Nummular Keratitis Etiology
Nummular keratitis with uniform, coin-shaped lesions distributed across the cornea without visual axis involvement is most likely due to post-adenoviral infection (epidemic keratoconjunctivitis), not HSV.
Key Distinguishing Features
Post-Adenoviral (EKC) Nummular Keratitis
The clinical presentation you describe is classic for subepithelial corneal infiltrates following adenoviral epidemic keratoconjunctivitis (EKC) 1:
- Multifocal, coin-shaped (nummular) lesions distributed uniformly across the cornea
- Subepithelial infiltrates that develop as a sequela of severe adenoviral conjunctivitis
- Typically appear weeks after the initial conjunctivitis episode
- Can persist for months to years after the acute infection resolves 1
- Often bilateral and may spare or involve the visual axis variably 1
The uniform distribution pattern across the cornea without preferential visual axis involvement strongly suggests post-adenoviral etiology rather than HSV 1.
HSV Keratitis Pattern - Different Presentation
HSV keratitis presents with distinctly different morphology 1, 2:
- Dendritic or geographic ulcers with excavated, pleomorphic epithelial defects (not coin-shaped infiltrates) 1
- Stromal keratitis when present shows focal, often central involvement with neovascularization 1
- Typically unilateral (bilateral only in atopic or immunocompromised patients) 1
- Associated with vesicular eyelid lesions or history of cold sores 1
- Nummular opacities in HSV are typically residual scars from resolved disease, not active multifocal infiltrates 3
Clinical Algorithm for Differentiation
History Assessment:
- Recent viral conjunctivitis with watery discharge, follicular reaction, and preauricular lymphadenopathy suggests adenoviral origin 1
- History of recurrent "cold sores," stress triggers, or UV exposure suggests HSV 1
Examination Findings:
- Multiple uniform coin-shaped subepithelial infiltrates = Post-adenoviral 1
- Dendritic/geographic epithelial defects with terminal bulbs = Active HSV 1, 2
- Bilateral presentation favors adenoviral (HSV usually unilateral) 1
Fluorescein Staining Pattern:
- Adenoviral: Minimal or no epithelial staining over the infiltrates 1
- HSV: Bright dendritic staining pattern with excavated borders 1, 2
Management Implications
For Post-Adenoviral Nummular Keratitis
- Self-limited condition that typically resolves over months 1
- Topical corticosteroids may be considered if vision is significantly affected, but must be tapered carefully to avoid rebound 1
- No antiviral therapy indicated 1
Critical Pitfall to Avoid
Never use topical corticosteroids if HSV cannot be definitively excluded, as steroids are absolutely contraindicated in HSV epithelial keratitis and will potentiate viral replication 2. If diagnostic uncertainty exists, consider corneal culture or PCR testing before initiating steroid therapy 1.
The uniform, multifocal nummular pattern you describe, especially if bilateral and occurring after a conjunctivitis episode, is pathognomonic for post-adenoviral subepithelial infiltrates rather than HSV keratitis 1.