Herpes Simplex Keratitis: Recurring Eye Infections

The herpes simplex virus can affect multiple layers of the cornea, and the specific layer involved determines the type of keratitis, its severity, and the treatment approach. Epithelial keratitis is the most common form of herpes simplex keratitis and involves the outermost layer of the cornea. The virus actively replicates in the epithelial cells, creating a characteristic branching pattern known as a dendritic ulcer. This form typically responds well to antiviral medication when treated promptly. Without treatment, the dendritic ulcer can enlarge into a broader geographic ulcer, which takes longer to heal and carries a higher risk of complications.

Stromal keratitis involves the middle, structural layer of the cornea and is primarily caused by the body's own immune response to viral proteins rather than active viral replication. This immune-mediated inflammation can lead to corneal swelling, scarring, and new blood vessel growth within the normally clear cornea. Stromal keratitis is the form most likely to cause permanent vision loss and often requires a combination of antiviral medication and carefully managed anti-inflammatory treatment.

Endotheliitis targets the innermost layer of the cornea, the endothelium, which is responsible for keeping the cornea clear by pumping excess fluid out of the corneal tissue. When the endothelium becomes inflamed, the cornea swells and vision becomes cloudy. This form of herpes keratitis can sometimes be mistaken for other causes of corneal edema and requires prompt evaluation to prevent lasting endothelial cell damage.

Repeated episodes of herpes keratitis can damage the corneal nerves, leading to a condition called neurotrophic keratopathy. When corneal sensation is reduced, the normal healing and protective reflexes of the eye are impaired. Patients with neurotrophic keratopathy may develop persistent epithelial defects that are slow to heal, increasing the risk of secondary infections and further corneal damage.

Diagnosis begins with a comprehensive slit-lamp examination. Fluorescein dye is applied to the eye to highlight the characteristic dendritic or geographic ulcer pattern on the corneal surface. Reduced corneal sensation, tested with a fine wisp of cotton or a device called an esthesiometer, is another hallmark finding. In cases where the presentation is atypical, a polymerase chain reaction test of corneal or tear fluid can confirm the presence of herpes simplex virus DNA.

The primary antiviral medications include oral valacyclovir and oral acyclovir, which are effective for both epithelial and stromal disease. Topical antiviral options include ganciclovir ophthalmic gel and trifluridine drops. For stromal keratitis, a topical corticosteroid may be prescribed alongside the antiviral to control the immune-mediated inflammation, but corticosteroids should never be used without antiviral coverage because they can worsen active viral replication.

Yes, herpes keratitis can lead to permanent vision loss, particularly when the stromal layer is involved. Repeated episodes of stromal keratitis can cause progressive corneal scarring, thinning, and neovascularization that permanently reduce visual clarity. However, with early and appropriate treatment, many patients maintain good functional vision throughout their lives. The key to preserving sight is prompt treatment of each episode and a long-term plan to reduce recurrence frequency.

Prevention strategies focus on reducing known triggers and, in many cases, using long-term antiviral medication. Wearing UV-protective sunglasses outdoors, managing stress, maintaining overall health, and getting adequate sleep can all help reduce reactivation risk. Avoiding eye rubbing and protecting the eyes during activities that could cause trauma are also recommended. For patients with frequent recurrences, daily oral antiviral prophylaxis is the most effective prevention tool currently available.

The landmark Herpetic Eye Disease Study demonstrated that taking oral acyclovir daily reduced the recurrence rate of herpes keratitis by approximately 50%. Based on this evidence, long-term prophylaxis is commonly recommended for patients who have had two or more episodes, particularly those with stromal involvement. The medication is generally well tolerated, and the benefits of fewer recurrences and reduced corneal damage typically outweigh the minimal risks of extended use.

In severe cases where repeated episodes have caused significant corneal scarring or thinning, a corneal transplant may become necessary to restore vision. Both full-thickness and partial-thickness transplant techniques can be considered depending on the extent of damage. However, herpes keratitis can recur in a transplanted cornea, so patients typically continue antiviral prophylaxis indefinitely after transplant surgery.