Herpes simplex keratitis: when a red eye needs urgent assessment
A red eye is often blamed on tiredness, allergy, or conjunctivitis. But when redness comes with pain, light sensitivity, tearing, or blurred vision, the cornea may be involved. One possible cause is herpes simplex keratitis. It should not be self-treated because the right therapy depends on which layer of the cornea is affected.
What is herpes simplex keratitis?
Keratitis is inflammation of the cornea, the clear front surface of the eye. Herpes simplex keratitis is most often caused by herpes simplex virus type 1 (HSV-1), the virus commonly responsible for cold sores. After the first infection, HSV remains inactive in the nervous system and can later reactivate. Eye disease is usually a reactivation of an earlier infection, not proof of recent transmission.
The condition usually affects one eye. It may involve only the surface epithelium or extend into deeper corneal layers. Severe or repeated episodes can scar the cornea and permanently reduce vision. With prompt treatment, however, most episodes resolve without permanent sight loss.
Symptoms not to ignore
According to the CDC, possible symptoms include eye pain, redness, watering, blurred vision, and sensitivity to light. Blisters may sometimes appear on the eyelid or nearby skin. A history of cold sores can provide a clue, but their absence does not rule out ocular HSV.
Seek urgent same-day eye care if a red eye is painful, vision changes, light hurts, or symptoms worsen quickly. Prompt assessment is especially important for people with significant immune suppression. Sudden major vision loss, trauma, or a chemical eye injury requires emergency care.
Why symptoms alone cannot confirm the diagnosis
Similar symptoms occur with bacterial keratitis, shingles affecting the eye, uveitis, acute glaucoma, and other conditions. In contact lens users, clinicians also consider lens-related infections, including Acanthamoeba keratitis. A photograph, symptom description, or history of cold sores cannot reliably identify the cause.
An ophthalmologist examines the cornea with a slit lamp and fluorescein dye. A characteristic branching surface ulcer can support the diagnosis. The CDC notes that laboratory testing is not usually needed, although it can help in atypical or complicated cases.
Treatment and the danger of unsupervised steroid drops
Treatment is based on antiviral medicine applied to the eye and/or taken by mouth; an ophthalmologist chooses the appropriate option. Inflammation in deeper layers is managed differently from active surface infection.
Do not use leftover, borrowed, or newly purchased steroid eye drops without an examination. In active epithelial herpes keratitis, steroids can allow the ulcer to enlarge. In some deeper forms, steroids may instead be part of specialist treatment, but only under close supervision and usually with antiviral cover. There is no single safe treatment for every red eye.
If you wear contact lenses, remove them and do not restart until an eye-care professional says it is safe. Avoid rubbing or touching the eye, wash your hands before touching your face, and never share eye medicines.
Can it come back?
Recurrences can happen after an episode. They do not imply a new exposure or personal fault: HSV can persist in nerve cells and reactivate. For repeated disease, an ophthalmologist may discuss longer-term antiviral prevention. In the randomized Herpetic Eye Disease Study, one year of oral acyclovir reduced ocular HSV recurrences while treatment was being taken. Whether prevention is appropriate depends on a person’s history and risks.
What to do now
- Arrange urgent same-day eye assessment for pain, light sensitivity, or any vision change.
- Remove contact lenses.
- Do not start steroid or antiviral eye drops without a prescription.
- Bring a list of eye drops and medicines and mention any previous similar episode.
Early assessment matters not only to confirm herpes, but also to rule out other causes that can quickly threaten sight.
Sources
- CDC: HSV keratitis
- College of Optometrists: clinical management guideline
- NHS: herpes simplex eye infections
- Herpetic Eye Disease Study Group, NEJM
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