What are the causes of keratitis (inflammation of the cornea)?

From the Guidelines

Keratitis is primarily caused by infections, including bacterial, viral, fungal, and parasitic agents, with bacterial keratitis often resulting from Staphylococcus aureus, Pseudomonas aeruginosa, or Streptococcus pneumoniae infections, particularly following corneal injury or improper contact lens use, as reported in the most recent study 1.

Causes of Keratitis

The causes of keratitis can be categorized into:

• Infectious causes:
  • Bacterial keratitis: often caused by Staphylococcus aureus, Pseudomonas aeruginosa, or Streptococcus pneumoniae, particularly following corneal injury or improper contact lens use 1
  • Viral keratitis: commonly caused by herpes simplex virus (HSV-1) or varicella-zoster virus, which can remain dormant in nerve tissues and reactivate
  • Fungal keratitis: typically involves Fusarium, Aspergillus, or Candida species, especially after plant material injuries or in immunocompromised individuals
  • Acanthamoeba keratitis: occurs mainly in contact lens wearers who use contaminated solutions or swim while wearing lenses
• Non-infectious causes:
  • Dry eye syndrome
  • Exposure keratitis from incomplete eyelid closure
  • Allergic reactions
  • Trauma from foreign bodies, chemical burns, or radiation exposure

Risk Factors

Certain risk factors increase the likelihood of developing keratitis, including:

• Contact lens wear, particularly overnight wear or improper lens care 1
• Trauma to the cornea
• Corneal surgery
• Ocular surface disease
• Systemic diseases, such as autoimmune disorders or immunosuppression
• Vitamin A deficiency
• Neurotrophic conditions that reduce corneal sensation

Importance of Prompt Diagnosis and Treatment

Prompt diagnosis and treatment are essential to prevent vision-threatening complications like corneal scarring or perforation, as highlighted in the study 1. Topical antibiotics should be prescribed to prevent acute infection in patients with a corneal abrasion who wear contact lenses or suffered trauma, and corticosteroids may be considered after 48 hours of antibiotic therapy when the causative organism is identified and/or the infection has responded to therapy 1.

From the FDA Drug Label

INDICATIONS AND USAGE: NATACYN ® (natamycin ophthalmic suspension) 5% is indicated for the treatment of fungal blepharitis, conjunctivitis, and keratitis caused by susceptible organisms including Fusarium solanikeratitis. The causes of keratitis mentioned in the drug label are:

• Fungal infections, specifically those caused by susceptible organisms including Fusarium solani 2 The FDA label does not provide a comprehensive list of all possible causes of keratitis, only those related to fungal infections that the drug is indicated to treat.

From the Research

Causes of Keratitis

The causes of keratitis can be categorized into infectious and non-infectious agents.

• Infectious agents include:
  • Bacteria 3, 4, 5
  • Viruses, such as herpes simplex virus (HSV), varicella-zoster virus, and adenoviruses 3, 6, 7
  • Fungi 3, 4
  • Parasites 3, 4
• Non-infectious agents include:
  • Physical or chemical trauma 3
  • Previous corneal surgery, such as refractive corneal surgery or penetrating keratoplasty 3
  • Extended wear contact lens use 3, 4, 5
  • Pre-existing ocular surface diseases, such as dry eye or epithelial defect 3
  • Ocular trauma, including agriculture- or farm-related trauma 3

Risk Factors

Certain risk factors can increase the likelihood of developing keratitis, including:

• Systemic immunosuppression, due to conditions such as malnutrition, alcoholism, diabetes, or steroid use 3
• Previous corneal surgery 3
• Extended wear contact lens use 3, 4, 5
• Pre-existing ocular surface diseases 3
• Ocular trauma 3