## Most Common Cause of Viral Keratitis **Key Point:** Herpes simplex virus type 1 (HSV-1) is the most common cause of infectious keratitis worldwide and the leading cause of corneal blindness in developed nations. ### Clinical Features of HSV Keratitis | Feature | HSV-1 Keratitis | |---------|------------------| | **Ulcer morphology** | Dendritiform (tree-like) with terminal bulbs | | **Sensation** | Reduced corneal sensation (pathognomonic) | | **Recurrence** | Common (50% within 5 years) | | **Laterality** | Usually unilateral | | **Associated signs** | Vesicular lid involvement, conjunctivitis | ### Epidemiology **High-Yield:** HSV-1 accounts for ~90% of all herpetic keratitis cases. Primary infection usually occurs in childhood (asymptomatic or mild); recurrent keratitis develops in seropositive individuals due to reactivation of latent virus in trigeminal ganglion. ### Pathogenesis 1. Primary infection → latency in trigeminal nerve 2. Reactivation triggered by stress, fever, immunosuppression, or UV exposure 3. Virus travels along nerve axons to cornea 4. Epithelial ulceration with characteristic dendritic pattern ### Diagnostic Clue **Clinical Pearl:** The combination of dendritiform ulcer with **reduced corneal sensation** (due to trigeminal nerve involvement) is virtually diagnostic of HSV keratitis. This distinguishes it from other viral causes. ### Treatment Rationale - **Topical acyclovir** 5 times daily is first-line for epithelial keratitis - Oral acyclovir for recurrent disease and prophylaxis - Avoid topical corticosteroids in epithelial disease (risk of geographic ulcer) **Warning:** Do not confuse HSV keratitis with adenoviral keratoconjunctivitis, which presents with follicular conjunctivitis and subepithelial infiltrates rather than dendritiform ulcers.
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