Herpes Simplex Keratitis

Herpes simplex keratitis (HSK) is an infection of the cornea caused by the herpes simplex virus (HSV), most commonly HSV-1—the same virus that causes cold sores. It is the leading infectious cause of corneal blindness in developed countries. Prompt recognition and treatment are critical to prevent scarring and vision loss.

Overview

After the initial HSV-1 infection (often in childhood), the virus travels to the trigeminal nerve ganglion where it remains dormant for life. Reactivation can send the virus to the cornea, causing keratitis. Recurrent episodes can lead to progressive scarring and vision loss, which is why prevention of recurrences is a key part of management.

Types of Herpes Simplex Keratitis

Epithelial Keratitis (Most Common)

• Virus actively infects the corneal surface cells
• Classic dendritic ulcer — branching, tree-like pattern with terminal bulbs
• Geographic ulcer — larger, map-shaped ulcer (often from steroid misuse)
• Diagnosed on slit-lamp with fluorescein staining
• Treated with antivirals alone — no steroids

Stromal Keratitis

• Immune-mediated inflammation in the corneal stroma (middle layer)
• Causes corneal haze, edema, and potential scarring
• Two subtypes:
  • Immune stromal (interstitial) — disc-shaped inflammation without active virus
  • Necrotizing stromal — more severe, with active viral involvement
• Treated with antivirals plus topical steroids (to control immune response)

Endothelial Keratitis

• Affects the innermost corneal layer (endothelium)
• Causes corneal swelling (edema) and keratic precipitates
• Treated with antivirals plus topical steroids

Symptoms

• Pain and redness in one eye
• Light sensitivity (often severe)
• Tearing and watery discharge
• Blurred vision
• Foreign body sensation
• Decreased corneal sensation (the cornea may feel numb)

Causes and Risk Factors

Triggers for Reactivation

• Stress (physical or emotional)
• Illness, fever, or immunosuppression
• Sun exposure (UV light)
• Eye surgery or trauma
• Menstruation
• Topical steroid use (can trigger or worsen epithelial disease)

Risk Factors for Recurrence

• History of previous HSK episode (recurrence rate ~30% within 5 years)
• Immunosuppression
• Frequent cold sores
• UV exposure without protection

Diagnosis

• Slit-lamp exam with fluorescein staining — reveals the characteristic dendritic or geographic ulcer pattern
• Corneal sensation testing — reduced in HSK (the virus damages corneal nerves)
• Clinical appearance is usually diagnostic — lab testing rarely needed
• PCR testing of corneal swab available for atypical cases

The dendritic ulcer is one of the most recognizable findings in ophthalmology — a branching pattern with terminal bulbs that stains brightly with fluorescein dye.

Treatment

Epithelial Disease

Antiviral therapy (first-line):

• Oral valacyclovir 500 mg three times daily for 7-10 days
• Oral acyclovir 400 mg five times daily (alternative)
• Topical trifluridine 1% drops or ganciclovir gel 0.15% (topical alternatives)

Stromal and Endothelial Disease

• Topical corticosteroid (prednisolone acetate 1%) — to control immune-mediated inflammation
• Combined with oral antiviral (valacyclovir 500 mg twice daily) — to prevent viral reactivation while on steroids
• Slow steroid taper over weeks to months
• Abrupt steroid discontinuation can trigger recurrence

Recurrence Prevention

Prophylactic antiviral therapy:

• Oral acyclovir 400 mg twice daily or valacyclovir 500 mg once daily
• Reduces recurrence rate by approximately 50%
• Recommended for patients with:
  • Frequent recurrences
  • Previous stromal keratitis with scarring
  • Vision-threatening recurrences
• Can be continued long-term (years)

Surgical Options

For severe scarring affecting vision:

• Corneal transplant (penetrating or lamellar keratoplasty)
• Higher rejection risk than transplants for other conditions
• Prophylactic antivirals mandatory before and after transplant
• Recurrence in graft is possible

When to See a Doctor

Complications

• Corneal scarring with permanent vision loss
• Corneal thinning or perforation (rare)
• Secondary bacterial infection of the corneal ulcer
• Chronic dry eye from nerve damage
• Need for corneal transplant

Frequently Asked Questions

Is herpes keratitis the same as pink eye?

No. While both cause a red eye, herpes keratitis is a viral corneal infection that can threaten vision, while most cases of conjunctivitis are self-limited. The distinction matters because treatment is completely different.

Can I spread herpes keratitis to someone else?

The herpes virus itself can be transmitted through direct contact (such as during an active cold sore), but corneal herpes is a reactivation of a virus already in your body. You don't spread keratitis directly. However, avoid touching your eyes and then touching others during active episodes.

Will I keep getting recurrences?

Recurrences are unpredictable. About 30% of patients have a recurrence within 5 years. Each recurrence risks additional scarring. Prophylactic antiviral therapy significantly reduces this risk.

Can I wear contact lenses with herpes keratitis?

Contact lens wear should be stopped during active disease. After resolution, lenses may be resumed with caution. Discuss timing with your ophthalmologist. Contact lens wear itself can trigger reactivation.

How is this different from herpes zoster (shingles) of the eye?

Herpes simplex keratitis is caused by HSV-1. Herpes zoster ophthalmicus is caused by the varicella-zoster virus (chickenpox/shingles virus). Both can affect the cornea, but shingles typically involves a painful skin rash along a nerve distribution and is more common in older adults.

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