A 68-year-old man with dense nuclear sclerotic cataract presents for phacoemulsification. During surgery, the anterior chamber becomes shallow and the pupil constricts intraoperatively. Which is the drug of choice to maintain mydriasis and deepen the anterior chamber during the procedure?

Explanation

## Intraoperative Mydriasis Maintenance in Cataract Surgery ### Role of Epinephrine in Irrigating Solution **Key Point:** Epinephrine (adrenaline) added to the irrigating solution at a concentration of 1:1,000,000 is the gold standard for maintaining mydriasis and anterior chamber depth during phacoemulsification. **Mechanism:** 1. Epinephrine acts on α-adrenergic receptors on the iris sphincter and dilator muscles 2. Produces sustained mydriasis throughout the surgical procedure 3. Maintains anterior chamber stability by preventing pupillary constriction 4. Improves visibility and reduces risk of posterior capsule rupture ### Comparison of Mydriatic Agents | Agent | Route | Onset | Duration | Intraop Use | Advantage | |-------|-------|-------|----------|-------------|----------| | **Epinephrine 1:1M** | Irrigating solution | Rapid | Sustained | **YES** | Maintains mydriasis throughout surgery | | Atropine 0.5% | Topical | 30–40 min | 7–14 days | No | Too prolonged; not suitable for intraop | | Tropicamide 1% | Topical | 20–40 min | 4–6 hours | No | Shorter duration; preoperative use only | | Phenylephrine 10% | Topical | 45–60 min | 3–5 hours | No | Preoperative only; does not sustain intraop mydriasis | **High-Yield:** Epinephrine in the irrigating solution is preferred because it is delivered directly to the anterior chamber, providing continuous mydriasis without systemic absorption concerns (unlike topical application). **Clinical Pearl:** The concentration 1:1,000,000 is critical—higher concentrations risk corneal toxicity and systemic effects; lower concentrations are ineffective. **Warning:** Epinephrine should NOT be used in patients with uncontrolled hypertension or significant cardiac arrhythmias, as systemic absorption can occur. However, at the standard irrigating concentration, systemic effects are minimal. ### Preoperative vs. Intraoperative Mydriasis - **Preoperative:** Tropicamide 1% or Phenylephrine 10% (topical) are used to dilate the pupil before surgery - **Intraoperative:** Epinephrine in irrigating solution maintains mydriasis during the procedure