Overview

If you're experiencing eye discomfort, blurry vision, or unexplained redness,  one possible cause is viral keratitis. The good news is that by understanding the key viruses behind this condition and how they differ, you’re already on the right track toward effective treatment. 

Viral keratitis is an infection of the cornea, most commonly caused by two viruses: Herpes Simplex Virus (HSV) and Varicella-Zoster Virus (VZV).^1,2

• HSV keratitis usually arises from HSV (the same virus responsible for cold sores). It often recurs, typically affecting just one eye, and causes pain, redness, tearing, and light sensitivity¹
• VZV keratitis occurs when the chickenpox virus reactivates as shingles and involves the eye, a condition known as herpes zoster ophthalmicus. This type is more common in older adults and is usually accompanied by a painful skin rash around the eye²

Both conditions require medical treatment to prevent vision damage, though their management differs depending on the virus involved.

Want to know how to recognise early signs, what treatments are available, and how to prevent future flare-ups? Let’s explore everything you need to protect your eyes.

What is keratitis?

In medicine, almost all words ending in itis refer to some kind of inflammation. In this case, keratitis refers to the inflammation of the cornea- the eye’s outer layer that helps you see clearly. 

There are two main types: infectious and non-infectious. The former is caused by bacteria, viruses, or other microorganisms. The latter is caused by injury, allergies, or other non-microbial factors.

When a virus is the cause, it’s called viral keratitis. While many viruses exist, the most common culprits are HSV and VZV.

Even though it may begin with mild symptoms like redness or itching, viral keratitis can progress to severe complications – even blindness – if not treated promptly.

What is viral keratitis?

The key difference between viral and bacterial/fungal keratitis is their causes. While an external infection could trigger bacterial and fungal keratitis, viral keratitis can be caused by a dormant virus already in the body. That is not the case with bacteria or fungi. 

Why do viruses affect the cornea?

Just thinking of the eyes makes you think they are a very vulnerable spot on our body, which is also true medically. The cornea is very exposed, and viruses often find it a good hiding spot where they rest. However, if there is a significant change in the organism due to stress or illness, it causes inflammation.

Causes of viral keratitis

Herpes simplex virus (HSV)

Most people associate HSV with cold sores (oral herpes). But this virus is also a dangerous eye pathogen because of its tendency to recur. 

Primary infection with this virus usually goes unnoticed and can happen during childhood. After that, it becomes latent (resting, not being active) in a nerve cluster near the eyes, the trigeminal ganglion. Reactivation can occur later, spreading to the eye and causing keratitis.³

Common triggers for reactivation³

• Stress (physical or emotional)
• Illness, particularly with fever
• Exposure to UV light (e.g., sunburn or tanning beds)
• Immunosuppression (e.g., due to medications or diseases)
• Eye injury or surgery

According to the Herpetic Eye Disease Study (HEDS), about 27% of patients experience a recurrence within 1 year of their initial episode, and up to 63% within 20 years.⁴

Varicella-zoster virus (VZV)

If you’ve had chickenpox, you already carry this virus. After the initial infection, it becomes dormant in sensory nerves. Later in life, it can reactivate as shingles (herpes zoster).⁵ 

Once the virus reaches the nerve connected to the eye itself, it can lead to swelling and irritation of the eye’s surface (the cornea), the lining of the eyelid (the conjunctiva), and nearby structures.⁵ 

Common triggers for VZV reactivation⁶

1. Age: risk increases sharply after age 50
2. Immune suppression: Conditions like HIV, cancer, or the use of immunosuppressive drugs (e.g. corticosteroids, chemotherapy, transplant medications) increase the likelihood of VZV reactivation
3. Stress or illness: further weakens immune defences

Symptoms and warning signs

Shared symptoms of viral keratitis include:⁷

• Eye pain
• Redness
• Light sensitivity
• Blurred vision
• Sensation of something in the eye

Clues to distinguish HSV vs.VZV:⁷

HSV keratitis:

• More common in younger individuals
• Usually affects one eye
• Presence of dendritic ulcers (branching corneal lesions)

VZV:

• More common in older adults
• Painful rash around the eye
• It may affect multiple eye structures
• Associated with Herpes Zoster Ophthalmicus

Diagnosis

An ophthalmologist can identify viral keratitis through a slit lamp evaluation. Diagnosis can be confirmed using multiple standard tests, including PCR (polymerase chain reaction – familiar from COVID testing), ELISA (enzyme-linked immunosorbent assay),  immunofluorescent antibody test, and viral cultures.^3,8

Because HSV and VZV require different treatments, accurate diagnosis is critical. The wrong therapy could worsen inflammation and increase complications.

Treatment options

Antiviral medications (oral/topical)

Doctors may prescribe oral antivirals like acyclovir, valacyclovir, or famciclovir for HSV keratitis. Topical antiviral eye drops or gels such as trifluridine or ganciclovir may also treat the infected eye directly.⁹

More complex systemic antiviral therapy is required for VZV keratitis, starting 72 hours before the rash’s appearance. With this condition, prevention shouldn’t be taken lightly, so it is recommended to avoid known triggers or use suppressive antiviral therapy.¹⁰

Possible complications if untreated

• Vision loss, scarring, recurrent infections
• There is a need for a corneal transplant in severe cases

FAQs

Can viral keratitis cause permanent blindness?

Yes. Without treatment, scarring and complications can lead to irreversible vision loss.

Is it contagious?

The viruses (HSV, VZV) are contagious, but viral keratitis itself is not easily spread. Good hygiene reduces the risk.

How can I reduce the risk of recurrence?

Avoid stress, protect your eyes from UV light and trauma, and discuss preventive antiviral therapy with your doctor.

Can I wear contact lenses if I’ve had viral keratitis?

Possibly. It depends on corneal damage. Your eye doctor can advise.

Should I get the shingles vaccine?

Yes. Vaccination reduces the risk of shingles and related eye complications, especially for those over 50.

Conclusion

Viral keratitis is more than just a minor eye irritation; it’s a serious condition that can lead to vision-threatening complications if not treated properly. While both HSV and VZV are common culprits, they differ in how they manifest, who they affect, and how they should be treated. 

The keys to protecting your vision are early detection and proper diagnosis. Don't ignore the warning signs like redness, sensitivity to light, or blurred vision, especially if you have a history of cold sores or shingles.

With modern diagnostic tools and effective antiviral therapies, viral keratitis is manageable. Preventive measures, such as the shingles vaccine and lifestyle adjustments, can significantly reduce the risk of recurrence.

Ultimately, recognising the signs and acting quickly can mean the difference between full recovery and permanent damage. Whether you’re a patient, caregiver, or simply curious about eye health, understanding viral keratitis gives you the power to make informed decisions.