Herpes Simplex Keratitis (HSK)

The damage that HSV causes to the eye depends on which corneal layer is involved and whether the injury results from active viral replication or the body's immune response to the virus. A primary HSV infection of the eye may be mild or even go unnoticed, sometimes appearing as a simple case of conjunctivitis. After the initial episode resolves, the virus does not leave the body. Instead, it retreats into the trigeminal nerve ganglion and enters a dormant phase. This ability to persist indefinitely is what makes HSK a potentially recurring condition.

When the virus reactivates and reaches the corneal surface, it directly infects and destroys epithelial cells. This produces the hallmark dendritic ulcer, a branching, tree-like pattern visible with fluorescein staining under a slit lamp. If untreated, a dendritic ulcer can enlarge into a broader geographic ulcer, increasing the risk of deeper corneal involvement. Epithelial disease is driven by active viral replication and responds well to antiviral therapy.

Stromal keratitis occurs when the body's immune system mounts an inflammatory response against viral particles within the deeper cornea. This inflammation can cause corneal haze, scarring, thinning, and new blood vessel growth (neovascularization) in the normally clear cornea. Stromal keratitis is the form of HSK most likely to result in permanent vision loss if not managed carefully. Treatment typically involves a combination of antiviral medication and carefully monitored anti-inflammatory therapy.

In less common cases, HSV targets the endothelial cells lining the inner surface of the cornea. These cells are responsible for pumping fluid out of the cornea to maintain its clarity. Damage to the endothelium can cause the cornea to swell (corneal edema), leading to blurry vision. Endotheliitis often requires a combination of antiviral and anti-inflammatory treatment to preserve endothelial function.

Treatment depends on the type and severity of the infection. Epithelial keratitis is treated with antiviral medications, either oral (such as valacyclovir or acyclovir) or topical (such as ganciclovir ophthalmic gel). Stromal keratitis typically requires an antiviral combined with a carefully dosed topical corticosteroid to control the immune-mediated inflammation. Corticosteroids should never be used without antiviral coverage, as this can worsen active viral infection. Our ophthalmologists tailor each treatment plan to the specific form and stage of your infection.

Yes, particularly when stromal keratitis leads to corneal scarring, thinning, or neovascularization. Repeated episodes of inflammation cause cumulative damage that can significantly reduce vision clarity. In advanced cases where the cornea is severely scarred, a corneal transplant may be necessary to restore sight. Early treatment and long-term preventive care help reduce the risk of reaching that point.

Recurrence is one of the defining challenges of this condition. Research from the Herpetic Eye Disease Study (HEDS) found that roughly 20 to 30 percent of patients experience a recurrence within two years of their first episode. Each subsequent recurrence carries additional risk of deeper corneal damage. For patients with frequent recurrences, long-term oral antiviral prophylaxis can reduce the recurrence rate by approximately 50 percent.

Bilateral herpes keratitis is uncommon in patients with healthy immune systems, affecting fewer than 5 percent of cases. However, it is more frequently seen in immunocompromised individuals, including those taking immunosuppressive medications. Good hygiene practices, such as avoiding touching your eyes and washing your hands frequently during an active episode, help minimize any risk of spread. If you develop symptoms in your other eye, report them to your ophthalmologist right away.

Unlike bacterial or viral conjunctivitis (pink eye), herpes keratitis specifically targets the cornea and can cause deep structural damage over time. Bacterial keratitis, often linked to contact lens wear, tends to produce a more diffuse white corneal infiltrate, while HSK produces a characteristic dendritic branching pattern. Another key difference is that HSK involves a virus that remains in the body permanently and can reactivate, whereas most other eye infections resolve completely. Conditions like scleritis can also cause eye pain and redness but affect different structures of the eye and have distinct underlying causes.

Known triggers include physical or emotional stress, fever, prolonged sun exposure (ultraviolet light), illness, fatigue, hormonal changes, and immunosuppression. Eye trauma or surgery can also reactivate the virus in some patients. While it is not always possible to avoid every trigger, managing stress, wearing UV-protective sunglasses, and maintaining overall health can reduce your risk. Patients with a history of HSK who are planning ocular surgery should discuss prophylactic antiviral therapy with their ophthalmologist beforehand.