A 28-year-old woman presents with severe left eye pain, photophobia, and blurred vision for 3 days. On examination, she has conjunctival injection, a dendritic ulcer on the cornea staining with fluorescein, and reduced corneal sensation. She reports a history of recurrent oral cold sores. What is the most likely diagnosis?

## Diagnosis: HSV-1 Keratitis **Key Point:** The dendritic ulcer is pathognomonic for HSV keratitis. This branching epithelial defect stains with fluorescein and is caused by viral replication in corneal epithelial cells with cell-to-cell spread. **Clinical Pearl:** HSV-1 is the most common cause of infectious keratitis in developed countries. The history of recurrent oral cold sores (labial herpes) strongly suggests HSV-1 as the causative agent, as the virus can reactivate and spread to the eye via the trigeminal nerve. **High-Yield:** HSV keratitis presents with: - Unilateral eye involvement - Dendritic ulcer (pathognomonic) - Reduced corneal sensation (due to trigeminal nerve involvement) - Conjunctival injection and photophobia - History of recurrent oral herpes in 50% of cases ### Pathophysiology HSV-1 establishes latency in the trigeminal ganglion. Reactivation leads to anterograde transport along sensory nerve endings to the cornea, causing epithelial infection and the characteristic dendritic ulcer pattern. ### Management Topical acyclovir 5% ointment or ganciclovir 0.15% gel is first-line. Systemic acyclovir may be added for severe cases. Topical corticosteroids are contraindicated in epithelial keratitis as they worsen viral replication and delay healing.