Herpes Zoster Ophthalmicus
THE CLINICAL CHALLENGE
Herpes zoster, commonly known as shingles, occurs when the human herpesvirus type 3, the virus responsible for varicella infection, is reactivated in the neurosensory ganglia, often years or decades after the primary infection. Herpes zoster classically results in a unilateral inflammatory reaction causing pain and a vesicular rash in the distribution of a neurosensory dermatome (Figure 32.1). According to the Centers for Disease Control and Prevention, there are an estimated 1 million annual cases of herpes zoster in the United States, and nearly one in three people will develop herpes zoster in their lifetime.1 Herpes zoster ophthalmicus (HZO) is a commonly encountered disorder in emergency departments (EDs) and urgent care settings and accounts for 10% to 20% of herpes zoster cases.2
Herpes zoster and HZO primarily affect the elderly and immunocompromised. Decreased cellular immunity as a result of advanced age, immunosuppression, or physical stress allows the virus that had been dormant for years and suppressed by the immune system to reactivate. Early diagnosis, treatment with antivirals, and, when there is concern for eye involvement, ophthalmologic consultation is essential in decreasing the duration of symptoms and complications of herpes zoster and HZO such as permanent vision loss, prolonged or permanent pain, and scarring.
HZO results from the reactivation of the varicella virus (human herpesvirus 3) in the ophthalmic branch of the trigeminal nerve (Figure 32.2). Primary varicella infection most commonly occurs in childhood and presents as a febrile illness and diffuse pustular rash. During the primary infection, viral particles are believed to spread from infected skin along sensory nerve endings to the nerve ganglia. An alternative hypothesis is that the virus gains access to the nerve ganglia via hematologic spread during primary illness. Viral particles then remain dormant for years in the spinal and cranial nerve ganglia, suppressed by the host’s immune system.1
Reactivation of the varicella virus occurs when the host’s cellular immunity fails to continue suppressing the virus. This may occur secondary to advanced age, immunocompromised states, physical stress, or malnutrition. When no longer suppressed, the viral particles replicate and migrate peripherally along sensory nerves, triggering an inflammatory response. During this period of viral replication, some patients may experience a prodromal phase with symptoms of fatigue and low-grade fever. Local inflammatory response to the virus as it reaches distal nerve endings leads to neuropathic pain in affected dermatome, the vesicular rash and, when affecting the ophthalmic nerve, ocular inflammation.
Figure 32.1: Herpes zoster affecting the ophthalmic branch of the trigeminal nerve. (From Rapuano CJ. Wills Eye Institute: Cornea. 3rd ed. Wolters Kluwer; 2019. Figure 7.9a.)
Figure 32.2: Dermatomes of the trigeminal nerve. (From Parent A. Carpenter’s Human Neuroanatomy. 9th ed. Wolters Kluwer; 1996:505.)
When herpes zoster involves the ophthalmic nerve, patients typically develop pain over the affected V1 dermatome and a unilateral erythematous rash over the forehead with progression to vesicles that erupt and crust over. Rash over the tip of the nose, Hutchinson sign (Figure 32.3) indicates involvement of the nasociliary nerve (a branch of the ophthalmic nerve) and is highly correlated with ocular involvement.3 Ocular involvement may manifest as a rash over the eyelid, conjunctivitis (35% to 70%), keratitis (13% to 75%) (punctate epithelial keratitis, pseudodendritic lesions, erosions, persistent defects), uveitis (18% to 47%), acute retinal necrosis, optic neuritis or rarely oculomotor palsies.4 Ocular complications could progress to permanent visual loss, scarring, and pain.2
Keratitis typically develops within a month of dermatitis and may affect all layers of the cornea (epithelium, stroma, and endothelium). Early signs include punctate epithelial keratitis, presenting 2 days after vesicle formation, and pseudodendrites, about 4 to 6 days after presentation. These signs are seen in 5% to 51% of patients with ocular involvement. Other complications include blepharitis and secondary glaucoma.4
Necrotizing retinitis is an uncommon complication of HZO that can lead to retinal tears, retinal detachment, and subsequent permanent vision changes. These patients typically present in the acute setting with far worse visual acuity. There are two forms of necrotizing retinitis: acute retinal necrosis (ARN) and progressive outer retinal necrosis (PORN).
ARN (Figure 32.4) is typically seen in immunocompetent individuals. Patients typically report pain, decreased vision, and floaters at the time of presentation. ARN commonly causes retinal detachments (50% to 75%) with multiple holes and giant retinal tears, conferring poor visual prognosis. Only 30% of patients achieve final visual acuity better than 20/200.5
PORN (Figure 32.5) is typically found in immunocompromised patients. Although there is less inflammation owing to their immunocompromised state, and therefore lower incidence of floaters, it has a much faster progression and worse outcome when compared with ARN.6