Keratitis is painful inflammation of the eye’s clear top layer, the cornea. It can stem from an infection or injury, and it makes vision blurry and the eyes sensitive to light.

Anyone with these symptoms should seek medical care. Without treatment, severe complications can arise, including vision loss.

The eye is sensitive, and it has many ways of protecting itself against damage. For example, the eyelid covers the eye, while tears and fluid ward off infection. The cornea is the eye’s main barrier against dirt, germs, and disease.

Because the cornea is one of the eye’s first lines of defense, it can easily become sore and swollen. This condition is known as keratitis.

Depending on the cause, keratitis symptoms may vary, but pain and redness are key indicators. The cornea helps focus sight, so any inflammation can make vision blurred or cloudy. In some cases, the affected eye swells shut.

Another symptom is a feeling of something gritty in the eye. Also, it may burn, weep, or drain yellow-green fluid.

A person with keratitis may have sensitivity to light, called photophobia. As a result, they may avoid bright lights indoors or strong sunlight.

Anyone with any keratitis symptoms should see an eye doctor as soon as possible. If keratitis gets worse, it may damage the eye or cause blindness.

There are two main types of keratitis: infectious and noninfectious. Each type has many forms and needs different treatment.

Noninfectious keratitis

Surgery, injuries, or diseases that weaken the eye can cause swelling and soreness without infection. This type of inflammation of the cornea may come from:

  • wearing contact lenses too long
  • surgical wounds
  • objects in the eye, such as fragments of wood, metal, sand, or glass
  • a chemical in the eye
  • scratches, scrapes, or punctures
  • dryness of the eyes
  • a low or overactive immune system
  • allergies, such as makeup, pollution, or pollen
  • a lack of vitamin A in the diet
  • scars from a previous injury or surgery
  • windburn of the eye
  • sunburn of the eye, especially from sunlight reflecting off snow or water

Infectious keratitis

The infectious type of keratitis often occurs after the cornea is already damaged. Then, germs, fungi, or other organisms get into the injured eye and cause a corneal infection.

Infectious keratitis may be:

  • Bacterial: This usually stems from unclean contact lenses.
  • Fungal: Injury involving a tree branch or other plant matter tends to cause this, but it can also result from wearing unclean contacts.
  • Viral: This occurs due to an infection with the herpes or shingles virus.
  • Parasitic: This type of infection may stem from swimming in lakes or rivers or wearing unclean contacts. For example, 85% of cases of acanthamoeba keratitis occur in contact lens wearers.

The most common type is bacterial keratitis.

Keratitis develops when something causes inflammation of the cornea. Certain factors make this more likely.

Causes of noninfectious keratitis

Wearing contact lenses is the most common risk factor for keratitis. It can cause corneal scratches, dryness, or soreness. This eye damage tends to stem from wearing the lenses for too long, such as while sleeping.

A related risk factor is dry eye or reduced volume of tears in the eye.

Photokeratitis is an injury that results from exposure to bright light. People who do not protect their eyes in bright sunlight — such as at the beach or skiing — in tanning beds, or while watching eclipses are at risk.

Other risk factors for noninfectious keratitis include working with chemicals or machinery, seasonal allergies, and overuse of steroid eye drops.

Causes of infectious keratitis

Risk factors for viral, bacterial, fungal, or parasitic keratitis include:

  • the use of unclean eye drops or contact solutions
  • stress reactivating the herpes simplex virus
  • the flu, shingles, or other viral infections
  • a health condition that limits the immune system or causes it to be overactive

Also, when part of a tree or another plant injures the eye, this can cause fungal keratitis. People who work on farms or with plants are more likely to develop this condition, though dirty contact lenses can also lead to it.

Parasites live in ocean water, rivers, lakes, hot tubs, and tap water. Swimming with contact lenses can increase the risk of parasitic keratitis, which is hard to treat.

Keratitis can become serious quickly. A person needs immediate medical care to prevent further problems, such as:

  • open sores on the surface of the eye
  • permanent scarring that limits vision
  • increased eye pressure called glaucoma, which can reduce vision
  • blindness
  • the need for a replacement cornea
  • the need for eye removal

Anyone with keratitis should consult a doctor before trying any over-the-counter eye drops, as some can make keratitis worse.

Seeing an eye doctor as soon as symptoms develop is crucial in preventing long-lasting damage. If a doctor diagnoses keratitis early, it is much easier to treat.

An eye doctor can check for keratitis by conducting an eye exam with a bright light. They also ask questions about the person’s medical history and when the symptoms developed.

The doctor may need to use special eye drops that stain the eye and make any scratches or scrapes more visible.

If the doctor suspects fungal or bacterial keratitis, they take a sample with a swab and send it to a lab for evaluation. To treat parasitic keratitis, the doctor must identify the parasite responsible for the infection.

Diagnosing viral keratitis does not require testing. Instead, the doctor considers the person’s medical history.

First, anyone with symptoms of keratitis who wears contacts should remove them and keep them off until the condition has gone away.

The best approach to medical treatment depends on the type of keratitis.

Mild, noninfectious keratitis tends to heal on its own. The doctor may suggest artificial tears, eye ointments, cold compresses, an eye patch, and rest to treat stinging, burning, and soreness. If there is a lot of swelling, the doctor can prescribe steroid eye drops.

If a person has a mild bacterial infection, the doctor may recommend antibacterial eye drops. For more serious cases, they may prescribe oral antibiotics. And adding steroid eye drops to the treatment plan can reduce swelling if the keratitis is severe.

For viral keratitis, a doctor prescribes antiviral eye drops or oral medications. These infections have no cure and may reappear during times of illness or stress. Some people with viral keratitis need routine antiviral medication to prevent outbreaks.

Treating fungal keratitis involves using oral and eye drop antifungal medication for months. Parasitic keratitis is difficult to treat, and a pharmacist needs to prepare special eye drops.

Severe cases of fungal or parasitic infections may require corneal transplant surgery or removal of the eye.

It is essential to use oral or eye drop treatments for the full prescribed length of time — even if the symptoms go away beforehand.

During treatment, visit the eye doctor if:

  • The symptoms are not improving.
  • Sight becomes blurred.
  • There is more pain or redness.
  • Any white spot on the cornea grows.

The most common cause of keratitis is contact lens use. Proper cleaning, storage, and use are crucial. Anyone who wears contacts can help prevent keratitis by:

  • following all the guidance of their eye doctor
  • washing and drying their hands with soap and water before touching the eyes or contacts
  • removing the lenses before swimming, showering, or sleeping
  • using a recommended cleaning solution
  • rinsing and storing contact lenses in fresh solution
  • cleansing the storage case with a clean solution and allowing it to air dry
  • not using tap water or saliva to clean or store contact lenses
  • discarding expired eye drops or cleaning solution
  • having a spare pair of eyeglasses, in case anything gets in the way of proper contact care
  • visiting an eye doctor regularly
  • contacting them about any eye symptoms

Beyond contact lens care, a person can take these steps to prevent keratitis:

  • washing the hands well with soap and water before touching the eyes
  • wearing safety goggles or glasses when working with plants, sharp objects, or chemicals
  • wearing sunglasses in bright sunlight
  • using artificial tears, for those with dry eyes or conditions affecting the immune system
  • not sharing eye drops and using only those a doctor has recommended
  • avoiding contact with any allergens
  • getting a shingles vaccine
  • having a diet that includes vitamin A, which is found in milk and eggs, as well as in many multivitamins

Overall, the best way to prevent keratitis is to keep the hands and area around the eyes clean and avoid touching the eyes.

The outlook depends on the type and severity of keratitis. The condition is treatable, but it is crucial to receive medical attention as soon as the symptoms develop.

People who wear contact lenses have the greatest risk, and following all cleaning, storage, and use advice is key.

Below, find answers to some common questions about keratitis.

Can keratitis heal on its own?

Mild swelling, scratches, or scrapes without infection can heal on their own. However, if a person has any symptoms, an eye doctor should check to determine the severity of the issue.

Is keratitis serious?

Without treatment, keratitis can quickly become serious. If an infection develops, ulcers, scarring, and vision loss can follow. In severe cases, it may be necessary to remove the eye.

What is the most common cause of keratitis?

The most common cause is improper use and care of contact lenses. Using dirty contacts or leaving them in overnight can damage the cornea and lead to infection.

How does keratitis compare with conjunctivitis?

Keratitis is inflammation and soreness of the eye’s clear outer layer, the cornea. Conjunctivitis is inflammation of the clear membrane that covers the inside of the eyelids and the white part of the eye.

The two issues can both cause redness, pain, blurry vision, and sensitivity to light, though keratitis tends to be more painful.