), which is the opposite of what is needed and increases risk of posterior capsular rupture and zonular damage during phacoemulsification. ### Why Tropicamide + Phenylephrine is Preferred 1. **Rapid onset** — mydriasis achieved within 30–40 minutes 2. **Sustained duration** — adequate for surgery (3–5 hours) 3. **Synergistic effect** — combination provides superior dilation compared to either agent alone 4. **Reduced posterior synechiae risk** — cycloplegia prevents iris-lens contact during inflammation 5. **Standard practice** — guideline-recommended in cataract surgery protocols [cite:Parson's Diseases of the Eye 22e Ch 9]