How do I diagnose corneal infiltrates or keratitis?

Identifying Corneal Infiltrates or Keratitis

A thorough slit-lamp biomicroscopy examination with fluorescein staining is essential for identifying corneal infiltrates or keratitis, focusing on specific corneal features including epithelial defects, stromal infiltrates, and anterior chamber reaction. 1

Key Diagnostic Features to Evaluate

Epithelium Assessment

• Look for epithelial defects using fluorescein staining
• Evaluate for punctate keratopathy, edema, and epithelial movement patterns
• Assess for dendrites or pseudodendrites (suggesting viral etiology)
• Differentiate between true staining of epithelial defects versus pooling in areas of corneal thinning 1

Stromal Evaluation

• Examine infiltrates carefully, noting:
  • Location (central, peripheral, inferior, perineural, surgical, or traumatic wound)
  • Density, size, shape (ring formation), number (satellite lesions)
  • Depth of involvement
  • Character of infiltrate margins (suppuration, necrosis, feathery, soft, crystalline)
  • Color of the infiltrate 2
• Check 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

Anterior Chamber Assessment

• Evaluate for inflammation (cell and flare)
• Note presence of hypopyon, fibrin, or hyphema
• Hypopyon may present as blunting of the inferior angle or at 3:00 or 9:00 if the patient had recently been lying down 2

Differentiating Infectious vs. Non-infectious Causes

Infectious Keratitis Signs

• Significant pain
• Discharge
• Epithelial staining
• Anterior chamber reaction 3
• Central, large infiltrates (≥2 mm)
• Significant stromal involvement or melting 2

Sterile Infiltrates Signs

• Usually smaller
• Multiple or arcuate pattern
• Without significant pain
• Minimal epithelial staining
• Minimal anterior chamber reaction 3

When to Perform Cultures and Smears

Cultures and smears are specifically recommended prior to initiating antimicrobial therapy when:

• Central, large corneal infiltrate (within 3 mm of corneal center and ≥2 mm in size)
• Presence of ≥2 adjacent lesions
• Associated significant stromal involvement or melting
• ≥1+ cells in the anterior chamber
• History of corneal surgery
• Atypical clinical features suggestive of fungal, amoebic, or mycobacterial keratitis
• Multiple corneal infiltrates 2

Special Considerations for Different Etiologies

• Bacterial keratitis: Often presents with rapid onset, suppurative infiltrate with distinct borders
• Fungal keratitis: Typically has feathery borders, satellite lesions, and slower progression
• Acanthamoeba keratitis: Often presents with severe pain, ring infiltrate, and radial keratoneuritis
• Viral keratitis: May present with dendrites (HSV), pseudodendrites, or immunologically mediated infiltrates 2

Advanced Diagnostic Techniques

• Scanning laser confocal microscopy: Useful for imaging various levels of the cornea, particularly helpful in diagnosing fungal and Acanthamoeba keratitis 2
• Optical coherence tomography: Helpful in determining depth of involvement 2
• Corneal biopsy: Consider when response to treatment is poor or repeated cultures have been negative despite clinical suspicion of infection 2

Pitfalls to Avoid

• Clinical features alone may be insufficient to differentiate between bacterial and fungal keratitis, with cornea specialists correctly differentiating between the two in less than 70% of cases based on appearance alone 2
• Contact lens wearers are at higher risk for Pseudomoeba infection, which can rapidly destroy corneal tissue 1
• Avoid confusing pooling of fluorescein stain in areas of corneal thinning with true epithelial staining (pooling can be wicked away with a cotton swab or by irrigating the cornea) 2
• Remember to examine the contralateral eye for clues to etiology and possible similar underlying pathology 2

By following this systematic approach to identifying corneal infiltrates and keratitis, you can make an accurate diagnosis and initiate appropriate treatment promptly to prevent vision-threatening complications.