Bacterial Keratitis

Bacterial Keratitis: Corneal Culprits - Eye's Enemy No.1

• Definition: Suppurative corneal inflammation; a critical sight-threatening emergency.
• Most Common Culprits:
  • Pseudomonas aeruginosa: Highly aggressive, esp. in contact lens (CL) wearers.
  • Staphylococcus aureus: Common Gram-positive.
  • Streptococcus pneumoniae: Often post-trauma.
  • Moraxella spp.: Typically in immunocompromised.
  • Enterobacteriaceae
• Distinguishing Features:
  • Pseudomonas: Rapid onset, dense infiltrate, greenish discharge, ring infiltrate.
  • Pneumococcus: Serpiginous ulcer, hypopyon common.

⭐ Pseudomonas aeruginosa is notorious for its rapid progression, ability to penetrate an intact Descemet's membrane, and severe outcomes, especially in soft contact lens wearers.

Risk Factors & Invasion: Opening the Gates - Cornea's Weak Spots

• Risk Factors: 📌 Mnemonic: CL SODAS
  • Contact Lens wear: Esp. extended/overnight, poor hygiene.

    ⭐ Overnight soft contact lens wear ↑ risk of microbial keratitis by 10-15 times vs. daily wear.

  • Ocular Surface Disease: Dry eye, bullous keratopathy, exposure keratitis.
  • Ocular Trauma: Abrasion, foreign body, surgical.
  • Systemic/Local Factors:
    • Dacryocystitis (chronic), Vitamin A Deficiency.
    • Immunosuppression (Autoimmune, Steroids).
• Pathogenesis Snippet: Epithelial breach → Adherence/colonization → Stromal invasion/multiplication → Inflammation (PMNs, cytokines) → Tissue destruction (collagenases).

Clinical Features: Red Alert Symptoms - Painful Blurry Mess

• Symptoms: 📌 Painful Blurry Mess
  • Severe eye pain (often out of proportion)
  • Photophobia, foreign body sensation
  • Blurred/↓ vision
  • Redness (ciliary/circumcorneal congestion)
  • Mucopurulent discharge
• Signs:
  • Corneal infiltrate: Dense, yellowish-white stromal opacity
  • Epithelial defect overlying infiltrate (stains with fluorescein)
  • Stromal edema, folds in Descemet's membrane
  • Anterior chamber reaction: Cells, flare, hypopyon
  • Conjunctival injection (often intense), lid edema
  • Specific signs:
    • Ring infiltrate (e.g., Pseudomonas)
    • Endothelial plaque
    • Satellite lesions (fungi, but can be severe bacteria)

⭐ A hypopyon in bacterial keratitis is typically sterile, consisting of inflammatory cells, not bacteria, unless there is a corneal perforation.

Diagnosis: Unmasking the Microbe - Lab Detective Work

Primarily clinical. Lab tests confirm pathogen & guide therapy.

• Corneal Scraping: Key diagnostic step.
  • Indications: Central ulcers, >2 mm size, stromal melt, atypical presentation, unresponsive to initial therapy, post-keratoplasty.

  ⭐ Corneal scraping for microbiological evaluation should ideally be performed before initiating antibiotic therapy to maximize diagnostic yield.

  • Microscopy:
    • Gram stain: Bacteria, morphology.
    • Giemsa stain: Cell types, Acanthamoeba cysts, fungi.
    • KOH wet mount: Fungi.
  • Culture & Sensitivity:
    • Blood Agar (most bacteria)
    • Chocolate Agar (Haemophilus, Neisseria)
    • Sabouraud Dextrose Agar (SDA) (fungi)
    • Thioglycolate broth (anaerobes)

Treatment Strategy: Eradicating the Invaders - Antibiotic Armada

Ophthalmic emergency! Prompt, intensive topical bactericidal antibiotics crucial.

• Dosing: Loading dose (q5-15min for 30-60min), then hourly, tapered.
• Cycloplegics: Atropine 1% / Homatropine 2%: pain relief, prevent synechiae.
• Topical Steroids: Controversial. Consider after 24-48h effective antibiotics & improvement. Avoid if fungal/poor response.
• Systemic Antibiotics: Scleral extension, perforation, endophthalmitis risk, specific organisms (N. gonorrhoeae, severe Pseudomonas).
• Surgical: Therapeutic Penetrating Keratoplasty (TPK) if non-healing, perforation, severe scarring.

⭐ For severe bacterial keratitis, fortified topical antibiotics are preferred over commercial preparations due to higher concentrations, achieving better corneal penetration and bactericidal effect.

High-Yield Points - ⚡ Biggest Takeaways

• Most common organisms: Pseudomonas aeruginosa (esp. contact lens wearers), Staphylococcus aureus.
• Symptoms: Severe ocular pain, photophobia, mucopurulent discharge, ↓vision.
• Signs: Corneal infiltrate (stromal abscess), epithelial defect, hypopyon.
• Primary risk factor: Improper contact lens use; corneal trauma.
• Diagnosis: Clinical; supported by corneal scraping (Gram stain, culture).
• Management: Intensive topical fortified antibiotics (e.g., vancomycin/cefazolin + tobramycin/gentamicin) or fluoroquinolones.
• Pseudomonas infection: Rapidly progressive, can lead to perforation.