How would you rule out keratitis or corneal involvement?

Ruling Out Keratitis or Corneal Involvement

To rule out keratitis or corneal involvement, a thorough slit-lamp biomicroscopy examination with fluorescein staining is essential, focusing on specific corneal features including epithelial defects, stromal infiltrates, and anterior chamber reaction. 1

Comprehensive Slit-Lamp Biomicroscopy Examination

Corneal Assessment

• Epithelium evaluation:

  • Look for epithelial defects, punctate keratopathy, edema, and epithelial movement patterns
  • Assess for dendrites, pseudodendrites which may indicate viral etiology
  • Evaluate for epithelial basement membrane dystrophy 1

• Stromal evaluation:

  • Check for infiltrates (location, density, size, shape, number, depth)
  • Note character of infiltrate margins (suppuration, necrosis, feathery, soft, crystalline)
  • Assess for ulceration, thinning, perforation, and edema
  • Look for signs of previous inflammation (scarring, neovascularization) 1

• Endothelium evaluation:

  • Check for endothelial plaques
  • Look for Descemet membrane folds, tears, or detachment 1

Vital Staining

• Fluorescein staining: Essential to identify epithelial defects characteristic of infectious keratitis

  • Differentiate between true staining of epithelial defects versus pooling in areas of corneal thinning
  • Pooling can be wicked away with a cotton swab or by irrigating the cornea 1

• Rose bengal/lissamine green staining: May provide additional information about devitalized epithelium 1

Anterior Chamber Evaluation

• Check for presence of inflammation (cell and flare)
• Look for hypopyon, which may present as blunting of the inferior angle or at 3:00 or 9:00 if the patient was recently lying down
• Assess for fibrin or hyphema 1

Additional Diagnostic Steps

Culture and Smear Considerations

Cultures and smears are indicated if:

• Corneal infiltrate is central, large (≥2 mm), and/or associated with significant stromal involvement or melting
• There are ≥1+ cells in the anterior chamber
• History of corneal surgery is present
• Atypical clinical features suggest fungal, amoebic, or mycobacterial keratitis
• Multiple corneal infiltrates are present 1

Risk Assessment

Pay special attention to high-risk features that may indicate severe keratitis:

• Presence of hypopyon (increases odds of perforation by 2.28 times) 2
• Infiltrate involving posterior one-third of cornea (71.4% risk of perforation) 2
• Larger infiltrate size (each 1-mm increase raises odds of perforation by 1.37) 2

Common Pitfalls to Avoid

1. Failure to differentiate staining patterns: Ensure you distinguish between true epithelial defects (staining with fluorescein) versus pooling in areas of thinning with intact epithelium 1

2. Overlooking contact lens history: Contact lens wearers are at higher risk for Pseudomonas infection, which can rapidly destroy corneal tissue 3

3. Missing fungal keratitis: Clinical features alone may be insufficient; studies show cornea specialists correctly differentiated bacterial and fungal keratitis in less than 70% of cases based on appearance alone 1

4. Premature steroid use: Corticosteroids should not be used without proper diagnosis as they can worsen fungal infections. As noted in prednisolone labeling: "fungal infections of the cornea are particularly prone to develop coincidentally with long-term local corticosteroid applications" 4

5. Inadequate examination technique: Always examine with magnification. FDA labeling for antibiotics like gatifloxacin and moxifloxacin specifically states: "Whenever clinical judgment dictates, examine the patient with the aid of magnification, such as slit lamp biomicroscopy and where appropriate, fluorescein staining" 5, 6

By following this systematic approach to corneal examination with particular attention to epithelial integrity, stromal features, and anterior chamber reaction, you can effectively rule out keratitis or corneal involvement.