A 32-year-old woman presents with unilateral eye pain, photophobia, and blurred vision for 5 days. Slit-lamp examination reveals a dendritic ulcer with terminal bulbs on the cornea. What is the most common causative organism of this presentation?

Explanation

## Most Common Viral Keratitis: HSV-1 ### Epidemiology and Frequency **Key Point:** Herpes simplex virus type 1 (HSV-1) is responsible for >90% of all herpetic keratitis cases worldwide, including in India. It is the leading infectious cause of corneal blindness in developed nations. ### Clinical Presentation of HSV-1 Keratitis | Feature | HSV-1 Keratitis | | --- | --- | | **Ulcer morphology** | Dendritic (branching, tree-like) with terminal bulbs | | **Staining pattern** | Central ulcer stains with fluorescein; edges stain with rose bengal | | **Associated symptoms** | Unilateral eye pain, photophobia, tearing, blepharospasm | | **Recurrence rate** | High (up to 50% within 5 years) | | **Age of onset** | Can occur at any age; primary infection often in childhood | ### Pathophysiology 1. Primary infection → latency in trigeminal ganglion 2. Reactivation triggered by stress, fever, immunosuppression, or UV exposure 3. Viral replication in corneal epithelium → dendritic ulcer formation 4. Repeated episodes → stromal keratitis and scarring **High-Yield:** The **dendritic ulcer with terminal bulbs** is pathognomonic for HSV-1 keratitis. This morphology results from viral spread along nerve endings in the corneal epithelium. ### Why HSV-1 is Most Common - Seroprevalence of HSV-1 in India: ~60–80% of population - Reactivation keratitis more common than primary infection - HSV-2 primarily causes genital herpes; ocular involvement rare (~5% of herpetic keratitis) - VZV and CMV cause keratitis in specific populations (immunocompromised, dermatomal distribution for VZV) **Clinical Pearl:** Always suspect HSV-1 in a patient with recurrent unilateral dendritic keratitis. Recurrent episodes may present as geographic ulcers (coalescence of dendrites) or stromal keratitis with immune-mediated inflammation. ### Diagnostic Confirmation - **Giemsa staining** or **immunofluorescence** of corneal scrapings shows multinucleated giant cells - **PCR** of corneal fluid (most sensitive and specific) - **Viral culture** (less commonly used; slow) ### Management Approach ```mermaid flowchart TD A[Suspected HSV-1 Keratitis]:::outcome --> B{Ulcer type?}:::decision B -->|Epithelial dendritic| C[Topical antivirals]:::action B -->|Geographic| D[Topical antivirals + systemic acyclovir]:::action B -->|Stromal/endothelial| E[Topical antivirals + topical steroids]:::action C --> F[Acyclovir 5% ointment 5x daily OR Ganciclovir 0.15%]:::action D --> G[Add systemic acyclovir 400 mg 5x daily]:::action E --> H[Prednisolone 1% 4–6x daily + antivirals]:::action F --> I[Epithelialization in 7–10 days]:::outcome G --> J[Monitor for recurrence]:::outcome H --> K[Risk of perforation if untreated]:::urgent ``` **Tip:** Avoid topical steroids in epithelial keratitis (risk of geographic ulcer); reserve steroids for stromal disease with immune inflammation.