Shingles (Herpes Zoster) is caused by the reactivation of the varicella-zoster virus (VZV), the same virus responsible for chickenpox. After recovery from chickenpox, VZV remains dormant within nerve cells but can reactivate later in life. When this viral reactivation occurs in the nerve pathway supplying the eye and surrounding structures, the condition is termed Herpes Zoster Ophthalmicus (HZO). HZO is considered an ophthalmologic emergency due to the high risk of permanent damage and vision loss if not treated quickly.
The Mechanism of Viral Spread to the Eye
VZV reactivates from its latent state within the trigeminal ganglion, a sensory nerve center. This ganglion controls the trigeminal nerve, which has three main divisions providing sensation to the face. HZO specifically involves the ophthalmic division (V1), which supplies the skin of the forehead, upper eyelid, and the eye itself.
The reactivated virus travels along the V1 sensory nerve fibers, causing a painful rash in the supplied skin area. A strong indicator of high risk for eye involvement is the presence of a vesicular rash on the tip or side of the nose, known as Hutchinson sign. This sign signals the involvement of the nasociliary branch of the V1 nerve, which provides sensation to the internal structures of the eye.
Acute Symptoms and Urgent Warning Signs
HZO onset is often preceded by a prodrome phase lasting two to five days before the rash appears. During this time, patients may experience general symptoms like headache, malaise, or a low-grade fever. Characteristically, there is severe, sharp, or burning pain, tingling, or itching localized to one side of the forehead, scalp, or upper eyelid.
Within days, the characteristic rash emerges as painful, fluid-filled blisters (vesicles) on the affected skin. The appearance of any skin lesion on the forehead or eyelid must prompt an immediate medical evaluation for potential eye involvement. Initial ocular symptoms demanding urgent attention include severe eye pain, redness, excessive tearing, and sensitivity to light (photophobia). These signs indicate the virus has progressed beyond the skin and is infecting the eye’s surface or internal structures.
Specific Ocular Structures Affected
Shingles can damage nearly all parts of the eye, leading to conditions that threaten vision.
Cornea and Anterior Structures
The cornea, the clear front window of the eye, is a common target, resulting in inflammation called keratitis. This may manifest as viral ulcers, progressing to deep scarring or chronic nerve damage, which can lead to neurotrophic keratopathy. Inflammation can also affect the middle layer of the eye (the uvea), causing iritis or uveitis. This inflammation may lead to increased pressure inside the eye, potentially resulting in secondary glaucoma if untreated. The external layers are also affected, commonly presenting as episcleritis or inflammation of the conjunctiva, the clear membrane covering the white of the eye.
Posterior Segment Complications
The most severe, though less common, complications involve the back of the eye. The virus can cause acute retinal necrosis (ARN), a rapid, destructive inflammation of the retina that leads to profound and irreversible vision loss. Inflammation of the optic nerve, called optic neuritis, is also a possibility, causing sudden loss of vision.
Immediate Medical Treatment and Management
The medical management of HZO is time-sensitive; the primary goal is to halt viral replication and prevent permanent eye damage. Treatment with systemic antiviral medications must ideally begin within 72 hours of the rash onset to be most effective in shortening the illness and reducing ocular complications. Commonly prescribed oral antivirals include valacyclovir, acyclovir, or famciclovir.
An ophthalmologist manages ocular inflammation with topical treatments tailored to the specific structures affected. This may involve steroid eye drops to control internal inflammation, which must be used cautiously and tapered slowly over months. Other topical medications, such as drops to manage eye pressure, may also be necessary, along with general pain relievers. Prompt consultation with an eye care specialist is required for anyone with suspected HZO, even if eye symptoms are not immediately present.
Preventing Ocular Shingles
The most proactive measure against HZO is vaccination, which boosts the immune system’s ability to keep VZV dormant. The recombinant zoster vaccine (Shingrix) is the primary preventative tool recommended for adults aged 50 years and older. This vaccine is highly effective against shingles overall and has demonstrated an effectiveness of nearly 90% in preventing HZO specifically.
Preventing the initial shingles episode significantly lowers the chance of the virus reaching the ophthalmic nerve division. Even if shingles occurs after vaccination, the severity and duration of the illness are often reduced, decreasing the potential for long-term complications like postherpetic neuralgia and vision-threatening HZO. The vaccine is administered in two doses spaced two to six months apart.