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 of 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 in bacterial keratitis
- Neural 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 adapted 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
