Microbial inflammation of the cornea is not uncommon and can be sight-threatening. Culture is the key to diagnosis and management.
Bacterial Keratitis
Bacterial keratitis is typically seen in contact lens wearers and in post-op patients.
Pathogens
- Pseudomonas aeruginosa - commonest cause of bacterial keratitis in contact lens wearers.
- Other causes include: Staphylococcus aureus and Streptococci.
Pathology
Presentation
- Keratitis typically presents with an acutely painful unilateral red eye with discharge.
- Pseudomonas infection is seen in prolonged contact lens wear.
Investigations
- Corneal scraping for microbiology.
Management
- Topical broad-spectrum antibiotics (e.g., fluoroquinolones such as ofloxacin).
- Subsequent specific antibiotics are guided by sensitivity testing.
Fungal Keratitis
Presenting symptoms are milder than bacterial infections. Look for immunocompromise or trauma associated with plants/soil in the history.
Candida
- Patients with AIDS/immunocompromise/diabetes.
- Plaque corneal ulcer with expanding infiltrate.
Aspergillus/Fusarium
- History of trauma associated with contact with plants or soil.
- White, feathery corneal lesions.
Management
- Corneal scraping for microbiology.
- Candida → Voriconazole or amphotericin B drops.
- Filamentous (aspergillus/fusarium) → Natamycin drops.
- Severe infection → add Chlorhexidine.
Confocal microscopy can provide a faster diagnosis than culture.
Acanthamoeba keratitis
A protozoan disease that can be clinically severe and is notoriously difficult to treat.
Pathology
- Caused by the protozoan: Acanthamoeba.
- Lives in soil, fresh water and the upper respiratory tract.
Presentation
- Initial presentation is similar to bacterial keratitis.
- Radial ring-shaped corneal infiltrates are specific and develop over time.
Investigations
- Culture medium is non-nutrient agar with E. coli.
- Confocal microscopy shows amoebic cysts.
Infection is associated with exposure to freshwater or soil, especially in contact lens wearers.
Management
- Topical polyhexamethylene biguanide (PHMB) or chlorhexidine.
Acanthamoeba keratitis is widely considered to be an orphan disease. Drug companies haven't developed specific treatments because of the rarity of the disease.
Marginal Keratitis
An autoimmune reaction against Staphylococcal toxin, which characteristically affects the peripheral cornea.
Pathology
- A type 3 autoimmune inflammation of the peripheral cornea.
- Triggered by hypersensitivity to Staphylococcal toxin (most commonly Staph epidermidis).
- Inflammation occurs at the superior and inferior limbus where the lid contacts the cornea.
- More common in patients with staph-associated infections such as blepharitis and acne rosacea.
Management
- Steroid drops.
- Lid hygiene for blepharitis.
