Signs of Bacterial Keratitis
Bacterial keratitis presents with suppurative stromal infiltrates (particularly those >1 mm in size) with indistinct edges, surrounding stromal edema and white cell infiltration, typically accompanied by an epithelial defect and anterior chamber reaction. 1
Clinical Presentation
Symptoms
The cardinal symptoms that patients report include: 1
- Pain (often severe and out of proportion to findings in Acanthamoeba cases)
- Redness (conjunctival injection and chemosis)
- Discharge (purulent or mucopurulent)
- Blurred vision (may be severely compromised)
- Photophobia
Slit-Lamp Examination Findings
Corneal Signs: 1
- Suppurative stromal infiltrates - the hallmark finding, especially when >1 mm
- Indistinct, feathered edges of the infiltrate
- Epithelial defect - typically present at the site of infection
- Surrounding stromal edema and white cell infiltration
- Corneal ulceration with tissue loss in progressive cases
Associated Ocular Signs: 1
- Anterior chamber reaction - cells and flare, often prominent
- Hypopyon - layered white cells in severe cases
- Conjunctival injection and chemosis
- Eyelid edema in severe presentations
Disease Progression Patterns
The clinical appearance varies significantly based on the causative organism: 1
Highly Virulent Organisms (Pseudomonas aeruginosa, Streptococcus pneumoniae, Neisseria gonorrhoeae):
- Rapid tissue destruction - can occur within 24 hours
- Extensive suppuration with marked infiltration
- Risk of corneal perforation if untreated
Less Virulent Organisms (nontuberculous mycobacteria, Streptococcus viridans):
- Indolent course with slower progression
- Less dramatic inflammatory response
Polymicrobial Keratitis: 1
- Greater number of infiltrates
- Longer duration of infiltrates
- More common in patients with systemic and/or multiple risk factors
Location and Severity Indicators
Central or paracentral involvement is of paramount importance as scarring in this location causes substantial visual loss even with successful eradication of the organism. 1
Critical Examination Elements
When evaluating suspected bacterial keratitis, document: 1
External Examination:
- General appearance including skin conditions and hygiene
- Facial examination for rosacea or herpes zoster
- Eyelid anatomy, function, and closure adequacy
- Nasolacrimal apparatus assessment
Visual Acuity:
- Baseline measurement (though often compromised by discomfort, tearing, and inflammation) 1
Corneal Sensation:
- Testing should be considered if appropriate (neurotrophic keratopathy is a risk factor) 1
Common Pitfalls
Do not assume all corneal infiltrates are bacterial - the differential includes fungal keratitis (dry appearance, feathered edges, satellite lesions), Acanthamoeba (radial keratoneuritis, ring infiltrate, pain exceeding findings), viral keratitis (HSV, VZV), and noninfectious causes (sterile infiltrates from contact lens wear, autoimmune disease). 1
Recognize that some bacteria can invade intact epithelium (Neisseria gonorrhoeae, Pseudomonas aeruginosa), though most cases develop at sites of epithelial abnormality or defect. 1
Central/paracentral location demands urgent attention regardless of size, as scarring here causes permanent visual impairment even with successful treatment. 1