Bacterial

• Common causes:

  • Staphylococcus
  • Streptococcus
  • Pseudomonas
• Other causes:

  • Neisseria gonorrhoeae
  • Neisseria meningitides
  • Corynebacterium diphtheria
• Risk factors for bacterial keratitis are those which disrupt the healthy corneal epithelium. These include:

  • Contact lens wear: most common risk factor, especially in prolonged use and poor lens hygiene
  • Corneal trauma: including previous ocular surgery, foreign body, chemical injury
  • Ocular surface disease: dry eye, lid malposition, chronic blepharitis
  • Immunosuppression: drugs, immunodeficiency syndromes, diabetes
• Bacterial keratitis commonly causes unilateral symptoms. Typical symptoms may include:

  • Ocular pain: this may be moderate or severe and include symptoms of irritation and foreign body sensation
  • Red eye
  • Reduced visual acuity: this may be near normal to markedly reduced
  • Photophobia: intolerance to sunlight or normal room lighting
  • Purulent discharge
• A history of contact lens wear is essential:

  • Type of contact lenses used: daily disposable, monthly or extended-wear
  • Duration of wear per day
  • If they have ever slept, showered, or swam with their lenses in
• Typical clinical findings may include:

  • Lids and lashes: eyelid oedema in moderate to severe cases
  • Conjunctiva: pattern of injection may be circumlimbal (around the cornea) or diffuse
  • Cornea: a yellow-white opacity which represents the area of inflammation (infiltrate) with clearly defined margins.
  • Anterior chamber and pupil: hypopyon (pus-level) and posterior synechiae (adhesion between the pupil margin and anterior lens surface) in severe cases
  • Pupil assessment for direct and consensual response to light: may show a relative afferent pupillary defect
• Bacterial keratitis is a clinical diagnosis.

  Relevant investigations may include:

  • Corneal scrapes and conjunctival swabs: these are performed in severe or treatment-resistant cases to allow identification of the causative organism and determine antibiotic sensitivities
  • Contact lenses, cases and solutions should also be sent for culture and sensitivity
• Management:

  • Discontinue contact lenses immediately
  • Topical antibiotics - initially broad spectrum e.g. fluoroquinolone
  • Oral antibiotics in severe cases
  • Surgery e.g. corneal transplantation is rarely required
• Complications of bacterial keratitis include:

  • Spread of infection: the infection may spread beyond the cornea into the sclera or within the deeper tissues of the eye, leading to endophthalmitis.
  • Corneal perforation in severe cases
  • Residual dense corneal scarring
  • Irregular astigmatism
  • Formation of cataract: secondary lens opacification is common following severe inflammation
• The corneal epithelium forms the primary barrier to microbes