A 52-year-old farmer from rural Maharashtra presents with a 10-day history of painful red eye with photophobia and blurred vision. Slit-lamp examination reveals a central corneal ulcer with raised, infiltrated borders and a hypopyon. The ulcer has a feathery margin and satellite lesions. Which investigation is most appropriate to confirm the diagnosis and guide therapy?

Explanation

## Investigation of Choice for Corneal Ulcer **Key Point:** Corneal scraping with Gram stain, culture, and sensitivity is the gold standard for diagnosing bacterial and fungal corneal ulcers and determining antimicrobial susceptibility. ### Clinical Presentation Analysis The patient's presentation is highly suggestive of a **fungal corneal ulcer**: - Rural/agricultural occupation (high fungal exposure) - Feathery margins with satellite lesions (classic fungal pattern) - Raised, infiltrated borders - Hypopyon formation - Prolonged course (10 days) ### Why Corneal Scraping Is Essential | Feature | Corneal Scraping | AS-OCT | Confocal | Tear Osmolarity | |---------|------------------|--------|----------|------------------| | **Identifies organism** | ✓ Yes | ✗ No | Partial | ✗ No | | **Culture & sensitivity** | ✓ Yes | ✗ No | ✗ No | ✗ No | | **Guides therapy** | ✓ Yes | ✗ No | ✗ No | ✗ No | | **Diagnostic yield** | 70–80% | N/A | Limited | N/A | | **Bedside feasibility** | ✓ Yes | ✗ No | ✗ No | ✓ Yes | **High-Yield:** Gram stain differentiates: - **Gram-positive cocci:** *Staphylococcus aureus*, *Streptococcus pneumoniae* - **Gram-negative rods:** *Pseudomonas aeruginosa*, *Moraxella* - **Fungal hyphae:** KOH mount or Gram stain may show branching filaments ### Specimen Collection Protocol 1. Topical anesthesia (proparacaine 0.5%) 2. Sterile spatula or Kimura platinum spatula 3. Scrape the ulcer base and margins (not the surrounding cornea) 4. Inoculate directly onto: - Blood agar - Chocolate agar - Sabouraud dextrose agar (fungal) - Thioglycollate broth (enrichment) 5. Prepare smears for Gram stain and KOH mount **Clinical Pearl:** In suspected fungal ulcers, always inoculate Sabouraud dextrose agar and request KOH mount; fungal cultures may take 2–4 weeks, so early suspicion guides empiric therapy. ### Empiric Therapy Pending Culture **Bacterial ulcer:** Fluoroquinolone (moxifloxacin 0.5%) ± cephalosporin (cefazolin 5%) **Fungal ulcer:** Natamycin 5% (polyene) ± voriconazole 1% (azole) [cite:Kanski Clinical Ophthalmology 9e Ch 6]