A 32-year-old woman presents with severe left-sided facial pain and vesicular rash in the distribution of the ophthalmic division of the trigeminal nerve. She has fever, photophobia, and conjunctivitis. Corneal examination reveals dendritic ulcers. What is the most likely diagnosis and which antiviral agent is contraindicated in this condition?

Explanation

## Clinical Diagnosis **Key Point:** Dendritic ulcers on corneal examination are pathognomonic for HSV-1 keratitis. The distribution of vesicles in the ophthalmic division (V1) of the trigeminal nerve, combined with photophobia and conjunctivitis, confirms herpes simplex virus infection of the eye. ## Antiviral Considerations **High-Yield:** Idoxuridine (IDU) is a nucleoside analog that was historically used for HSV keratitis but is now largely avoided due to: - Corneal toxicity and epithelial defects with prolonged use - Poor penetration into deeper corneal layers - Teratogenicity (contraindicated in pregnancy) **Clinical Pearl:** Acyclovir (IV or topical) is the current standard of care for HSV keratitis because it has superior efficacy, better corneal penetration, and a safer toxicity profile. ## Differential Features | Feature | HSV-1 Keratitis | VZV Keratitis | CMV Retinitis | EBV Keratitis | |---------|-----------------|---------------|---------------|---------------| | **Ulcer morphology** | Dendritic (branching) | Geographic (larger, irregular) | Granular infiltrates | Rare | | **Vesicle distribution** | Dermatomal or non-dermatomal | Dermatomal (V1, V2, V3) | None (retinal) | None | | **Photophobia** | Marked | Marked | Absent | Rare | | **Antiviral of choice** | Acyclovir | Acyclovir | Ganciclovir/Foscarnet | Acyclovir | | **Contraindicated drug** | Idoxuridine | — | — | — | **Mnemonic: DENDRITIC = HSV** — Dendritic ulcers are the hallmark of HSV keratitis.