Herpes simplex keratitis

Lore & Background

Herpes simplex keratitis is initiated by HSV infection of epithelial cells on the eye surface, followed by retrograde infection of corneal nerves. Primary infection often manifests as blepharoconjunctivitis with small white itchy lesions, which may range from superficial punctate keratitis to dendritic ulcers. Most primary infections resolve spontaneously within weeks, aided by oral or topical antivirals. Recurrences, triggered by factors such as illness, fever, sun exposure, or stress, can be more severe, with larger dendritic ulcers, white plaques, and sloughing of the epithelial layer. Repeated recurrences may lead to corneal anesthesia and chronic dry eye.

Reader's Guide

Herpes simplex keratitis is a significant public health problem worldwide, with an estimated one third of the global population experiencing recurrent HSV infection. It is the leading cause of cornea-derived blindness in developed nations, with roughly 1.5 million new cases annually, including 40,000 cases of severe monocular visual impairment or blindness. The disease progresses from epithelial keratitis (dendritic ulcers) to immune-mediated stromal keratitis, where antibody responses can destroy the corneal stroma and cause vision loss due to opacification. Diagnosis is typically clinical based on characteristic dendritic ulcers, though laboratory tests like viral culture or DNA testing are used in uncertain cases. Treatment varies by presentation: epithelial keratitis responds to topical or oral antivirals, while stromal keratitis requires corticosteroids with prophylactic antivirals. Metaherpetic ulcers, not caused by live virus, are managed with lubricants and supportive measures. The condition underscores the need for effective antiviral therapies and careful management to prevent blindness.

Did You Know?

• Herpes simplex keratitis is the most common cause of cornea-derived blindness in developed nations.
• The classic herpetic lesion is a dendritic ulcer, a linear branching corneal ulcer that stains with fluorescein dye.
• Topical corticosteroids are contraindicated in active herpetic epithelial keratitis.
• Oral acyclovir is as effective as topical antivirals for treating epithelial keratitis and avoids eye surface toxicity.

From Nerve to Cornea: The Life Cycle of Infection

Herpes simplex keratitis begins when HSV-1, a double-stranded DNA virus with an icosahedral capsid, invades epithelial cells on the corneal surface and then travels backward along the sensory nerves supplying the eye. A primary episode typically presents as swelling of the eyelids and conjunctiva, small itchy white spots on the cornea, a deep dull ache, dryness, and occasionally sinusitis. The infection always strikes one eye at a time and usually resolves on its own within a few weeks, though oral and topical antivirals can speed healing. The virus does not leave the body; it settles into a dormant state within nerve cells, cycling between inactivity and activity. Reactivation can be prompted by fever, sun exposure, emotional stress, injury, surgery, or the menstrual cycle. Once reactivated in a sensory ganglion, the virus rides down the nerve axon back to the ocular surface, where it may produce larger dendritic ulcers, white plaques, and progressive loss of corneal sensation. If viral DNA accumulates past a critical threshold, antibody responses against viral antigens in the stroma can trigger a massive immune attack that destroys corneal tissue, leaving a permanently opaque cornea. This immune-mediated stromal keratitis is a leading cause of irreversible vision loss.

A Spectrum of Corneal Lesions

Because the virus can attack different layers of the cornea, herpes simplex keratitis presents in several distinct clinical forms. The most recognizable is the dendritic ulcer of epithelial keratitis: a linear, branching defect that becomes visible only after the eye is stained with fluorescein dye. Patients report a foreign-body sensation, light sensitivity, redness, and blurred vision, while the underlying cornea shows minimal inflammation. Repeated episodes progressively reduce corneal sensation, and in immunocompromised patients or those on corticosteroids the ulcer can expand into a large geographic lesion. A second major form, disciform or endothelial keratitis, appears as a central disc-shaped area of endothelial inflammation. Prolonged corneal edema in this form leads to permanent scarring and is the principal driver of decreased vision associated with HSV. Other presentations include metaherpetic ulcer, which arises not from live virus but from the corneal surface's inability to heal; necrotizing keratitis; and keratouveitis, a granulomatous form of uveitis marked by large keratic precipitates on the endothelium. Each form demands a different therapeutic strategy, underscoring why accurate classification is central to management.

A Global Burden on Vision

Although many people carry the virus without ever developing eye disease, the public-health footprint of herpes simplex keratitis is enormous. It is estimated that roughly one-third of the world's population experiences recurrent HSV infection, and the virus's ability to reactivate under common triggers—fever, sunlight, stress, injury, surgery, or hormonal changes—means that a single primary episode can foreshadow a lifetime of potential recurrences. In developed nations, HSV keratitis stands as the most common cause of blindness attributable to corneal disease. Globally, the incidence of new herpes keratitis cases is estimated at approximately 1.5 million per year, and within that figure some 40,000 individuals each year suffer severe monocular visual impairment or outright blindness. Because the disease is unilateral, it spares the fellow eye, yet the loss in one eye profoundly affects depth perception and functional vision. The combination of high prevalence, recurrent potential, and the risk of immune-mediated stromal destruction makes HSV keratitis a persistent and significant worldwide public-health challenge, particularly in populations with limited access to ophthalmic care.

Diagnosis and Targeted Treatment

In most cases of dendritic keratitis, an ophthalmologist or optometrist can reach a confident clinical diagnosis simply by recognizing the characteristic branching ulcer pattern after fluorescein staining, making laboratory testing unnecessary. In complicated presentations or suspected neonatal herpes, however, additional workup is warranted. Corneal smears can be examined by culture, antigen detection, or fluorescent antibody methods; a Tzanck smear may reveal multinucleated giant cells and intranuclear inclusions, though its sensitivity and specificity are limited. DNA-based assays are rapid, sensitive, and specific but remain expensive, restricting their use largely to research settings. Serologic tests can document a rising antibody titer during primary infection but offer little help during recurrences. Treatment is tailored to the underlying mechanism: epithelial keratitis, driven by live virus, responds well to topical antivirals such as aciclovir ointment or trifluridine drops, typically administered for ten to fourteen days with low resistance rates. Stromal disease reflects an immune-mediated process rather than active viral replication, and metaherpetic ulcer stems from the epithelium's failure to heal—each requiring a fundamentally different therapeutic approach.

Gallery