A 32-year-old factory worker presents to the emergency department 2 hours after a splash of lime powder (calcium oxide) into both eyes. He reports severe pain, photophobia, and blurred vision. On examination, the cornea appears hazy and the anterior chamber is difficult to visualize. Which investigation is most appropriate to assess the depth and extent of corneal involvement and guide management?

Explanation

## Investigation of Choice in Chemical Eye Injury ### Why AS-OCT is Correct **High-Yield:** AS-OCT (Anterior Segment OCT) is the gold standard non-contact imaging modality for assessing corneal thickness, stromal edema, and depth of chemical burn involvement in the acute phase of chemical injury. **Key Point:** In alkaline chemical injuries (lime, ammonia), rapid penetration into deeper corneal and anterior chamber structures occurs. AS-OCT provides: - Real-time, non-contact assessment (crucial when cornea is fragile and painful) - Quantitative measurement of corneal thickness and stromal changes - Detection of Descemet's membrane involvement - Serial monitoring to assess healing and predict visual prognosis ### Clinical Context: Lime Injury Pathophysiology Lime (CaO) undergoes hydration in the aqueous environment, generating heat and releasing hydroxyl ions. This causes: 1. Immediate coagulation necrosis of epithelium and Bowman's layer 2. Rapid stromal penetration (within minutes to hours) 3. Anterior chamber inflammation and potential angle involvement AS-OCT quantifies stromal edema depth, which correlates with prognosis and guides intensity of anti-inflammatory therapy. ### Why Other Investigations Are Suboptimal | Investigation | Limitation in Acute Chemical Injury | |---|---| | **Schirmer's test** | Measures tear production; not relevant in acute phase; patient too symptomatic | | **Gonioscopy** | Contraindicated in acute injury (risk of further trauma); angle assessment comes later | | **FFA** | Assesses retinal perfusion; not indicated in acute corneal injury; posterior segment usually unaffected initially | **Clinical Pearl:** Slit-lamp examination with fluorescein staining remains the bedside clinical assessment, but AS-OCT provides objective, quantifiable data for prognostication and treatment intensity titration. [cite:Kanski's Clinical Ophthalmology 9e Ch 5]