A 62-year-old woman from Bangalore with a history of hyperopia and shallow anterior chamber presents with her right eye having been treated for acute angle-closure glaucoma 6 months ago with Nd:YAG laser peripheral iridotomy. She now reports gradual dimming of vision in the left eye over 3 weeks with occasional mild discomfort. Examination of the left eye reveals: visual acuity 6/12, IOP 24 mmHg, anterior chamber depth 2.0 mm, and gonioscopy shows a narrow angle (Shaffer grade 1) with the angle not yet occluded. What is the most appropriate management for the left eye?

Explanation

## Clinical Diagnosis **Key Point:** This is a narrow-angle eye at high risk for angle-closure. The contralateral eye has already suffered an acute attack. Prophylactic laser peripheral iridotomy is indicated to prevent acute angle-closure glaucoma in the fellow eye. ### Risk Stratification: Narrow vs. Closed Angle | Feature | Narrow Angle (Shaffer 1–2) | Closed Angle (Shaffer 0) | |---------|---------------------------|-------------------------| | Gonioscopic view | Angle recess not visible | Angle recess completely obscured | | Trabecular meshwork | Not visible | Not visible | | Risk of closure | High (especially with mydriasis) | Imminent or present | | Management | Prophylactic LPI | Urgent LPI | **High-Yield:** Shaffer grade 1 angle = narrow angle. The trabecular meshwork is not visible. This patient is at **imminent risk** of angle-closure, especially given: 1. Bilateral narrow angles (anatomical predisposition) 2. Contralateral eye already had acute PACG 3. Shallow anterior chamber (2.0 mm is very shallow) 4. Age >60 (lens thickening increases pupillary block) ### Prophylactic LPI Indications **Mnemonic — NARROW ANGLE PROPHYLAXIS: RISK** - **R**isk factors present (hyperopia, shallow AC, narrow angle) - **I**mminent closure (Shaffer 0–1, especially with fellow eye history) - **S**ymptomatic prodrome (blurred vision, halos — early warning) - **K**eep both eyes safe (bilateral disease common) ### Why Prophylactic LPI Now? ```mermaid flowchart TD A["Narrow angle + Fellow eye PACG history"]:::outcome --> B{"Perform prophylactic LPI?"}:::decision B -->|"Yes (Recommended)"|C["Nd:YAG LPI immediately"]:::action B -->|"No (Observe)"|D["Risk of acute closure"]:::urgent C --> E["Angle opens<br/>IOP controlled"]:::outcome D --> F{"Angle closes?"}:::decision F -->|"Yes"|G["Acute PACG<br/>Emergency treatment"]:::urgent F -->|"No"|H["Fortunate, but delayed"]:::outcome ``` **Clinical Pearl:** The presence of acute PACG in the fellow eye is a **strong indication** for prophylactic LPI in the other eye. Studies show 50–80% of untreated narrow-angle eyes will develop acute closure within 5–10 years. With a known acute attack in the contralateral eye, the risk is even higher. ### Mechanism of Prophylactic LPI 1. **Laser creates patent iridotomy** → peripheral iris perforated 2. **Eliminates pupillary block** → aqueous flows directly from posterior to anterior chamber 3. **Iris-lens diaphragm moves posteriorly** → angle widens 4. **Trabecular meshwork exposed** → aqueous drainage restored **Key Point:** LPI is **not** a treatment for existing elevated IOP — it is a **preventive** procedure to keep the angle open and prevent acute closure. ### Why Not Observation? While the angle is not yet completely closed (Shaffer 1 vs. 0), observation carries significant risk: - Acute closure can occur suddenly (hours to days) - Once acute PACG occurs, vision may be permanently damaged - The fellow eye already suffered this complication - IOP 24 mmHg is borderline elevated for a narrow-angle eye **Warning:** "Observe and treat only if IOP rises or angle closes" is **not** the standard of care for a narrow-angle eye with a history of acute PACG in the fellow eye. This is a missed opportunity for prevention. ### Why Not Topical PGA Alone? Prostaglandin analogues reduce IOP but do **not** address the underlying anatomical problem (pupillary block and narrow angle). They may temporarily lower IOP but cannot prevent acute closure. ### Why Not Anterior Chamber Deepening Surgery? Anterior chamber reformation is **not** indicated for primary angle-closure. LPI is the gold standard. Surgery is reserved for: - LPI failure or complications - Plateau iris (angle remains narrow despite patent LPI) - Secondary angle-closure (e.g., phacomorphic glaucoma) [cite:Khurana Comprehensive Ophthalmology Ch 11; Riordan-Eva & Whitcher Ophthalmology 5e Ch 10]