Microbial Keratitis

Risk factors

• Trauma/abrasion
• CL wear especially extended wear and with poor hygiene
• Iatrogenic: suture removal, LASIK, topical therapy especially steroid
• Ocular surface disease/exposure, blepharokeratoconjunctivitis
• Lid disease: entropion/trichiasis
• Nasolacrimal disease: chronic dacryocystitis
• Immunosuppression
• Nutritional: vitamin A deficiency

Complications

• Limbal/scleral extension
• Perforation
• Endophthalmitis (eg. gonococcus, fungi or perforation)

Management

See Microbiology section for stains/culture media.

• Admit if necessary
• Identify risk factors (as above)
• Perform corneal scrape

Sterilization phase

• Admission and stop CLs

• Intensive topical antibiotics: typically combined therapy with cephalosporin (eg. cefuroxime 5%) and fluoroquinolone (eg. moxifloxacin 0.5% which has superior ocular penetration or ofloxacin 0.3%) or gentamicin forte (1.5%). Hourly day and night instillation for 24-48 hours

  • Quinolone monotherapy is inadequate against resistant species of Staph and Pseudomonas
  • Prolonged use of fortified aminoglycoside is toxic to the epithelium and can lead to necrosis

• Consider oral antibiotics (typically ciprofloxacin) if limbal disease, perforation or risk of endophthalmitis or bacterial scleritis

• Oral tetracyclines (and vitamin C) can promote healing (inhibit MMPs and inflammatory cytokines)

• Cycloplegia and oral analgesia for comfort

Healing phase

• Taper therapy with improvement
• Add lubricant
• Add non-preserved topical steroid to reduce inflammation (typically only after re-epithelisation)
  • Steroids are contraindicated in fungal or mycobacterial cases (risk factors include previous refractive surgery and trauma involving vegetation)
  • Steroids can retard the eyes response to the microbes and retard epithelisation

• Where there are no positive microbiology results and initial treatment is ineffective, consider with-holding treatment and re-scraping (or corneal biopsy, PCR or confocal microscopy)
  • Restart intensive antibiotics
  • Consider alternative diagnoses eg sterile ulcer
  • Therapeutic penetrating keratoplasty
  • Gunderson flap for non-healing ulcers

Sterile ulcers

• Post-infective eg. herpetic, fungal

• Nearby ocular surface inflammation

  • Lids/lashes
  • Skin: SJS, OCP, rosacea
  • Lacrimal gland: sicca

• Neurotrophic

  • Diabetes, herpetic

• Exposure

  • Facial palsy
  • Lagophthalmos
  • Proptosis

• Nutritional: vitamin A deficiency

• Neoplasia: acute leukaemia

• Immune-mediated

  • Connective tissues disease/PUK
  • Mooren’s
  • Marginal keratitis
  • Allergic keratitis

• Iatrogenic/self-inflicted

Fungal keratitis

• Filamentous (septate eg. Fusarium and Aspergillus, and non-septate) vs yeasts
• Risk factors
  • Trauma with organic matter
  • Ocular surface disease
  • Systemic/local immunosuppression or steroids

Features

• Fluffy/feathery white ulcer
• Satellite lesions
• Ring infiltrate
• Endothelial plaque

Management

• Antifungals interfere with ergosterol metabolism
• Amphoteracin B 0.015% is a polyene (yeasts)
• Natamycin 5% (filamentous)
• Azoles can be used systemically but are toxic
• Topical voriconazole 0.1%

Persistent epithelial defect

• Remember that drug toxicity may cause symptoms even after the infection is eradicated
• Defined as a defect for >2 weeks
• Use non-preserved preparations
• Reduce frequency of therapy
• Add lubricant
• Ocular surface protection: tarsorrhaphy

Perforation

• Causes

  • Infectious:

    • Diphtheria and gonococcus can cause extremely rapid onset perforation due to their virulence
    • Shigella, Listeria, and Haemophilus aegyptus also classical penetrate intact corneal epithelium

  • Surface related

  • Autoimmune: eg collagen vascular diseases like RA, SLE, GPA, sarcoid and IBD

  • Other: Moorens

Management

• Therapeutic contact lenses: if no tissue loss or very small. Use with PF antibiotics
• Corneal glue: if less than 2mm. Used with polythene patches and hydrogel contact lenses to reduce discomfort.
• Amniotic membrane: for larger perforations. Provides biologically active anti-inflammatory and anti-scarring mediators
• Lamellar or full-thickness keratoplasty reconstructions for larger perforations