Herpes zoster ophthalmicus

HZO results from reactivation of latent VZV residing in the trigeminal (Gasserian) ganglion, typically in older or immunocompromised patients. Primary infection (chickenpox) establishes latency; reactivation causes a dermatomal vesicular eruption following the V1 distribution—forehead, upper eyelid, and tip of the nose. Hutchinson's sign (vesicles on the tip or side of the nose, indicating nasociliary nerve involvement) is a strong predictor of ocular involvement because the nasociliary nerve also innervates the globe.

Clinical features include prodromal pain/paresthesia followed by a vesicular rash that crusts over 2-4 weeks. Ocular complications occur in up to 50% of cases and include conjunctivitis, episcleritis, keratitis (can lead to corneal scarring and reduced vision), anterior uveitis, elevated intraocular pressure, and rarely retinitis (acute retinal necrosis) or optic neuritis. Chronic complications include postherpetic neuralgia and recurrent keratouveitis.

Diagnosis is primarily clinical based on the dermatomal rash; Tzanck smear, PCR, or direct fluorescent antibody testing can confirm VZV if needed. Slit-lamp examination is essential to assess for keratitis/uveitis.

Management: Early initiation (within 72 hours of rash onset) of oral antivirals (valacyclovir, famciclovir, or acyclovir) reduces severity, duration, and risk of ocular complications and postherpetic neuralgia. Ophthalmology referral is warranted for any ocular involvement; topical corticosteroids may be used for keratitis/uveitis under specialist guidance, and cycloplegics for photophobia/pain. IV acyclovir is reserved for immunocompromised patients or severe disease (e.g., retinitis). The zoster vaccine (recombinant, Shingrix) reduces incidence of HZ and HZO in older adults.

Key board points: Hutchinson's sign = ocular involvement risk; V1 dermatome; antiviral therapy within 72 hours; differentiate from herpes simplex keratitis (dendritic ulcers, but HZO can also cause pseudodendrites).