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Keratitis: What It Is, Symptoms, Causes and Treatment
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Keratitis (noun): keratitis is inflammation of the cornea, the clear front window of the eye. It is most often caused by infection with bacteria, viruses, fungi or the Acanthamoeba parasite, but injury, dry eye and ultraviolet light can cause it too. A painful, red, light-sensitive eye, especially in a contact lens wearer, needs an urgent examination, because untreated infectious keratitis can permanently damage vision. Cornea specialist Doç. Dr. Muhammet Derda Özer (Doç. means Associate Professor) leads corneal care at Laser Istanbul Clinic.
Keratitis: key facts
- What it is
- Inflammation of the cornea; when infection or injury opens a sore in the cornea it is called a corneal ulcer
- Main infectious causes
- Bacteria, viruses (herpes simplex, varicella-zoster), fungi, Acanthamoeba
- Non-infectious causes
- Scratches and injuries, chemical burns, severe dry eye, eyelids that do not close properly, ultraviolet light
- Biggest risk factor
- Contact lens wear, especially poor lens hygiene and sleeping in lenses
- Typical symptoms
- Redness, pain, a feeling of something in the eye, watering, discharge, light sensitivity, blurred vision, sometimes a white spot on the cornea
- Main treatments
- Antibiotic, antiviral or antifungal eye drops chosen to match the cause; steroid drops only in selected cases, once infection is controlled
- Urgency
- Same-day eye assessment; the American Academy of Ophthalmology warns ulcers can cause permanent vision loss and even blindness if untreated
- Specialist
- Cornea specialist (ophthalmologist); at Laser Istanbul Clinic, Doç. Dr. Muhammet Derda Özer
What is keratitis?
Keratitis (from the Greek kerato-, cornea, and -itis, inflammation) means that the cornea is inflamed. The cornea is the dome at the front of the eye that covers the iris and pupil and does most of the eye's focusing. Because it has no blood vessels and must stay perfectly clear, any inflammation, swelling or scarring can blur vision.
Keratitis is either infectious or non-infectious. Infectious keratitis (microbial keratitis) is caused by germs getting into the cornea and is the dangerous form. Non-infectious keratitis follows an injury, ultraviolet exposure, dry eye or an eyelid problem, though a damaged surface can become infected.
Is keratitis the same as a corneal ulcer?
Not exactly. Keratitis is the inflammation; a corneal ulcer is an open sore in the cornea that can develop when keratitis is severe. The American Academy of Ophthalmology uses the terms together ("corneal ulcer (keratitis)"), and in everyday use "infected corneal ulcer", "corneal infection" and "infectious keratitis" usually mean the same emergency.
Is keratitis the same as conjunctivitis?
No. Conjunctivitis ("pink eye") is inflammation of the conjunctiva, the thin membrane over the white of the eye and inside the eyelids. It is usually milder. Keratitis affects the cornea, is usually more painful, and can threaten sight. A red eye with pain or light sensitivity should not be assumed to be conjunctivitis. Glossary: Conjunctivitis →
Keratitis causes: types of keratitis
The cause decides the treatment, which is why doctors try to identify it early.
| Type | What causes it | Typical clues |
|---|---|---|
| Bacterial keratitis | Bacteria, most often Staphylococcus, Streptococcus and Pseudomonas, which together cause about 80% of bacterial cases according to EyeWiki | Rapid-onset pain, redness, discharge, a white or grey patch; often contact lens related |
| Viral keratitis | Herpes simplex virus (HSV) or the shingles virus (varicella-zoster) | Pain, watering, light sensitivity; HSV can leave a branching "dendrite" pattern on the surface; can recur |
| Fungal keratitis | Fungi such as Fusarium, Aspergillus and Candida | Often follows an eye injury involving plant material, steroid-drop use or contact lenses; may develop more slowly |
| Acanthamoeba keratitis | A microscopic amoeba found in water | Mostly contact lens wearers; severe pain, often out of proportion to how the eye looks |
| Non-infectious keratitis | Scratches, chemical burns, severe dry eye, eyelid problems, ultraviolet light | Pain and watering after an injury, welding or snow glare |
Bacterial keratitis
Bacterial keratitis is a serious corneal infection that can cause vision loss. EyeWiki reports that about 80% of cases are caused by Staphylococcus, Streptococcus and Pseudomonas species, and that contact lens wear is the leading risk factor, linked to 19% to 42% of culture-proven corneal infections. It can progress quickly, so even a short delay can matter.
Herpes keratitis (viral keratitis)
Herpes simplex keratitis is a leading cause of corneal blindness worldwide; EyeWiki cites an incidence of about 1.5 million cases a year globally. The virus stays dormant in the nerves after the first infection and can reactivate, so episodes tend to return. Typical signs include pain, tearing, light sensitivity and blurred vision. In the surface form, the cornea shows small branching lines (dendrites). Repeated episodes can scar the cornea and reduce its sensation, which in turn makes it heal poorly (a neurotrophic cornea).
Shingles and the eye
The varicella-zoster virus that causes chickenpox and shingles can also inflame the cornea (herpes zoster ophthalmicus). Shingles lesions on the tip of the nose (Hutchinson's sign) are described by EyeWiki as a strong predictor of ocular inflammation, so anyone with a shingles rash near the eye should be checked by an eye doctor. The recombinant shingles vaccine Shingrix showed over 90% efficacy against shingles in the trials that led to its US approval.
Fungal keratitis
Fungal keratitis is more common after injuries involving plant matter, in people using steroid eye drops, and in contact lens wearers. It can develop slowly, which delays diagnosis, and it is hard to treat: EyeWiki reports that in published series 26% to 63% of eyes experienced severe visual loss, and a proportion needed a corneal transplant or even removal of the eye. These figures come from older case series and are not predictions for any one patient, but they show why early treatment matters.
Acanthamoeba keratitis
Acanthamoeba is a free-living amoeba found in water. The CDC notes that most people in the United States who get this infection wear contact lenses, and EyeWiki reports that contact lens wear accounts for over 80% of cases, with daily-wear reusable lenses carrying a threefold higher risk than daily disposables. It is typically very painful, and the prognosis is worse than for many other types of infectious keratitis. Early diagnosis, before the infection reaches the deeper layers of the cornea, gives the best outcomes.
Non-infectious keratitis
Not all keratitis is infectious. Photokeratitis, sometimes called "snow blindness" or "welder's flash", is a sunburn of the corneal surface caused by ultraviolet light from arc welding, snow glare, tanning beds or sun lamps. Symptoms appear 30 minutes to 12 hours after exposure, usually in both eyes, and the surface normally heals within 24 to 72 hours. Surface scratches, chemical splashes, severe dry eye and eyelids that do not close properly can also inflame the cornea, and eyelid disease such as blepharitis can contribute. Glossary: Blepharitis →
Keratitis symptoms: how do I know if I have it?
The American Academy of Ophthalmology lists these keratitis symptoms: redness, intense pain, a feeling of something in the eye, excessive tearing, discharge, blurred vision, sensitivity to light, eyelid swelling and sometimes a visible white spot on the cornea.
| Symptom | What it suggests |
|---|---|
| Painful red eye | Infectious keratitis or corneal ulcer, abrasion, inflammation |
| Light sensitivity (photophobia) | Corneal inflammation of any kind |
| Watering and a gritty or "something in the eye" feeling | Surface damage, early infection |
| Thick or sticky discharge | Possible bacterial infection |
| White or grey spot on the cornea | Corneal infiltrate or ulcer: urgent |
| Blurred or hazy vision | Swelling, infiltrate or scarring |
| Severe pain that seems greater than the look of the eye | Possible Acanthamoeba keratitis |
| Pain after welding or snow glare, starting hours later | Photokeratitis |
Pain is the symptom that separates keratitis from most simple red eyes. Contact lens wearers should treat any new redness, pain or blurred vision as a reason to take the lenses out and get examined.
Contact lens keratitis: who is at risk?
Contact lens wearers are the group most at risk of infectious keratitis. The CDC says serious infections, especially microbial keratitis, are linked to contact lens wear, that failure to wear, clean and store lenses as directed increases the risk, and that most wearers do not follow proper hygiene. Since 2006 the CDC has recorded outbreaks of Acanthamoeba and fungal keratitis in the United States, both capable of causing vision loss or blindness. About 45 million Americans wear contact lenses.
Other people at higher risk include those with:
- a past eye injury, especially from plant matter
- a history of herpes simplex or shingles affecting the eye
- long-term steroid eye drop use
- severe dry eye, or eyelids that do not cover the eye properly
- a weakened immune system, or earlier surgery on the eye
How is keratitis diagnosed?
The ophthalmologist asks about your lenses, injuries and past eye problems, then examines the eye:
Slit-lamp examination
A microscope with a bright, thin beam of light shows the surface and the depth of the cornea. Fluorescein dye makes surface defects and ulcers show up under blue light.
Corneal scrapings
For larger or deeper infiltrates (EyeWiki mentions those over 2 mm), or when the infection is severe, a few cells are scraped from the sore and sent for Gram and Giemsa staining and culture to identify the germ. Fungal cultures can take about three weeks, which is why treatment usually starts before the result is back.
Further tests
Confocal microscopy (a very detailed image of the cornea's cells) and PCR testing can improve detection of Acanthamoeba and other infections where available. If cultures are negative and infection is still suspected, a small corneal biopsy may be needed.
Corneal imaging
OCT and topography scans can show how deep a scar goes and how it has changed the cornea's shape, which matters for planning later treatment.
Keratitis treatment: how is keratitis treated?
Treatment matches the cause, and should start as early as possible. Do not use leftover antibiotic drops or steroid drops from a previous problem: steroids are contraindicated in some infections, such as active herpes surface disease, and are linked to fungal keratitis.
| Cause | Main treatment |
|---|---|
| Bacterial | Stop wearing contact lenses; broad-spectrum antibiotic drops. In severe cases, strong "fortified" antibiotic drops are given every hour around the clock. Steroid drops may be considered after 24 to 48 hours once the germ has been identified (EyeWiki) |
| Herpes simplex | Antiviral treatment, for example topical ganciclovir or trifluridine drops during active disease; topical steroids are avoided while the surface is active. Long-term oral aciclovir (400 mg twice daily for a year in one landmark trial) almost halved the risk of repeat epithelial and stromal disease |
| Shingles (zoster) | Oral antiviral medicine such as valaciclovir, plus drops for inflammation as advised by the eye doctor |
| Fungal | Antifungal drops (natamycin 5% is the only FDA-approved topical antifungal for the eye, per EyeWiki); surgery for resistant cases |
| Acanthamoeba | Prolonged courses of specific anti-amoebic drops (biguanides, with or without diamidines), tapered very slowly and sometimes continued for many months |
| Photokeratitis and abrasions | Lubricating drops or ointment, pain relief, and antibiotic ointment to prevent secondary infection; the surface usually heals in days |
What happens at home. Drops may be needed very often at first, including through the night in severe cases, so follow the schedule exactly and attend every review: the doctor needs to see whether the ulcer is shrinking. Do not wear contact lenses until the eye specialist says it is safe, and do not rub the eye.
When scarring remains. When an infection heals with a scar in the centre of the cornea, vision can stay blurred. Options can include special contact lenses, laser treatment to the surface for some superficial scars, or a corneal transplant (keratoplasty) for deep scars or a badly damaged cornea. Doç. Dr. Muhammet Derda Özer, who leads cornea care at Laser Istanbul Clinic, can review your scans and reports before you travel.
Complications: can keratitis cause blindness?
Yes, it can, especially if it is not treated promptly. The American Academy of Ophthalmology states that corneal ulcers can badly and permanently damage vision and even cause blindness if untreated. Possible complications of infectious keratitis include:
- scarring of the cornea, which blurs vision or causes glare
- irregular astigmatism, where the scarred surface distorts the image
- spread of infection to the white of the eye (sclera) or deeper
- perforation, a hole in the cornea
- a poorly healing cornea with reduced sensation after herpes
- vision loss, sometimes requiring a corneal transplant
Most mild non-infectious keratitis, for example photokeratitis, heals within days. For infectious keratitis the outcome depends on the organism, how early treatment began, and how deep the infection went. No doctor can guarantee a result, but treatment started on the day symptoms appear gives the best chance of keeping your vision.
Can keratitis be prevented?
Many cases can be prevented. These measures come from the CDC's contact lens advice and from the causes above:
- Do not sleep in contact lenses unless your eye care provider has specifically told you to.
- Wash and dry your hands before touching your lenses.
- Keep lenses away from water: remove them before swimming or showering. Acanthamoeba lives in water, and EyeWiki advises lens wearers to avoid tap water.
- Use fresh lens solution each time, never top up old solution, and replace the lens case at least every three months.
- Have a yearly check with your eye care provider, and carry back-up glasses so you are never tempted to wear lenses on a sore eye.
- Remove your lenses and contact an eye doctor if the eye is uncomfortable, red or painful.
- Protect your eyes from injury and ultraviolet light, with safety eyewear for hazardous work and welding shields or UV-rated sunglasses where needed.
- Treat dry eye and eyelid disease (for example blepharitis) so the surface stays healthy.
- Ask your doctor about the shingles vaccine if you are in an eligible age group.
When to see a doctor about keratitis
Seek same-day care from an eye doctor or eye emergency service if you have:
- a painful red eye, especially with light sensitivity, blurred vision or discharge
- a white or grey spot on the cornea
- any new redness or pain while wearing contact lenses (remove the lenses first, and take the lenses and case with you)
- a shingles rash on the forehead or the tip of the nose
- an eye injury, chemical splash, or exposure to welding light or snow glare followed by severe pain
- worsening symptoms during treatment
Book a routine appointment if you notice:
- repeated mild redness, grittiness or watering
- a history of cold sores or shingles and a change in your vision
- a scar or blurred patch after a past eye infection
If you already have a diagnosis or a corneal scar and want a specialist's second opinion, you can send your reports and scans for review before you travel.
Frequently asked questions
Keratitis is inflammation of the cornea, the clear front window of the eye. It may be caused by infection (bacteria, viruses, fungi, Acanthamoeba) or by injury, dry eye or ultraviolet light. Infectious keratitis is an emergency because it can permanently damage vision.
Infectious keratitis is caused by bacteria, herpes simplex or shingles viruses, fungi and the Acanthamoeba amoeba. The biggest risk factor is contact lens wear with poor hygiene. Non-infectious causes include scratches, chemical burns, severe dry eye, eyelid problems and ultraviolet light.
Typical symptoms are redness, eye pain, a feeling that something is in the eye, watering, discharge, sensitivity to light, blurred vision and sometimes a white spot on the cornea. Pain and light sensitivity separate keratitis from most mild red eyes.
It depends on the cause. Infectious forms such as herpes and bacterial keratitis can potentially be passed on through contact with infected eye fluid, so wash your hands, do not share towels or make-up, and avoid touching your eyes. Photokeratitis, scratches and dry-eye keratitis are not contagious. Contact lens keratitis usually comes from germs on the lens, case or water rather than from another person.
It depends on the cause. Photokeratitis usually heals in 24 to 72 hours. Infectious keratitis takes much longer, and Acanthamoeba keratitis in particular may need treatment for many months, according to EyeWiki. Your doctor will review the eye often until it has healed.
Yes. The American Academy of Ophthalmology warns that corneal ulcers can badly and permanently damage vision and even cause blindness if they are not treated. Seeing a doctor on the same day, and following treatment closely, gives the best chance of protecting your sight.
No. Stop wearing lenses at the first sign of redness or pain and do not resume until your eye specialist says it is safe. After an infection, the doctor may advise changing lens type, replacing your case and solution, or avoiding lenses altogether.
Yes, if the eye is painful, red and sensitive to light, particularly in a contact lens wearer. Infection can worsen quickly and leave a permanent scar. Go to an eye emergency service or an ophthalmologist the same day.
Sources for the facts on this page
- American Academy of Ophthalmology. What Is a Corneal Ulcer (Keratitis)? https://www.aao.org/eye-health/diseases/corneal-ulcer
- EyeWiki (AAO). Bacterial Keratitis. https://eyewiki.org/Bacterial_Keratitis
- EyeWiki (AAO). Fungal Keratitis. https://eyewiki.org/Fungal_Keratitis
- EyeWiki (AAO). Acanthamoeba Keratitis. https://eyewiki.org/Acanthamoeba_Keratitis
- EyeWiki (AAO). Herpes Simplex Virus Keratitis. https://eyewiki.org/Herpes_Simplex_Virus_Keratitis
- EyeWiki (AAO). Herpes Zoster Ophthalmicus. https://eyewiki.org/Herpes_Zoster_Ophthalmicus
- EyeWiki (AAO). Photokeratitis. https://eyewiki.org/Photokeratitis
- CDC. Contact Lens-Related Eye Infections. https://www.cdc.gov/contact-lenses/about/index.html
- CDC. Healthy Contact Lens Habits (prevention). https://www.cdc.gov/contact-lenses/prevention/index.html
- CDC. About Acanthamoeba Keratitis. https://www.cdc.gov/acanthamoeba/about/index.html
Had an eye infection or been left with a corneal scar?
Send us your eye report or scans. Doç. Dr. Muhammet Derda Özer, our cornea specialist, will review them and tell you which options may suit your eyes, with no obligation. If your eye is red and painful right now, do not wait: see an eye doctor today.
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