What is Keratitis?
Keratitis is an infection or inflammation of the cornea (the clear front surface of the eye) that can be caused by infectious agents (bacteria, viruses, fungi, or parasites) or non-infectious factors (trauma, autoimmune disease, contact lens wear). 1
Clinical Presentation
Patients with keratitis typically present with:
- Pain (often severe, especially in Acanthamoeba cases)
- Redness
- Blurred vision
- Photophobia (light sensitivity)
- Discharge
- Corneal infiltrates and ulcerations
- Anterior chamber inflammation 1
Types of Keratitis
Infectious Keratitis
Bacterial Keratitis is the most common form in developed countries, caused primarily by:
- Staphylococcus species (most common)
- Pseudomonas aeruginosa (especially in contact lens wearers)
- Streptococcus pneumoniae 1
Fungal Keratitis presents with distinctive features:
- Dry (rather than suppurative) appearance
- Feathered edges
- Satellite lesions
- Posterior plaque
- Ring infiltrate pattern 1
Viral Keratitis is commonly caused by:
- Herpes simplex virus (HSV)
- Varicella zoster virus (VZV)
- Can produce immunologically mediated corneal infiltrates 1
Parasitic Keratitis (Acanthamoeba) shows characteristic findings:
- Radial keratoneuritis (inflammation along corneal nerves)
- Ring infiltrate
- Severe pain disproportionate to clinical findings
- Associated with contact lens wear and water exposure 1, 2
Non-Infectious Keratitis
Can result from:
- Contact lens wear (sterile infiltrates)
- Autoimmune diseases (rheumatoid arthritis, lupus, vasculitis)
- Corneal trauma (chemical, thermal, foreign bodies)
- Ocular surface disease (severe dry eye, exposure)
- Allergic conditions (vernal or atopic keratoconjunctivitis) 1
Major Risk Factors
Contact lens wear is the number one risk factor in the United States, particularly overnight wear. In other parts of the world, trauma is the leading cause. 1
Additional risk factors include:
- Corneal trauma or foreign bodies
- Previous eye surgery
- Ocular surface disease (dry eye, exposure)
- Immunosuppression
- Diabetes mellitus
- Chronic steroid use
- Eyelid abnormalities 1
Epidemiology
Approximately 71,000 cases of microbial keratitis occur annually in the United States, with increasing incidence. Infectious keratitis is globally the fifth leading cause of blindness. 1, 3
Clinical Significance
Untreated or severe keratitis can progress rapidly—within 24-48 hours for virulent organisms like Pseudomonas or Neisseria gonorrhoeae—leading to corneal perforation, endophthalmitis, and potential loss of the eye. 1, 4 Even with successful treatment, central corneal scarring can cause substantial permanent vision loss.
Diagnostic Approach
The diagnosis is primarily clinical, supplemented by:
- Corneal scraping for culture (indicated for severe cases, contact lens-related cases, or treatment failures)
- Confocal microscopy (particularly useful for Acanthamoeba)
- PCR testing for viral and atypical pathogens
- Anterior segment OCT to assess depth of involvement 1, 3
Treatment Principles
Topical antibiotics are the mainstay of treatment for bacterial keratitis, achieving high corneal tissue levels. Most community-acquired small non-central ulcers resolve with empiric topical therapy. 1
Key treatment considerations:
- Fluoroquinolones or fortified antibiotics for bacterial keratitis
- Natamycin for fungal keratitis
- Antivirals for HSV keratitis
- Polyhexamethylene biguanide or chlorhexidine for Acanthamoeba 3
Corticosteroids may be considered after 48 hours of antibiotic therapy once the organism is identified and infection is responding, but should be avoided in suspected Acanthamoeba, Nocardia, or fungal cases. 1
Prevention
Critical preventive measures include:
- Proper contact lens hygiene and avoiding overnight wear
- Prompt treatment of corneal abrasions in contact lens wearers with prophylactic antibiotics
- Never patch eyes with contact lens-related abrasions (increases infection risk)
- Management of underlying ocular surface disease 1