What is a Corneal Ulcer?
A corneal ulcer is an infection of the cornea caused by bacteria or other microorganisms, characterized by a defect in both the corneal epithelium and the underlying stroma. 1, 2
Clinical Definition and Pathophysiology
A corneal ulcer represents a break in the corneal surface that extends beyond the epithelium into the stromal layer. While the term "corneal ulcer" is often used interchangeably with bacterial keratitis in clinical practice, it specifically refers to the tissue defect itself. Most cases of bacterial keratitis develop at sites where there is an abnormality or defect in the corneal surface, though highly virulent organisms like Neisseria gonorrhoeae and Pseudomonas aeruginosa can invade even intact corneal epithelium. 1
The cornea normally resists infection due to its natural defense mechanisms, but predisposing factors can compromise these barriers and allow bacterial invasion. 1
Clinical Presentation
Patients with corneal ulcers typically present with:
- Pain (often severe)
- Redness of the eye
- Blurred vision
- Photophobia (light sensitivity)
- Discharge from the eye
- Visible corneal infiltrates and ulceration on examination
- Anterior chamber inflammation (may include hypopyon - pus in the anterior chamber) 1, 2
Natural History and Prognosis
Untreated or severe bacterial keratitis can result in corneal perforation and has the potential to develop into endophthalmitis, resulting in loss of the eye. 1 The process of corneal tissue destruction can occur rapidly—within 24 hours when caused by virulent organisms like Pseudomonas, Streptococcus pneumoniae, or N. gonorrhoeae. 1
Key Prognostic Factors:
- Location matters critically: Central or paracentral corneal ulcers are of paramount importance because scarring in these locations causes substantial visual loss, even if the infection is successfully eradicated 1
- Organism virulence: Highly virulent organisms cause rapid tissue destruction, while organisms like nontuberculous mycobacteria and Streptococcus viridans follow a more indolent course 1
- Host factors: Patients with systemic and/or multiple risk factors have higher risk of polymicrobial keratitis with greater number and longer duration of infiltrates 1
Major Risk Factors
Contact lens wear is the number-one risk factor for microbial keratitis in the United States, with overnight wear (including orthokeratology) being a major risk factor. 1 In many other parts of the world, trauma is the leading risk factor. 1
Other significant risk factors include:
- Corneal trauma and foreign bodies
- Previous ocular surgery (cataract, refractive, glaucoma surgery, keratoplasty)
- Tear-film deficiencies and dry eye
- Eyelid abnormalities and exposure
- Immunosuppression (topical or systemic)
- Diabetes mellitus
- Contaminated ocular medications 1
Clinical Significance
Loss of vision from bacterial keratitis frequently occurs due to corneal scarring or contour irregularity. 1 Approximately 71,000 cases of microbial keratitis occur annually in the United States, with an increasing incidence. 1 Because corneal tissue loss can occur rapidly, optimal management requires prompt recognition, timely institution of therapy, and appropriate follow-up to prevent permanent visual loss. 1
The condition represents an ophthalmologic emergency requiring urgent evaluation and treatment to prevent vision-threatening complications. 2