Herpes zoster ophthalmicus.

Herpes zoster ophthalmicus (HZO) occurs when latent varicella zoster virus reactivates in the ophthalmic division of the fifth cranial nerve (CNV1). HZO commonly affects older and immunocompromised patients. This disease is considered an ophthalmic emergency due to the wide range of associated ocular symptoms, including severe chronic pain and vision loss. HZO is typically a clinical diagnosis due to its classic presentation of a unilateral vesicular eruption in the dermatomes corresponding to CNV1. Timely treatment is imperative to minimize ocular morbidity in HZO, given that ocular involvement is present in 50% of affected patients.